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Nitrogen fertilizers
Nitrogen fertilizers are mineral fertilizers that meet the nitrogen requirements of crops.
- Mineral fertilizers
- Nitrogen fertilizers (Русская версия)
Nitrogen fertilizer production
Sources of producing nitrogen fertilizers
From 1830 until 1914 the main nitrogen fertilizer was Chilean nitrate, whose deposits are concentrated in South America. Ammonia from coke ovens of the metallurgical industry was also used as a nitrogen fertilizer.
By the beginning of the 20th century natural deposits of Chilean nitrate were almost exhausted, so the issue of industrial-scale production of nitrogen fertilisers arose. The use of atmospheric nitrogen for the production of nitrogen fertilizers was promising, which in a 15 kilometer layer of air over an area of 1 hectare amounts to about 78 thousand tons of molecular nitrogen.
At the end of the 19th century, a way was found in the laboratory to bind molecular nitrogen with oxygen by passing air through a voltaic arc discharge with a temperature of about 3000 °C:
N2 + O2 = 2NO.
The resulting nitrogen monoxide is oxidized by air oxygen to nitrogen dioxide, which in interaction with water forms nitric acid.
The first plant using this technology was built in Norway, where natural conditions allow obtaining relatively cheap electric power. Its production focused on the production of Ca(NO3)2. Hence the calcium nitrate was called “Norwegian nitrate”. The obvious disadvantage of this technology was high energy costs, and the calcium nitrate produced is very hygroscopic and inconvenient to use. Therefore, the method was not further disseminated.
A method of fixing atmospheric nitrogen was proposed, based on nitrogen fixing by calcium carbide at 700-800 °C:
N2 + CaC2 = CaCN2 + C.
The method of calcium cyanamide production is technologically simpler and cheaper, but it is also not widespread due to the discovery of a method for producing ammonia from molecular nitrogen and hydrogen.
The method of ammonia synthesis was discovered by the German chemist Gaber. Of all the ways to bind molecular nitrogen, his method turned out to be the cheapest and is currently the main one in the production of nitrogen fertilizers.
Ammonia production
Ammonia is produced by the interaction of nitrogen and hydrogen. For this purpose, a mixture of gases in a 1:3 ratio is compressed under high pressure and fed into a contact furnace (synthesis chamber), where ammonia is synthesized at 400-500 °C, pressure and in the presence of catalysts (iron with additions of aluminum and potassium oxides):
N2 + 3H2 = 2NH3
The source of nitrogen is air. One of the methods is used for nitrogen extraction from air:
Atmospheric air is passed through a generator filled with burning coke, the oxygen is completely burned out, and a mixture of nitrogen and carbon dioxide comes from the generator. The latter is absorbed by water at a pressure of 25 atm.
The air is liquefied and then separated into nitrogen and oxygen due to the difference in boiling point: oxygen boils at -183 °C, nitrogen – at -196 °C.
Up to 50% of the cost of ammonia production is spent on hydrogen production. Natural and associated petroleum gases or waste gases from coke ovens are used as hydrogen sources. Hydrogen can be produced by electrolysis of water. The latter method allows obtaining pure hydrogen, but requires high energy costs.
The ammonia produced is used directly as a fertilizer, to produce ammonium fertilizers, nitric acid, urea.
Obtaining nitric acid
Nitric acid is produced by catalytic oxidation of ammonia with air oxygen. This is the main method for producing nitric acid. The reaction takes place in several stages. First, ammonia is oxidized to nitric oxide:
4NH3 + 5O2 → 4NO + 6H2O.
Nitrogen oxide enters the oxidation towers, where it is oxidized to nitrogen dioxide by oxygen:
2NO + O2 = 2NO2.
NO2 enters absorption towers (absorbers) where it is absorbed by water to form nitric and nitrous acids:
2NO2 + H2O = HNO3 + HNO2;
3NO2 + H2O = 2HNO3 + NO.
Nitric acid HNO2 is unstable and decomposes quickly:
2HNO2 = NO + NO2 + H2O.
The resulting nitrogen oxides NO and NO2 are returned to the same oxidizing and absorbing units.
Ammonia and nitric acid obtained by industrial methods are the main sources of nitrogen fertilizers.
Classification of nitrogen fertilizers
Depending on the form of nitrogen, nitrogen fertilizers are classified into:
- nitrate – sodium (NaNO3) and calcium [Ca(NO3)2] nitrate;
- ammonium – sulfate [(NH4)2SO4] and ammonium chloride (NH4Cl),
- carbonate [(NH4)2CO3] and ammonium bicarbonate (NH4HCO3);
- ammonium-nitrate – ammonium nitrate (NH4NO3), ammonium sulfonitrate [(NH4)2SO4 ⋅ 2NH4NO3];
- ammonia – anhydrous ammonia, ammonia water;
- amide – urea [CO(NH2)2] and calcium cyanamide (CaCN2).
Nitrogen fertilizers may have mixed forms. A separate group includes slow-acting forms, such as urea-formaldehyde and encapsulated fertilizers.
Nitrate fertilizers
Nitrate fertilizers are nitrogen fertilizers that contain nitrogen in the form of the nitrate group NO3-. For example, sodium nitrate, or sodium nitrate, NaNO3 and calcium nitrate, or calcium nitrate, Ca(NO3)2. In Russia, the use of nitrate forms is less than 1%.
Sodium nitrate
Sodium nitrate, or sodium nitrate, or sodium nitrate, or Chilean nitrate – NaNO3. It contains 16% nitrogen and 26% sodium. It was the first mineral nitrogen fertilizer. The largest natural deposit was in Chile. Significant deposits were found in California, in southwest Africa.
Nowadays sodium nitrate is obtained as a byproduct in the production of nitric acid from ammonia. Nitric oxides NO and NO2 (the “tail gases”) that have not been adsorbed by the water in the absorption towers are passed through additional absorption towers sprayed with a solution of sodium carbonate or sodium hydroxide to produce a mixture of sodium nitrate and sodium nitrite:
Na2CO3 + 2NO2 = NaNO3 + NaNO2 + CO2.
Nitrite when acidified with dilute nitric acid turns into nitrate:
3NaNO2 + 2HNO3 = 3NaNO3 + 2NO + H2O.
Nitrogen monoxide returns to the oxidation tower. The acidified sodium nitrate solution is neutralized, evaporated and the NaNO3 precipitate is separated from the mother liquor.
Sodium nitrate is a fine crystalline salt of white, gray or brownish-yellow color, well soluble in water, hygroscopic, with high humidity is able to recrystallize into larger crystals. In dry condition and proper storage, it does not caking and retains its flowability.
Calcium nitrate
Calcium nitrate, or calcium nitrate, or calcium nitrate, or Norwegian nitrate – Ca(NO3)2. It contains 17% of nitrogen. First industrially synthesized in 1905 in Norway.
Currently, it is produced as a by-product of obtaining nitric acid from ammonia: in neutralization of tail gases (nitric oxides NO and NO2) by aqueous calcium hydroxide solutions Ca(OH)2 (milk of lime), as well as in the production of complex fertilizers by nitric acid decomposition of phosphate raw materials.
Calcium nitrate is highly hygroscopic (9.5 out of 10). Under normal storage conditions, it tends to get very damp, spongy and caked. It is transported and stored in moisture-proof bags. To reduce hygroscopic properties, hydrophobic additives (gypsum, paraffin oil) up to 0.5% of salt weight are added to commercial calcium nitrate.
To improve physical properties, 4-7% ammonium nitrate is added to calcium nitrate solution during production. Calcium nitrate is produced in granular form, which is obtained by adding 4-7% ammonium nitrate to evaporated concentrated nitrate solution and subsequent granulation.
Application of nitrate fertilizers
Nitrate fertilizers can be used on a variety of soils for all crops. Because of their low nitrogen content their use is more expensive economically, they are more often used in areas near industries.
Calcium and sodium nitrate are of equal value for most plants. The exception is sugar beet and other root crops: sodium nitrate is more effective due to the positive effect of sodium on these crops. The latter is due to the positive effect of sodium on the outflow of carbohydrates from the leaves to the roots, and thus increasing the yield of roots and the content of sugars in them.
When applied to the soil, nitrate fertilizers quickly dissolve in the soil solution, Na+ and Ca2+ cations enter into exchange reactions with the soil absorbing complex (SAC), pass into the exchange-absorbed state:
[SAC](Ca, K) + 3NaNO3 → [SAC]Na3 + Ca(NO3)2 + KNO3;
[SAC](H, NH4) + Ca(NO3)2 → [SAC]Ca + HNO3 + NH4NO3.
Systematic application of calcium nitrate contributes to the replenishment of SAC with calcium.
Nitrate ion NO3- forms soluble salts or nitric acid with cations displaced from the soil absorbing complex. It does not undergo physicochemical or chemical absorption. Nitrate can bind in the soil only through biological absorption during the warm period of the year. In the autumn-winter period, biological absorption is almost completely absent. For this reason, nitrate fertilizers are inexpedient to apply in autumn, especially in areas with flush water regime.
Sodium and calcium nitrates are used in spring for pre-sowing cultivation and as top dressing during the growing season. In summer, nitrates can be washed out in conditions of excessive moisture, irrigation and easily drained soils due to their high mobility. Therefore, in regions with humid climates and in irrigated areas, ammonium forms are applied for rice and other crops.
Sodium nitrate is also applied in rows with seeds, calcium nitrate is of little use because of its high hygroscopic properties. Sodium nitrate must not be applied on saline soils and salts.
Sodium and calcium nitrates are physiologically alkaline fertilizers, as plants absorb the anion NО3- more than Na+ or Ca2+ cations. Some of the cations remaining in the soil alkalize the soil solution. Prolonged use of nitrate fertilizers on acidic sod-podzolic and light low-buffered soils contributes to their neutralization. Therefore, on sod-podzolic soils nitrate fertilizers show greater efficiency than physiologically acidic ammonia fertilizers. On chernozems this advantage is lost.
Ammonium fertilizers
Ammonium fertilizers are a form of nitrogen fertilizer that contains nitrogen in the form of the ammonium group NH4+. They include ammonium sulfate, ammonium chloride, ammonium carbonate. Their production is relatively easier than that of nitrate fertilizers, as there is no stage of ammonia oxidation to nitric acid.
Ammonium sulfate
Ammonium sulfate, or ammonium sulfate, (NH4)2SO4 pure salt contains 21.2% of nitrogen, in the technical product – 20.5%. In the world production of nitrogen fertilizers its share is about 25%, in Russia – less than 6%. The large share of ammonium sulfate in world production is explained by its wide use in irrigated agriculture for rice and cotton and in areas of excessive moisture (tropics).
In Russia, production of ammonium sulphate began in Donbass at Shcherbinsky mine in 1899 by capturing and neutralizing ammonia from coking coal with sulphuric acid. The same technological scheme is used at present as well.
Ammonium sulfate can be produced by absorption of ammonia with sulfuric acid according to the reaction:
H2SO4 + 2NH3 = (NH4)2SO4.
The reaction proceeds with the release of heat, which is spent on evaporation of the solution, when the saturated solution is cooled ammonium sulfate precipitates as a crystalline precipitate, which is separated and dried. Sulphuric acid can be replaced with cheaper natural minerals: gypsum (CaSO4⋅2H2O), mirabilite (Glauber salt, Na2SO4⋅10H2O) or phosphogypsum, a waste product of phosphate fertilizers.
Finely ground gypsum is shaken in ammonia water, through which carbon dioxide is passed. The interaction of ammonia, carbon dioxide and gypsum produces ammonium sulphate:
2NH3 + CO2 + H2O = (NH4)2CO3;
(NH4)2CO3 + CaSO4 = (NH4)2SO4 + CaCO3.
Calcium carbonate insoluble in water is filtered off, and the solution containing (NH4)2SO4 is evaporated to crystallization, separated from the mother liquor and dried.
Due to the cheaper cost of ammonia obtained from the coke off-gases, coke-oven ammonium sulfate is obtained more cheaply.
Ammonium sulphate is well soluble in water: 76.3 g (NH4)2SO4 per 100 cm3 of water at 20 °C. In the dry condition fertilizer has a small hygroscopic properties, little caking during storage, does not disperse in the air, retains loose and well dispersed by fertilizer aggregates.
Ammonium sulphate is a white crystalline substance with various paints depending on the method of production. It contains 0,2-0,3% of moisture, an impurity of Ca, Mg, SiO2, 0,025-0,05% (0,2-0,5%) of free sulfuric acid, which gives fertilizer slightly acidic reaction. Coke sulfate ammonium contains a small amount of organic impurities – resinous substances, phenol, up to 0.1% rhodanide ammonium (NH4SCN). These impurities may cause gray, bluish or reddish coloration.
Because of the toxicity to plants of ammonium rhodanide, its content should not exceed 0.1%, especially on soils with low humus and calcium content. Ammonium sulfate contains 24% sulfur, so it is a source of sulfur nutrition for plants.
After application to the soil, most of the NH4+ ammonium ions are included in the absorbing complex:
[SAC]Ca2 + (NH4)2SO4 = [SAC](Ca, (NH4)2) + CaSO4.
The soil’s ability to absorb ammonium protects it from leaching; however, it may not be used in fertilization.
As a result of nitrification, some of the ammonia nitrogen is converted to the nitrate form, which leads to acidification of the soil solution. Acidification is also caused by the physiological acidity of the fertilizer. Systematic application of normal doses of ammonium sulfate leads to a change in the reaction of the soil environment. On acidic soils the negative effect appears after a few years. On chernozem soils it can be applied for a longer time. According to data from Myronivska experimental station in Ukraine, the use of (NH4)2SO4 in 14 years led to changes in soil reaction: pH from 6.0 to 4.9; exchange acidity increased by 1.5, hydrolytic – in 2.5 times. This did not affect the yields due to the high content of humus, high buffer and absorption capacity of chernozem. On chestnut soils and gray soils acidification of carbonate soils with physiologically acidic fertilizers is not dangerous.
On sod-podzolic soils in combination with liming ammonium sulfate is not inferior to other nitrogen fertilizers. However, prolonged use in high doses without liming on these soils deteriorates their properties, growth and productivity of plants. Such crops as oats, winter rye, flax, potatoes, rutabaga react weaker to acidifying action of ammonium sulfate than beets, corn, hemp, barley and spring wheat.
Because of the weak migration of ammonium ions, this fertilizer is effective on light soils and in areas of sufficient moisture. Ammonium sulfate is less effective than other nitrogen fertilizers when applied in rows and as a top dressing.
Ammonium-sodium sulfate
Ammonium-sodium sulfate – (NH4)2SO4⋅Na2SO4, contains up to 16% of nitrogen, 9% of Na2O, up to 2.5% of organic impurities, is a waste product of caprolactam production. It is a yellowish crystalline salt. It is a good fertilizer for sugar beet and cruciferous plants, which are responsive to sodium and sulfur. It can be used to fertilize hayfields and pastures.
Ammonium chloride
Ammonium chloride, NH4Cl, is a byproduct of the production of baking soda (sodium hydrogen carbonate):
NH3 + CO2 + H2O + NaCl = NaHCO3 + NH4Cl.
Ammonium chloride is a fine-crystalline white or yellowish powder, contains up to 26% nitrogen, dissolves in 100 cm3 of water at 20 °C 37.2 g, slightly hygroscopic, does not cake, well dispersed. It is characterized by high physiological acidity and contains up to 60% chlorine, which negatively affects chlorophobic crops such as potatoes, tobacco, grapes, onions, cabbage, hemp, flax, buckwheat, citrus fruits, vegetables, fruits and berries. Therefore, it is introduced in autumn to chlorine washed out of the root layer by atmospheric precipitation.
In soils, ammonium chloride enters into exchange reactions with the absorbing complex:
[SAC]Ca + 2NH4Cl = [SAC](NH4)2 + CaCl2.
In the soil is partially subjected to nitrification. Increase the effectiveness of ammonium chloride can also, as well as ammonium sulfate: liming, pre-neutralization fertilizer (1 kg NH4Cl 1.4 kg CaCO3), joint application with physiologically alkaline fertilizers, a combination with organic fertilizers.
NH4Cl is usually inferior to (NH4)2SO4 in its fertilizing effect. For crops at normal doses, the effectiveness of chloride and sulfate are equal. For crops sensitive to chlorine increased doses are not used, applied in advance as a basic fertilizer.
Ammonium carbonate and hydrogen carbonate
Ammonium carbonate (NH4)2CO3 and ammonium hydrogen carbonate NH4HCO3 are used as fertilizer in small quantities.
Ammonium carbonate is a white crystalline substance obtained by passing carbon dioxide through an aqueous ammonia solution, followed by evaporation of the resulting salt. Carbonate is unstable, and may decompose in the open air, releasing ammonia and forming ammonium hydrogen carbonate. The technical product contains 21-24% nitrogen; it is a mixture of ammonium carbonate, hydrocarbonate and carbamate.
Ammonium hydrogen carbonate, or bicarbonate, is produced by adsorbing gaseous ammonia and carbon dioxide with a solution of ammonium carbonate. It contains about 17% of nitrogen. It is relatively more stable than carbonate, but also has ammonia losses during storage, transportation and application. It should be incorporated into the soil immediately when it is applied on the surface.
Application of ammonium fertilizers
When applied to the soil, ammonium fertilizers are dissolved and the NH4+ ion enters into exchange reactions with the soil solid phase. Most of the NH4+ cations are included in the soil uptake complex, displacing an equivalent amount of cations from it:
[SAC](Ca, H) + NH4Cl = [SAC](Ca, NH4) + HCl;
[SAC]Ca2 + (NH4)2SO4 = [SAC](Ca, (NH4)2) + CaSO4.
When converted to the metabolized state, ammonium is fixed in the soil, thereby preventing its leaching. At the same time, in the exchanged-absorbed state, ammonium remains available to plants.
Partly under the influence of nitrification, ammonia nitrogen is converted into nitrate form. The rate of this process depends on temperature, humidity, aeration, biological activity and reaction of the soil, the degree of cultivation. Thus, in a microfield experiment conducted on poorly cultivated sod-podzolic soils in 15 days of nitrification was 12% ammonium sulfate, after 30 days – 24%, whereas in well-cultivated soils nitrification was 79 and 96% of the introduced amount, respectively.
Overwetting and increased acidity inhibit the process of nitrification. Lime application to acidic soils speeds up the process.
Ammonium chloride nitrifies slower than sulfate due to the inhibiting effect of chlorine on the activity of nitrifying bacteria.
Once ammonium nitrogen is converted into nitrate nitrogen becomes a nitrate fertilizer. In the process of nitrification, nitric, hydrochloric or sulfuric acid is formed in the soil:
NH4Cl + 2O2 = HNO3 + HCl + H2O,
or
(NH4)2SO4 + 4O2 = 2HNO3 + H2SO4 + 2H2O.
In soil, acids are neutralized by the hydrocarbonates of the soil solution and by the cations of the soil absorption complex:
2HNO3 + Ca(HCO3)2 = Ca(NO3)2 + 2H2O + 2CO2;
2HCl + Ca(HCO3)2 = CaCl2 + H2O + CO2;
[SAC]Ca2 + 2HNO3 = [SAC](Ca, H2) + Ca(NO3)2;
[SAC]Ca2 + 2H2SO4 = [SAC](Ca, H2) + CaSO4.
Neutralization of mineral acids is accompanied by consumption of soil solution hydrocarbonates and displacement of bases from the soil absorbing complex with hydrogen, which reduces the buffering capacity and increases soil acidity.
The change in reaction when ammonium fertilizers are applied is also related to their physiological acidity. From (NH4)2SO4 and NH4Cl plants absorb the cation faster than the anion, respectively, acidic residues accumulate. Their systematic application is accompanied by acidification of the soil environment. The degree of acidification is the greater the smaller the buffer capacity.
Table. Effect of fertilizers on acidity and the amount of absorbed bases of gray forest soil (according to the Research Institute of Bast Crops)
| Control (without fertilizer) | ||||
| Manure, 40 t/ha | ||||
| NPK in doses equivalent to 40 tons of manure (nitrogen in the form of (NH4)2SO4) | ||||
On sod-podzolic and gray forest soils with low sum of absorbed bases and organic matter content acidification is manifested faster compared to chernozems and chestnut soils. Thus, long-term application of ammonium sulfate (as part of NPK) on gray forest soils led to an increase in hydrolytic acidity, a decrease in the amount of absorbed bases and the degree of saturation with bases.
To prevent the negative acidifying effect of ammonium fertilizers on such soils prior liming or neutralization of sulfate and ammonium chloride before making the calculation 130-140 kg of lime per 100 kg of fertilizer. Neutralisation of fertilizers is carried out just before application.
Features transformation of ammonium fertilizers in soils predetermine the technology of their effective use. These fertilizers are usually made before sowing as the main fertilizer, and both in spring and autumn, without fear of nitrogen washout.
The effectiveness of ammonium fertilizers depends on the acidity and buffer soils, and biological characteristics of crops.
On soils of the Non-Black Earth zone, ammonium fertilizers can increase the effectiveness of phosphate meal. Physiological acidity of these fertilizers contributes to the dissolution of calcium phosphate.
The effectiveness of ammonium fertilizers depends on the characteristics of the crops grown. Less sensitive crops such as rye, oats, potatoes, flax, buckwheat are less responsive to acidification. Sensitive crops (root crops, most vegetables and legumes, barley, wheat, sunflowers), respond negatively to acidification with repeated applications of ammonium fertilizers.
Crops sensitive to high chlorine content react negatively. For example, the starch content of potatoes decreases in excess chlorine. Therefore, ammonium sulphate is used for chlorophobic crops, or ammonium chloride is added in autumn.
Ammonium nitrogen due to low mobility is localized in the soil where it is applied. Therefore, ammonium fertilizers are of little use for inter-row fertilizing and local application. In the initial phases of growth, the root system of crops is poorly developed and may not reach the fertilizer localization zone.
Ammonium fertilizers are also not used for pre-sowing applications in rows or under pre-sowing cultivation due to the fact that the intensive entry of ammonium nitrogen in young plants can lead to “ammonia poisoning” due to its excessive accumulation.
Ammonium-nitrate fertilizers
Ammonium-nitrate fertilizers are a group of nitrogen fertilizers that include both ammonium and nitrate forms of nitrogen. This group includes ammonium nitrate, ammonium sulfo-nitrate, and lime ammonium nitrate.
Ammonium nitrate
Ammonium nitrate, or ammonium nitrate, ammonium nitrate, ammonium nitrate, NH4NO3, contains 35% nitrate and ammonium nitrogen in a 1:1 ratio. It is obtained by neutralizing nitric acid with ammonia:
HNO3 + NH3 = NH4NO3 + 144.9 kJ.
The resulting solution of ammonium nitrate is evaporated, recrystallized and dried. The heat of the neutralization reaction is used for evaporation. The result is a white crystalline substance containing up to 98-99% NH4NO3. Additives are used to improve the physico-chemical properties.
Ammonium nitrate is well soluble in water: at 20 °C in 100 cm3 of water dissolves 192 g of salt is very hygroscopic, the air dries up and cakes. Depending on the temperature it has five crystalline modifications. Transitions from one modification occur, at temperatures of +32.1 and -16 °C. If during the storage of ammonium nitrate there were sharp temperature changes, capturing these temperature points, there will be a recrystallization of one form into another with an increase in volume. The fertilizer will then thicken greatly, turning into lumps, clumps, and the bags in which it was stored may burst.
To prevent caking of ammonium nitrate it is added hydrophobic and hardening additives: ground limestone, chalk, phosphate flour, phosphogypsum, kaolinite, magnesium nitrate, fatty acids and their amines, and others. The total content of additives ranges from 3.0% to 5.0%. The additives may impart a yellow tint. Fuchsin, which imparts a red color, may be introduced as an additive.
The physical properties of ammonium nitrate depend on the size and shape of the resulting crystals and pellets. The chemical industry produces ammonium nitrate in the form of 1-4 mm granules and flakes (flake nitrate). Granulated ammonium nitrate is characterized by good physical properties.
Moisture content should be no more than 0.3-0.4%, the reaction is neutral or weakly acidic, and the content of insoluble impurities – no more than 0.1%.
To prevent moisture and reduce caking ammonium nitrate is packed in dense, tightly sealed containers – polyethylene or laminated paper bags. For storage, the bags must not be stacked in high piles or stacks, as the bottom layers of the pile strongly compact the bags and they become caked.
To improve physical properties, nitrate can be mixed with precipitate and phosphate flour (for podzolic soils) during storage. Immediately before application to podzolic soils ammonium nitrate may be mixed with 30-40% calcium carbonate, which greatly reduces hygroscopicity and increases the convenience of machine sowing.
Ammonium nitrate is flammable and may explode under certain conditions. At temperatures above 200-270 °C, it decomposes with the release of heat and strong oxidants that accelerate combustion. Rapid heating to 400-500 °C leads to an explosion. Mixtures with combustible materials (sawdust, diesel fuel, paper dust, dry peat, oil) contribute to the manifestation of flammable and explosive properties.
For the first time pure ammonium nitrate was used in our country. Due to the high nitrogen content, the cost of transportation and application is much lower than that of other nitrogen fertilizers except urea and liquid ammonia. Due to the combination of mobile nitrate nitrogen and less mobile ammonium nitrogen, it is possible to vary the methods, doses and timing of its application depending on the soil and climatic conditions and biological characteristics of crops.
When applied to the soil, ammonium nitrate is dissolved by soil moisture. Nitrogen NH4NO3 is absorbed by microorganisms, and at their dying out and mineralization becomes available to plants. In soil, ammonium reacts with the soil absorbing complex:
[SAC]Ca2 + 2NH4NO3 = [SAC](Ca, (NH4)2) + Ca(NO3)2.
When calcium deficiency on acidic podzolic soils, the application of ammonium nitrate leads to acidification of the soil solution. The experiments of D.N. Pryanishnikov established that from the solution of ammonium nitrate the cation NH4+ is absorbed faster than NО3–. Therefore, ammonium nitrate refers to physiologically acidic fertilizers. However, its physiological acidity is lower than that of ammonium fertilizers.
On soils saturated with bases (chernozem, gray soil), the systematic application of high doses of ammonium nitrate does not lead to acidification of the soil solution. Local acidification is temporary, but can have a negative effect on the initial phases of plant growth and increase the mobility of toxic compounds of aluminum, manganese and iron.
On acidic sod-podzolic soils, the application of ammonium nitrate can lead to even greater acidification, which is temporary in nature: the absorption of nitrate nitrogen restores the reaction of the environment to its original value.
Ammonium can undergo nitrification, which also temporarily acidifies the soil. Part of the nitrate nitrogen is lost during denitrification in the form of gaseous compounds (N2, N2O, NO). In the first year after application 40-50% of nitrogen is used; 10-20% of nitrate nitrogen and 20-40% of ammonia nitrogen are transformed into an organic form (immobilized), and only 10-15%, i.e. 2-3% of the introduced nitrogen is assimilated by plants in the second year. The process of immobilization is accelerated by stocking crop residues with low nitrogen content and high carbon content, such as straw, straw manure. Fertilizer nitrogen mobilizes soil nitrogen, which leads to higher utilization factor.
Ammonium nitrate in high doses on low-buffered light soils increases the nitrate content in plants. The use of such plants in animal feed can lead to metabolic disorders and poisoning. Microflora in the rumen of ruminants reduce nitrates to nitrites, which, once in the blood, bind hemoglobin and block its ability to carry oxygen. Increased concentration of methemoglobin in the blood of animals leads to asphyxiation and death in severe poisoning.
The effectiveness of ammonium nitrate when applied to acidic soils is influenced by timely liming. The negative effect of potential acidity can be eliminated by neutralizing the fertilizer with lime or dolomite at the rate of 1 ton of CaCO3 per 1 ton of fertilizer.
