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Zinc fertilizers
Zinc fertilizers – microfertilizers that meet the needs of crops in the trace element zinc.
Zinc in plant life
Field crops with the yield bear from 75 to 2250 g/ha of zinc. Crops with increased sensitivity to zinc deficiency include buckwheat, hops, beets, potatoes, and meadow clover. Weedy plants contain more zinc than cultivated ones. Coniferous plants have an increased zinc content; the highest content is in poisonous mushrooms. Field crops need less zinc than fruit crops.
Zinc’s effect on respiratory stabilization during rapid temperature changes increases heat and frost tolerance of plants. It affects phosphorus utilization by plants. Zinc deficiency results in high concentration of inorganic phosphorus in plants. In pea and tomato plants, zinc deficiency results in increased phosphorus intake but impaired phosphorus utilization, with several times higher inorganic phosphorus content and lower nucleotide, lipid and nucleic acid content. After zinc is added to the nutrient solution, the use of absorbed phosphorus is normalized.
Zinc alters phosphorus accumulation by roots and slows down phosphorus transport to above-ground organs. Zinc is able to chemically bind soluble phosphorus compounds. Zinc deficiency inhibits conversion of inorganic phosphates into organic forms.
Zinc is involved in biosynthesis of chlorophyll precursors and in photosynthesis. Zinc protoporphyrin was found in etiolated and green corn leaves, which is probably a precursor of iron and magnesium porphyrins.
The zinc-containing enzyme carboanhydrase may be involved in photosynthesis, trapping carbon dioxide that is released into the atmosphere during photorespiration. Carboanhydrase is necessary for carbon dioxide or hydrocarbonate ions to penetrate the chloroplast envelope.
More than 200 zinc-activated enzymes are known. Carboanhydrase contains 0.31-0.34% zinc. It is also a part of alkaline phosphatase, malate dehydrogenase, alcohol dehydrogenase, glutamate dehydrogenase, etc.
Zinc-containing carboanhydrase was found in oat, parsley, pea, and tomato chloroplasts. Zinc is a component of dehydrogenases that require the presence of NAD.
Zinc deficiency in plants leads to accumulation of reducing sugars, decreases sucrose and starch content, increases accumulation of organic acids, decreases auxin content, impairs protein synthesis and accumulation of nitrogenous non-protein soluble compounds. Cell division is suppressed 2-3 times, which causes morphological changes in leaves, cell stretching and tissue differentiation are impaired, meristematic cells are hypertrophied, columnar cells of longitudinal stretching in flax are suppressed and chloroplasts are reduced in size. A large number of mitochondria are formed if the content is sufficient.
Fruit crops, especially citrus, are sensitive to zinc deficiency. Apple, apricot, peach, quince, and cherry trees show small-leaved and rosette leaves, while citrus trees show leaf spotting. Corn shows white-white, or chlorosis, on the upper leaves; tomato shows small-leaved leaves and curling of leaf blades and petioles; stunting is typical for all plants.
Zinc deficiency may occur in acidic strongly podzolized light soils, carbonate and highly humusous soils. High doses of phosphorus fertilizers and strong plowing of subsoil to arable horizon aggravate deficiency.
Zinc fertilizers increase corn yield by 0.5-0.7 t/ha, raw cotton by 0.2-0.4 t/ha, and wheat grain by 0.15-0.2 t/ha. On the background of zinc deficiency, zinc fertilizers increase the yield of garlic, peas, beans, tomatoes; the sugar content of tomato fruits increases, the vitamin C content increases, the brown spot disease incidence decreases, and the red fruit yield increases. Zinc fertilizers promote potato resistance to phytophthora and other diseases.
Zinc content in soil
The highest gross zinc content is in tundra (53-76 mg/kg) and chernozem (24-90 mg/kg) soils, the lowest – in sod-podzol soils (20-67 mg/kg). Zinc deficiency often occurs in neutral and slightly alkaline carbonate soils. In acidic soils, it is more mobile and available to plants.