Ammonium nitrate is used as a pre-sowing (basic) and in-line (at sowing) fertilizer, for fertilizing during the growing season.
Under irrigation conditions, sufficient or excessive moisture, especially on light soils with granulometric composition, the introduction of ammonium nitrate in autumn under autumn plowing is inexpedient because of the possible washout of nitrate nitrogen. In these circumstances, it can be used directly at the time of the highest nitrogen consumption by plants. In small doses of 10-15 kg/ha nitrate is made in conjunction with phosphorus and potash fertilizers in the rows when sowing sugar beets and vegetable crops, in the wells when planting potatoes. High efficiency is noted when feeding winter cereals and row crops.
Ammonium nitrate is also used for early spring fertilizing of winter crops and perennial grasses. It can be used for top dressing of row crops and vegetable crops during inter-row cultivation with embedding to a depth of 10-15 cm by plant-feeder cultivators.
Ammonium sulfo-nitrate
Ammonium sulfo-nitrate, or ammonium sulfate-nitrate, leyna-selitra, montane-selitra, (NH4)2SO4⋅2NH4NO3 with an admixture of (NH4)2SO4. It contains up to 25-27% of nitrogen, including in the ammonium form – 18-19%, in the nitrate form – 7-8%. It is a grayish fine-crystalline or granular substance.
It is produced by mechanical mixing of 65% ammonium sulphate and 35% ammonium nitrate or by adding dry ammonium sulphate to nitrate alloy, followed by drying and grinding the mixture. The product obtained by the latter method is also called leyna-selitra. Another method of production is the neutralization of sulfuric and nitric acids with ammonia – montan-selitra.
Ammonium sulfate-nitrate is well soluble in water, less hygroscopic than ammonium nitrate. When stored in dry conditions, it does not caking and retains its flowability.
Its efficiency is similar to that of ammonium sulfate. It has a significant potential acidity, so its use on acidic soils requires prior liming or neutralizing fertilizer before applying.
Lime-ammonium nitrate
Lime-ammonium nitrate, NH4NO3⋅СаСО3. It is obtained by fusion of ammonium nitrate with limestone. Available in the form of granules with different ratios of NH4NO3:CaCO3 – from 80:20 to 53:47. Optimal physical and mechanical properties of the product has 60:40 with a nitrogen content of 20.5%.
This fertilizer is less hygroscopic, non-explosive and can be transported in bulk (bulk) mode compared to ammonium nitrate. It is widely used in Western Europe. It is not produced in Russia due to the high cost of transportation (the lower the content of the active substance, the more expensive transportation).
Liquid ammonia fertilizers
Liquid ammonia fertilizers are liquid (anhydrous) and aqueous solutions (ammonia water) of ammonia as well as ammoniates. In terms of their effect on plants, they show the same effectiveness as solid nitrogen fertilizers. Their production is cheaper than that of solid nitrogen fertilizers. Thus, the unit cost of nitrogen of liquid ammonia is about 35-40% cheaper than that of ammonium nitrate (the cheapest of solid nitrogen fertilizers). It is used on the largest scale in the United States.
The use of liquid ammonia fertilizers allows full mechanization of loading and unloading operations and their application. It requires 2-3 times less labour than solid nitrogen fertilisers. Liquid fertilizers are more evenly distributed in the soil, do not have caking and segregation (stratification).
The use of liquid fertilizers has several disadvantages: storage requires special large-capacity tanks, requires the organization of the distribution points, the use of special equipment for the application, the fleet of road and rail tank for transportation.
Liquid nitrogen fertilizer is made by special machines with immediate embedding to a depth of at least 10-12 cm on heavy soils and 14-18 cm – on light soils to avoid loss of ammonia. Losses are possible on the highly carbonate soils with alkaline reaction. Superficial application of liquid ammonia fertilizers is unacceptable. Shallow embedding in the dry topsoil is also associated with large losses of ammonia.
In all cases, anhydrous ammonia is embedded at a depth of at least 14-15 cm, aqueous solution – at least 10-12 cm. In the case of coarse lumpy soil, the depth of embedding is increased by 1.2-1.5 times. They are applied as a basic fertilizer under autumn plowing in autumn, in spring – under pre-sowing cultivation and top dressing of row crops in doses (nitrogen), as well as for solid nitrogen fertilizers. On light soils with low absorption capacity, applying high doses in the fall associated with a possible loss of ammonia, as it can not be completely adsorbed by the soil absorbing complex.
Since liquid ammonia fertilizers are made locally, the coulters of fertilizer machines for solid crops are set at 20-25 cm in meadows and pastures – 30-35 cm when feeding row crops is determined by the width of the row spacing. The technology of using liquid ammonia fertilizers requires higher qualification of specialists.
When fertilizing to avoid possible damage to young plants, excessive ammonia, fertilizers are applied in the middle of the row spacing or at a distance of 15-10 cm from the rows. For uniform distribution in the soil, carry out subsequent inter-row tillage. With nitrification, the formed nitrates become mobile and are transported with soil moisture to the root zone. The intensity of nitrification is determined by soil properties: in chernozem and cultivated sod-podzolic soils, it proceeds faster than in acidic podzolic soils. Synthetic aqueous ammonia undergoes nitrification faster than coke ammonia, as impurities contained in the latter inhibit the activity of nitrifying bacteria.
When liquid ammonia fertilizers are used properly, their effectiveness is not inferior to ammonium nitrate.
Liquid ammonia
Liquid ammonia, NH3 is the most concentrated ballast-free nitrogen fertilizer and contains 82.3% of nitrogen. It is produced by liquefying gaseous ammonia under pressure. It is a colorless liquid with a density of 0.61 kg/m3 at 20 °С. Freezing point is -77.7 °С, boiling point -33 °С. At normal temperature it quickly turns into gas. When stored in open vessels, ammonia quickly evaporates with strong cooling. Elasticity of liquid ammonia vapors:
| Ammonia vapor pressure, Pa | |||||||
|---|---|---|---|---|---|---|---|
| Temperature, °C |
To prevent volatilization of liquid ammonia, it is stored and transported in special steel tanks designed for pressure of 2.5-3.0 MPa. At 20-40° its vapor pressure is 9-18 atm. Elasticity of vapor, density and nitrogen content in 1 m3 depend on temperature. When ammonia is stored in closed vessels under pressure, it is separated into two phases: liquid and gaseous. Due to the high elasticity of vapors, storage and transportation tanks are not filled completely. Liquid ammonia corrodes copper, zinc and their alloys, does not react with iron, cast iron and steel.
Liquid ammonia is a highly toxic substance; mixture with air at volume concentration of ammonia 15-27% is explosive. An explosion may be caused by a spark and any open source of fire. Skin contact causes burns, frostbite when evaporated.
Liquid ammonia turns into gas in soil, adsorbed by soil colloids and absorbed by soil moisture. Well soluble in water: under normal conditions (at 20 °C and atmospheric pressure) in 1 volume of water dissolves 702 volumes of ammonia.
The rate and degree of ammonia adsorption by soil is determined by the absorption capacity and humidity, method and depth of application. On heavy soils with a high organic matter content and normal moisture content, the absorption is greater than on light, humus-poor soils. On light or dry soils, ammonia is retained in gaseous form for a long time, which leads to volatilization losses.
After liquid ammonia application the soil reaction shifts to an alkaline pH of 9 in the first days. In the zone of fertilizer application the soil is temporarily sterilized, which suspends the nitrification process of ammonia nitrogen. In 1-2 weeks the microbiological activity is restored. Under optimal conditions, complete ammonia nitrification occurs within a month.
In terms of payback on additional yield liquid ammonia is comparable to solid nitrogen fertilizers, on light soils, under irrigation or excessive moisture surpasses them.
Ammonia water
Ammonia aqueous solution, or ammonia water, NH3 + H2O. It is a clear liquid, sometimes with a yellowish tint. In aqueous ammonia solution there is always an equilibrium between ammonia absorbed by water and gaseous above the solution surface, which causes its loss when stored in open vessels.
Two grades of ammonia solution are produced: the first with 20.5% nitrogen, or 25% ammonia, and the second with 16.4% nitrogen, or 20% ammonia. Coke-oven aqueous solution contains impurities of hydrogen sulfide, phenols, rhodanides and cyanides.
Ammonia water has a small elasticity of ammonia vapor (25% solution – 0.15 kgf/cm2 at 40 ° C), does not corrode ferrous metals, freezes at temperatures: 25% – at -56 ° C, 20% – at -33 ° C). The density at 15 ° C of the first grade – 0.910 kg/m3, the second – 0.927 kg/m3.
It is stored and transported in leak-tight carbon steel tanks designed for pressure up to 0.4 kgf/cm2. Ammonia water corrodes non-ferrous metals (copper, zinc, tin) and their alloys (bronze, brass), therefore all technological units must be made of ferrous metals. It is inert towards aluminum and rubber.
When applied to soil, ammonia is adsorbed by soil colloids and therefore weakly migrates. Over time, ammonia nitrogen is nitrified, with increased mobility. The use of ammonia water is technically easier and safer than liquid ammonia. The intensity of ammonia absorption by soil is influenced by the granulometric composition, humus content, moisture, depth of embedding. On heavy, well-cultivated soils with high organic matter content, ammonia absorption is higher than on light, dry soils poor in humus, losses from volatilization on which are much greater.
The disadvantage of ammonia water is low nitrogen content, which leads to higher costs for transportation, storage and application. Therefore, its use is advisable in farms located near the sites of fertilizer production.
Amide fertilizers
Urea
Urea, or urea, CO(NH2)2, contains 46.7% nitrogen, one of the most concentrated solid nitrogen fertilizers. The nitrogen in urea is in the amide form of carbamic acid. It is obtained from ammonia and carbon dioxide at a pressure of 30.3⋅105 to 202⋅105 Pa and a temperature of 150-220 ° C. At the first stage of the process ammonium carbamate is formed:
2NH3 + CO2 → NH4COONH3,
followed by urea during its dehydration:
NH4COONH2 → CO(NH2)2 + H2O.
Urea is a white or yellowish crystalline substance, well soluble in water: at 20 ° C in 100 cm3 of water dissolves 51.8 g of urea. It is characterized by a relatively small hygroscopicity; at 20 °С it is close to ammonium sulfate in hygroscopicity, at higher temperatures it absorbs moisture more strongly. It can freeze during storage.
It is available in granular form with 1 – 3 mm granules. During granulation it can be covered with hydrophobic additives. Granulated urea has good physical and mechanical properties, practically does not caking, retains flowability and dispersibility.
In the process of granulation under the influence of elevated temperatures an impurity is formed – biuret:
2CO(NH2)2 → (CONH2)2HN + NH3.
When its content exceeds 3%, it becomes toxic to plants.
Biuret decomposes in the soil within 10-15 days. Therefore, applying urea with high content of biuret 1 month before sowing does not have a negative effect on plants. At present, granulated urea is produced with biuret content not exceeding 1%, which does not have a depressing effect on plants regardless of the application period.
In the soil, urea dissolves with soil moisture and under the influence of the enzyme urease of plant residues and microflora undergoes ammonification, turning into ammonium carbonate:
CO(NH2)2 + 2H2O = (NH4)2CO3.
Under favorable conditions in cultivated soils, the conversion occurs within 1-3 days.On poorly fertile sandy and overwatered soils the process takes up to 3 weeks. Urea dissolved in the soil solution before ammonification can be washed out.
The resulting ammonium carbonate is unstable, decomposes in the air to form ammonium hydrocarbonate and ammonia gas:
(NH4)2CO3 → NH4HCO3 + NH3.
Therefore, at surface application of urea without embedding and with insufficient moisture content, ammonia losses may occur. Losses are enhanced on soils with neutral and alkaline reactions. Ammonium carbonate undergoes hydrolysis with the formation of ammonium hydrogen carbonate, NH3 and water, which leads to an alkaline environment:
(NH4)2CO3 + H2O = NH4HCO3 + NH3 + H2O.
Over time, the ammonium is nitrified and the soil reaction shifts to the acidic side. As plants absorb nitrogen, no alkaline and acidic residues of fertilizer remain in the soil, and the reaction of the medium is restored.
Urea is used as the main fertilizer on all types of soils for any crop. In rainfed conditions its effectiveness is equal to ammonium nitrate, in irrigated conditions – to ammonium sulfate. Under conditions of leaching water regime of the soil urea is more effective than ammonium nitrate due to the fact that the amide nitrogen quickly turning into ammonia nitrogen is absorbed by the soil without washout from the root layer.
Urea is used for fertilizing winter crops in early spring with immediate incorporation by harrowing. According to experiments, embedding urea even 1.5 cm dramatically reduces ammonia losses. Urea is used for top dressing of row crops and vegetable crops by plant feeder cultivators. However, in hayfields and pastures surface introduction of urea shows the effectiveness by 15-20% lower than ammonium nitrate due to the significant losses of ammonia from ammonification of urea.
Urea is the best form for foliar fertilizing of plants, especially wheat, especially to increase grain protein content, due to the fact that even in higher concentrations (1% solution) it does not lead to leaf burns and is well absorbed by plants. Urea is absorbed by leaf cells as a whole molecule and assimilated by plants both in the form of ammonia after ammonification, and by direct involvement in the cycle of nitrogen transformations. For foliar dressing it is desirable to use the crystalline form, because its content of biuret is lower than 0.2 – 0.3%.
The use of urea as a pre-sowing fertilizer (in rows) may lead to retardation of seed germination due to the inhibiting effect of excess free ammonia.
Because of its high nitrogen content, it is essential to apply urea evenly to the soil. For uniform spreading, it is thoroughly mixed with other fertilizers immediately before application.
In the global range of nitrogen fertilizers, the proportion of urea use is increasing steadily. Urea production technologies are continuously improved to produce higher quality urea at lower production costs.
Urea is used in production of complex and slow acting nitrogen fertilisers. Due to higher cost effectiveness of urea and other high-nitrogen fertilizers low-nitrogen fertilizers are losing their importance in the nitrogen fertilizer consumption balance.
Calcium cyanamide
Calcium cyanamide, CaCN2 contains 20-21% nitrogen. It is a light powder of black or dark gray color, dusty when dispersed, can lead to inflammation when in contact with eyes and respiratory tract. It is a physiologically alkaline fertilizer as it contains up to 20-28% CaO. Factory technical cyanamide contains impurities of carbon – 9-12%, silicic acid, iron and aluminum oxides.
Its systematic use on acidic soils leads to improvement of their physicochemical properties through neutralizing acidity and enrichment with calcium. It is applied 7-10 days before sowing or in autumn under the winter tillage. It is not recommended for top dressing as calcium cyanamide undergoes hydrolysis in soil and interacts with absorbing complex to form cyanamide H2CN2, which is toxic for plants.
It is almost never used as a fertilizer; it is more commonly used for preharvest removal of cotton and sunflower leaves during harvesting for seed.
Mixed nitrogen fertilizers
Ammonia complexes
Ammonium complexes (ammoniacs) are nitrogen fertilizers that are aqueous solutions of ammonia and ammonium nitrate, ammonium and calcium nitrate, urea or ammonium nitrate and urea. They contain from 30 to 50% nitrogen. Ammonium nitrates are produced in special mixers by introducing a hot solution of ammonium nitrate (urea or calcium nitrate) into a 10-15% ammonia solution.
Ammonia complexes are liquids of light yellow color; depending on the composition, ammonia vapour elasticity at 32 °C is from 0.2 to 3.6 atm. According to vapour elasticity, ammonia compounds are divided into two groups:
- with moderate vapor elasticity – 0.2-0.7 atm, with 35-40% of nitrogen;
- with higher vapour elasticity – 0.7-3.6 atm, with 40-50% of nitrogen.
Ammonia complexes differ in crystallization start temperature: from 14 to 70 °С. Ammonia is produced with low crystallization temperature in winter and with higher one in summer.
Ammonia complexes can corrode copper and ferrous metals alloys, that is why tanks and equipment are made of alloyed steel, aluminum and its alloys, or steel tanks with protective anti-corrosion coating (epoxy resins) are used, as well as tanks of polymeric materials. Nitrogen is transported and stored in special, sealed tanks designed for low pressure. 20-40% of nitrogen in ammonia complexes are in the form of ammonia and 60-80% in the form of ammonium salt or urea.
The application of ammonia complexes requires the same application conditions as ammonia liquid fertilizers, that is, compliance with the depth of embedding, depending on the granulometric composition. In soil, the diffusion of ammonia is usually not more than 8-10 cm, so the distance between the coulters when applying the ammonia complexes should be no more than 20-25 cm. When making ammonia complexes as fertilizer for row crops the distance between the coulters is set equal to the width of the row spacing.
By the effect on crops, ammonia complexes are equal to the solid nitrogen fertilizers. In Russia, the most widely used carbon-ammonium complexes – ammonia solutions of ammonium carbonate and hydrocarbonate and urea, containing 4-7% ammonia and 18-35% of total nitrogen.
Urea-ammonium nitrate
Urea-ammonium nitrate (UAN) is a nitrogen fertilizer, which is an aqueous solution of urea and ammonium nitrate.
UAN with a nitrogen content of 28-32% has several advantages over solid and liquid nitrogen fertilizers: they do not contain free ammonia, so they are more technologically advanced and easy to use; they can be stored in open tanks without nitrogen losses. Urea and ammonium nitrate in solutions produce a mutual dissolution effect, which allows obtaining more concentrated fertilizers without the risk of crystallization. UAN solutions are transparent or yellowish liquids with a density of 1.26-1.33 g/cm3 and a neutral or slightly alkaline reaction.
UAN solutions are prepared in industrial conditions from unevaporated melts of urea and ammonium nitrate. By eliminating the stages of evaporation, pelletizing, conditioning and packaging, the cost of their production is reduced.
Changing the ratio of urea and ammonium nitrate allows to regulate the crystallization temperature (salting-out), which allows to use them in different regions, terms and seasons.
UAN solution grades are selected taking into account storage and use temperatures to prevent crystallization.
Table. Composition and properties of solutions of different brands of UAN[1] Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Composition by weight, %: | |||
| NH4NO3 | |||
| CO(NH2)2 | |||
| H2O | |||
| Density at 15.6 °C, t/m3 | |||
| Temperature of crystal precipitation, °C | |||
UAN solutions can be used as a basis for complex fertilizers with macro- and microelements, such as salts of cobalt, boron, copper, molybdenum, herbicides, retardants.
UAN solutions are transported by carbon steel railroad tanks or by tank-cars using corrosion inhibitors. UAN-32 contains 1.3 times more nitrogen than granulated urea at equal volume, and 1.5 times more than ammonium nitrate, which reduces transportation and storage costs. For on-farm transportation and application of UAN to soil, the same technique can be used as for other liquid fertilizers, ammonia water or herbicides.
UAN solutions are used as the main fertilizer and top dressing. For the main application, you can use the application directly into the soil or superficially, followed by embedding. They can be used for root fertilization of row crops and for foliar fertilization of cereals. UAN solutions can be applied together with irrigation water by sprinkler systems.
Slow-acting nitrogen fertilizers
The production of slow-acting fertilizers is developing in different directions, for example:
- obtaining compounds with limited solubility in water (ureaforms);
- coating fertilizer particles with substances that slow down dissolution (wax, paraffin, oils, resins, polymers);
- introduction of nitrification inhibitors into the fertilizer.
Advantages of slow-acting fertilizers:
- reduced nutrient losses from application to plant uptake;
- higher coefficient of fertilizer use;
- reducing the negative impact on the environment;
- higher product quality due to lower nitrate content;
- reducing labor costs by replacing fractional application with a single application;
- preservation of fertilizer quality during storage and transportation.
The largest producers of slow-acting fertilizers are the USA and Japan.
Aldehydes are used to produce slow acting fertilizers: formaldehyde, acetaldehyde, croton and isobutyric aldehyde etc. This produces, respectively: urea-formaldehyde fertilizer, or ureaform, with a nitrogen content of 38-40%, 28-32% of which is insoluble in water, crotonylidene-diurea with a nitrogen content of about 32%, isobutylene-diurea, with 31% of low-soluble nitrogen, urea-form-acetaldehyde.
The use of low-soluble forms of nitrogen fertilizers is promising in conditions of excessive moisture and irrigation, as well as when applied to vegetable crops, grasses, grasses on sports grounds and lawns, for which nitrogen is applied in large doses and in several steps.
In normal doses in the first year after application, these fertilizers are less effective than urea. However, at high doses, they do not create an excessively high concentration, the nitrogen is almost not washed out, less subjected to denitrification, as it decomposes over a long period is used by plants. Slow-acting nitrogen fertilizers can be made in high doses once every 2-3 years without fear of nitrogen loss.
The disadvantages of slow-acting fertilizers are high cost compared with traditional nitrogen fertilizers, the rate of nitrogen release does not always correspond to the rate of absorption by most crops during the growing season, which causes less efficiency compared to urea in the first year after application.
Encapsulated nitrogen fertilizers
The development of encapsulated nitrogen fertilizers is promising. Encapsulated fertilizers are the usual water-soluble forms, but their granules are covered with films that slow down dissolution. Encapsulated fertilizers have good physical and mechanical properties: less hygroscopic, granules are more durable, do not caking. When released into the soil from granules, nitrogen is gradually released and assimilated by plants as the capsules break down. Depending on the composition and thickness of the capsules it is possible to adjust the dissolution rate of fertilizer in accordance with the biological needs of crops and the frequency of feeding.
Paraffin, polyethylene emulsion, sulfur compounds, acrylic resin, polyacrylic acid are used for encapsulation.
Experiments show that the use of encapsulated nitrogen fertilizers is promising for rice, meadows and long-term pastures, vegetable crops, especially in areas with excessive moisture and under irrigation. In cereal crops the advantages of encapsulated fertilizers over conventional fertilizers are practically absent. The main disadvantage is the high cost, so these fertilizers are used in agriculture to a limited extent.
Nitrification inhibiting fertilizers
Among nitrification inhibitors, cianguanidine (dicyandiamide), the American drug N-serve, or nitripyrine (2-chloro-6-trichloromethyl)pyridine or the Japanese drug AM (2-amino-4-chloro-6-methylpyrimidine) are used. In Russia, the inhibitors picochlor and jacos, which are nitripyrin derivatives, are produced. The application of these inhibitors in mixtures with solid or liquid ammonia fertilizers in the doses of N-serve 0.5-1%, AM 1-3% of the nitrogen content inhibits the nitrification processes up to 1.5-2 months, that is, for the period of intense nitrogen consumption by plants.
The rate of decomposition of inhibitors in the soil and, accordingly, the duration of their action is affected by the granulometric composition of the soil, moisture, environmental reaction, temperature, and humus content.
Inhibitors, by slowing down nitrification, reduce nitrogen losses in gaseous form, flushing with surface runoff and leaching. This leads to increased yields, primarily of cotton, rice, vegetable crops, corn for grain and silage, row crops and fodder crops grown under irrigation or excessive moisture.
The use of inhibitors positively affects product quality because it prevents accumulation of nitrates and reduces the incidence of some diseases. Due to the increased coefficient of nitrogen use, doses of nitrogen fertilizers are reduced, and fractional application is replaced by applying the whole dose in one go.
Table. Effect of nitrification inhibitor N-Serve on the efficiency of nitrogen fertilizers and nitrate accumulation in green mass of winter rape (All-Russian Institute of Fertilizers and Agrochemistry)
Urea-formaldehyde fertilizer (UFF)
Urea-formaldehyde fertilizers (UFF), or ureaform, ureaform, are products of the chemical condensation of urea CO(NH2)2 and formaldehyde (CH2O). Condensation takes place in concentrated solutions at equivalent ratios of urea and formaldehyde in an acidified medium to pH 3, at a temperature of 30-60°. This produces monomethylurea CONHCH2NH2OH, which reacts again with urea and converts to methylenediurea NH2CONHCH2NHCONH2 with evolution of water. The resulting condensate is filtered off, dried, crushed and, if necessary, pelleted. The reaction product is usually a white, crumbly powder that does not cake and retains its flowability even at high humidity.
The nitrogen content of UFF is 38-40%, the water-soluble part accounts for 8-10%, the insoluble part remains available to plants.
One of the main indicators of UFF is the index of assimilation – the amount of nitrogen insoluble in water, which dissolves after boiling for 1 hour. It is expressed as a percentage of water-soluble nitrogen. The digestibility index depends on the reaction, temperature, molar ratio of urea to formaldehyde, and duration of condensation. It varies from 15 to 55%.
In some foreign countries, the index of assimilation is conventionally taken equal to the amount of nitrogen, which is nitrified for 6 months of location of fertilizer in the soil. The degree of nitrification of MFP – an indicator of their effectiveness, depending on the assimilability index and soil properties. UFF with a high digestibility index corresponds to a greater and more rapid accumulation of nitrate nitrogen in the soil.
Acidic soil reaction reduces the rate of conversion of UFF, so liming increases the rate of nitrification. High doses of UFFs alkalize the soil, with gradual acidification occurring as they mineralize.
Under certain conditions of the reaction of condensation, for example, at a temperature of 30-40 °, get UFFs with a high content of available nitrogen for plants, approaching the soluble nitrogen fertilizers. In this case, they lose their purpose as a slow-acting fertilizer.
Urea-formaldehyde fertilizers production is promising because all nitrogen fertilizers are well soluble, but applying them in large doses creates a high concentration and osmotic pressure of the soil solution, which adversely affects plants in the initial stages of growth, especially crops sensitive to high concentrations of salts, such as corn and flax. In addition, in areas of sufficient moisture, especially on light soils, and with irrigation, nitrogen losses from leaching are possible.
On sod-podzolic soils with different degrees of cultivation and different links of field crop rotations the advantages of UFF over soluble nitrogen fertilizers in terms of yield and product quality were not revealed. On heavy sod-podzolic soils the effectiveness of MFP on the yield of green mass of maize was lower.
Fertilizer nitrogen use coefficients
Effective use of nitrogen fertilizers is possible only when taking into account their properties and peculiarities of nitrogen transformation in soils. All nitrogen fertilizers, with the exception of slow-acting forms, are well soluble in water. Nitrate fertilizers migrate in the soil with soil moisture and, except for biological, no type of absorption. Biological absorption occurs only in warm seasons. Therefore, nitrates in the conditions of flushing water regime of soil can be leached, especially on light soils. At higher doses on soils of light granulometric composition in fallow fields under conditions of excessive moisture or irrigation losses of nitrate nitrogen can reach 10-25% of the applied.
Ammonium and ammonium forms when entering the soil are absorbed by the soil absorbing complex. In this form, they lose their mobility, but remain available to plants, are not washed out, except for light soils with low absorption capacity. Under favorable conditions, as a result of nitrification, they are transformed into nitrates, acquiring their properties. Similarly, urea behaves in the soil after it is converted into ammonium forms as a result of the activity of urobacteria.
All nitrogen fertilizers initially or during nitrification accumulate in the soil as nitrates. Nitrates are subject to denitrification processes, which are characteristic of almost all soils, and the main losses of nitrogen are associated with them. According to experiments, nitrogen losses from denitrification for ammonium and amide forms are about 20%, for nitrate – up to 30% of the applied amount. In pure steam and with increasing doses nitrogen losses increase up to 50%.
From an ecological point of view, denitrification has a positive value, as it “frees” the soil from the excess of unused nitrates, preventing their penetration into groundwater and water bodies.
In the soil, part of the nitrogen of fertilizers as a result of microorganisms’ activity is transformed into organic forms that are inaccessible to plants. As a result of immobilization approximately 10-12% of nitrate nitrogen and 30-40% of ammonium, ammonia and amide fertilizers are fixed in organic form. The intensity of immobilization increases with the introduction of organic fertilizers with low nitrogen content and high carbon (stubble, straw, straw manure).
Previously, it was assumed that plants in the first year of nitrogen fertilizer application use 60-70% of the nitrogen received. These data were obtained in field experiments using the difference method by comparing nitrogen export in control variants (without fertilizer) and in variants with fertilizer. Later research using labeled nitrogen atoms showed that under field conditions plants absorb 30-50% of nitrogen from fertilizers, but at the same time the use of soil nitrogen by plants increased by 20-30% in the fertilized variants. As a result, total nitrogen removal in fertilized variants increases by 20-30%, and as a result nitrogen use coefficients calculated by the difference method are by 20-30% overstated from the actual ones.
Nevertheless, for practical purposes, such as the calculation of nitrogen balance and doses of nitrogen fertilizers, the nitrogen use coefficient obtained by the difference method is used, because it characterizes the total nitrogen consumption by plants. Balance calculations made in multi-year experiments, including several crop rotation rotations, confirm these conclusions. The coefficients of the use of fertilizer nitrogen by the balance method are 60-70%.
Most of the fertilizer nitrogen applied to the soil is spent during the growing season for plant consumption, immobilization, denitrification, leaching and erosion. Therefore, the effect of nitrogen fertilizers is not taken into account.
Nitrogen fertilizer efficiency
The efficiency of nitrogen fertilizers is associated with an increase in the use of nitrogen by plants and with a decrease in irretrievable losses. The general solution is to optimize the conditions and regimes of nitrogen nutrition, improve the level of agrotechnics and reclamation measures.
Optimization of plant nitrogen nutrition conditions includes:
- Application of optimal doses and forms of nitrogen fertilizers, taking into account biological characteristics of crops and properties of fertilizers, soil and climatic conditions, the results of plant nutrition diagnostics.
The basis for determining the optimal doses of nitrogen fertilizers based on the results of field experiments carried out in different soil and climatic zones. These data are compared with the results of soil and plant diagnostics, which are the basis for recommendations for the use of fertilizers, methods and ways of adjusting doses depending on specific conditions.
Methods to optimize nitrogen fertilizer doses by the content of mineral nitrogen in the soil are widespread. Effective doses for different crops depend on soil and climatic conditions.
Table. Winter wheat grain yield and efficiency of nitrogen fertilizers depending on the content of mineral nitrogen in the soil (according to the All-Russian Institute of Fertilizers and Agrochemistry)
Depending on the provision of soils with mineral nitrogen they are divided into 5 groups: from very low – group I, to high – group V. Provision of soils with mineral nitrogen affects the effectiveness of nitrogen fertilizers: very high in soils with a nitrogen content of less than 80 kg/ha, low with a content of over 130 kg / ha. The largest increases in grain yield were observed when fertilizers were applied in two applications: the first application in spring, the second – in the phase of the emergence of the tube.
For areas of Western Siberia in Russia, depending on the content in the soil layer 0-40 cm developed a scale of grain crops need for nitrogen fertilizers.
Table. Nitrogen fertilizer demand of grain crops depending on N-NO3 content in the soil layer 0-40 cm in autumn or spring (by Kochergin)
The same methods with changes and modifications are used in other regions of the country.
For optimization of nitrogen fertilizer doses, balance-calculation methods are also used, which are based on nitrogen removal with the planned yield.
- Maximum shift in the timing of fertilizer application to the period of intensive consumption of nitrogen by plants, fractional application of the total dose of fertilizer in several steps.
Table. Nitrogen use of ammonium sulfate depending on the timing of its application (according to the All-Russian Institute of Fertilizers and Agrochemistry)
| РК + (15NH4)2SO4 before sowing | ||||||
| РК + (15NH4)2SO4 piecemeal | ||||||
Closer timing of spring nitrogen dressing of winter wheat and perennial grasses to the beginning of intensive nitrogen consumption significantly increases the effectiveness of dressing. The period of active nitrogen consumption after overwintering occurs 15-20 days after snow melting, i.e. after soil warming. Before that time nitrogen fertilizers are not absorbed in significant quantities and can be washed out and subjected to denitrification. For example, in experiments, VIUA on average for 3 years yield increase of winter wheat grain in 3 times lower when making nitrogen fertilizers on the snow layer 5-7 cm than when making 10-15 days after snowfall.
Experiments were carried out on light soils with a granulometric composition in Yegoryevsk district, Moscow region, and showed a sharp increase in the effectiveness of nitrogen fertilizers in meadows when making the application at the beginning of active grass growth. The application of ammonium nitrate immediately after snowfall on a dry hayfield with temporary excessive moisture increased hay yield by 2 times. Fertilization in the same doses in 20-30 days after the snow melt and drainage of excess moisture increased hay yield 4 times. At the same time collection of protein from 1 hectare increased by 2 times, the coefficient of utilization of nitrogen fertilizer increased by 4 times.
Table. Effect of ammonium nitrate on hay yield (dryland haying of temporary excess moisture) depending on the timing of its application (All-Russian Institute of Fertilizers and Agrochemistry, average for 3 years)
- Application of slow-acting and encapsulated forms of nitrogen fertilizers with controlled rate of nitrogen release.
- Application of nitrification inhibitors, resulting in a 10-15% increase in fertilizer nitrogen utilization factor.
Unproductive nitrogen losses can be reduced by introducing intermediate and stubble crops.
The introduction of 1 kg of nitrogen mineral fertilizers yields 8-15 kg of grain, 50-70 kg of potatoes, 20-30 kg of meadow grass hay, 30-40 kg of sugar beet root crops, about 3 kg of flax fiber.
In the zonal aspect the efficiency of nitrogen fertilizers depends on moisture conditions and the level of natural soil fertility. There are high efficiency and sustained effect of nitrogen fertilizers in the Non-Black Earth zone on humus-poor sod-podzolic, gray forest soils, podzolic and leached chernozems, and the more leached, the higher the efficiency. High efficiency is shown on light soils characterized by constant nitrogen deficiency.
Table. Effects of nitrogen fertilizers on winter wheat by natural-agricultural zones (CINAO)
| Southern taiga-forest | ||||||||||
| Forest-steppe | ||||||||||
| Steppe | ||||||||||
| Dry-steppe | ||||||||||
| Mountainous areas | ||||||||||
| On average in Russia | ||||||||||
On drained peat-bog soils, their effect is reduced, as potassium and phosphorus are in the first minimum. However, in the first years of peatland development in the central and northwestern areas of the Non-Black Soil Zone, nitrogen efficiency increases.
Moving from north to south and from west to east within the European part of Russia, the continentality of the climate increases, and the amount of precipitation decreases, which affects the efficiency of nitrogen fertilizers. The provision of soils with nitrogen also changes.
The efficiency increases in the series sod-podzolic soils → gray forest → black earth. Decrease is observed in steppe areas due to decrease of moisture supply and more favorable conditions of nitrogen nutrition.
Nitrogen fertilizers are also effective in the eastern regions of the country: in the forest-steppe of the Trans-Urals and Eastern Siberia it is higher, in the forest-steppe of Western Siberia with a more continental climate – lower. In the Trans-Urals 1 kg of mineral fertilizer nitrogen gives an increase in grain yield of spring wheat – 10 kg/ha, in Eastern Siberia – 11 kg/ha, in Western Siberia – 5 kg/ha.
In the steppe regions of the European part of Russia on heavy, ordinary and southern black soils due to high nitrogen content in the soil and moisture deficit, the effectiveness of nitrogen fertilizers decreases and becomes unstable. To an even greater extent it is noted on chestnut and light chestnut soils of arid regions of the south-east.
Measures for the accumulation, conservation of soil moisture, as well as under irrigation, the effectiveness of low doses of nitrogen fertilizers in these areas is quite high, and it turns out more than phosphorus and potassium fertilizers.
Table. Increase in potato yield from mineral fertilizers on different soils (All-Russian Institute of Fertilizers and Agrochemistry)
| Podzolic sandy loam | |||||
| Podzolic loamy | |||||
| Grey forests | |||||
| Leached black soils | |||||
Importance of nitrogen fertilizers
Nitrogen fertilizers increase the yield and quality of agricultural products: the protein and gluten content of cereal grains increases, which improves the baking quality of flour.
Assessment of the quality of wheat grain is carried out taking into account a number of indicators. For example, soft wheat is considered to be strong if it has a raw protein content of at least 14%, gluten content of at least 28%, gluten quality not lower than the first group, flour strength of 200-300 conventional units, volume yield of bread over 500 cm3/100 g of flour.
Late fertilization of crops with nitrogen fertilizers has little effect on grain yield, but it increases the protein and gluten content and improves the technological quality.
Table. Effect of mineral fertilizers on the yield and grain quality of winter wheat variety Mironovskaya 808 (Central Experimental Station of the All-Russian Institute of Fertilizers and Agrochemistry)
| Without fertilizers | |||||||
| P90K90 | |||||||
| N90P90K90 | |||||||
| N180P90K90 | |||||||
| N180P120K90 | |||||||
| N90P120K90 + N90 in the spring | |||||||
| N90P120K90 + N90 in the spring + N60 at the flowering time |
Balanced use of nitrogen fertilizers increases the content of vitamins, ascorbic acid, carotene, thiamine, riboflavin and myosin. Nitrate forms contribute to the accumulation of ascorbic acid in plants more than ammonium forms.
Nitrogen fertilizers affect the quality of sugar beet. Thus, the introduction of N60 increases the sugar content of root crops by 0.2-0.4%, the dose of N120, by contrast, reduces by 0.1-0.2%. Doses of nitrogen fertilizer above the optimum increases the content of “harmful” nitrogen in root crops.
Excess nitrogen in the soil at high doses of fertilizers leads to an accumulation of nitrates and nitrites in plants.
Ways to increase the efficiency of nitrogen fertilizers
The effectiveness of nitrogen fertilizers depends on:
- zonal characteristics;
- complex of agronomic and reclamation measures used in crop rotation and for specific crops;
- technology of nitrogen fertilizers application (timing and methods of application, doses, forms);
- methods of plant nutrition diagnostics.
A set of agrochemical methods has been developed in Russia to increase the efficiency of nitrogen fertilizers:
- Compliance with the agronomic technology of application of nitrogen fertilizers, taking into account the doses, forms, timing and methods of application.
- Optimal ratio of nitrogen and other macro- and microelements, taking into account soil fertility and biological characteristics of the crop.
- Optimization of nitrogen nutrition of crops during the growing season.
- Take into account the direct effect of fertilizers as a source of nutrition, and indirect effects associated with the mobilization of nitrogen due to the activation of mineralization processes of soil organic matter. This is important, as the amount of nitrogen formed from mineralization is the most difficult to take into account by existing methods. Nitrogen from mineralization of organic matter can create an excess of nitrogen in the soil, which leads to lodging of crops, deterioration of product quality, a negative impact on groundwater.
- Application of nitrification inhibitors. Despite the fact that this technique is temporary, nitrification inhibition can help to reduce nitrogen losses at the stage of developing comprehensive measures to improve efficiency.
Improvement of slow-acting forms of nitrogen fertilizers: technology for the production of urea-formaldehyde forms (MFU) and encapsulated nitrogen fertilizers, as well as the search for new forms of mineral fertilizers with a gradual transfer of fertilizer nutrients into the soil. - The use of lime in the rotation in the systematic application of nitrogen fertilizers on acidic soils, especially sod-podzolic soils.
- Application of agrotechnical methods aimed at regulating nitrogen mobilization and immobilization processes and humification processes.
Soil nitrogen mineralization when applying nitrogen fertilizers is influenced by:
- the degree of cultivation of sod-podzolic soils: easily hydrolyzed humus compounds prevail in cultivated soils;
- activity of soil microorganisms;
- Increased absorptive capacity of the root system of plants;
- form of nitrogen fertilizer, e.g. ammonium forms promote better nitrogen assimilation than nitrate forms;
- liming;
- application of organic fertilizers, which increase the amount of microflora.
Nitrate and ammonium forms of nitrogen can be immobilized by interaction with soil organic matter, fixation by soil microorganisms, and fixation by clay minerals of ammonium forms. Immobilization absorbs 20-60% of the applied nitrogen, its value depends on:
- forms of nitrogen fertilizers: amide and ammonium forms are fixed 1.5-2 times more than nitrate forms;
- fertilizer dosage: with the increase of dosage the absolute amount of immobilized nitrogen increases while the relative amount – the share of applied nitrogen – decreases;
- the amount of fixed nitrogen: in soils with high humus content the nitrogen content is higher than in low humus soils;
- content of energy material, which simultaneously with mineral fertilizers increases immobilization of fertilizer nitrogen;
- C : N ratio in the soil: the more carbon and less nitrogen, the more is immobilized.
Zonal features
In areas with high efficiency of nitrogen fertilizers, per 1 ton of applied nitrogen you get an additional 10-15 tons of grain, 30-40 tons – root crops of sugar beet, 5-6 tons – raw cotton, about 2 tons – flax fiber, 20-30 tons of meadow grass hay.
The effect of nitrogen fertilizers can manifest itself differently within large agricultural regions of Russia. For example, in the Nonchernozem zone from the introduction of 1 kg of nitrogen in optimum doses allows for additional 8-15 kg of grain, 50-70 kg – potatoes, 3.5 kg – flax fiber, 70-100 kg of silage corn. The high effect of nitrogen fertilizers in this zone is shown on sandy loam and sandy soils, where nitrogen deficiency is almost always observed. Under conditions of washed water regime due to nitrogen losses in the autumn-winter-spring period, application in spring is much more effective than in autumn.
On the podzolized and leached chernozem forest-steppe zone of Ukraine return on nitrogen fertilizer is more than in the right-bank forest-steppe, but less than the left-bank.
In different regions of the steppe zone, for example, in Moldova, large yield increases from the application of nitrogen fertilizers are obtained on typical black soils, smaller increases – on ordinary and carbonate soils. On 1 kg of nitrogen fertilizer you get an additional 6 kg of grain of winter wheat, up to 7 kg of corn, 2.5-3 kg of sunflower seeds, 40-60 kg of root crops of sugar beets.
In the steppe regions of Ukraine on ordinary chernozems nitrogen fertilizers are effective on crops of winter wheat, sugar beet and corn. Their effect weakens from west to east. In the steppe of the European part of Russia a positive effect is noted on ordinary and carbonate chernozems of Kuban, in the foothills of the North Caucasus, on North-Azov chernozems. On carbonate chernozems of Rostov region and ordinary chernozems of the Volga region the effect of nitrogen fertilizers is reduced.
The effect of nitrogen fertilizers on chestnut soils with low humus content is shown in regions with good moisture, such as Ukraine, Transcaucasia, the mountainous regions of the Northern Caucasus. In conditions of severe arid climate of Stavropol, Rostov region, the Volga region, Northern Kazakhstan the effect of nitrogen fertilizers on chestnut soils is often weak. The same is typical for ordinary and southern chernozems and chestnut soils of the Asian flat part of Russia.
Influence of agromeliorative measures on nitrogen fertilizer efficiency
Efficiency of nitrogen fertilizers is connected with timely and quality agronomic, reclamation and soil-protection measures, with high culture of agriculture: absence of weed vegetation, provision of optimal soil regimes, sowing of highly productive varieties and hybrids, comprehensive system of plant protection. All measures for reproduction of fertility and cultivation contribute to increase of efficiency of nitrogen fertilizers and greater payback. The balance of soil organic matter should be positive or deficit-free.
Organic fertilizers reduce the negative effects of high doses of mineral nitrogen and contribute to its more efficient use. Mineral nitrogen should be in the soil in an optimal ratio with other nutrients, corresponding to the requirements of the cultivated crop.
Liming of acidic soils significantly increases the effectiveness of nitrogen fertilizers by better use of nitrogen, increasing its mobilization, improved phosphorus nutrition. In the arid steppe and dry-steppe areas the positive effect of nitrogen fertilizer is possible under the conditions of optimal doses and regimes of irrigation.
Under conditions of risk of erosion processes efficiency of nitrogen fertilizers depends on soil-protecting complex and anti-erosion soil treatment system, such as contour-meliorative plowing across the slope, combined plowing, slotting slopes, creating shafts, furrowing of plowed autumn soil, which reduce water runoff and soil washout.
Doses of nitrogen fertilizers
In the future, the relevance of nitrogen in agriculture and its share in the composition of mineral fertilizers will increase, which is associated with the lability and inability to be fixed in the soil. Increasing the content of other biogenic elements in the soil, its fertility and cultivation leads to the fact that nitrogen becomes a limiting factor in the size and quality of the crop. This trend is observed in a number of countries where high doses of phosphorus-potassium and other mineral fertilizers have been used for decades and a sufficient supply of these elements in the soil has been created.
The need of agriculture in nitrogen fertilizers, depending on the natural and economic zones of the country is projected according to the Geographic Network of field experiments, as well as scientific institutions. On the basis of these studies, the norms of nitrogen fertilizer inputs for crop yield increase have been developed. Modern computer technology allows you to summarize the data of field experiments, to carry out their analysis and to develop programs which allow to adjust the optimal nitrogen demand depending on the availability of fertilizers, the structure of cultivated areas, the planned yields, weather forecasts, etc.
The optimal solution for determination of optimal doses of nitrogen fertilizers for a specific crop is based on the data of field experiments held under local soil and climatic conditions, as well as on the results of agrochemical analysis of soils for the content of organic matter, easily hydrolyzable forms of organic nitrogen, nitrification ability of soil and the content of mineral nitrogen forms.
Optimization of nitrogen fertilizer doses depending on the content of mineral (nitrate and ammonia) nitrogen in the soil (NMIN method) is widespread in the practice of world agriculture.
Effective doses of nitrogen for specific crops depend on zonal characteristics, so methods of nitrogen nutrition diagnostics have their zonal modifications. There are different approaches to determine nitrogen fertilizer doses by mineral nitrogen content in soil when applying NMIN method.
- It is allowed for plants to consume equal amounts of mineral nitrogen from soil and fertilizer. Knowing the plant’s nitrogen requirement for the planned yield and the mineral nitrogen content in the soil, the difference is compensated by applying nitrogen fertilizer.
This method does not take into account:
- effects of organic and mineral fertilizers,
- mobilization of additional “extra” nitrogen from activation of mineralization of soil organic matter,
- the effect of the preceding crop rotation on the nitrogen regime of the soil,
nitrification ability of the soil, - periodicity of nitrogen nutrition of plants,
- depth of soil sampling for agrochemical analysis by crop and in the zonal aspect,
- coefficient of soil nitrogen and fertilizer use depending on crop, soil properties, climatic conditions.
Therefore, this method requires refinement.
Table. Doses of nitrogen fertilizer required to obtain the planned yields of winter wheat depending on the provision of soils with assimilable nitrogen before sowing (0-60 cm layer) (Nikitishen, 1986)
The second variant of the NMIN method consists in determining the indices of soil nitrate nitrogen availability and establishing the crop nitrogen requirement and dose. This method is well grounded scientifically and received wide practical application in diagnostics of crop nitrogen nutrition for Siberian regions. For example, a scale of nitrogen fertilizer requirements for grain crops was developed for the regions of Western Siberia.
To calculate the doses of nitrogen fertilizers for the planned yield the formula is also used:
where R – nitrogen removal with the planned yield of the main and by-products, kg/ha; Nin – nitrate nitrogen in the soil layer 0-50 cm before sowing, kg/ha; Ncurrent – nitrogen of current nitrification during the growing season of the crop, kg/ha; n – coefficient of nitrate nitrogen use in the soil; K – coefficient of mineral fertilizer nitrogen use by plants. Conventionally accepted n = 0.8 and K = 0.6; coefficients are different for each zone.
Table. Nitrogen fertilizer demand of grain crops depending on N-NO3 content in the soil layer 0-40 cm in autumn or spring (by Kochergin)
Table. Content of mobile nitrogen in the soil in the layer 0-40 cm before sowing winter crops and the need for nitrogen fertilizers on chernozem[2]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
*Nitrification capacity without deduction of initial nitrate content
**Feeding only
Determination of the need for nitrogen fertilizers and indicative doses for specific crops can be carried out by the content of mineral nitrogen in the soil and the value of nitrification capacity. The method was developed for the districts of the Volga region and the Orenburg region and is recommended for wide application in farming practice.
In various modifications these diagnostic methods are used in other regions of Russia.
Calculations of nitrogen fertilizer doses can be carried out by the balance method. In our country, A.V. Sokolov, Z.I. Zhurbitsky, I.S. Shatilov, and N.K. Boldyrev contributed to the development and improvement of these methods.
Calculation of the amount of effective nitrogen (Nef), which enters the plants from the soil itself during the growing season, by the content of NMIN at the beginning of the growing season is determined by the formula:
and calculation of the nitrogen dose for the planned yield or its increase by the formula:
where DN – dose of nitrogen for the planned yield, kg/ha; R – nitrogen removal with the planned yield, kg/ha; NMIN – mineral (nitrate and ammonium) nitrogen content in soil, mg/kg; Nef (kg/ha) – amount of effective nitrogen that plants receive from soil (a certain soil layer), taking into account the current nitrification capacity determined by the mineral nitrogen use factor of soil, %; FNMIN – coefficient of mineral nitrogen use by soil, % (for nitrate nitrogen in 0-30 cm layer of chernozem soil equals 200%); Ffertilizer – coefficient of mineral fertilizer nitrogen use; d – volume weight of 1 cm3; h – soil layer depth (cm); dh/10 – soil layer weight, million kg, for converting mineral nitrogen from mg/kg to kg/ha; 100 – converting percent FNMIN and Ffertilizer, %.
Example. Calculation of nitrogen fertilizer doses by the balance method: the content of nitrate nitrogen in the layer 0-30 cm of ordinary chernozem is 10 mg/kg, h = 30 cm, d = 1.2 g/cm3; FNMIN = 200%, Ffertilizer N = 60%, B – nitrogen withdrawal at a grain yield of 4.0 t/ha is 120 kg/ha.
then according to the formula:
Y = Nef / NY,
where NY is the nitrogen content in the grain, kg/100 kg.
The yield of wheat (Y) due to soil nitrogen will be equal to:
72 (kg/ha) / 3 (kg/100 kg) = 2.4 t/ha.
And the dose of nitrogen according to the balance method will be:
Of the 80 kg of nitrogen applied to wheat, the plants use 60%, i.e. 48 kg, which will provide a yield increase equal to:
48 (kg/ha) / (3 kg/100 kg) = 1.6 t/ha.
As a result, the planned yield is provided by soil nitrogen (2.4 t/ha) and fertilizer (1.6 t/ha).
Experimental data allow some researchers to disregard FNMIN and Ffertilizer for nitrogen. In this case, the formula for calculating nitrogen doses takes the form:
The disadvantage of the balance method is the need for optimal values of the indicators included in the above equation.
Modifications of NMIN or balance method allow to set nitrogen fertilizer dosage accurately enough to obtain the planned yield of winter wheat. The method of plant diagnostics allows controlling the level of nitrogen nutrition in plants and timely correcting spring and late nitrogen fertilizing of crops. The combination of soil and plant diagnostics allows to regulate the level of nitrogen nutrition of winter wheat taking into account the soil and climatic and agrotechnical factors.
In Czechoslovakia, a system was developed to monitor the nutritional conditions of cereal crops based on plant analysis data. For this purpose, plant samples are taken in the phase of tubing (5 leaves) and the content of nitrogen, phosphorus, potassium and other elements is determined. According to the ratio of these elements determine the need of crops in fertilizers and the optimal doses for fertilizing.
Table. Optimization of fertilizer nitrogen doses during fertilization of winter wheat in the trumpeting phase based on chemical analysis of plants (by Bayer)
100 and below | high | 80-100 |
||
> 100 | very weak | 30-40 |
||
> 100 | plants are provided for | feeding is unnecessary |
||
> 100 | very weak | 30-40 |
||
> 100 | plants are provided for | feeding is unnecessary |
||
Diagnosis of plant nitrogen nutrition
Nitrogen nutrition of plants due to the mobility of nitrogen in the soil and the need for periodic plant nutrition requires optimization during the growing season through fractional fertilizer application. This is possible with the use of complex soil and plant diagnostics of nitrogen nutrition of plants. In our country the issues of plant diagnostics and optimization of mineral nutrition of crops were addressed by K.P. Magnitsky, V.V. Tserling, N.K. Boldyrev, Y.I. Ermokhin.
V.V. Tserling proposed to determine nitrogen security of winter cereals by the content of nitrate and total nitrogen in plants in bushing and trumpeting phases.
Table. Nitrogen supply in winter cereals by its content in plants by development phases
Based on data on the content of nitrate and total nitrogen in plants according to the state of crops after the wintering and at the time of sampling, taking into account the planned harvest, determine doses of nitrogen fertilizers to fertilize winter crops in the appropriate phase.
Table. Application of nitrogen fertilizer doses for winter crops fertilization in the phase of tubing (4-5 leaves) according to the results of plant analysis, d.v. kg/ha[3]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
The entire aboveground part or individual (indicator) organs are used for plant diagnostics. Portable field laboratories are used for plant diagnostics. For analysis, the lower part of the stem (1-2 mm) of selected plants is cut off, placed on a glass, sap is squeezed out with a glass pestle, and 1-2 drops of 1% diphenylamine solution in concentrated sulfuric acid are applied to it. The intensity of the color is compared with the comparison scale. For an objective assessment, at least 10-15 determinations with subsequent averaging of the results are carried out.
Forms, timing and methods of nitrogen fertilizer application
Forms
The effectiveness of nitrogen fertilizers depends not only on the optimal nutritional regime of the crop during the growing season, but also on the form, timing and method of application. At present, in Russia there is a tendency to increase the share of urea application.
Urea has a number of advantages: it is well absorbed by the soil, travels little in the soil profile, its effect surpasses ammonium nitrate. Its effectiveness increases when applied as the main fertilizer in irrigation conditions and sufficient moisture, especially on light soils, not inferior to ammonium sulfate. Surface application of urea, for example, when fertilizing winter crops in the spring, in meadows and pastures, its effectiveness is lower than that of ammonium nitrate, which is associated with nitrogen loss.
In practice, it is often necessary to combine the application of several forms of fertilizers for the same crop. For example, to obtain a high quality yield of raw cotton 30-50% of the total dose of nitrogen is applied as ammonium and amide forms before sowing, and the rest is in the form of ammonium nitrate as fertilizer. Such a combination is also important in the cultivation of winter and row crops. Or, under conditions of irrigation or excessive moisture can be made slow nitrogen fertilizers as the main, and during the growing season to optimize nitrogen nutrition by feeding ammonium nitrate during the growing season.
For foliar fertilizing of winter wheat to increase protein content in grain urea is preferred because the amide form is well absorbed by plant leaves and does not cause burns even in high concentrations (20-30%).
Liquid nitrogen fertilizers show high efficiency when applied mainly to all crops and when fertilizing row crops. The most effective is liquid ammonia.
Timing of fertilizer application
Under field conditions the nitrogen utilization rate of mineral fertilizers is on average 40-50%. The main part is fixed by the soil in the form of hard-to-hydrolyze organic compounds, which are not available to plants, or is lost as a result of denitrification and leaching. The amount of losses depends on the timing and methods of application, biological characteristics of crops, soil and climatic conditions. Therefore, for nitrogen fertilizers it is important to apply in periods of intensive nitrogen consumption.
Thus, the period of active nitrogen consumption by winter crops in spring begins about 5-15 days after snow melting. By this time, fields are free from excess moisture and the soil is sufficiently warmed. The same applies to meadows, which are fertilized 1 to 3 weeks after snow melt and the outflow of excess water. Application of nitrogen fertilizers immediately after snow melt on dry grasslands with excessive moisture reduces the efficiency of feeding due to gaseous nitrogen losses.