In soils, it is present in cationic form, adsorbed by cation exchange in acidic or chemisorption in alkaline media. Zn2+ zinc ion is well mobile in soil. The pH value and the content of clay minerals influence the mobility. At pH<6 the mobility increases, which may lead to its leaching. The mobility of zinc ions is lost when it enters the interstitial spaces of the crystal lattice of montmorillonite. Zinc forms stable compounds with soil organic matter, so it mainly accumulates in soil layers with high humus content and in peat.
Zinc fertilizers are most effective on sod-carbonate, humus-carbonate, chestnut soils of Transcaucasia, brown, gray-meadow, gray-meadow, chernozem and sandy soils. Acidic sod-podzolic and peat-gley soils are generally high in zinc and do not require zinc fertilizers.
Zinc fertilizers are used mainly in Central Asia for cotton, in the Caucasus – for corn. Primarily applied on soils with neutral reaction, rich in organic matter. Such soils are common in the Middle and Lower Volga region, the North Caucasus, Orenburg Region, and Krasnoyarsk Territory of Russia.
The effect of zinc fertilizers depends on the content of mobile forms of zinc in the soil. Lime and soil organic matter reduce solubility of zinc and its availability to plants. Zinc enters into exchange reactions with humic and fulvic acids, and is fixed in the soil due to formation of poorly soluble compounds. Phosphates reduce zinc mobility, since resulting zinc phosphate is poorly soluble. Zinc solubility increases in the presence of mineral salts, carbon dioxide and hydrocarbonates in the soil solution.
Zinc fertilizers
Some industrial wastes, sulfuric zinc and complex polymicrofertilizers are used as zinc fertilizers.
Zinc sulfate (ZnSO4⋅7H2O), containing 25% of zinc, is a white crystalline powder, well soluble in water.
Zinc polymicrofertilizer – slag waste from chemical plants, for example, during the production of zinc whitewash. They are a dark-gray powder of varying composition. On average they contain 19,6% of zinc oxide, 17,4% of zinc silicate, 21% of iron and aluminium oxides, admixtures of copper, magnesium, manganese, boron, calcium, silicon, traces of molybdenum and other microelements.
Copper smelter slags may contain up to 2-7% zinc.
Application of zinc fertilizers in agriculture
Zinc fertilizers are applied when the content of zinc in mobile form in soils of the Non-Black Soil Zone is less than 0.2-1.0 mg/kg of soil, in the Black Soil Zone – less than 0.3-2.0 mg/kg of soil.
It is used for pre-planting, pre-sowing seed treatment and foliar dressing. When applied to soil, the dose is 3-5 kg/ha of zinc. Copper smelter slags at a dose of 50-150 kg/ha (depending on zinc content) or zinc sulphate are suitable for this purpose.
To reduce binding processes into inaccessible forms, frites obtained by fusing broken glass with micronutrients and subsequent grinding, and chelates are used. In these compounds, trace elements are well soluble in water and accessible to plants, they are not fixed by soil.
Seed pre-treatment is carried out by spraying or powdering with zinc sulfate. Seed treatment requires a 0.05-0.1% solution (2-4 g zinc sulphate per 4 liters of water). For 100 kg, 6-8 liters of the solution are used. To sprinkle corn seeds, 100 g of polymicrofertilizer per 100 kg. Sprinkling of seeds is carried out with zinc sulfate powder or polymicrofertilizer. For better adhesion to the seeds, it is mixed with talc. For 100 kg of seeds 400-500 grams of fertilizer.
Root feeding is carried out with a solution of zinc sulfate. Consumption is 100 g per 100 liters of water per 1 ha of seeds; if aerial spraying is used, 150-200 g per 1 ha. For foliar feeding of row crops by land sprayers, 100 gr per 300-400 liters of water per 1 ha is used. Foliar feeding of fruit crops is carried out by foliar application on dormant buds (2-3% solution), as well as during vegetation of plants (0.05-0.1% solution). Vineyards are sprayed with 0.05% solution during vegetation. In a solution of zinc sulfate add 0.2-0.5% hydrated lime to neutralize excessive acidity of the solution, to prevent leaf scorch.