Table. Influence of temperature and humidity on the size of gaseous losses of nitrogen[4]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
In the forest-steppe, especially in the southern regions, and in the steppe zone, the soil dries up quickly in spring, so a late fertilization of winter crops with nitrogen reduces the effectiveness of this technique. In these regions there is no water flow along the soil profile. Therefore, on flat fields, winter crops are fertilized immediately after snowmelt. In the most continental areas of the steppe with little snowy winters, for example, in the Volga region, the North Caucasus and Ukraine, the same effect of nitrogen fertilization of winter crops in early spring and late fall, when a steady cold snap occurs, and even under the winter is often observed on flat land.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.
Fertilizers
Fertilizers are substances designed to improve plant nutrition and soil fertility in order to increase crop yields and improve the quality of crop production.
The word “fertilizer” in Russian has a double meaning. First, it denotes the technological process of fertilizing the soil, and second, it denotes the substances used for this purpose. D.N. Pryanishnikov put into the concept of “fertilizer” the following meaning: fertilizer is food for plants that can increase the mobilization of nutrients in the soil, increase the energy of life processes and change the properties of the soil, that is, fertilizer has a multilateral direct and indirect impact on the soil and plants.
Fertilizers (Русская версия)
Importance of fertilizers
Due to the multifunctional role of fertilizers in the agrocenosis, their importance increases with increasing agricultural productivity, which is confirmed by the experience of farming in many highly developed countries of the world.
Organic and mineral fertilizers influence the soil structure, reaction of soil solution, the rate of microbiological processes, actively participate in fertility reproduction, influence nutrition, plant growth and development, resistance to adverse external factors and, in general, the yield and its quality. For example, soils systematically fertilized with manure are characterized by lower acidity, higher content of phosphorus forms available for plants, increased amount of humus and total nitrogen, a greater degree of saturation with bases. Fertilizers are the basis for the chemicalization of agriculture.
Cultivation of crops results in alienation of nutrients with crops, loss with surface runoff and infiltration into deep layers, erosion. As a result, the balance of nutrients is changed, fertility, crop yields and product quality are reduced. Fertilizers are used to level out the deficit of nutrients in the soil.
Plants form dry matter in the process of their life by absorbing air carbon dioxide, water and soil minerals. As a result, plants accumulate certain substances that characterize the chemical composition of plants.
The most important, so-called biophilic, nutrients are nitrogen, phosphorus and potassium. The amount of nutrients absorbed by plants, contained in all organs and in the entire mass of the crop, allows us to determine their need for nutrients. The consumption of nutrients is expressed in kg per 1 ha or kg per 1 ton of marketable products, including by-products. The optimum content and ratio of nutrients in the soil under the condition of sufficiency of other factors of plant life allows you to get the highest possible yields of crops with high quality.
D.N. Pryanishnikov noted: it took 100 years for Western European countries to increase wheat yield from 0.7 to 1.6 tons per hectare by application of the fruit-change cropping system and improved tillage, and 25 years to increase the yield from 1.6 to 3 tons by application of fertilizers.
In Russia, the use of fertilizers provides up to half of the total increase in crop yields. For example, the application of fertilizers on the soils of the Non-Black Soil Zone, characterized by low natural fertility, or on the southern soils with limited moisture supply, allows a yield increase of up to 75%.
Physical and mechanical properties of fertilizers
Fertilizer losses during transportation and storage can be related to their ability to segregate (for mixed fertilizers), vapor elasticity and viscosity (for liquid forms), bulk density and the angle of natural slope (for powder forms). Organization of transportation and storage of fertilizers is also associated with fire and explosive properties, residual acidity, rate and conditions of decomposition, and toxicity. For example, potassium nitrate when mixed with sawdust is capable of forming fire- and explosive mixtures, and liquid ammonia or its aqueous solutions have a strong asphyxiant stock.
Properties of fertilizers can vary widely depending on the technical features of production, raw materials and their composition, are regulated by technical specifications (regulatory documents). For example, for urea allowable moisture is not more than 0.2-0.3%, calcium nitrate – not more than 14%, powdered superphosphate – not more than 12%, potassium fertilizers – from 1 to 6%. Failure to meet the requirements entails changes in the physical and mechanical properties of fertilizers, which makes them of little use.
One of the properties of fertilisers that greatly affects their use is hygroscopic properties, i.e. their ability to absorb moisture from the air. Among the highly hygroscopic fertilizers are calcium nitrate (9.5 points out of 10 possible) and ammonium nitrate (9.3 points), potassium chloride 3.2-4.4 points, potassium sulfate 0.2 points. Conditions for storage, transportation and packaging of fertilizers are determined by this property. Strongly hygroscopic fertilizers are stored and transported in sealed containers, often in polyethylene bags.
Friability – the suitability of fertilizers for mechanical spreading with fertilizer spreaders, depends on the moisture capacity. The maximum moisture content of mineral fertilizers corresponds to the maximum moisture content, at which the ability to disperse with fertilizer sowing machines is retained.
Fertilisers may cake if stored or transported for an extended period of time. Fertilisers that are caked on the ground require more grinding before spreading. The amount of caking depends on hygroscopicity, moisture, particle size distribution, storage conditions and duration. Traceability is estimated on a 7-point scale and is determined by the resistance to breakdown of caked fertilizer. Simple powder-like superphosphate (7 points), fine-crystal potassium chloride (6 points) are prone to strong caking, ammonium sulfate is weak (2-3 points), resistant to caking potassium sulfate, potassium magnesia (1 point).
Physical and mechanical properties of mineral fertilizers associated with granulometric composition, i.e. particle size. It is determined by the method of sieves. Granulometric composition affects the uniformity of application over the area of the field. Homogeneous granulometric composition when spreading with centrifugal spreaders provides uniform distribution across the width of the machine. When the grain size distribution is not uniform, separation, i.e. scattering of fertilizer particles of different sizes and weights at different distances from the fertilizer spreading unit is observed: larger and heavier particles are thrown at a greater distance, which creates an uneven distribution.
Preservation of granulometric composition during storage, transportation and application in the soil depends on the strength of granules, which is characterized by the mechanical crushing strength (in kgf/cm3) and abrasion (in %). The strength of granules is related to humidity, size and shape of the particles, the presence of hydrophobic additives, the density of fertilizer packaging, and the duration of storage.
Fertilizer spreadability, or flowability, is the mobility of fertilizer particles at their application with fertilizer seeders. Fertilizer spreadability is evaluated with a 12-point system.
When transporting fertilizers and calculating the size of storage space, we take into account the density of fertilizers, that is, the volume per unit mass (1 t/m3) and weight per unit volume. The least dense are ammonium chloride and urea (0.58-0.65 t/m3), heavy – tomaslak, limestone and phosphate rock (2.01-1.62 t/m3).
Some fertilizers with good physical and mechanical properties, such as ammonium sulfate, potassium sulfate, allowed to transport and store bulk – in bulk. When storing them take into account the angle of natural slope (rest), which is formed by the horizontal plane (surface) and the slope line of the fertilizer heap.
Fertilizer application timing and incorporation methods influence efficiency and rational use of fertilizer.
Table. Yield increment of sugar beet (t/ha) depending on the time of application and methods of fertilization
| Kharkovskaya | ||
| Mironovskaya | ||
| Kurskaya | ||
The efficiency of mineral fertilizers increases under conditions of irrigation or sufficient moisture due to precipitation.
A deficit of moisture in the soil reduces the effectiveness of fertilizers, but excessive moisture also has a negative impact on efficiency due to leaching of nutrients.
Soil fertility is another factor in fertilizer efficiency. High weed infestation, poor tillage, violation of agrotechnical requirements reduces the effectiveness of fertilizers. For example, an increase in grain yield per 1 kg of the active substance of fertilizers on average more than 4 kg of grain. Depending on nutritional conditions it varies for different crops: winter wheat – 3,2-5,8 kg, spring wheat – 2-6,2 kg, corn – 3,3-7,6 kg of grain, sugar beet – 19,3-37,8 kg of root crops, potatoes – 25-37,6 kg of tubers.
Fertilizer efficiency
The effectiveness of the fertilizer depends on:
- type and form of fertilizer;
- optimal dosage;
- ratio of the nutrients to be applied;
- timing of application;
- methods of application.
When selecting fertilizers take into account the properties of soils and climatic conditions, biological and varietal characteristics of crops grown. When choosing the form of fertilizer – the attitude of plants to its ionic composition, the physiological reaction of fertilizer, the ability of the root system to absorb nutrients from the hardly soluble forms.
Proper determination of fertilizers requires knowledge of the nature of the interaction of the fertilizer in the system soil – plant – fertilizer – environment.
For effective use of fertilizers, it is important conditions of transportation, storage, preparation for application to the soil. Therefore it is necessary to consider the physical, mechanical and chemical properties of fertilizers, such as solubility, hygroscopicity, caking, moisture capacity, dispersibility, granulometric composition, the strength of granules.
The use of fertilizers is in most cases economically profitable. According to calculations, 1 ruble spent on mineral fertilizers provides an increase in yield at an average cost of 2.2 rubles. The share of economic costs for the purchase and use of mineral fertilizers in the country as a whole until 1990 was 15-17% of all crop production costs.
The economic return of fertilizers depends on the natural fertility of the soil. For example, in the Non-Black Earth zone with high moisture availability, but low natural fertility for grain crops yield 3 t/ha as a result of fertilizer is obtained 70-80% increase in yield. In the dry steppe, fertilizers account for 50% of the growth.
Fertilizer is a major factor in increasing yields
Global farming practices show that yields are related to the amount of fertilizer used.
Table. Mineral fertilizer application and cereal yield (average 1986-1988, Popov, 1999)
| Russia | ||
| USA | ||
| England | ||
| Germany (FRG) | ||
| Holland |
The relationship between grain production and the use of mineral fertilizers can be clearly seen in Russia, where there has been a sharp decline in the use of mineral fertilizers and soil fertility.
Table. Mineral fertilizer use and grain production in Russia (annual average, Popov, 1999)
| Mineral fertilizers supplied | |||
| - million tonnes a.s. | |||
| - kg/ha of arable land | |||
| Gross harvest of grain, million tons | |||
| Grain yields, t/ha |
Table. Balance of nutrients in farming in Russia, kg/ha (annual average, Popov, 1999)
According to field experiments of the agrochemical service of Russia, the yield increase from the use of mineral fertilizers is: winter wheat – 0.49-1.27 t/ha; winter rye – 0.48-1.08 t/ha; spring barley – 0.32-1.29 t/ha; corn (grain) – 0.65-2 t/ha; potatoes – 4.9-9.1 t/ha; sugar beet – 5-14.4 t/ha; corn for silage – 2.3-18.1 t/ha; natural grass for hay – 0.6-3 t/ha.
Intensification of farming leads to a further increase in yields, accelerates the removal of nutrients from the soil and the mineralization of humus. The regulation of these processes becomes possible through the application of fertilizers. In the 80s, about 60% of the nutrients were introduced into the soil with mineral fertilizers, and the use of organic fertilizers amounted to more than 4 tons per 1 ha per year. In the 90s, the application of organic fertilizers decreased by more than 5 times, and mineral fertilizers – 10 times. The deficit of humus was 0.52 t per 1 ha of arable land, the need for manure to cover the deficit was 6.5 t/ha.
In the middle of the XX century, the so-called “green revolution” took place, the foundations of which were laid by Norman Borlaug. Countries with a high level of chemicalization of agriculture are characterized by higher yields, the increase of which is based on new varieties of intensive type and progressive farming techniques.
According to summarized data of Russian Academy of Agricultural Sciences academician V.F. Ladonin (1999) grain production in the world grew 3 times: from 630 million tons in 1950 to 1970 million tons in 1990 During the same period application of mineral fertilizers grew 10 times: from 14 up to 140 million tons. At the same time, grain production increased due to the intensification of farming rather than the expansion of cultivated areas. Grain yields in the second half of the XX century increased 2.5 times, an average of 2.1% per year.
In developed countries from 1970 to 1990 fertilizer use increased from 26 to 83 kg/ha, in East Asia and the Pacific from 36 to 190 kg/ha, in Europe from 88 to 142 kg/ha, in the former USSR and China from 46 to 110 kg/ha. In 1990 the grain yield in the DPRK was 4.2 t/ha. The world records for wheat were more than 16 t/ha and for corn more than 22 t/ha.
Crop yield increases of 50% are determined by fertilizers, the remaining 50% come from other factors. According to studies in the U.S., yield increases in the postwar years were 41% due to mineral fertilizers, 15-20% to herbicides and crop protection chemicals, 15% to agronomic practices, 8% to hybrid seeds, 5% to irrigation, and 11-18% to other factors.
Increasing yields lead to increased nutrient uptake by plants, so the higher the planned yield of a crop, the more fertilizer is needed. However, the yield increases in direct correlation with increasing fertilizer doses to a certain level, at which the maximum payment per unit of fertilizer received agricultural products is achieved.
Increasing fertilizer doses is economically justified until the cost of applying additional fertilizers fully recoups the increase in yield.
Effective fertilizer application is possible with a high degree of agronomic technique.
Table. Effect of the complex of agricultural practices on the yield of potatoes on sandy soils
| Without fertilizer, late planting, small tubers, insufficient care | ||
| Fertilizer | ||
| Improved farming techniques, without fertilizers | ||
| Improved farming techniques, with fertilizer |
Numerous experiments in different soil and climatic conditions proved the influence of doses and forms of nitrogen fertilizers on grain quality, especially the protein content of winter wheat grain.
Chemical farming does not replace organic fertilizers. D.N. Pryanishnikov believed: the wrong attitude towards manure is the wrong attitude towards the nutritional elements of mineral fertilizers. Organic fertilizers are one of the basic elements of the fertilizer system.
For example, in the Non-Black Earth zone 20-30 tons of manure per hectare, give an increase in grain yield 0.6-0.7 t / ha, potatoes 6-7 t / ha, root crops to 15 t / ha, silage crops 15-20 t / ha. The effect of manure lasts for 4-5 years. During this time, one ton of manure gives 0.1 tons of increased production in terms of grain.
In experiments Dolgoprudny station introduction of 36 t/ha of manure on four crops of rotation allowed to obtain 3.4 t/ha of additional production in terms of grain.
Table. Yield increments in the crop rotation from the application of 36 t/ha of manure (average for 15 years)
| Rye (grain) | ||
| Oats (grain) | ||
| Clover (hay) | ||
| Fodder beet (roots) | ||
| Total |
Fertilizer classification
According to the nature of the impact on the soil
According to the nature of the impact on the soil and plant nutrient regime fertilizers are divided into direct and indirect.
Fertilizers of direct action – fertilizers that improve plant nutrition by nutrients. This group includes all kinds of minerals, respectively, nitrogen, phosphate, potash, etc., and organic fertilizers.
Indirect fertilizers improve soil properties, mobilize available reserves of nutrients. The indirect include means of chemical reclamation of soils (lime, gypsum), bacterial fertilizers.
Division of fertilizers into direct and indirect conventional, as each of them can have both direct and indirect effects. Getting into the soil, fertilizers improve the mineral nutrition of plants and affect the agrochemical properties. For example, lime or gypsum eliminate excessive acidity or alkalinity of the soil and are at the same time a source of calcium for plant nutrition.
According to the chemical composition
According to the chemical composition, or origin, fertilizers are divided into:
- mineral (nitrogen, phosphate, potash, complex, microfertilizers);
- organic (manure, compost, slurry, poultry manure, straw (for fertilizer), green fertilizer (green manure));
- microbiological.
Mineral fertilizers, depending on their composition, are divided into:
- single-component, or simple, or one-sided – containing only one nutrient element;
- complex – containing two or more nutrients.
According to the types of nutrients, mineral fertilizers are divided into nitrogen, phosphorus, potassium, zinc, etc. In turn, each type can be subdivided according to forms, for example, nitrogen includes nitrate, ammonium, ammonium-nitrate and amide forms.
Depending on the main component, fertilizers are subdivided into macro- and micro-fertilizers.
According to the effect on the reaction of the soil solution mineral fertilizers are distinguished:
- physiologically acidic;
- physiologically alkaline;
- physiologically neutral.
Physiologically acidic fertilizers include fertilizers, cations of which are absorbed by plants to a greater extent than anions. Correspondingly, physiologically alkaline fertilizers are fertilizers, the anions of which are more absorbed by the plants. Physiologically neutral mineral fertilizers have no effect on the reaction of the soil solution.
According to the method of production
According to the method of production fertilizers are divided into:
- industrial;
- local (bone meal, wood ash, limestone, dolomites, gypsum-containing materials, sapropel);
- non-traditional (phosphate slag, phosphogypsum, defecate, shale ash, sewage sludge).
Industrial fertilizers – mineral fertilizers produced at chemical plants.
Local fertilizers – fertilizers obtained in places of application, directly in farms or near them. Local fertilizers include manure, slurry, poultry manure, compost, peat, ash, lime tuff, green fertilizer.
According to their aggregate state
According to their aggregate state, fertilizers are divided into:
- solid:
- powdery, with a particle size of less than 1 mm;
- crystalline, with the size of crystals over 0.5 mm;
- granulated, with the size of granules over 1 mm;
- liquid;
- gaseous.
Mineral fertilizers
Mineral fertilizers are industrial substances or minerals that contain one or more plant nutrients, more often in mineral form, less often in organic form. Currently, mineral fertilizers account for about 60% of the amount of nutrients applied to the soil.
The active ingredient is the nutrient contained in the fertilizer. The content of a fertilizer active substance is expressed as a percentage of weight: for nitrogen fertilizers – per N, phosphorus – on P2O5, potassium – on K2O, magnesium – on MgO, calcium – in CaO or CaCO3, in a micro fertilizer – for the corresponding microelement.
The composition of complex fertilizers is usually expressed in the content of the active substances in numbers, separated from each other by a dash or colon. The first number usually indicates the percentage of nitrogen (N), the second – phosphorus (P2O5), the third – potassium (K2O). For example, N:P:K is 17:17:17.
The ratio of active substances in complex fertilizers is commonly denoted by numbers, with the nitrogen content being taken as one. For the example above, the ratio would be 1:1:1.
The application rate or fertilizer dose is usually indicated in the active ingredient (kg/ha) as a subscript: N60P90K30.
Organic fertilizers
Main article: Organic fertilizers
Organic fertilizers – fresh or biologically processed substances of complex composition of plant or animal origin, used as a fertilizer.
Microbiological fertilizers
Main article: Microbial and bacterial fertilizers
Microbiological fertilizers – preparations containing a culture of microorganisms, the vital activity of which when entering the soil improves the composition, increasing the activity of the microbial community of the soil, thus creating favorable conditions for plant nutrition.
Fertilizer interaction with soil
When applied to the soil fertilizer as a result of interaction with the soil and under the influence of soil microorganisms is subjected to various transformations, which affects the ability to move in the soil, solubility and accessibility to plants. For example, on sandy soils, the rate of decomposition of organic fertilizers is higher than on loamy and clay soils. Phosphate meal under the influence of acidic soil reaction or acidic excreta of the root system, for example, lupine passes into soluble plant-accessible form.
Mineral fertilizers can enter into exchange reactions with soil colloids or absorbed by microorganisms, temporarily fixed in the living plasma.
The rate of fertilizer transformation processes in the soil depends on:
- the nature of the fertilizer,
- soil properties,
- climatic conditions,
- complex agrotechnical measures.
The interaction of fertilizers with the soil can be both positive and negative for plant nutrition. The positive effect of the systematic application of organic and mineral fertilizers is manifested in changes in the physical and chemical properties of soils. Thus, long-term application of manure leads to an increase in the content of organic matter in the soil, increasing the capacity of absorption, reduced exchange and hydrolytic acidity, increased degree of saturation with bases.
Negative effect from the long-term use of mineral fertilizers associated with acidification of the reaction of the soil solution due to the displacement of hydrogen and aluminum ions from the absorption complex, the use of physiologically acidic nitrogen and potassium fertilizers. Negative effects are often a consequence of improper use of agrochemicals, as the current level of scientifically sound fertilizer system can avoid negative effects. For example, a combination of mineral and organic fertilizers, liming, the use of neutralizing additives in physiologically acidic fertilizers eliminates the increase in soil acidity.
Fertilizers change soil properties: solution reaction, intensity and direction of microbiological processes, i.e. have a direct impact on soil fertility.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Fundamentals of Agronomy: Tutorial/Y.V. Evtefeev, G.M. Kazantsev. – M.: FORUM, 2013. – 368 p.: ill.
Soil gypsum
Soil gypsum is a method of chemical reclamation of saline soils with a large proportion of sodium in the soil absorbing complex (SAC) and alkaline reaction using gypsum (CaSO4⋅2H2O). Saline soils are characterized by unfavorable physical, chemical, physical-chemical and biological properties and low fertility.
The method of soil gypsum is scientifically grounded and developed by domestic scientists. The main merit in the study of solonetz soils belongs to academician K.K. Gedroyts.
Properties of alkaline (sodic) soils
Sodic soils (solonets and solonchaks) occupy more than 30 million ha (26 million ha) in Russia, of which about 11 million ha are arable. Overall, sodic soils occupy about 115 million ha in CIS countries, of which 23.9 million ha are arable.
Solonetz are widespread in the southern regions of the Volga region, Western and Eastern Siberia, the Southern Urals and Northern Caucasus, the steppe regions of Kazakhstan. There are separate areas of solonetz in the form of inclusions in the main land massifs.
These soils are characterized by high cohesion, poor physical and chemical properties. In a damp condition they disperse under the influence of high concentrations of sodium, turning into a smeary mass. Processing of such soils leads to high clumpiness. In dry condition their processing is impossible. Yields in this case are low and of poor quality. Microbiological activity is weakened because of high alkalinity and unstable water regime.
Improvement of sodic soils by changing reaction and composition of cations is achieved by application of gypsum.
K.K. Gedroyts suggested method of gypsumification of solonetz soils, which consists in displacement of Na+ cations from soil absorbing complex and replacing them with Ca2+ with simultaneous application of organic fertilizers.
At the same time, organic and mineral colloids peptized with sodium are washed out of the upper soil layers into the lower ones, forming a dense solonetz horizon. Sodium absorbed by SAC is displaced by carbon dioxide solution (carbonic acid), forming carbonates and hydrocarbonates – hydrolytically alkaline sodium salts, the alkalinity (pH) of the soil solution thus becomes more than 9:
[SAC]Na2 + H2O + CO2 → [SAC](Na, H) + NaHCO3;
[SAC](Na, H) + NaHCO3 → [SAC]H2 + Na2CO3.
Alkaline soil reaction is unfavorable for most crops and soil microorganisms. It reduces the availability of phosphorus, iron, manganese, and boron to plants.
Often solonetz are located in spots of different size (from several meters to hundreds of meters across) among the prevailing zonal soils, such as chestnut, brown, chernozem soils of forest-steppe, steppe and semi-desert zones.
Radical improvement of solonetz is achieved by displacement of sodium from soil absorbing complex (SAC) and its replacement with calcium cations, removal of formed sodium salts by leaching and destruction of solonetz horizon. For reclamation of solonetz soils, carbonate sodium salts are eliminated by replacing it with calcium, and the formed Na2SO4 – by leaching.
Negative effect of sodium on physical properties of soil depends on its content in SAC. Significant effect of sodium on soil properties and crop yields is noted at the content of exchangeable sodium more than 10% of the cation exchange capacity. Therefore, gypsum is carried out, if the share of exchangeable sodium in the SAC is more than 10%.
Along with sodium in the composition of exchangeable cations can contain up to 15-35% magnesium.
Importance of soil gypsum
Soil gypsum contributes to improvement of soil water regime, physical and chemical properties of salts, increases their fertility, reduces alkalinity and content of exchangeable sodium in SAC, increases the degree of its saturation with calcium.
According to field experiments, the application of gypsum as a fertilizer on heavy loamy sod-podzolic soils at a dose of 300-500 kg/ha for clover yields an average increase in hay yield 1.62 t/ha, on medium and light loamy soils – 1.11 t/ha, on sandy loam – 0.72 t/ha, on gray forest and leached chernozem soils – 0.65 t/ha. The effect of gypsum on crop yield on acidic soils is due to increased calcium and sulfur nutrition of plants, as well as increased availability of potassium, which is more displaced from SAC.
The average efficiency of gypsum application on the chernozem soils is 0.3-0.6 t/ha of grain and on chestnut soils – 0.2-0.3 t/ha. Gypsum preparation gives an increase in grain yield by 0.3-0.6 t/ha, clover hay – by 0.6-1 t/ha, sugar beet yield increases.
The efficiency of gypsumification of forest-steppe zone solonchaks is proved in experimental and production conditions. Increase in grain yields of cereal crops annually for 7-8 years after a single application of gypsum at a dose of 10 t/ha amounts to 0.5 t/ha. In the steppe zone the efficiency of gypsum application decreases: on meadow-steppe solonchaks the annual increase in grain yield for 8-10 years is on average 0.3-0.4 t/ha.
Classification of sodic soils
Depending on the content of sodium in the soil absorption complex soils are divided into:
- non-solonetzic with a share of sodium up to 3-5% of the absorptive capacity;
- slightly solonetzic – 5-10%;
- solonetzic – 10-20%;
- solonets – more than 20%.
Solonetses are also subdivided into shallow, or corky, with deep occurrence of solonet horizon up to 7 cm, medium – with a depth of occurrence of 7-15 cm, and deep-columnar – with occurrence at a depth of over 15 cm.
Saline soils (solonchaks) are widespread apart from solonets. According to the degree of salinization, i.e. according to the amount of salts and depth of occurrence of saline horizons, saline soils are subdivided into:
- slightly solonchaky with a share of salts more than 0.25% at a depth of 80-150 cm;
- solonchak with salts over 0.25% at a depth of 30-80 cm
- solonchak with saline horizon at a depth of 5-30 cm;
- solonchaks with no less than 1% of salts in the upper layer, sometimes reaching more than 10%.
According to the salt composition, solonchaks are divided into:
- sulfate with a predominant content of Na2SO4,
- soda – Na2CO3 and NaHCO3,
- chloride – NaCl and MgCl2,
- mixed.
Processes occurring during the application of gypsum to the soil
When gypsum gets into an alkaline environment, it reacts:
Na2CO3 + CaSO4 → CaCO3 + Na2SO4,
calcium gradually displaces sodium from the soil absorption complex (SAC):
[SAC]Na2 + CaSO4 → [SAC]Ca + Na2SO4.
The resulting sodium sulfate is a hydrolytic neutral salt, in small quantities is not harmful to plants, but when gypsum salts, where sodium content is more than 20% of the cationic absorption capacity, it is removed by leaching from the root-containing layer.
The removal of sodium carbonate from the soil solution and replacement of sodium with calcium in the SAC, if not eliminates, then reduces the alkalinity of the environment. At the same time there is a coagulation of soil colloids, improving physical, physico-chemical and biological properties of solonetz soils (improved processing conditions, aeration and water permeability).
Gypsum is simultaneously a source of calcium and sulfur for plant nutrition.
Efficiency of soil gypsum
The increase in the efficiency of soil gypsum has an impact on:
- irrigation;
- deep plowing;
- snow retention;
- application of local and industrial fertilizers;
- when applying manure, yield increases from gypsum and manure are summed up.
Optimal forms of fertilizers on solonetz soils are ammonium sulfate and simple superphosphate.
The changes caused by gypsum are retained for many years.
In the forest-steppe zone gypsuming of solonetz soils is more effective than in the steppe zone, mainly solonetz spots with participation of up to 30% in meadow-steppe complexes with depth of groundwater occurrence more than 1.5-2.0 m are subjected to gypsuming. Solonetz soils of the steppe zone are subjected to self-melioration instead of gypsumization, i.e. they are cultivated with three-tier ploughs or reclamation ploughs to plow CaCO3 or CaSO4 underlying the solonetz horizon.
Some solonetz undergo complex reclamation, including reclamation treatment with surface application of starter doses of gypsum to eliminate soil crust, as well as phytomelioration to activate self-melioration at the expense of intra-soil calcium reserves.
Along with plastering, the system of agrotechnical reclamation measures includes sowing perennial grasses, application of organic and mineral fertilizers. On slightly saline soils, increased doses of manure, compost and other organic fertilizers, applied under deep plowing, contribute to their improvement.
Soils of arid-steppe and semi-desert zones, as a rule, are characterized by high content of absorbed calcium. With development of solonetzation the share of absorbed calcium decreases and absorbed sodium and magnesium increases. The process of desalinization should be accompanied by replacement of exchangeable sodium and part of magnesium by calcium. Radical transformation of solonets is possible at:
- replacement of sodium by calcium, with a sodium content of more than 10% of the sum of cations;
- displacement of a part of absorbed magnesium, which is more than 30% of the sum of cations;
- saturation with calcium of absorbing complex up to 70% of the sum of cations.
Skewness in structure of sown areas of meliorative crop rotations, for example, predominance of perennial grasses in rainfed conditions of steppe zone leads to decrease of desalinization intensity or predominance of grain and fallow links in crop rotation leads to deficit of organic matter in soil.
In rainfed (non-irrigated) conditions due to slow interaction of meliorants with soil positive effect lasts for a long time, the full effect is manifested in 4-5 years. To increase efficiency of gypsum formation it is necessary to improve moisture availability of rainfed soils, for which snow retention and deep embedding of meliorants are used. Under irrigation there is a risk of secondary salinization of solonetz soils.
Efficiency of soil gypsum increases in combination with the introduction of organic and mineral fertilizers. Among mineral fertilizers the greatest effect is achieved by physiologically and hydrolytically acidic forms.
Changes in agrochemical and physical properties of saline soils occur slowly, remain for a long time, so repeated reclamation if necessary is carried out not earlier than in 10 years or more.
Doses, timing and methods of application of gypsum
The degree of saturation of the soil absorbing complex with calcium is the basis for calculating the need for chemical reclamation of solonetz soils.The need for chemical reclamation of solonetz soils increases with transition from slightly solonetzic soils to solonetzic soils and solonets, i.e. with increase of sodium share in cation exchange capacity (CEC) from 5-10 to 20% and more.
From the equation of chemical reaction of interaction of gypsum and sodium carbonate of soil it follows that 0.086 g of CaSO4⋅2H2O is needed to replace 1 g of sodium by equivalent mass, then 0.086⋅(Na – K⋅T)/100 g (CaSO4⋅2H2O) is needed to replace excess sodium in 1 g of soil to safe content (K). For a 1-cm-thick soil layer in a 1 ha area (108 cm2), the dose of gypsum D (t/ha) would be:
where Na – sodium content, mmol per 100 g of soil; K – coefficient of safe sodium content, usually equal to 0.1 (10%); T – absorption capacity, mmol per 100 g of soil.
For the whole reclaimed layer (H, cm) of soil at volume weight d (g/cm3) the equivalent dose of gypsum D (t/ha) will be:
D = 0.086⋅(Na – KT)⋅Hd,
where 0.086 – mg-eq CaSO4⋅2H2O, g; Na – sodium content, mmol per 100 g of soil; K – coefficient of safe sodium content, usually equal to 0.1 (10%); T – absorption capacity, mg-eq/100 g of soil; H – thickness of reclaimed layer, cm; d – volume mass of reclaimed layer, g/cm3.
Example. A mass of southern chernozem solonets is characterized by absorption capacity T = 25 mmol/100 g of soil; sodium content Nа = 6 mg-eq/100 g of soil; thickness of reclaimed layer H = 25 cm; volume weight of reclaimed layer d = 1.6 g/cm3. The dose of gypsum CaSO4⋅2H2O (D) in this case will be:
D = 0,086 (5 – 0,1 ⋅ 20) ⋅ 20 ⋅ 1,7 = 12,0 t/ha.
According to the degree of calcium saturation of solonets they are subdivided into:
- unsaturated with calcium – when its content in the absorbing complex is less than 70%. Such solonets are found in semi-desert zone;
- calcium-saturated – with its content in the absorbing complex of about 70% of the sum of cations. Gypsum dosage for reclamation of such solonets can be determined by the above formula.
Unsaturated solonetz may be high-sodium, or typical, and low-sodium, i.e. with absorbed sodium content less than 10% of the sum of cations. The rate of gypsum application for high-sodium solonets should correspond to the sum of substituted absorbed sodium up to 10% and the part of magnesium that exceeds 30% of the sum of cations:
T = 0.086(Na – 0.1T) + (Mg – 0.3T)Hd.
For low-sodium solonets, gypsum doses are determined by the content of absorbed magnesium:
T = 0.086(Mg – 0.3T)Hd.
For solonetz soils containing sodium carbonate (soda), the rate of gypsum application is increased to neutralize the negative effect of soda on plants. The saturation of the soil absorbing complex with calcium of soils of arid-steppe and semi-desert zones up to 65-70% contributes to suppression of the dispersing role of sodium and magnesium.
In the conditions of steppe rainfed (non-irrigated) agriculture soil gypsum is effective under the condition of average annual precipitation of more than 400 mm. In dry steppe zone with average annual precipitation less than 300-350 mm chemical melioration is effective only with irrigation.
Large doses of gypsum can be applied in stages over 2-3 years. The best place in the crop rotation for applying gypsum are bare fallows and row crops. It is usually applied under autumn plowing. It is allowed to apply gypsum under spring wheat and annual grasses. On crust solonets, gypsum is applied after plowing with incorporation by cultivators. On medium and deep columnar solonetz with thickness of humus layer more than 20 cm gypsum is brought in by ploughs with skimmers. On solonets with lower thickness of humus layer gypsum is applied in two ways: before plowing and under cultivation after plowing. And the ratio of the first and second parts of the dose depends on the amount of turned out by plows on the surface of the solonetz horizon: the more it is, the greater part of the dose is applied after plowing.
Solonets and saline soils, as a rule, are found in spots among zonal soils. If they occupy up to 30% of the field area, gypsum is applied to solonetz spots, if more than 30%, gypsum is applied to the whole area.
To take into account the content of the active substance in the materials used for gypsum application, the application rate is adjusted by the formula:
where Df is the actual rate of application of material for soil gypsum, t/ha, Da.s. – application rate of pure gypsum, t/ha, %a.s.– content of gypsum in the material intended for soil gypsuming, %.
Zonal recommendations can be used to determine approximate rates of gypsum application:
- in the zone of chernozems:
- on crusted sodic solonets the rate is 8-10 t/ha,
- at weak alkalinity – 3-4 t/ha,
- on medium and deep columnar solonets – 3-4 t/ha,
- in the presence of soda 5-10 t/ha;
- in the zones of chestnut and brown soils:
- on solonetzic soils – 1-3 t/ha,
- on medium and deep columnar solonets – 3-5 t/ha,
- on crust chloride-sulfate solonets – 5-8 t/ha.
Table. Approximate rates of gypsum, t/ha
| Crust solonets | ||
| а) soda | ||
| if the gypsum is slightly alkaline | ||
| б) chloride-sulfate medium and deep columnar solonets | ||
| in the presence of soda | ||
| Solonetzic soils | ||
Ameliorating effect of gypsum materials depends on its solubility, determined by soil moisture, granulometric composition of ameliorant and degree of mixing with saline layer. Therefore, in irrigated conditions gypsum doses can be reduced by 25-30%, in rainfed conditions it is better to apply it under bare fallow, in their absence – in the main tillage under annual grasses, row crops or spring crops.
Materials for soil gypsum
Raw gypsum (CaSO4⋅2H2O) is a gray or white soft powder containing 71-73% (Class B) and 85% (Class A) of CaSO4⋅2H2O. It is obtained by grinding natural gypsum. The remainder on a sieve with a mesh size of 0.25 mm should not be more than 25% of CaSO4. Produced by grinding natural gypsum. It is poorly soluble in water, so the efficiency is affected by the fineness of grinding. Granulometric composition: all particles should have a size < 1 mm, at least 70% of particles < 0.25 mm with a humidity of no more than 8%. Higher humidity leads to caking of gypsum, turning it into blocks.
Phosphogypsum is a waste from the production of double superphosphate, precipitate and wet-process phosphoric acid, is a gray or white powder containing 70-75% (89-93%) CaSO4 and 1,5-3% P2O5 (15-25 kg / t). It surpasses gypsum in efficiency. At high humidity, it freezes, so, as well as crushed gypsum, it is stored in dry warehouses. When using it, take into account the phosphorus it contains.
Crushed gypsum and phosphogypsum can be used as a calcium fertilizer for legume crops at the rate of 300-400 kg/ha.
Clay gypsum is a natural deposits of loose, unmilled rock containing up to 60-90% CaSO4 and 1-11% clay.
Pyritic pellets and technical acids such as sulfuric H2SO4, nitric HNO3 and phosphoric H3PO4 can also be used to acidify alkaline soils. Acidification is a faster and more efficient, but economically more costly way to eliminate alkalinity in the soil solution by replacing sodium with hydrogen in the SAC. Despite this, plant nutrition and availability of nitrogen, phosphorus and other nutrients are improved.
Calcium-containing industrial wastes, such as defecate, can be used to replace sodium in the soil absorption complex, but their use is limited.
Soil self-gypsum
Some chloride-sulfate and sulfate-chloride solonets of chestnut soils may contain layers of gypsum at a depth of 35-45 cm. To improve the state of cultivation of such soils, self-gypsum is used, i.e. a three-tiered plough is plowed to a depth of 45-50 cm, during which the gypsum-bearing layer is mixed with the upper solonetz horizon. In spring, after deep plowing, the field is kept under fallow for up to 1.5 months, then disced and plowed every 30-40 days. In winter, snow retention is used, and the following year spring wheat is sown with a seeding of perennial grasses, such as alfalfa, vetch, melilot, and others.
With high content of calcium carbonate (calcareous rocks) in the subsoil layer, it can also be used for self-reclamation of saline soils, but the effect of CaCO3 is much inferior to gypsum CaSO4⋅2H2O. The formed Na2SO4 is removed by irrigation. For self-reclamation the treatment of steppe and meadow-steppe solonets is carried out with three-tier ploughs or other ameliorative ploughs. With a single tillage in the steppe zone, a stable increase of grain crops yields of 0.4-0.6 t/ha and grass hay yields of 0.7-0.8 t/ha is obtained.
Sometimes method of leveling is used, i.e. non-saline soil is transported to solonetz plots during 3-5 years at the rate of 500 tons per 1 hectare. The method is labor-consuming, requires high economic expenses and cannot be widely spread.
To improve properties of poorly saline soils, as a rule, self-melioration, earth-melioration and phytomelioration are resorted to.
Earth-melioration (earthing) – method of moving by scraper (bulldozer) on solonetzic spots of fertile soil of adjacent basic zonal type of soils, most often chernozems, with a layer of 15-20 cm. Approximately 10 tons of calcium per 1 ha, part of which is involved in reclamation of the underlying solonetz horizon.
Phytoreclamation is effective with any type of land reclamation, provided the proper selection of crops, alternation and optimal cultivation technologies. For different regions of Russia grouping of crops by salt and solonetz resistance, resistance to drought, overwatering and other adverse conditions have been developed. Thus, in the structure of meliorative crop rotation, the ratio of fallow areas and crops should contribute to intensive desalinization and desalinization taking into account the types of melioration used (gypsumification, acidification, self-gypsumification, earthing).
Phytomelioration in combination with other types of melioration should help to provide optimal regime of soil organic matter to improve watertight structure, increase biological activity and activation of meliorant interaction with SAC.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Lime fertilizers
Lime fertilizers – materials and mixtures of substances containing compounds (carbonates, hydroxides, oxides) of calcium, sometimes magnesium, used for liming acidic soils and as a source of calcium and magnesium in plant nutrition.
Lime fertilizers are subdivided into:
- solid lime rocks, suitable for use after milling or roasting;
- soft limestone rocks;
- industrial wastes, with a high lime content.
- Soil liming
- Lime fertilizers (Русская версия)
Importance of liming
Solid carbonate rocks, depending on their calcium and magnesium content, are divided into:
- limestones (50-56% CaO, 0.9% MgO),
- dolomitized limestones (42-55% СаО, 0.9-9.0% MgO),
- dolomites (30-32% СаО, 18-20% MgO).
Depending on the content of impurities (clay, sand) lime fertilizers are divided into:
- pure with impurities up to 5% (dolomite, limestone);
- marl or sandy with an admixture of 5 to 25%;
- marl, or sandy with an admixture of 25 to 50%; – marl, or sandy with an admixture of 25 to 50%.
The use of calcareous rocks with impurities over 15-20% is reasonable in the absence of cleaner materials. The effect of fertilizers with high impurity content is slow.
Soft lime rocks include lime tuffs containing 80-98% СаСO3; lake lime, or lake lime – 80-95% СаСO3.
Industrial waste include: shale ash with 30-50% СаО, 1,5-4,0% MgO; defekat – 60-75% СаСO3 and 10-15% of organic matter with admixtures of nitrogen, phosphorus and potassium-containing substances.
The main lime fertilizers include limestone, the proportion of calcium and magnesium in which is 75-100% CaCO3.
Limestone and dolomite flour, lime tuff, chalk and other carbonate forms of lime fertilizer can be applied simultaneously with manure, peat or compost, mixed or composted with organic fertilizers. There is no loss of nitrogen.
Ammonia forms of nitrogen fertilizers can be mixed with carbonate forms of lime fertilizers to improve their physical properties. Calcium fertilizers containing calcium and magnesium oxides and hydroxides are not allowed to mix with ammonia forms of nitrogen fertilizers because of the large losses of nitrogen.
The need for lime fertilizers is often covered by local resources – lime-containing industrial waste or local deposits of carbonate rocks. In most cases it is loose chalk, lime tuffs, lake lime, dolomite flour. However, in Russia as a whole, local lime materials and lime-containing industrial wastes do not play a large role in the balance of lime fertilizers.
Limestone and dolomite flour
Limestone and dolomite flour is obtained by crushing and grinding limestone and dolomite. In Russia (in accordance with GOST 14050-78), limestone flour is produced in two classes and two varieties, in dusty with a moisture content of up to 1.5% and weakly dusty (4-6% moisture) forms. Grades of flour are distinguished by the neutralizing ability: I grade not less than 88%, II grade – not less than 85% CaCO3. According to granulometric composition – the first class is finer grinding than the second. Classes within the grades differ in particle size distribution, the second class is finer than the first, the fractions differ: < 0.25 mm by 5-10%, < 1 mm by 3-10%.
The main component of limestone is calcium carbonate CaCO3, often including up to 10-15% MgO in the form of magnesium carbonate. The presence of MgCO3 increases the hardness of dolomitized limestone. White, gray, yellowish and brownish colors of limestone are due to impurities, which may include organic substances, various compounds of iron and manganese.
Pure dolomites consist of calcium carbonate (up to 54.4% CaCO3) and magnesium carbonate (up to 45.6%).
According to field experiments, summarized by the All-Russian Institute of Fertilizers and Agrochemistry, on average for five years, showed that the most effective is finely ground, that is less than 0.25 mm, fraction of limestone flour. This is explained by the fact that the coarse fraction reacts more slowly with the soil, so in the first years after application contributes little to improve soil properties.
Decrease in the effectiveness of limestone flour with an increase in the proportion of particles larger than 0.25 mm, increases with the transition from pure limestone to dolomitized, that is, to more hard grindable rocks.
Table. Efficiency of lime flour fractions of different granulometric composition (according to the recommendations of the All-Russian Institute of Fertilizers and Agrochemistry, 1992)
Dolomitized limestone with the content of 79-109% of the active substance in terms of CaCO3 can be used in crop rotations, saturated with legumes, potatoes, flax, root crops, as well as on heavily ashed soils.
Dolomite and magnesium limestone flour in the first place is advisable to use on light soils with a granulometric composition.
Magnesium-containing lime materials are optimal forms of lime fertilizers in crop rotations with flax, potatoes and lupine.
Industrial waste
Industrial wastes as lime fertilizers take the second place by total volume of application in Russia. They are often as effective as lime flour.
Economically, the use of industrial waste is often more profitable, since there are no costs for extraction and processing. Ecologically, industrial waste is more appropriate, provided there are no dangerous impurities, than industrial lime fertilizers.
Many wastes from various industries, such as cement dust, waste from pulp and paper mills and factories, soda, soap, leather and other industries, containing calcium oxide, hydroxide, carbonate or silicate can be used as lime fertilizer if there are no hazardous impurities.
Dust from kilns and cement plants with CaCO3 content of more than 60% is used in farms located near cement plants. These materials by machines with closed containers and with pneumatic devices.
Cement dust contains significant impurities of potassium, has a fine particle size distribution and is a fast-acting lime fertilizer. It is effective on soils poor in mobile potassium and for crops sensitive to potassium deficiency.
Burnt and slaked lime
Burnt lime contains more than 170% CaCO3 and is a fast-acting lime fertilizer. It is made by roasting carbonate rocks according to the reaction:
CaCO3 ⋅ MgCO3 → CaO + MgO + 2CO2.
During long-term storage calcium and magnesium oxides absorb moisture and form hydroxides of calcium and magnesium – slaked lime, powdery lime:
CaO + H2O = Ca(OH)2.
Solubility of Ca (OH)2 is much higher than CaCO3, (Mg (OH)2 in water is poorly soluble), so in the first years after making slaked lime more effective than limestone meal, but in subsequent periods of their action is aligned, the duration of after action is less because of the rapid washout of calcium.
Slaked lime contains up to 135% in recalculation on CaCO3, is received as a waste product in lime plants, as well as in the manufacture of bleached lime.
Neutralizing capacity of 1 ton of Ca(OH)2 corresponds to 1.35 tons of CaCO3.
Shale ash
Oil shale ash is produced by burning oil shale. It contains 30-40% CaO, 1.5-3.8% MgO, impurities of compounds of potassium, sodium, phosphorus, sulfur, some microelements. It is a dust-like material and is used in the Baltic States and Belarus.
According to Russian normative requirements (TU 46-7-71) for shale ash:
- neutralizing capacity should be not less than 60% CaCO3;
- moisture content no more than 2%;
- by particle size distribution 97% of the mass must be less than 1 mm.
Most of the calcium and magnesium in the ash is contained in the form of silicic acid forms, which are less soluble than CaCO3, so the neutralization of acidity is much slower. Even at high doses (20 t/ha) ash has a positive effect on crops poorly tolerant to excess calcium (flax, potatoes).
Defecation mud (defecate)
Defecation mud, or defecate, is a waste product from sugar beet factories containing CaCO3 and Ca(OH)2.
According to the Russian regulatory documents (TU 570-74) defecate of the first class is subject to the requirements:
- neutralizing ability should correspond to the content of CaCO3 not less than 60%;
- moisture content – no more than 20%.
For defecate of the second class:
- neutralizing capacity – not less than 40% CaCO3;
- moisture content – not more than 30%.
Defecate with 20-30% moisture content is loose and contains 10-15% of organic matter, 0.2-0.7% of nitrogen, 0.2-0.9 P2O5 and 0.3-1.0% of K2O. When applied in CaO-equivalent amounts, defecate is superior to lime flour in terms of efficiency for all crops. Defecate is important not only on acidic soils, but also on chernozem soils in the areas of sugar beet cultivation.
Steelmaking slags
Steelmaking slag – open-hearth, electric steelmaking, blast furnace slag.
According to the Russian regulatory requirements (ChMTU 11-37-69) they have the following requirements:
- neutralizing capacity must be not less than 80% CaCO3;
- humidity not more than 2%;
- particle size distribution: 70% of the mass must have a particle size of less than 0.25 mm, 90% less than 0.5 mm.
Most of the calcium is contained in the form of silicates, which are less soluble than CaCO3. For this reason, the effectiveness of steelmaking slag as a lime fertilizer depends on the fineness of the grinding.
In addition to calcium, magnesium and silicon, slags contain phosphorus, manganese and sulfur in their impurities. Therefore, the effectiveness of slags is often higher than equivalent doses of limestone and dolomite meal. The silicic acid contained is capable of chemically binding mobile aluminum, indirectly contributing to an increase in mobile forms of phosphorus in the soil.
Belite flour
Belite flour is a waste (sludge) in the production of aluminum. It contains 45-50% СаО, 25% mixture of Na2O and К2O, up to 30% SiO2, 3.4% Al2O3, impurities of phosphorus, sulfur and trace elements.
According to the particle size distribution 50% of flour should have particle size less than 0.15 mm, 90% – less than 1 mm. Belite flour is not inferior to other slags in efficiency.
Local lime fertilizers
Local lime fertilizers consist of loose (soft) carbonate rocks. In terms of their use in Russia, they are in third place. They do not require milling, exhibit faster action and efficiency than ground limestone.
Often local deposits of soft rocks are in areas of acidic soils, so their use to lime the surrounding areas agronomically and economically beneficial. The difference in the effectiveness of coarse and fine fractions of these fertilizers is expressed much weaker than the hard. According to the All-Russian Institute of Fertilizers and Agrochemistry, for 11 years all fractions smaller than 3 mm showed approximately the same effect on crop yields.
Limestone tuffs (spring lime)
Lime tuffs, or spring lime, consists of 70-98% CaCO3 with admixtures of organic matter, up to 25% clay and sand, 0.1% P2O5.
It is found in coastal floodplains, in places where springs emerge, and in the lowlands of the Non-Black Earth zone. In appearance they are loose, porous, easily crumbling mass of gray, sometimes rusty, brown or dark color.
Limestone tuffs with up to 30% moisture content and 85% of the mass is finer than 5 mm, according to the content of CaCO3 is subdivided into:
- first grade with more than 80% CaCO3;
- second grade with 70-80% СаСO3.
In terms of speed of action are superior to limestone.
Lake lime (gaja)
The lake lime, or gaja, is close to lime tuff in its chemical and granulometric composition. At humidity of 15-20% it contains up to 75-80% СаСО3 with admixtures of mineral and organic substances.
Deposits are more often found in dried up reservoirs, also collected by cleaning the bottom of existing reservoirs with subsequent drying. Lake lime has a fine-grained texture, easily scattered. It is a highly effective lime fertilizer.
Peat-tuffs
Peat-tuffs are lowland peats containing from 10-20% to 50% CaCO3. They are a valuable lime-organic fertilizer. Effective on soils poor in organic matter and in need of liming.
The disadvantage of this type of lime fertilizer is the low profitability of their application, so it is advisable to use them at a small distance from the fields.
Marl
Marl contains 25-75% CaCO3, more than 1% MgCO3, and 20-40% sand and clay admixtures. Deposits occur as loose and dense masses. The action is slow.
Dense marl for the winter is advisable to remove to the fields, placing in small piles, which under the influence of changing temperatures and humidity in the spring scatter into small particles. After embedding in the soil in terms of efficiency, they are not inferior to lime meal. More often used on light soils.
Chalk
Chalk contains 90-100% CaCO3 (up to 55% in terms of CaO) with an admixture of up to 0.6% MgO. The effect is superior to limestone, especially in the first years after application, in finely ground form is a good lime fertilizer.
Dolomite natural flour
Dolomite natural flour at moisture content up to 12% consists of 80% or more of calcium and magnesium carbonates in terms of CaCO3 with impurities.
According to its size distribution is a mass, 50-70% of which – particles smaller than 0.25 mm, up to 85% – less than 5 mm. It is a valuable lime fertilizer, and due to the magnesium it contains, it may be more effective than limestone meal on soils with light granulometric composition. Works slower than lime tuff.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Soil liming
Soil liming is a chemical reclamation technique that involves adding calcium and/or magnesium carbonate, oxide, or hydroxide to the soil to neutralize excessive acidity.
Source: commons.wikimedia.org©Mark Robinson (CC BY 2.0)
- Soil liming (Русская версия)
Importance of soil liming
The average annual increase in yields of crops on sandy loam soil in the long-term experiment, depending on the doses of lime (0.5-2.5 on hydrolytic acidity) was 0.31-0.7 tons of grain units from 1 hectare. Net income increased at a decreasing rate with increasing doses of lime and mineral fertilizers, cost recovery was reduced, the maximum cost-effectiveness corresponded to doses of 0.5-1.5 hydrolytic acidity.
In another long-term experiment of the All-Russian Institute of Fertilizers and Agrochemistry (VIUA) on light loamy soils, the maximum average annual productivity increase over 9 years (960 kg of grain units from 1 ha) was achieved at a dose of 1.5 Hg lime, one ruble cost recovery for liming with increasing doses (0.5-1.5 Hg) decreased from 4.0 to 1.8 rubles.
Table. Effect of soil agrochemical properties on barley yield (after 18 years of ammonium nitrate application)[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Barley | ||||
| Clover (1st year of use) | ||||
| Clover (2nd year of use) | ||||
| Flax | ||||
| Oats | ||||
| Potato | ||||
| Winter rye | ||||
Supportive liming of weakly acidic soils also shows economic efficiency. At increase in doses of lime from 2.1 to 6.3 t/ha recoupment of one ruble of expenses on crop rotation in average for 11 years was 3.6-3.9 rubles.
Economic efficiency in specific production conditions can strongly depend on market conditions, economic opportunities of the enterprise, payback on soil liming under individual crops.
According to generalized data of All-Russian Institute of Fertilizers and Agrochemistry 2300 experiments under individual crops and in agrocenoses, the effectiveness of liming increases with increasing soil acidity, as well as on soils with the same acidity with increasing doses of lime.
Table. Average annual increase in yields t/ha of crops different in acidity sod-podzolic soils depending on doses of lime (according to the recommendations of the All-Russian Institute of Fertilizers and Agrochemistry, 1992)
| Winter wheat | |||||
| Barley | |||||
| Winter wheat | |||||
| Oats | |||||
| Spring wheat | |||||
| Perennial grasses (hay) | |||||
| Annual grasses (hay) | |||||
| Forage root crops | |||||
| Potato | |||||
| Flax (straw) | |||||
| Cabbage | |||||
| Legume-cereal seeded meadows (hay) | |||||
| Natural meadows (hay) | |||||
Soil liming helps to improve product quality: the content of sugars in root crops, fat and protein in seeds, carotene and ascorbic acid in vegetables and herbs increases, and the seeding quality of seeds is improved.
Lime treatment of acidic soils is a way to reduce the intake of radionuclides into plants. According to the data of Belorussian scientists, the introduction of lime in doses equivalent to hydrolytic acidity reduces the content of strontium-90 and cesium-137 in products 1.5-2 times, in some cases – 3 times. Doses of lime fertilizers on such soils depend on the level of contamination with radionuclides.
In the Republic of Belarus at the first contamination level, i.e. 1-5 Ci/km2 of caesium-137 and 0.15-0.3 Ci/km2 of strontium-90 the doses of lime fertilizers are increased only on the peaty soils, loosened loamy-sandy soils with рНKСІ 5,51-5,75; loamy-sandy – with рНKСІ 5,51-6,00 are additionally limeed. At the second level of contamination (5-40 Ci/km2 Caesium-137 and 0,30-3,0 Ci/km2 Strontium-90) doses of lime fertilizers are determined on the basis of normalization of the environment to optimum levels in one step.
Table. Average doses of lime fertilizers (t/ha CaCO3) for liming of acidic sod-podzolic and peaty soils at the density of radionuclide contamination by 5,0-40,0 Ci/km2 cesium-137 or 0,30-3,0 strontium-90[2]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. - 854 с.
* (19,0) – for soils with рНKСІ 4.0 and below.
Processes occurring in the soil during liming
The neutralizing effect of calcium and magnesium carbonates is the interaction of carbon dioxide solution (carbonic acid) of the soil solution with the gradual formation of soluble hydrocarbonates, which are hydrolytic alkaline salts:
CaCO3 + H2O + CO2 = Ca(HCO3)2;
Ca(HCO3)2 + 2H2O = Ca2+ + 2OH– + 2H2O + 2CO2.
The appearance of Ca2+ and Mg2+ cations in the soil solution leads to the displacement of hydrogen, aluminum, iron, and manganese cations from the soil absorption complex (SAC):
[SAC](Ca, Al, H3) + 3Ca(OH)2 → [SAC]Ca4 + Al(OH)3↓ + 3H2O.
Calcium and magnesium carbonates interact with humic, fulvic acids, amino acids and other soil organic and mineral acids:
CaCO3 + 2RCOOH → (RCOO)2Ca + H2O + CO2;
CaCO3 + 2HNO3 → Ca(NO3)2 + H2O + CO2.
When making a full dose of lime in acidic soils, actual and exchange acidity is eliminated, hydrolytic acidity is reduced, the content of mobile forms of aluminum, iron, manganese and heavy metals copper, lead, arsenic toxic to plants is reduced.
Balance of calcium and magnesium in the soil
The calcium balance is a theoretical basis for the calcium supply to plants and soils in liming, to assess its effectiveness and to predict changes in the reaction of the soil environment. According to lysimetric experiments, the calcium balance shows that in acid soils there is a constant deficit of calcium, i.e. there is a constant depletion of the arable soil layer with this element.
Calcium balance data are an indicator of stabilization of soil acidity at an optimum level and show the need and timing of supporting liming in a particular agrocenosis, and also serve as a theoretically justified method for determining the rates of lime application for supporting liming for individual crops.
Depending on the ratio of calcium balance inputs and outputs, soil liming can be divided into:
- basic, or ameliorative, which provides a shift in the reaction of the environment to an optimum pH value;
- maintenance, which compensates for the loss of calcium and stabilizes the achieved level of reaction.
Even in highly acidic soils, the exchangeable calcium content often exceeds the needs of crops, and growth and development are severely inhibited by an unfavorable reaction. Therefore, only compounds affecting the reaction are accounted for in calcium balance inputs: lime fertilizers, phosphorit flour, manure and high-ash lowland peat, including composts based on them, calcium cyanamide, and calcium nitrate. Calcium falling out with atmospheric precipitation and dust can be included in the income items if there are relevant data. According to the All-Russian Institute of Fertilizers and Agrochemistry, this amount for Moscow and Kaluga regions is 40-70 kg/ha (according to other data 15-25 kg/ha). However, atmospheric precipitation includes a sufficient amount of sulfate forming substances, which causes an acidic reaction of precipitation, which can lead to accelerated acidification of soils. In such cases calcium and acids that come with precipitation are taken into account, otherwise refrain from accounting for these balance items.
Additional sources of calcium can be organic fertilizers, in which calcium content in terms of CaCO3 reaches 0.32-0.40%, phosphate meal with neutralizing ability of about 22% CaCO3. Calcium contained in superphosphate does not significantly affect soil pH.
Leaching (leaching) of calcium by infiltration waters from soil profile and domestic removal with crops prevail among expenditure items. Calcium leaching increases with the application of mineral, primarily physiologically acidic forms. In the absence of data on the effect on calcium losses from the quantity and quality of applied mineral fertilizers, the amount of calcium necessary to eliminate the acidifying (cumulative for the rotation of crop rotation) effect of specific forms of nitrogen and potassium fertilizers is added to the expense items. For example, to neutralize 100 kg of fertilizer requires the amount of CaCO3 (kg): NH4NO3 – 75 kg, liquid ammonia – 50-150 kg, (NH4)2SO4 – 120-170 kg, NH4Cl – 140 kg, CO (NH2)2 – 80-120 kg, KCl – 50 kg, Ca(H2PO4)2 – 10 kg. Application of acidic (upland and transitional) peats as organic fertilizers is also an additional item of consumption in the balance.
Table. Calcium and magnesium removal from crops (kg per 1 ton of production) in terms of CaCO3[3]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. - 854 с.
| Winter rye* | |||
| Winter wheat* | |||
| Spring wheat* | |||
| Spring barley* | |||
| Oats* | |||
| Buckwheat* | |||
| Peas* | |||
| Fiber flax* | |||
| Sugar beet (roots) | |||
| Potato (tubers) | |||
| Forage root crops | |||
| Fodder lupine (green mass) | |||
| Red clover (hay) | |||
| Lucerne | |||
| Perennial grasses (hay) | |||
| Annual grasses (hay) | |||
| Cabbage | |||
| Meadow legume-cereal grasses (hay) | |||
| Meadow cereals grasses (hay) |
* Grain + straw
** Calcium and magnesium removal from limed soils is 10-20% higher
Changes caused by lime in the soil
Correlation analysis according to more than 500 field experiments summarized by the All-Russian Institute of Fertilizers and Agrochemistry established a direct relationship between the effect and aftereffect of lime doses (in t CaCO3/ha) and pH value shifts (ΔрН): increasing doses of CaCO3 leads to an increase in pH shift. The effect of lime on the pH shift reaches its maximum in the first two years after application. Over the next five years there is a gradual acidification and loss of 29% of the achieved shift to a neutral area. After 7-8 years, the loss reaches 50% of the pH level obtained in the first two years.
At equal values of pH in calcareous soils (at applied doses of full hydrolytic acidity) for a long time (before reaching the initial pH value) exchange acidity and the content of mobile forms of aluminum at a high degree of saturation with bases are at a low level. On sour loamy and heavy loamy soils application of full hydrolytic acidity doses of lime may be insufficient to achieve optimum pH values.
Doses and forms of lime fertilizers affect the dynamics of the magnitude and structure of acidity, the degree of saturation of the bases, the content and form of calcium, magnesium and other elements. For example, in long-term studies of the All-Russian Institute of Fertilizers and Agrochemistry, on sod-podzolic light loamy soils, the maximum effect of limestone flour on agrochemical parameters manifested in 2-3 years, dolomite flour – in 5-6 years after application.
The dynamics of soil reaction after liming depends on the created level of environmental reaction. The larger the dose, the higher the pH value is achieved. However, the higher the pH at liming, especially at pH>6, the faster subsequent acidification occurs, which is caused by growth of losses of calcium and magnesium. Therefore, soil liming by high doses “in reserve” is economically and agronomically inexpedient and will create a negative impact on the environment.
Application of high doses of lime does not have a significant impact on the content of humus in the soil, but its quality is improved. In the organic matter at the same time improves the ratio of carbon and nitrogen, increasing the content of more valuable humic acids. Mineralization of organic fertilizers is faster and more stable humic substances are formed.
Soil liming improves the supply of nitrogen and ash elements to plants and promotes the conversion of iron and aluminum phosphates into calcium phosphate salts available to plants.
After liming boron passes to less accessible to plants compounds, forming insoluble compounds with calcium. Increased microbiological activity also increases boron uptake by bacteria. The resulting lack of boron is eliminated by applying boron fertilizer.
Changes caused by lime in the soil
The need for soil liming arises when there is a mismatch between the reaction of the soil and the requirements of the crops being cultivated. The need for liming is determined by the following characteristics.
- Poor growth and development of cultivated crops with good agrotechnics and fertilization. In this case, crops that require a neutral or weakly acidic reaction (barley, corn, sugar beet, wheat, legumes) grow poorly, and weed plants (sorrel (Rumex), horsetail (Equisetum), Sitnik (Juncus), pike (Deschampsia), etc.) are common. In meadow lands with acidic reaction are common: whitegrass (Nardus), pikegrass (Deschampsia), creeping buttercup (Ranunculus repens), bentgrass (Agrostis), heather (Calluna), rosemary (Ledum), frogweed (Juncus bufonius), field broom (Spergula arvensis), pickleweed (Galeopsis), while clover (Trifolium), foxtail (Alopecurus), hedgehog (Dactylis glomerata) and other sweet grasses are absent.
- Low pH. To determine the need for liming, determine the reaction of the soil environment (pH of the salt extract) and the degree of saturation with bases (V). The following limits are adopted: pH less than 4.5 – the need for liming is high; pH 4.6-5.0 – medium need; pH 5.1-5.5 – weak; more than 5.5 – none. According to the degree of saturation of the bases (V) clarify the need for liming soils: V < 50% – strong, V = 51-70% – average, V = 71-80% – weak, V > 80% – is not present.
- Indicators of hydrolytic acidity, the amount of absorbed bases, granulometric composition, the content of mobile aluminum and manganese, the specialization of crop rotation. On soils with heavy granulometric composition the need for liming is higher than on light soils. The presence of mobile aluminum also increases the need for liming.
- Acidic sod-podzolic soils with well developed white podzolic horizon at least 8-10 cm deep, strongly swamped surface of the arable layer; often manifested surface crust, lack of structure. If the subsoil horizon is not clearly expressed and has small podzolic layers, such soils are characterized by low acidity and do not need liming or weakly need liming. This pattern appears on loamy and clayey soils. Sandy and sandy loam soils even in the absence of whitish podzolic horizon are limed with small doses. Soils underlain by calcareous rocks at a depth of 40-50 cm usually do not need liming.
When setting the sequence of liming in the rotation take into account agrochemical parameters and biological characteristics of crops. Different plants have different attitudes to lime: most respond positively to the introduction of lime, but crops such as potatoes, flax, lupine, can reduce yield and product quality. In this case, apply small doses of lime or combine with manure. For crops most sensitive to acidity, lime is applied in the first place.
Table. Priority of liming of soils depending on the type of crop rotation[4]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
Soils of the third stage are limed in cases of economic feasibility of this method. In crop rotations with intensive crops and vegetable rotations soils are limed regardless of the need. Crop rotations of potato or lye specialization are limed only in case of high soil needs. In meadows liming is carried out in the second and third turn.
First of all, lime is applied to strongly and moderately acidic soils for crops more sensitive to acidity, i.e. in vegetable, forage and field crop rotations (with perennial grasses), as well as acidic soils when establishing cultivated meadows and pastures before sowing grass mixtures. Surface soil liming is less effective and is carried out on natural forage lands.
Research results show that the danger of negative effects of full doses of lime on flax, potatoes and lupine is exaggerated. Systematic application of organic and mineral fertilizers, high soil fertility, the combination of liming with the application of magnesium, boron and increased doses of potassium fertilizers can recommend on sandy and sandy loam soils 1/2-2/3 of the norm of lime, on loamy – 3/4-1 of the full dose.
The effectiveness of potassium, magnesium and boron fertilizers increases with high doses of lime. In flax crop rotations, lime is introduced under the cover crop for perennial grasses, if the grasses are after flax. In other cases, lime is brought closer to the sowing of flax.
In specialized potato crop rotations with 30-40% in the structure of sowing areas, lime doses are reduced. Liming is brought closer to the planting of potatoes to reduce the common scab.
When determining the place of lime application in the rotation, the following shall be taken into account:
- sensitivity of cultivated crops to acid reaction and the content of aluminum and manganese;
- period from applying till manifestation of maximum neutralizing ability of a particular type of lime fertilizers;
- organizational and technical possibilities of carrying out lime treatment works.
The need for liming increases with the systematic application of high doses of physiologically acidic mineral fertilizers, as well as with the development of new lands that require cultivation of the arable layer.
Table. Classification of arable soils according to the degree of need for lime treatment (according to the recommendations of the All-Russian Institute of Fertilizers and Agrochemistry, 1992)
| Sandy | |||||||
| Sandy loam and light loam | |||||||
| Medium and heavy loam | |||||||
| Heavy clays | |||||||
| Peaty | |||||||
* Level of possible harmful effects of soil reaction
When soil pH exceeds 6.0, calcium losses from leaching increase, so the All-Russian Institute of Fertilizers and Agrochemistry has proposed levels of possible harmful effects of soil reaction.
First of all, highly needy soils of the fifth group, which, as a rule, are the least fertile, are subject to liming. However, if for financial and economic reasons there is no possibility to perform liming of all the available areas of acidic soils, it is advisable to liming first medium- and weakly acidic soils, which are more fertile. This approach allows for lower costs (with lower doses of lime and fertilizers) to obtain higher yields of the most valuable crops.
Effectiveness of liming
The effectiveness of liming is affected by:
- soil acidity;
- relation of crops in the crop rotation to liming;
- norms, scales, methods of applying lime fertilizers;
- combination of liming with the introduction of organic and mineral fertilizers;
- evenness of application;
- types and quality of lime fertilizers;
- properties and granulometric composition of soils.
Table. Effect of the combination of lime, mineral fertilizers and manure on crop yields (average for 6 years) in fodder units of 100 kg/ha[5]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| Mineral fertilizers - background | ||||
| Background + lime | ||||
| Background + manure 80 t/ha | ||||
| Background + lime + manure | ||||
Soil liming is most effective when combined with the application of mineral fertilizers and manure. Yields are then equalized on strongly acidic and moderately acidic soils. Liming should be preceded or combined with the application of organic and mineral fertilizers. Under the influence of lime accelerates the mineralization of organic fertilizers. The combination of lime with organic fertilizers can halve the norms of application without reducing efficiency under the first crop and at the expense of this doubling the fertilized area.
The effectiveness of mineral fertilizers, especially physiologically acidic forms, increases by 2-3 times on the background of lime. Moreover, the increase in yields at simultaneous application of lime and mineral fertilizers is greater than the sum of additions at their separate use, especially this is noted on crops responsive to liming.
Application of physiologically acidic forms of mineral fertilizers leads to depletion of the arable horizon calcium and magnesium. Therefore, prolonged use of mineral fertilizers on acidic soils leads to their irrational use and has a negative impact on soil fertility, which is restored by subsequent liming very slowly and incompletely.
After liming on the hydrolytic acidity neutral reaction of the soil is usually established in 2-3 years.
Lime can be applied simultaneously with organic fertilizers in different ways. It is not recommended to apply manure together with burnt or slaked lime, as it leads to increased loss of ammonia. Also lime application is not compatible with the application of phosphate and bone meal (except composts) because of the transition of P2O5 in a form difficult for plants.
On sandy loam and sandy soils it is more appropriate to apply dolomite flour because of the deficit of magnesium on these soils. Sandy and sandy loamy soils are 5-6 times poorer in calcium and 15-20 times poorer in magnesium than loamy and clay soils. Dolomite flour is applied at 1/2 of the hydrolytic acidity.
When making lime or dolomite meal one of the agrotechnical requirements is the uniformity of distribution over the surface of the field. Uneven application leads to a local overabundance of lime, which can cause plants to die from an alkaline reaction. Dry lime fertilizers can be applied with a variety of fertilizer spreaders. The most favorable days for the application of lime fertilizer are windless days and days with thaws.
When liming the soils of fields with hilly terrain take into account:
- Lime spreading by pneumatic spreaders of РУП-8, АРУП-8 type on the fields with 7-10° slope is not recommended.
- On fields with steep slopes, it is recommended to use the РУМ-3 spreader which ensures normal spreading on slopes up to 15°.
- On slopes with a slope of 5-7°, spreaders can be oriented, depending on the wind, in any direction, including across the slope.
- In fields with a 10-15° slope, spreaders should drive uphill; if the slope is steeper than 15°, only drive downhill.
- The coefficient of non-uniformity of lime application on the field with hilly terrain may be by 5-10% higher than on level terrain.
Full doses of lime (by hydrolytic acidity, balance or pH shift), depending on economic opportunities, are made under a particular crop rotation or separately in several receptions. With a single application of a full dose is achieved rapid and complete neutralization of acidity of the arable layer for a long period (4-5 years or more) and provides the maximum increase in yield of crops. Full doses of lime is especially important to apply under the cultures sensitive to acidity on the strong, medium and weakly acidic soils, as well as during deepening of the arable layer of poorly cultivated acidic soils.
For economic reasons full doses can be reduced by 25-50%, a half dose allows doubling the treatment area; yield increases are 20-50% lower, but the total economic effect can be greater. In the first years the difference in efficiency of full and half doses is small, but after 3-5 years at half doses it decreases by 2 or more times.
With very limited financial and economic resources, soil liming is carried out at 20-25% of the full dose of lime (0.5-1.0 t/ha), applying it when sowing or planting acidity-sensitive crops. Such small doses reduce acidity in the root zone and provide an increase in yield only for crops under which lime is introduced, so they are carried out 4-5 times per rotation. At the same time the reduction of acidity of the arable layer in general is postponed for a long period, which leads to increased labor intensity and economic costs in the long term.
The results of numerous field experiments show the high economic return of lime treatment: all costs, depending on the composition of crops, doses of lime and fertilizers pay for themselves by an increase in the first yields of one, two, maximum three crops.
Fertilization system on acidic soils is effective if properly combined with liming. The combined application of lime and organic fertilizers changes the conditions of mineralization of organic matter.
Lime application rates (doses)
Lime application rates depend on the sensitivity of crops in the rotation to acidity, granulometric composition, environmental reaction, humus content, depth of the arable layer and the quality of lime fertilizers. Half doses of lime give an increase in yield, but do not provide a radical change in soil reaction.
Rates of lime fertilizers are calculated in most cases by the value of hydrolytic acidity of the soil, determined by the method of Kappen. To neutralize 1 mg-eq of acidity in 100 g of soil (Hg), 1 mg-eq (or 50 mg) of CaCO3 is needed. If this value is multiplied by the mass of arable layer of 1 ha, which on average for medium-loamy soils is 3⋅106 kg, and to convert milligrams to tons divide by 109, the total dose of СаСО3 (RCaCO3) will be equal:
RCaCO3 = Hg⋅50⋅10⋅3⋅106/109 = 1,5Нg t/ha.
If the content of the active substance in the lime fertilizer is not specified in the form of CaCO3, and in the form of MgCO3, CaO or Ca(OH)2, then the obtained value is recalculated by taking into account the equivalent mass of these compounds, ie multiplying by a factor of 0.84; 0.56; 0.74, respectively. Correction for the content of the active substance Df (t/ha) in a particular fertilizer, taking into account the ballast impurities is equal:
Df = Da.s.⋅100/%a.s. of fertilizer
Particles of lime material larger than 1 mm interact slowly with the soil. The dose of a particular lime fertilizer, taking into account all corrections, is calculated according to the formula:
where D – dose of lime fertilizer, t/ha; W – moisture content, %; N – number of particles larger than 1 mm, %; H – neutralizing capacity, % СаСО3; T – total dose of СаСО3, t/ha.
Doses of lime can be determined by the pH of the salt extract and the granulometric composition.
Table. CaCO3 doses for soils in the Central region of the Non-Black Earth zone, t/ha (All-Russian Institute of Fertilizers and Agrochemistry, 2003)
| Sandy | ||||||||||
| Sandy loamy | ||||||||||
| Light loamy | ||||||||||
| Medium loamy | ||||||||||
| Heavy loamy | ||||||||||
| Clayey | ||||||||||
For sod-podzolic and gray forest soils of Russia on the basis of numerous studies established the dependence between the values of pH and hydrolytic acidity (Hg), which allowed to determine for each region of the country full doses of lime fertilizers, taking into account the granulometric composition.
Table. Lime doses (t CaCO3/ha) for soils in the Moscow region with humus content less than 3% (according to the recommendation of All-Russian Institute of Fertilizers and Agrochemistry, 1992)
| Sandy | |||||||
| Sandy loamy | |||||||
| Light loamy | |||||||
| Medium loamy | |||||||
| Heavy loamy | |||||||
| Clayey | |||||||
Peat-bog soils with an acidic reaction have a high potential acidity due to the high concentration of hydrogen ions. At the same time, these soils are characterized by a high buffering capacity due to the high content of organic matter, so at pH above 5.0 do not need liming.
Table. Doses of lime (t/ha) depending on the acidity of peat-bog soils (as recommended by the All-Russian Institute of Fertilizers and Agrochemistry, 1992)
Table. CaCO3 doses for peat-bog soils, t/ha (All-Russian Institute of Fertilizers and Agrochemistry, 2003)
Lime application rates can be determined by taking into account the exchange (pHsalt), hydrolytic (Hg) acidity and the degree of saturation of the bases (V), taking into account the mass of the arable layer.
Black soils in rotations with sugar beet liming for hydrolytic acidity is more than 1.8 mmol and the degree of saturation of the bases below 93%. Doses of lime determined by the value of the hydrolytic acidity. The above rates of lime are suitable for plowing to a depth of 20 cm. At a different depth of plowing the dose is adjusted.
Table. Average doses of lime fertilizers (t/ha CaCO3) for liming acidic soils of hayfields and pastures[6]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. - 854 с.
| Sandy | ||||||||
| Loose-sandy loamy | ||||||||
| Cohesive-sandy loamy | ||||||||
| Light and medium loamy | ||||||||
| Heavy loamy | ||||||||
| Peaty | (12,0)* | |||||||
| Sandy | ||||||||
| Loose-sandy loamy | ||||||||
| Cohesive-sandy loamy | ||||||||
| Loamy and clayey | ||||||||
| Peaty | (19,0)* | |||||||
| Sandy | ||||||||
| Loose-sandy loamy | ||||||||
| Cohesive-sandy loamy | ||||||||
| Loamy and clayey | ||||||||
| Peaty | (19,0)* | |||||||
*- for soils with рНKСІ 4.0 and below
In crop rotations with a predominance of low-sensitivity to acidity crops such as potatoes, flax, rye, oats, goatgrass, lupine, seradella, complete elimination of acidity is not required, and it is only necessary to maintain an optimal low acidic reaction (pHKCl) of the soil. For these purposes, the method of calculating doses of lime is used according to the standard costs of shifting the pHKCl value. This method is also used to determine the need for lime fertilizers for the regions of Russia as a whole. The method is based on the dependence of pH-sol change on the doses of lime fertilizers in specific soil and climatic conditions. Thus, in the All-Russian Institute of Fertilizers and Agrochemistry, when summarizing the data from 575 field experiments, the dependences for sod-podzolic and gray forest soils with humus content less than 3 % were obtained.
Table. Effect of increasing doses of lime and its costs (t/ha) on the shift of reaction (pHsalt) of sod-podzolic and gray forest soils (Shilnikov generalization)
In practice, the rate of lime CaCO3 (t/ha) is calculated by the formula:
DCaCO3 = ΔрН⋅C⋅10,
where ΔpH is the planned pH change; C is the cost of CaCO3 to shift by 0.1 pH, t/ha; 10 is the coefficient for conversion to t/ha.
Approximate doses of lime can be determined by the value of pHsalt, taking into account the granulometric composition.
Table. CaCO3 doses (t/ha) depending on pH and granulometric composition of soil with organic matter content less than 3% (according to the recommendations of the All-Russian Institute of Fertilizers and Agrochemistry)
| Sandy loamy and light loamy | ||||||
| Medium- and heavy loamy | ||||||
For cabbage, beet dose of lime is calculated by full hydrolytic acidity. When saturation of crop rotation with potatoes, flax, or low-buffered light soils, the dose of lime is reduced to 1/2 hydrolytic acidity. In meadows, lime is made in doses of 1/2 and 3/4 of hydrolytic acidity in autumn or spring with harrowing. With radical improvement of meadows, make a full dose of lime under the plowing. All fruit and berry crops respond well to liming, so when establishing nurseries and orchards, the soil liming is carried out with full doses of lime.
In crop rotations with potato specialization (more than 40% of the sown areas) reduction of full doses by 20-25% is advisable on sandy and sandy loam soils. Magnesium-containing lime fertilizers (dolomite flour, dolomitized and magnesian limestone) are more preferable. To prevent scab infestation of tubers, lime is applied under potatoes before planting.
In crop rotations with flax specialization increase of pH over 6,0 is not recommended, the optimum values of pH in loamy varieties are 5,0-5,5, light and medium loamy – 5,3-5,8, heavy loam and clay – 5,5-6,0. With full doses of lime increase the norms of potash fertilizers, apply boric and, if necessary, manganese fertilizers.
Forage crop rotations, which are often cultivated sensitive to acidity crops, such as fodder root crops, clover, alfalfa, make full or half the hydrolytic acidity of lime doses, followed by periodic maintenance liming.
Vegetable crop rotations make full or on heavy soils half-and-half on hydrolytic acidity doses of lime with subsequent systematic supporting liming. In these crop rotations the most effective are lime-silicate (shale ash, cement dust) and magnesium-lime (dolomite flour) fertilizers.
According to the sensitivity to acidity, meadow grasses are divided into:
- the most sensitive – alfalfa, melilot, sainfoin;
- sensitive – meadow clover, hybrid and creeping clover;
- moderately sensitive – fescue, foxtail, awnless brome, timothy.
Rates of lime application to meadows and pastures during sowing or reseeding grasses do not differ from doses for arable soils of field crop rotations, but they are applied in layers: one half for the main tillage (plowing), the other half for pre-sowing (discing). On lands with low thickness turf lime is applied on the surface with subsequent embedding by discing or milling.
In spite of reduction of calcium leaching on meadows and pastures by 25-40% (120-140 kg СаСO3/ha) in comparison with arable lands, herbage as a result of annual economic calcium removal (100-120 kg СаСO3/ha) needs supporting liming.
Another reason for rapid restoration of acidity after liming in long-standing cultivated meadows and pastures is the application of large (up to 240-360 kg/ha) doses of nitrogen fertilizers to cereal grasses which require 500-700 kg CaCO3/ha annually for neutralization.
In short-term (5-6 years) use of meadows and pastures supporting liming as well as phosphoritization and application of organic fertilizers are carried out during the period of repairs (reclamation). With long-term (more than 10 years) intensive use the repeated soil liming is carried out every 5-6 years after mowing and levelling during the vegetation period with lime embedding by discing or milling.
Lime treatment of acidic soils is carried out during establishment of orchards and berries by full doses of lime, taking into account deepening of tillage horizon up to 35-40 cm in orchards and peculiarities of planted crops. Thus, for apple, pear, plum, cherry, and currant in loamy soils with strong and medium acidic pH, at least 6-8 tons of СаСО3/ha is applied; for light and weakly acidic – 4-6 tons of СаСО3/ha, for raspberry and gooseberry – 3-4 t СаСО3/ha and 2-3 t СаСО3/ha respectively.
When establishing orchards and berries, lime may be applied by mixing with soil to planting holes: plum and cherry – 3-5 kg СаСO3, apple and pear – 2-3 kg СаСO3, gooseberry – 0.1-0.2 kg СаСO3. Under mature fruit crops, if liming was not carried out before planting, lime is applied under the recultivation of bedding circles in the doses recommended during planting.
Timing and methods of liming
The following optimal periods of liming (for Russian conditions) are recommended.
Full and half hydrolytic acidity doses of lime are applied under the fall main tillage, under the plowing of the spring furrow or in the fallow field for winter crops. When deepening the topsoil of sod-podzolic soils lime is carried out to neutralize increased acidity of podzolic horizon, which is included in the topsoil.
If liming and phosphoritization are combined under the same crop, phosphoritic meal is put in autumn under the main treatment, and lime – in spring under the plowing or cultivation of the arable land.
In field crop rotations with cereals and perennial grasses it is optimal to apply lime under the cover crop.
When making 1/4-1/2 of the full dose of lime is carried out by cultivators or harrows. At lower doses, local application to wells during cabbage planting at the rate of 5-15 cwt/ha or banding together with seeds is used.
Plant response to lime fertilizers
Rye, spring wheat, and oats tolerate soil acidity relatively easily and respond weakly to liming, they are not depressed by increased doses of lime. Flax, potatoes, lupine, seradella give a yield increase only at moderate doses of lime with appropriate doses of mineral fertilizers, especially potassium.
Quality control of lime treatment works
When carrying out lime treatment systematically carry out agrochemical control over the fulfillment of agrotechnical requirements for the quality of work. The most important indicators include:
- non-uniformity of spreading over the working width;
- deviation from the calculated dose;
- spillage on the field and headlands;
- compliance with technological requirements at the headlands.
Table. Indicators for assessing the quality of work (uniformity) when applying lime fertilizers[7]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| a) with a centrifugal spreader | ||||
| b) with a pneumatic spreader | ||||
| Deviation from dose | ||||
| Working width | ||||
During the machine operation the spreading width, uniformity of lime fertilizer distribution and compliance with the application rates are monitored. The value of deviation of the working width should not be more than ± 10% of the recommended one. Unevenness of spreading – ± 25-30%.
Rate of lime application is determined by the actual weight of the fertilizer applied and the treated area. The frequency of determination depends on the application rate and the quality of the lime fertilizer. If the dose differs from the set dose by more than 10%, adjust the metering device of the spreader.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Chemical reclamation of soils
Chemical reclamation of soils is a regulation of cation composition of soil absorbing complex by replacing hydrogen, aluminum, iron, manganese in acidic soils or sodium, sometimes magnesium in alkaline soils, with calcium. On acidic soils carry out liming, on soils with an alkaline reaction – gypsum or acidification.
Russian scientists I.A. Stebut, D.I. Mendeleev, A.N. Engelhardt, P.A. Kostychev, D.N. Pryanishnikov, P.S. Kossovich, K.K. Gedroyts, O.K. Kedrov-Zikhman and others studied liming and its effect on soil fertility and crop productivity.
In the scientific basis of the theory and practice of liming was the doctrine of the soil absorbing complex, developed by K.K. Giedroytz. According to the provisions of the doctrine, many agronomic properties of the soil depend on the degree of saturation of the soil absorbing complex calcium.
Liming as a method of improving soil properties has been known for a long time, but its use for increasing crop yields has been carried out only since the last century. There is no alternative to liming in terms of economic efficiency and resource availability.
Chemical reclamation of soils (Русская версия)
Importance of liming
Main article: Soil liming
Liming is a technique of chemical reclamation of soils consisting in the application of carbonate, oxide or hydroxide of calcium and/or magnesium to the soil to neutralize excessive acidity. Liming improves agrochemical, agrophysical and biological properties of soil, increases the provision of calcium and magnesium for plants, mobilizes or immobilizes macro- and microelements, reduces the arrival of radionuclides and heavy metals in plants, improves soil factors of plant life.
Soils with excessive acidity are characterized by:
- low content of mobile forms of nitrogen, phosphorus, potassium, trace elements;
- unfavorable agrochemical, agrophysical properties;
- increased content of mobile forms of aluminum and manganese;
- low biological activity;
- negative influence of high concentration of hydrogen ions H+ on physical and chemical state of protoplasm, growth of root system and plant metabolism
development of pathogenic microflora, such as fungi Penecillium, Fusarium, Trichoderma; - mobilization of heavy metals.
The systematic application of physiologically acidic fertilizers, such as ammonium nitrate, degrades the agrochemical properties of the soil, which reduces crop yields.
Table. Effect of soil agrochemical properties on barley yield (after 18 years of ammonium nitrate application)[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/ Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
Liming allows:
- eliminate exchange acidity and reduce hydrolytic acidity;
- improve the cationic composition of the soil absorbing complex;
- activate microbiological processes;
- strengthen all types of nitrogen fixation;
- increase the content of nitrates, calcium, magnesium, mobile phosphorus;
- reduce the content of toxic forms of aluminum and manganese;
- reduce the availability of iron, copper, zinc, manganese, heavy metals to plants;
- increase the availability of nitrogen, phosphorus, calcium, sulfur, magnesium, molybdenum, potassium to plants;
Increase the quality of humus; - improve agrophysical properties of soils, water regime of soils;
- increase the efficiency of mineral fertilizers;
- improve the quality of products;
- due to calcium coagulation of soil colloids, improve soil structure, water permeability, permeability and aeration;
- reduce the possibility of crust formation;
- facilitate processing of heavy loam and clay soils.
Liming changes the ratio of calcium and potassium in the soil in the direction of the predominance of calcium, while worsening the potassium nutrition of plants, which negatively affects the development of potassium-loving crops such as flax, potatoes, lupine, grasses, and corn.
Liming reduces the solubility of phosphate meal and its effectiveness, so exclude direct contact of these fertilizers in the soil:
- lime and phosphoritic meal on the same plot are applied at different times for different crops (phosphoritic meal earlier and lime later);
- layer-by-layer application of these fertilizers – phosphorit flour under the plowing, lime under the cultivation;
- preliminary composting of phosphate meal with manure or peat to transfer phosphorus into available forms.
The use of phosphate meal is effective on the fields lime-fertilized with half doses of lime fertilizers. On soils where the reaction after liming does not exceed pH 5.1-5.2 in the salt extract, you can use phosphorit flour.
The total area of arable land in CIS countries with high acidity is about 45 million hectares (40 million hectares[2]Fundamentals of agricultural production technology. Farming and crop production. Edited by V.S. Niklyaev. – Moscow: “Bylina”, 2000. – 555 p.), needing lime – more than 60 million hectares (55 million hectares[3]Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: “Bylina”, 2000. – 555 p.). First of all, these include sod-podzolic, light gray and gray forest, swamp and red soil.
Reducing acidity contributes to an increase in grain yield by 0.25 t/ha, cabbage by 3-8 t/ha, and potatoes by 3 t/ha.
The table shows Shilnikov (2001) data on average crop yield gains from applying lime to soils of different acidity.
Table. Approximate yield increases of different crops depending on the dose of lime applied, 100 kg/ha (Shilnikov, 2001)
| Winter wheat | |||||
| Barley | |||||
| Winter rye | |||||
| Oats | |||||
| Corn (for silage) | |||||
| Spring wheat | |||||
| Perennial grasses (hay) | |||||
| Annual grasses (hay) | |||||
| Sugar beet | |||||
| Roots | |||||
| Potatoes | |||||
| Flax (straw) | |||||
| Cabbage | |||||
| Tomatoes | |||||
| Carrots | |||||
| Sown meadows and pastures and legume-grasses (hay) | |||||
| Natural meadows (hay) | |||||
| Soybeans (grain) | |||||
Of the cereal crops on acidic soils, winter wheat and barley respond well to lime treatment, of legumes – peas and fodder beans. Yield gains of these crops when lime is applied are higher than those of winter rye and oats. Clover as a cover crop also responds well to lime application.
According to calculations by specialists from Germany, an average annual increase in the pH of highly acidic soils by one unit can increase crop yields by 0.5-0.6 t/ha in terms of grain.
The cost of liming pays off as a rule within two years, and the effect of lime persists for a long time. The importance of liming of acidic soils increases with the transition to intensive farming systems.
Lime increases the protein content of legumes due to the activity of nodule bacteria. Plant products on calcareous soils contain 2-5% more protein than on acidic soils. Product quality increases due to immobilization of toxic elements and radionuclides.
Lime fertilizers
Main article: Lime fertilizers
Lime fertilizers – materials and mixtures of substances containing calcium compounds, sometimes magnesium, used for liming acidic soils and as a source of calcium and magnesium in plant nutrition.
Lime fertilizers are used as:
- lime flour and dolomite flour;
- industrial wastes (burnt and slaked lime, slate ash, defekat, slag, whitewash, etc.);
- local lime fertilizers (lime tuff, lake lime, peat tuff, marl, chalk).
Scientific rationale for liming
Influence on plant growth and development
Acidic reaction of the environment negatively affects the growth and development of plants. High concentration of hydrogen ions worsens physical and chemical state of protoplasm of cells of root system, prevents its growth, disturbs permeability of root membranes and metabolism in roots, thus worsening the nutritional conditions of plants.
The death of winter cereals and perennial grasses during overwintering under snow cover in the Non-Black Soil Zone is associated not with the effect of low temperatures, but with an acidic reaction of the environment and the increased content of mobile forms of aluminum. For example, during overwintering under the same temperature conditions of -12…-14°C (below which temperature under a snow cover of 15-20 cm rarely falls) plants of clover and winter wheat were completely lost on acidic, non-limey soils, while on limey soils they survived at 70-90% with yield of hay 5-8 t/ha and 2,5-3,5 t/ha of winter wheat grain.
The optimum soil reaction for most cultivated crops and soil biota is slightly acidic and close to neutral, i.e. with a pH of 6.0-7.5. For some crops, the optimum reaction can shift to a more acidic side or be in a wide pH range. All plants during the first 2-3 weeks from the moment of germination are sensitive to unfavorable reaction of the environment.
The reaction of the environment influences the nutrient regime of soils and plant nutrition conditions, mobility of macro- and microelements, microflora activity, and soil properties. Optimal pH values for growth and development of the same crop may differ depending on soil type. On soils with high organic matter content and light granulometric composition, the optimal pH interval shifts to the acid side.
In relation to soil acidity and responsiveness to lime application, crops are conventionally divided into five groups.
- The crops of the first group are the most sensitive to the reaction of the environment, the optimum is a slightly alkaline environment with рНH2O = 7,0-8,0; рНKСІ = 6,8-7,5. These include sugar, fodder and table beets, white cabbage, mustard, alfalfa, sainfoin, rape, onion, garlic, celery, spinach, pepper, parsnip, soybean, hemp, currant, cotton. These crops in very acidic soils reduce yields by 2-3 times and plants are severely affected by diseases. Soils intended for cultivation of crops of the first group are subject to liming in the first place.
- Crops of the second group are characterized by optimal soil reaction close to neutral, with an optimal value of рНКCІ = 6,0-6,5. Decrease in acidity to pH 4,5 leads to a decrease in the yield of crops of this group in 1,5-2 times and increases morbidity. Cultures of the second group include: wheat, barley, corn, clover, peas, vetch, beans, chickpeas, lentils, cauliflower and fodder cabbage, kohlrabi, turnips, rutabaga, lettuce, leeks, cucumber, chickpeas, foxtail. They respond well to liming.
- Crops of the third group tolerate moderately acidic and alkaline soils, do not have a pronounced optimum value of environmental reaction. Their growth is influenced by associated growth factors. With a favorable nutrient regime, they can give good yields in the range of рНКCІ from 5 to 7,5. A slightly acidic environment with a pH of 5.5-6.0 is considered optimal. Plants of the third group respond positively to liming of strongly and moderately acidic soils. Cultures of the third group include winter rye, oats, buckwheat, tomato, sunflower, carrot, pumpkin, zucchini, parsley, radish, turnip, rhubarb, topinambur, timothy.
- Cultures of the fourth group belong to cultures well tolerating moderately acidic soil reaction, the optimal value of рНKСІ = 5,1-5,6. For flax, the optimal values are in the range of pH 5,5-6,0, for potatoes and berry crops – pH 4,5-6,5. These crops respond positively to liming while maintaining an optimal ratio of calcium, potassium, magnesium, boron, and other nutrients. An excess of calcium causes a decrease in yield and quality of products, potatoes have an increased incidence of scab, flax has an increased incidence of bacteriosis. Neutralization of excessive acidity reduces the availability of boron, copper, zinc for these crops, and excessive calcium impedes the arrival of potassium and magnesium. Liming for crops of the fourth group is effective with a strongly acidic reaction of the environment. Crops of this group include potatoes, fiber flax, millet, sorghum, raspberries, strawberries, and gooseberries.
- Cultivars of the fifth group are characterized by optimal values of soil reaction at рНKСІ = 4,5-4,8. Cultivars of the fifth group are slightly sensitive to excessive acidity; liming is conducted only in very acidic soils with рНKСІ < 4,0 as calcium may negatively influence growth of these cultures, especially during germination and initial phases of growth. Crops of the fifth group include: sorrel, tea, coffee, cocoa, yellow and blue lupine, goatweed, seradella.
Most crops during germination and in the initial phases of growth require a medium close to neutral – pHKCl 5.8-6.2 or pHH2O – 6.4-7.0.
Physiological (biological) optimum of medium reaction for plants may differ from ecological (technological), which is associated with the mobility of nutrients and conditions of disease development. For example, for potato and flax plants, if the soil is not infected with diseases, the biological optimum is рНKСІ 6,0-6,2, but under disease-infested conditions (potato in neutral and weakly alkaline reaction is affected by scab caused by actinomycetes, flax by fusariosis), in field conditions the yield and quality of these crops are higher at рНKСІ 5,2-5,6, that is, at ecological optimum. The mismatch of biological and ecological optimum of environmental reaction for many crops is due to the change in the availability of nutrients when the soil pH changes.
In this regard, changes in the availability of macro- and micronutrients during liming should be considered. Liming the soil with a pH above 6.6 is ineffective, as the removal and leaching of calcium from the soil increases and the mobility of trace elements with the exception of molybdenum decreases.
Lime fertilizers have a long-lasting effect, so take into account the attitude of all (or leading) crops of the crop rotation, that is, the specialization of the crop rotation and the granulometric composition of the soil.
The table provides indicative optimum pHKCl levels of soils for crop rotations with different specialization.Optimal on sod-podzolic and gray forest soils are lime application rates close to full hydrolytic acidity, providing a pHsalt reaction of 5.4-5.8.
Table. Approximate optimal levels of soil reaction (pHKCl) for crop rotations of different types[4]Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. — М.: Колос, 2002. - 584 p.: ill.
| Sandy and sandy loam | |||||||
| Light and medium loamy | |||||||
| Heavy loam and clay | |||||||
| Peat | |||||||
Influence on soil properties
The colloidal part of soils is depleted of calcium, magnesium, but contains a large amount of hydrogen and mobile cations of aluminum, manganese and iron. This explains the low content of the colloidal fraction of acidic soils, the low absorption capacity and buffer, lack of structure.
In natural conditions the process of depletion of absorbing complex of soil by bases proceeds constantly. Under the influence of atmospheric precipitation and intensive application of fertilizers the share of calcium and magnesium in PPK is replaced by hydrogen. Soil absorbing complex is gradually destroyed.
Annual losses of calcium from soil according to lysimetric experiments amount to 187 kg/ha. Depending on the amount of precipitation the losses vary from 89 to 287 kg/ha.
Calcium contributes to the coagulation of soil colloids and delays their leaching. On sandy humus soils calcium provision contributes to water absorption capacity, on heavy clay soils – the formation of soil aggregates and clodding, their water permeability is improved.
Liming creates a positive balance of calcium, and with the addition of dolomite flour additionally magnesium.
Without the use of lime, the positive effect of physiologically acidic fertilizers fades over time and may have a negative effect, when areas with the use of mineral fertilizers yields are lower than unfertilized areas. The combination of liming with the use of fertilizers increases the effectiveness of the latter by 25-50%.
Toxic effects of mobile forms of aluminum and manganese
Acidic soils have increased content of mobile forms of aluminum, which has a negative effect on most plants.
Many crops begin to experience the toxic effects of mobile forms of aluminum at concentrations of more than 2 mg/100g of soil, the greatest sensitivity is noted in the first periods of growth and during overwintering.
According to plant sensitivity to mobile aluminum N.S. Avdonin divided all crops into four groups:
- most sensitive – oppression occurs at relatively small concentrations of aluminum. For example, the toxic effect on clover notes the content of aluminum ions more than 2 mg/100 g of soil, at a content of 6-8 mg/100 g of soil clover falls off strongly. The most sensitive include sugar beet and table beet, alfalfa, clover, winter wheat and winter rye (in overwintering);
- sensitive – flax, barley, spring wheat, peas, beans, buckwheat;
- resistant – lupine, potato, corn, millet;
- highly resistant – oats, timothy.
For some crops, no direct correlation between sensitivity to acidity and mobile aluminum was revealed. For example, maize does not tolerate high acidity, but shows resistance to high aluminum content. Flax, on the other hand, is sensitive to aluminum, but is tolerant of an acidic environment.
According to the sensitivity to the content of mobile forms of manganese in the soil, three groups of crops are distinguished according to the data of VIUA (1992):
- very sensitive – winter rye and wheat, sugar, table and fodder beets, flax, lucerne;
- spring wheat, barley, vetch, peas, white cabbage, cauliflower and fodder cabbage, rape, potato, clover meadow and hybrid, corn, turnip, carrot, rutabaga, cucumber, tomato, onion;
- relatively resistant – oats, creeping clover, timothy, meadow fescue.
There is also no direct correlation between the sensitivity of crops to environmental acidity and the concentration of mobile manganese. Thus, flax is resistant to acid medium, but sensitive to the concentration of mobile manganese. On the contrary, white cabbage has medium sensitivity to manganese, but cannot tolerate elevated acidity.
Suppression of biological activity of soils
On soils with excessive acidity the activity of useful microorganisms is suppressed, ammonifying, nitrifying, nitrogen-fixing and destroying organophosphorus bacteria do not develop, for which a neutral environmental reaction of pH 6.5-7.5 is more favorable.
On the contrary, favorable conditions are created for the development of pathogenic microflora and fungi such as Penicillium, Fusarium and Trichoderma.
Table. Optimal reaction of the medium for various soil microorganisms[5]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. - 854 p.
| Nitrogen fixers that bind molecular nitrogen in the air | Symbiotic (nodule): | ||
| Free-living: | |||
| Microorganisms that decompose plant residues | |||
| Microorganisms that mineralize humus substances | |||
Mobilization of heavy metals, radionuclides and toxic substances
Liming leads to the immobilization of heavy metals, radionuclides and toxic substances, reducing their entry into plants and products.
Soil gypsum
Main article: Soil gypsum
Soil gypsum is a method of chemical reclamation of saline soils with a large proportion of sodium in the soil absorbing complex (SAC) and alkaline reaction using gypsum (CaSO4⋅2H2O). Saline soils are characterized by unfavorable physical, chemical, physical-chemical and biological properties and low fertility. Gypsum treatment allows to improve soil properties and contributes to the normalization of plant growth conditions.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Fundamentals of agricultural production technology. Farming and crop production. Ed. by V.S. Niklyaev. – Moscow: Bylina, 2000. – 555 с.
Agrochemical characteristics of Russian soils
The agrochemical characteristics of all types of soils of the former USSR are set out in “Agrochemical characteristics of soils of the USSR” (M.: Nauka, 1962-1976).
Navigation
Agrochemical indicators of soil fertility
- Soil composition
- Absorption capacity of soils
- Soil acidity
- Base saturation and soil buffering
- Effect of fertilizers on soil properties
- Agrochemical characteristics of Russian soils (Русский Español)
Sod-podzolic soils
Sod-podzolic soils have:
- acidic reaction – pH 4-5;
- exchange acidity 1-2 mg-eq/100 g, of which 80-90% is due to aluminum;
- hydrolytic acidity 3-6 mg-eq/100 g;
- cation exchange capacity 5-15 mg-eq/100 g;
- degree of saturation with bases 30-70%.
In most cases sod-podzolic soils need liming.
Agrochemical indicators depend on the granulometric composition and the state of cultivation. Sandy and sandy loam soils are characterized by low humus content to 0.5-1.0%, nitrogen – 0.003-0.08%, phosphorus – 0.03-0.6%, potassium – 0.5-1.0%, calcium, magnesium, and other macro-and micronutrients. Loamy and clayey soils contain humus 2-4%, nitrogen 0.1-0.2%, phosphorus 0.07-0.12%, potassium more than 1.5%.
Most sod-podzolic soils are poor in mobile forms of nitrogen and phosphorus, light soils are poor in potassium. At high state of cultivation acidity decreases to pH 5.1-6.0 and increases the humus content to 2.5-4.0%, labile phosphorus forms to 150-200 mg/kg, potassium to 200-300 mg/kg, the capacity of cation exchange, the degree of saturation of the bases and the provision of other nutrients.
As these soils are mainly concentrated in a zone of sufficient moisture, the use of fertilizers and liming show high efficiency. In the first minimum is more nitrogen, on poorly cultivated soils also phosphorus. On light soils, along with nitrogen-phosphorus fertilizers, the use of potassium and magnesium fertilizers is effective.
Gray forest soils
The thickness of the humus horizon, humus content and the degree of podzolization for gray forest soils can vary greatly.
In light gray soil:
- pH 4.8-5.4,
- humus content 1.6-3.4%,
- Hg and S respectively 2.3-3.8 mg-eq/100 g and 10-18 mg-eq/100 g,
- V 72-82%,
- the content of mobile forms of phosphorus and potassium in corresponds to grade 3.
Indicators are better for gray forest soils and reach a maximum for dark gray forest soils:
- pH 5.5-6.0,
- humus 3.5-7.0%,
- Hg and S respectively 2.3-5.4 mg-eq/100 g and 20-36 mg-eq/100 g,
- V 80-86%,
- provision with mobile phosphorus and potassium corresponds to grade 4.
In the first minimum on the light gray and gray forest soils is nitrogen in the second – phosphorus, in dark gray soils, the reverse sequence is possible. The need for potassium fertilizers is manifested in the cultivation of potassium-loving crops.
Depending on the level of intensification of agriculture such agrochemical indicators as pH, provision with mobile forms of elements may change towards improvement or deterioration.
Black earth soils
Black earth soils contain in the arable horizon:
- humus 4-12%,
- total nitrogen content 0.2-0.5%,
- total phosphorus 0.1-0.3%,
- total potassium reserves 2.5-3.0%,
- the reaction is from neutral for typical chernozems to slightly acidic for leached and podzoled subtypes,
- hydrolytic acidity increases from typical to leached subtypes from 0.5-3.0 to 5-7 mg-eq/100 g.
As it transitions southward from the common to the southern subtype:
- pH 7-8,
- hydrolytic acidity disappears,
- cation exchange capacity 50-60 mg-eq/100 g,
- humus content 8-12%,
- total nitrogen reserves 0.4-0.5%,
- total phosphorus reserves 0.25-0.35% in typical chernozem decreases in the transition to the northern and southern subtypes.
Provision of old, poorly fertilized or unfertilized soils with mobile forms of phosphorus and nitrogen decreases and often does not exceed grade 2-4. On such soils are effective phosphorus, and under favorable conditions of moisture nitrogen fertilizers. On the old and poorly fertilized for potassium-loving crops along with phosphorus-nitrogen fertilizers are effective potash. In the wetted areas of the western Black Earth zone fertilizer efficiency is higher, in the east depending on the aridity of the climate efficiency decreases.
Chestnut soils
In the transition from north to south, chestnut soils are divided into subtypes: from dark to light chestnut soils. At the same time their fertility decreases. Humus content decreases from 4-5 to 2-3%, total nitrogen from 0.2-0.3% to 0.10-0.15%, phosphorus from 0.1-0.2% to 0.08-0.15%, cation exchange capacity from 30-35 mg-eq/100 g to 12-15 mg-eq/100 g, slightly alkaline reaction (рНsalt) from 7.0-7.2 to 7.4-8.0, among absorbed cations – sodium specific weight increases.
Chestnut soils contain sufficiently large reserves of potassium, but have a low supply of plant-available forms of nitrogen and phosphorus. With a lack of moisture efficiency of phosphorus and nitrogen fertilizers is reduced. In rainfed conditions on chestnut soils recommend minimum doses (10-15 kg/ha) of phosphate fertilizers, which are applied during sowing. Under irrigation conditions the efficiency of nitrogen and phosphorus fertilizers increases sharply, potash fertilizers are often ineffective.
Among chestnut and especially light chestnut soils with increasing proportion of sodium in the soil absorbing complex and alkalinity reaction occurs different degrees of alkalinity. In order to increase fertility of solonetzic soils the actual and exchange alkalinity is neutralized by gypsum or acidification.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Effect of fertilizers on soil properties
It is possible to study interaction of soils, plants and fertilizers in detail in long-term stationary experiments with systematic application of fertilizers. In such experiments conditions of standardization are created, allowing to study the effect of climatic and agrometeorological conditions on crops, soils and factors regulating soil fertility.
The main directions of research in long-term stationary experiments:
- comparative evaluation of doses, types and forms of mineral fertilizers;
- evaluating the effectiveness of mineral, organic and organomineral systems of fertilizers in crop rotations of different types;
- establishment of the optimal distribution of fertilizers on crops in the crop rotation;
- achieving maximum efficiency by combining fertilizer systems with chemical melioration, determination of their impact on soil properties and productivity of crop rotations;
- possibility of periodic application of phosphorus and potassium fertilizers;
- optimization of soil fertility and properties;
- regulation of biological cycle and balance of biogenic elements in agrocenosis;
- impact of agrochemical means on ecology.
Agrochemistry uses the following methods to study soil properties in long-term stationary experiments.
Agrochemical agents have a complex effect on soil fertility and properties:
- acidify or alkalize the soil solution;
- change agrochemical properties;
- Influence on biological and enzymatic activity of soil;
- strengthen or weaken physical-chemical and chemical absorption;
- affect mobilization or immobilization of toxic elements and radionuclides;
- increase mineralization or synthesis of humus;
- influence the intensity of nitrogen fixation from the atmosphere;
- strengthen or weaken the effect of other soil nutrients and fertilizers;
- influence the mobility of biogenic macro- and microelements in the soil;
- cause antagonism or synergism of ions when absorbed by plants.
Navigation
Agrochemical indicators of soil fertility
- Soil composition
- Absorption capacity of soils
- Soil acidity
- Base saturation and soil buffering
- Effect of fertilizers on soil properties (Русский Español)
- Agrochemical characteristics of Russian soils
Table. Methods of soil fertility research
| pH of salt extract | Potentiometric (1 n. KCl) | ГОСТ 26483-85 |
| Exchangeable acidity | Potentiometric (1 n. KCl) | ГОСТ 26484-85 |
| Hydrolytic acidity | Cullen's method (1 n. CH3COONa extraction) | ГОСТ 26212-84 |
| Exchangeable (mobile) aluminum | CRIASA method (1 n. KCl extraction) | ГОСТ 26485-85 |
| Sum of absorbed bases | Kappen-Hilgowitz method for non-carbonate soils (0.1 n. HCl treatment) Schmuck method for carbonate soils (1 n. NaCl extraction) | ГОСТ 27821-88 |
| Exchange potassium | Maslova method (1 n. CH3COONH4 extraction) | ГОСТ 26210-91 |
| Unexchanged potassium | Hedroitz method (10% HCl extraction with boiling) | |
| Granulometric | Kaczynski method | |
| Equilibrium density | Cutting ring method or gammascopic method | |
| Moisture of a steady wilting | Method for determining the loss of moisture during soil drying | ГОСТ 28268-89 |
| Total organic carbon content | Tyurin method modified by CRIASA (oxidation of organic matter with a solution of chromium mixture) | ГОСТ 25213-84 |
| Content of water-soluble humus substances | Hot water extraction method | |
| Content of mobile humus substances | Tyurin extraction method 0,1 n. NaOH | |
| Group composition of humus substances | Kononova-Belikova method (extracted with a mixture of Na4P2O7 and NaOH) | |
| Forms of mineral phosphates | Chang-Jackson method (sequential extractions 1 n. NH4Cl, 0,5 n. NH4F, 1 n. NaOH, 0,5 n. H2SO4) | |
| Total nitrogen content | Kjeldahl method (oxidation of soil with boiling concentrated H2SO4) | ГОСТ 26107-84 |
| Mobile phosphates and mobile potassium: Acidic soils Black earths Carbonate soils | Kirsanov's method modified by CRIASA (0,2 n. HCl extraction) Chirikov method modified by CRIASA (0,5 n. CH3COOH extraction) Machigin's method as modified by CRIASA (1% (NH4)2CO3 extraction) | ГОСТ Р 54650-2011 ГОСТ 26204-91 ГОСТ 26205-91 |
| Degree of mobility of phosphorus and potassium in soils | Scofield method 0,01 M CaCl2 extraction | ОСТ 10271-00 |
| Fixed ammonium nitrogen | Sylv and Bremner method modified by Kudeyarov (colorimetric determination in the extract from the mixture of HF and HCl) | |
| Nitrogen mobility and availability to plants | Method of vegetative experiment using 15N | |
| Mobility and plant availability of "residual" phosphate and potassium compounds | Vegetation experiment method | |
Physico-chemical properties of soils affect the nutrient regime of soils, their biological activity, determine the transformation of fertilizers introduced into the soil, under conditions of flushing water regime determine the possibility of movement of compounds into deeper soil layers.
Systematic application of organic and mineral fertilizers is accompanied by changes in the physical and chemical properties of soils. Application of manure for many years usually increases the content of organic matter and absorption capacity of soils, reduces metabolic and hydrolytic acidity and increases the degree of saturation with bases.
Table. Effect of systematic use of fertilizers on agrochemical and agrophysical properties of soil (powerful low-humus black earth, soil layer 0-30 cm)[1]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al; ed. by V.G. Mineev. - M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, … Continue reading
| pH | |||||
| H, mmol/100 g soil | |||||
| S, mmol/100 g soil | |||||
| V, % | |||||
| P2O5, mg/kg soil | |||||
| K2O, mg/kg soil | |||||
| Humus, t/ha | |||||
| Nitrogen, t/ha | |||||
| Volume weight, g/m3 | |||||
| Total moisture capacity, % | |||||
| Capillary moisture capacity, % | |||||
| Water permeability in the field conditions, mm/(h·cm2) | |||||
| Total porosity, % | |||||
The combined application of manure and mineral fertilizers for 15 years increased the humus content by 12,6 t/ha, nitrogen – by 0,7 t/ha, reduced the soil density by 0,08 g/cm3, total and capillary moisture capacity increased by more than 3%, water permeability – by 4,3 mm/(h·cm2), total porosity – by 3%.
With long-term use of mineral fertilizers soil properties may deteriorate. It is connected with acidification of reaction of a soil solution as a result of displacement from an absorbing complex of ions of hydrogen and aluminum, and also physiological acidity of some fertilizers. Proper use of fertilizers, that is on the background of manure and liming, the introduction of additives to neutralize the physiological acidity of fertilizers allows you to keep soil acidity at an acceptable level, and in some cases reducing it. On neutral and near-neutral chernozem soils slight acidification as a result of fertilizer application can be considered positive, as it increases mobility and availability of many compounds.
In conditions of leaching water regime of sod-podzolic and gray forest soils changes of properties under the influence of fertilizers occur in arable and in deeper layers. It is connected with increased precipitation and soil acidification at high doses of mineral fertilizers, formation of mobile organic compounds at manure application and peptization of soil colloids under the influence of monovalent cations included in fertilizers, and their washout beyond the arable layer. Migration of nutrients to the underlying layers due to peptization of colloids promotes the application of fertilizers in the fallow and under row crops, as well as frequent tillage. The process intensifies with a light granulometric composition of the soil and an increase in fertilizer doses.
Systematic application of fertilizers leads to an increase in the amount of crop-root residues, decomposition of which causes the new formation of organic colloids in the arable layer and simultaneously with the peptization of large soil particles leads to an increase in the content of silt fraction. In low-buffered soils of light granulometric composition colloid leaching may prevail over new formation.
Changes of physical and chemical properties on black earth soils are concentrated mainly in arable and subsoil layers that is connected with limited precipitation in steppe zone and shallow soil soaking. Prolonged application of fertilizers on these soils leads to accumulation of silt fraction and the value of absorption capacity. At the same time acidity against the background of manure decreases, and with the use of mineral fertilizers increases, which is explained by physiological acidity of fertilizers and non-exchangeable absorption of monovalent cations in the absence of leaching of hydrogen and acidic residue. Increasing the acidity of chernozems increases the mobility of some nutrients and increases their availability to plants.
Systematic use of organic and mineral fertilizers on gray soils has no significant effect on the reaction of the soil solution due to their carbonation and buffering. Some increase of silt fraction and absorption capacity of these soils in the upper layers is due to the formation of colloids from organic plant residues. The arable layer of sierozem preserves colloids, due to the large amount of calcium, which is absorbed by colloids, prevents their dispersion and washout. Movement of fertilizer nutrients deep down the profile in gray soils, as well as losses with groundwater and waste water during irrigation, are caused by flushing water regime and solubility of some compounds.
Long-term use of organic and mineral fertilizers increases the content of carbon and nitrogen in humus-poor sod-podzolic and gray soils, while having little effect on humus-rich black soils.
Table. Effect of long-term fertilizer application on the content of organic carbon and total nitrogen (Shevtsova L.K., 1993, 1998).
| Control | |||||
| Manure | |||||
| NPK | |||||
| Manure + NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| 1/2 Manure + 1/2 NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| 1/2 Manure + 1/2 NPK | |||||
| Control | |||||
| Manure | |||||
| NPK | |||||
| Manure + NPK | |||||
In variants with the application of manure an increase in the content of organic matter in the upper horizons is noted, and a weaker effect of mineral fertilizers is also manifested in the subsoil layer. Manure and mineral fertilizers do not affect the group composition of the organic matter of different types of soil. The composition of humus long fertilized soils retains the properties formed in the regional conditions of soil formation. With prolonged use of fertilizers soil enriched mobile organic matter, which are in the early (hydrophilic) stages of humification, more biochemically active organic compounds, as well as enrich the soil with mobile and available nitrogen. The strongest impact of fertilizers on this indicator was noted on sod-podzolic soils, weakest – on black soils, very weak – on gray soils.
The influence of mineral nitrogen and potassium fertilizers on soil fertility is associated with cation exchange. Systematic application of these fertilizers leads to fixation of monovalent potassium and ammonium cations contained in fertilizers by soil colloids, which is associated with the entry of cations inside the crystal lattice of minerals. This process is influenced by the type of clay mineral, granulometric composition, organic matter content, reaction of soil solution, concentration of potassium and ammonium cations in the soil solution, composition and concentration of other cations, degree of saturation of the absorbing complex with these cations, and hydrothermal conditions under which fixation occurs.
Non-exchangeable absorption of cations reduces their availability to plants and the coefficient of utilization of nitrogen and potassium fertilizers.
Application of ammonium forms of nitrogen fertilizers is accompanied by fixation (non-exchangeable absorption) of nitrogen in the form of NH4+ by clay minerals, which reduces its availability to plants. Nitrogen fixation in the arable and deeper layers can reach significant sizes and should be taken into account in the total nitrogen balance. Prolonged use of nitrogen fertilizers increases the amount of fixed ammonium. Fixation of ammonium on soils of light granulometric composition is less than on soils of heavier granulometric composition because fixation is connected with silt fraction and clay minerals composing it. Fixation of ammonium occurs in the arable and deeper soil layers, especially on soils with light granulometric composition. Probably, non-absorbed ammonium is washed into the lower layers with colloids, the content of which increases down the soil profile.
Table. Changes in the content of non-exchangeable ammonium nitrogen in the soil profile of long-term stationary experiments, mg N/kg soil. Grey forest medium-loam soil, Novosibirsk region (V.N. Yakimenko, 2009)
| Virgin land | ||||
| Fallow | ||||
| Control (vegetable crop rotation) | ||||
| Control (grain crop rotation) | ||||
| NP (vegetable crop rotation) | ||||
| NP (grain crop rotation) | ||||
| NPK* (vegetable crop rotation) | ||||
| NPK* (vegetable crop rotation) | ||||
Crops, depending on the structure of the root system and its absorptive capacity, affect the processes of migration of mineral forms of nitrogen and non-exchangeable absorption of ammonium.
At simultaneous application of nitrogen and potassium fertilizers ammonium fixation decreases due to the competing action of potassium.
Ammonium of mineral fertilizers is fixed faster than ammonium of manure since it has greater mobility. When manure is applied, non-exchange absorption of ammonium is less pronounced than when mineral fertilizers are applied. It is connected with increased fixation of potassium, improvement of physical and chemical properties of soil and strengthened nitrification ability of soils.
Nitrogen fixation in the form of non-exchangeable ammonium occurs in the first years of systematic fertilizer application, and there is no further increase in fixed ammonium from fertilizer application when the fixation tank is filled. Potassium, as well as ammonium, is actively fixed in the first years of fertilizer application, and when filling the tank of fixation of non-exchangeable potassium – decreases, its availability to plants and the coefficient of use by plants increases.
The nature of potassium transformation of fertilizers depends on soil and climatic conditions. In sod-podzolic and gray forest soils the amount of exchangeable potassium increases, while the content of non-exchangeable potassium changes little. Accumulation of exchangeable potassium is noted in the arable layer and in deeper layers. In the arable layer of chernozems non-exchangeable potassium uptake prevails, the amount of exchangeable potassium increases to a lesser extent. In gray soils, the content of exchangeable and non-exchangeable, absorbed potassium increases.
Table. Content of various forms of potassium in soils during long-term fertilizer application, mg К2O/100 g of soil[2]Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. - M.: Publishing house of the All-Russian Scientific and Research Institute named after D.N. Pryanishnikov, 2017. - 854 с.
| Sod-podzol dusty-sandy-loam (Moscow Agricultural Academy) | Control | ||||
| Manure | |||||
| NPK | |||||
| Sod-podzolic heavy loam (DAOS) | Control | ||||
| Manure | |||||
| NPK | |||||
| Grey forest light loamy (All-Russian Research Institute of Bast Crops) | Control | ||||
| Manure | |||||
| NPK | |||||
| Leached light loamy black soil (Myroniv Research Institute of Wheat Breeding and Seed Production) | Control | ||||
| Manure | |||||
| NPK | |||||
| Typical black soil (Ak-Kavakskaya experimental station) | Control | ||||
| Manure | |||||
| NPK | |||||
Leaching regime of light chestnut soils created by irrigation changes the content of non-exchangeable forms of potassium. The greatest changes are noted in the arable horizon, but the effect extends to the meter layer of soil.
Table. Influence of systematic fertilizer application on potassium regime of chestnut soils (Zhukova L.M., Nikitina L.V., 1986).
Cation fixation is determined by soil type. For example, sod-podzolic soils, in spite of high dispersion of minerals, are characterized by low potassium fixation capacity. It is connected with acid reaction of soil solution, unsaturated soils with bases, small content of organic matter and high soil humidity. Under these conditions non-exchangeable potassium uptake occurs in small amounts and only in the upper arable layer.
Liming and long-term application of manure increase the fixing capacity of potassium in acid soils compared with mineral fertilizers, which is due to an increase in the amount of organic matter and coagulating effect of divalent cations contained in the manure and lime fertilizers. Co-application of nitrogen and potassium fertilizers due to competition with NH4+ ions decreases potassium fixation by 2-3 times.
Potassium fixation on sod-podzolic soils is small and does not affect the application of fertilizers, as non-exchangeable potassium colloids soil is a source of replenishment of exchangeable potassium.
In gray forest soils, potassium and ammonium fixation is stronger than in sod-podzolic soils. The reaction of soil solution, mineralogical composition, and increased content of organic matter contribute to the process.
In black earth conditions for non-exchange fixation of cations are the most favorable: high saturation of the absorbing complex with bases, high pH value, high content of organic matter, mineralogical composition of the colloidal fraction with the predominance of minerals of montmorillonite group, periodic drying of the top layer, which leads to irreversible coagulation of colloids.
The simultaneous application of potassium and nitrogen fertilizers does not decrease potassium fixation as the processes of nitrification are active in black soils, which is the reason for a slight increase in the amount of fixed ammonium against the background of fertilizers. Fixation of potassium and ammonium occurs in the upper layers of chernozems.
In chestnut soils and gray soils prolonged use of fertilizers leads to an increase in the amount of non-exchangeable potassium and ammonium. Transition of these cations to non-exchangeable absorbed state is caused by predominance of minerals of hydromica type in silt fraction. These minerals have a high fixing ability with respect to monovalent cations. Alkaline reaction of soil, saturation by divalent bases and periodic drying of soils in conditions of climate of arid-steppe and desert zones are of importance.
Leaching regime contributes to the increase of fixed cations in the lower layers of the soil profile. Joint application of nitrogen and potassium fertilizers has little effect on cation fixation, as mineralogical composition of these soils has high capacity of single-valent cations fixation.
According to the content of exchangeable potassium and fixed ammonium soils can be arranged in the following sequence: sod-podzolic < gray forest < black soils < chestnut soils < gray soils.
Within the same soil type the amount of non-exchangeable cations increases from light soils to heavy ones. Stocks of non-exchangeable cations should be taken into account when assessing soil fertility and calculating nutrient balances.
Natural reserves of phosphorus in soils and their distribution across the profile depend on the content of phosphorus in the parent rocks and the nature of the soil formation process. With systematic fertilization the gross content and amount of mobile forms of phosphorus increases. The degree of change is determined by the doses of fertilizers, the duration of their application and soil properties. Most of the phosphorus accumulated as a result of fertilizer application is retained in the arable layer. At high doses of phosphorus enriched subsoil layer, and in cases of light soils without liming and under irrigation and deeper layers.
The composition of mineral phosphates in the profile is determined by genetic features of soils. Thus, in sod-podzolic soils phosphates of semi-hydrous oxides prevail, in black soils – calcium phosphates.
When mineral phosphorus fertilizers are applied, more phosphates of metals forming oxides like R2O3 are accumulated in soils compared to soils where manure was systematically applied.
Effect of fertilizers on biological and enzymatic activity of soils
Biological activity of soils is a set of biological and biochemical processes occurring in the soil. It depends on genetic features of soil, hydrothermal conditions, agrotechnical measures, the degree of mineralization and humification of plant residues, mobilization capacity of soils. Systematic use of fertilizers in crop rotations enhances the activity of soil biota.
On sod-podzolic acidic soils the activity of biological processes is influenced by lime application. Periodic liming reduces the content of mobile aluminum and exchangeable hydrogen, creates more favorable living conditions for microorganisms in the soil, increases the mineralization of organic matter.
A positive effect on biological activity has a manure in pure form and in combination with mineral fertilizers and liming. Liming enhances the effect of fertilizers on enzymatic activity.
Table. Effect of systematic fertilizer application on biological activity of chestnut soil. Winter wheat and alfalfa. (Numbers of microorganisms, thousand per 1 g of dry soil, average for vegetation season). Long-term experience of Gorsky Agricultural Research Institute (Dzhanaev G.G. et al., 2005)
| Control | |||||
| NPK | |||||
| 2 NPK | |||||
| Manure + NPK | |||||
| 3 NPK |
The effect of fertilizers on enzymatic activity of sod-podzolic soils is similar to the effect on biological activity. Maximum enzyme activity is noted on the background of manure.
On black earth, dark gray forest soils and gray soil, manure in pure form and together with the use of mineral fertilizers has a positive effect on the enzymatic activity. In most cases, an increase in urease activity is noted, which is due to favorable for urobacteria neutral or slightly alkaline reaction of soil. Under the influence of fertilizers, invertase activity increases, and the activity of decomposition and synthesis of nitrogen-free organic matter increases to the same extent against the background of manure and mineral fertilizers.
Sources
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Base saturation and soil buffering
Base saturation (V) is the sum of the absorbed bases expressed as a percentage of the cation exchange capacity (T).
The cation exchange capacity is equal to the sum of absorbed cations (S), such as Ca2+, Mg2+, K+, NH4+ and others, and cations H+, Al3+, Fe3+, Mn2+, causing hydrolytic acidity (H), is (in mg-eq/100 g of soil):
T = S + H.
The degree of saturation of bases is determined by the formula:
Base saturation of the soil is an indicator of the need to lime the soil. The lower it is, the higher the need for lime application. Thus, at identical hydrolytic acidity (H) of the two soils, for example, 5 mg-eq/100 g soil, but different values of the capacity of cation exchange (T), for example, the first – 10 mg-eq/100 g, the second 20 mg-eq/100 g, the degree of saturation with bases (V) in the first case is 50%, the second – 75%. Thus, with an equal value of hydrolytic acidity, the first soil is more acidic, as 50% of the capacity of cation exchange accounts for acidifying cations and it is more in need of replacing them with bases. If the values of cation exchange capacity are equal, the soil with a higher value of hydrolytic acidity will first need liming.
Soil buffering
Soil buffering is the ability to withstand a change in environmental reaction. Buffering capacity is characterized by the value of cationic absorption capacity (T), the composition of absorbed cations and cationic-anionic composition of the soil solution. The indicator is used to calculate the optimal doses, forms, timing and methods of applying fertilizers and ameliorants to crops. The higher is the value of cation exchange capacity, the higher is the buffering capacity of the soil.
Buffering properties against acidity increases with increasing saturation of soils with bases and with the transition from neutral to alkaline reaction of the environment. When hydrogen ions appear in the soil, for example, as a result of nitrification or physiological acidity fertilizer NH4NO3, they are exchanged with the cations of the soil absorbing complex (SAC), resulting in the formation of neutral salt and the reaction of the solution does not change:
[SAC](Ca, Mg) + 2 HNO3 → [SAC](H2, Mg) + Ca(NO3)2.
Buffering properties against alkalization increase in neutral soils with increasing hydrolytic acidity, with decreasing degree of base saturation and with transition from neutral soils to acidic soils. When hydroxide ions such as Ca(OH)2 appear in such soils as a result of introducing physiologically alkaline Ca(NO3)2, calcium cation is displaced from SAC an equivalent amount of hydrogen ions, resulting in the formation of water and the reaction of the solution does not change:
[SAC](H2, Ca) + Ca(OH)2 → [SAC]Ca2 + 2H2O.
Under the influence of acidifying and alkalizing factors the reaction of soil solution can change, but the rate of change in soils with low cation exchange capacity, such as sandy, sandy loam, podzolic soils, is much higher than in high capacity ones, such as loamy black earths.
In the soil solution, buffering is created by the presence of weak organic and mineral acids and their salts:
(CH3COO)2 + 2HNO3 = 2CH3COOH + Ca(NO3)2;
Ca(HCO3)2 + 2HNO3 = 2H2O + 2CO2 + Ca(NO3)2;
2CH3COOH + Ca(OH)2 = (CH3COO)2Ca + 2H2O;
Ca(HCO3)2 + Ca(OH)2 = 2CaCO3 + 2H2O.
Soil buffering also manifests itself in resistance to temporary changes in soil solution concentration caused by lack of moisture, irregular or periodic application of fertilizers and ameliorants. Soils with high buffer capacity, cation exchange capacity and diverse composition of absorbed ions easily retain maximum permissible single doses of ameliorants and fertilizers in the absorbed state without significant increase in concentration of soil solution.
Low buffered, low capacity soils cannot retain large single doses of ameliorants and fertilizers without increasing soil solution concentration and losses of elements from leaching, so on such soils fertilizers are applied fractionally.
Application of organic and mineral fertilizers in combination with periodic application of ameliorants allows to increase cation exchange capacity, regulate the composition of absorbed cations, increase soil buffering.
Sources
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.
Soil acidity
Soil acidity is a soil property due to the presence of hydrogen ions in the soil solution and exchangeable hydrogen and aluminum ions in the soil absorbing complex.
The pH interval of 5.5-7 corresponds to the most agronomically favorable soil structure, high quality of humus and optimal water regime.
Reaction of the soil solution medium
Reaction of the soil solution medium is the ratio of the concentration of H+ and OH-ions in the soil solution, expressed as the pH of the aqueous or saline extract. Fertilizers tend to change the reaction of the soil solution.
Soil reaction affects the nutrient regime of soils, plant growth, development and yields, the activity of soil microorganisms, the transformation of forms of nutrient elements of fertilizers and soil, agrophysical, agrochemical, physical and biological properties of soils. Fertilizers and ameliorants make it possible to regulate soil reaction in the desired direction for cultivated crops.
The reaction of the soil solution is determined by the concentration of hydrogen ions (H+) and hydroxide ions (OH–). In pure water with a neutral reaction, the concentration of hydrogen ions coincides with the concentration of hydroxide ion and is equal to 1⋅10-7 mol/L. When 1 mmol of hydrochloric acid and nitric acid are added to 1 L of water, which dissociate completely in aqueous solution, the concentration of hydrogen ions will be 1 mmol H+, or 1⋅103 mol/dm3. The concentration of hydrogen ions is expressed in terms of pH, which is equal to:
pH = -lg(CH+),
where CH+ is the concentration of hydrogen ions in the solution, mol/dm3.
In a solution with a neutral reaction, the concentration of hydrogen ions is 0.0000001 = 1 · 10-7 mol/dm3, or pH = 7.
According to the reaction of the medium (pH) soils are divided into:
- very strongly acidic – < 4.0 (pHsalt),
- very acidic – 4.1-4.5;
- moderately acidic – 4.6-5.0;
- slightly acidic – 5.1-6.0;
- neutral – 6.1-7.4;
- slightly alkaline – 7.5-8.5 (pH water);
- strongly alkaline – 8.6-10.0;
- sharply alkaline – >10.0.
The reaction of soil solutions can vary widely from pH = 3-3.5, which is typical for sphagnum peats and forest litter of sphagnum forests, to pH = 10-11 in saline soils.
Soils with neutral or near-neutral reaction are favorable for the majority of cultivated crops, but significant areas of agricultural lands are characterized by unfavorable reaction.
Soil acidity
The soil solution contains carbon dioxide (more precisely, hydrogen ion H+ and hydrocarbonate ion HCO3–, since the compound H2CO3 under normal conditions does not exist), which is formed as a result of the activity of soil biota and the dissolution of atmospheric carbon dioxide in water. It has acidifying effect on soil solution:
H2O + CO2 = H+ + HCO3–.
The acidity created in this case is neutralized by absorbed bases and calcium and magnesium carbonates:
(soil)=Ca + 2H2O + CO2 = (soil)=H2 + Ca(HCO3)2,
CaCO3 + H2O + CO2 = Ca(HCO3).
In the presence of sodium in the soil absorbing complex, sodium hydrogen carbonate or sodium carbonate may be formed in solution:
(soil)-Na + 2H2O + CO2 = (soil)-H + NaHCO3,
(soil)=Na2 + 2H2O + CO2 = (soil)=H2 + Na2CO3.
Hydrocarbonates in solution undergo dissociation:
Ca(HCO3)2 + 2H2O = Ca(OH)2 + 4H+ + 2CO32-,
NaHCO3 + H2O = NaOH + 2H+ + CO32-.
Carbonates and hydrocarbonates of calcium, magnesium and sodium in aqueous solutions have an alkaline side.
The reaction of soil solution of different soils depends on the composition of absorbed cations and carbonate content. If sodium content is high in absorbing complex, for example in salts and saline soils, reaction of soil solution is determined by presence of sodium carbonate. In these soils it reaches 8-8.5. If absorbing complex of calcium cations or calcium and magnesium carbonates prevail, for example in carbonate soils and many chernozems, reaction is mainly determined by calcium bicarbonate, and pH of such soils is within 7-8. If soils besides calcium and magnesium contain aluminum and hydrogen, for example, leached and degraded black earths, sod-podzolic soils, reaction of soil solution is conditioned by simultaneous presence of hydrogen ions and calcium hydrocarbonate ions, as well as soluble organic acids and their salts. The lower the concentration of calcium and more hydrogen, the more the reaction of the medium will shift to the acidic side from 5 to 7.
In addition to dissolved carbon dioxide and organic acids, aluminum salts can acidify the soil solution:
АlСl3 + 3Н2O = Аl(ОН)3 + 3НСl = Аl(ОН)3 + 3Н+ + 3Cl–.
Actual acidity
Actual acidity of the soil solution is due to the presence of hydrogen ions and hydrocarbonate monomers and partially soluble organic acids and hydrolytic acid salts. Appears when determining the pH of the soil solution or aqueous extract from the soil.
Actual acidity arises from the formation of organic and amino acids from decomposition of soil organic matter and organic fertilizers, as well as the presence of carbon dioxide and water. In addition, organic acids and amino acids are the products of root excretions of plants and soil microorganisms and carbon dioxide from the respiration of living organisms.
Also actual acidity of soils is created by nitric acid formed in the process of life activity of nitrifying bacteria and physiologically acidic ammonium fertilizers (NH4Cl; (NH4)2SO4).
Potential acidity
Potential acidity is due to the exchange-absorbed by the soil absorbing complex ions of hydrogen, aluminum, iron and manganese. Depending on the ability to exchange displacement of these ions by other ions, potential acidity is divided into exchangeable and hydrolytic.
Exchangeable acidity
Exchangeable acidity is due to the presence of ions of hydrogen, aluminum, iron and manganese in the soil absorbing complex (SAC), which can be displaced by cations of neutral salts, including those from fertilizers, such as KCl, KNO3, K2SO4:
[SAC](H2, Al2, Fe2) + nKCl → [SAC](HK, AlK3, FeK3) + HCl + AlCl3 + FeCl3 + (n-7)KCl;
AlCl3 + 3H2O → Al(OH)3 + 3HCl;
FeCl3 + 3H2O → Fe(OH)3 + 3HCl.
In weakly acid soils exchange acidity is insignificant, in alkaline – is absent. Exchangeable acidity of acidic soils turns into actual acidity in the interaction of the solid phase of the soil with water-soluble fertilizers, ameliorants and salts of the liquid phase.
Exchangeable acidity (рНsalt) is an indicator of the need to liming of soils.
The value of exchange acidity is expressed in pH of salt extract, i.e. soil suspension in 1 n. solution of KCl, or in milligram equivalents per 100 grams of soil. When treating the soil with neutral salt solution (KCl) in the soil suspension along with the existing actual acidity, cations displaced from the SAC appear, causing exchange acidity, so the value of exchange acidity is always greater than the actual acidity.
Hydrolytic acidity
Hydrolytic acidity is due to a portion of the potential acidity of the SAC cations, which can be displaced when treating the soil with a 1 n. alkaline salt solution, such as sodium acetate CH3COOHNa:
CH3COONa + H2O ⇔ CH3COOH + Na+ + OH–.
The alkaline reaction of the water solution of this salt allows for a more complete displacement of hydrogen, aluminum, iron and manganese ions from the SAC than the neutral KCl:
[SAC](H2, Al2, Fe2) + 14CH3COONa + 12H2O → [SAC](Na2, Na6, Na6) + 14CH3COOH + 2Al(OH)3 + 2Fe(OH)3.
Hydrolytic acidity (Hg) is defined as total acidity including actual, exchangeable and hydrolytic acidity. It is greater than exchange acidity and is expressed in milligram-equivalents per 100 g of soil.
In the absence of actual and metabolic acidity hydrolytic acidity is not harmful to plants and microorganisms. It is noted on all black earths, except for southern ones.
Hydrolytic acidity is important in determining the degree of saturation of soils with bases (G) and to justify the replacement of superphosphate with phosphate flour (phosphoritization). For acidic soils such as bog, podzolic and sod-podzolic, gray forest, red soils, yellow soils the value of hydrolytic acidity allows to determine the optimal rate of lime application.
Actual alkalinity
In alkaline soils, such as southern black earths, chestnut soils and solonetz soils, we distinguish between actual and potential alkalinity.
Actual alkalinity is due to the presence in the soil solution of hydrolytic alkaline salts such as Nа2СO3, К2СO3, NaНСO3, КНСO3, Мg(НСO3)2, Са(НСO3)2, МgСO3.
Actual alkalinity is manifested by soil treatment with water and is expressed in mg-eq/100 g of soil or pH-water. The values obtained show the degree to which soils need to neutralize excess alkalinity by gypsum or acidification.
Potential alkalinity
Potential alkalinity is manifested in soils whose SAC in the exchange-absorbed state contains sodium, which can increase the alkalinity of the soil solution when it is displaced into solution:
[SAC](Ca, Na2) + Ca(HCO3)2 ⇔ [SAC]Ca2 + 2NaHCO3.
According to the sodium content in the SAC the degree of the soil’s need for neutralization and the rate of consumption of gypsum-containing materials or technical acids are determined.
Sources
Agrochemistry. Textbook / V.G. Mineev, V.G. Sychev, G.P. Gamzikov et al. – M.: Publishing house of the All-Russian Scientific Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. – Moscow: Kolos, 2002. – 584 p.: ill.