Zinc fertilizers show good results on sugar beets, corn (grain), vineyards, alfalfa, fruit crops and some vegetable crops.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Molybdenum fertilizers
Molybdenum fertilizers are microfertilizers that provide the micronutrient molybdenum for crops.
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Molybdenum in plant life
Among crops, the highest amount of molybdenum is found in legumes. Legume grass seeds contain from 0.5 to 20.0 mg Mo per 1 kg of dry weight, in cereals – from 0.2 to 1.0 mg per 1 kg of dry weight. In general, the content of molybdenum in plants can vary in the range of 0.1 to 300 mg per 1 kg dry weight; its increased content occurs with unbalanced nutrition of plants.
Plants consume molybdenum in smaller amounts than boron, manganese, zinc and copper. It is localized in young growing organs. Leaves contain more of it than stems and roots. Much molybdenum is concentrated in chloroplasts.
The lower limit of molybdenum content for most crops is 0.10 mg per 1 kg of dry weight, for legumes – 0.40 mg per 1 kg. The content in plants in smaller amounts indicates molybdenum deficiency. With an average yield of wheat, up to 6 g is taken from 1 ha, with the yield of clover – up to 10 g.
In plants, molybdenum is a member of nitrate reductase enzyme which is involved in the reduction of nitrates, reduction of nitrates to nitrites. It is a member of nitrogenase – the enzyme that binds atmospheric nitrogen during nitrogen fixation.
Molybdenum deficiency in plants leads to disruption of nitrogen metabolism and the accumulation of nitrates in tissues. Under the influence of molybdenum in the nodules of legume crops increases the activity of dehydrogenases – enzymes that provide the flow of hydrogen to bind atmospheric nitrogen. Molybdenum is involved in the biosynthesis of nucleic acids, photosynthesis, respiration, synthesis of pigments, vitamins.
The role of molybdenum in the process of nitrogen fixation determines the improvement of nitrogen nutrition of legume crops when applying molybdenum fertilizers, increases the efficiency of phosphorus-potassium fertilizers. At the same time, the yield and protein content increase. The application of molybdenum to nonlegume crops by increasing the assimilation of nitrate nitrogen increases the use and assimilation of fertilizer and soil nitrogen and decreases unproductive losses of nitrogen by denitrification and nitrate leaching. This has been proven in studies with 15N on vegetable crops and cotton.
The crops most demanding of molybdenum fertilizers are clover, alfalfa, soybeans, peas, beans, beans, vetch, lupine, rape, some vegetable crops (lettuce, spinach, cauliflower, tomatoes). Molybdenum fertilizers are less likely to increase yields of nonlegume crops than legumes.
External signs of moderate molybdenum deficiency in legumes are similar to those of nitrogen deficiency. If the deficiency is more severe, the growth of plants slows down, roots do not develop nodules, plants turn pale green, leaf blades become deformed, and leaves die prematurely.
High doses of molybdenum are toxic to plants. Molybdenum content of 1 mg per 1 kg of dry weight in agricultural products is harmful to animals and humans. When the content of molybdenum in plants is more than 20 mg per 1 kg of dry weight, molybdenum toxicosis occurs in animals when eating fresh plants, in humans – endemic (molybdenum) gout. The toxic effect of molybdenum decreases when plants are dried or frozen, since this reduces the amount of soluble forms of molybdenum, as well as when copper is added to the food of animals and humans.
The positive effect on the yield and its quality of vegetable crops is due to the improvement of nitrogen nutrition of fertilizers and soil.
Table. Effect of molybdenum on lettuce utilization of soil nitrogen and fertilizer on sod-podzolic soil (by Muravin)
| РК | |||||
| РК + Мо | |||||
| NРК | |||||
| NРК + Мо | |||||
Improved nitrogen nutrition, in turn, contributes to a better use of other nutrients by crops. Application of molybdenum ensures a more complete incorporation of nitrogen received by plants into the composition of protein. In addition, it limits the accumulation in the products, especially in vegetables and pasture forage, nitrates when using high doses of nitrogen fertilizers and organogenic soils with intensive mineralization of nitrogen. This makes it advisable to apply molybdenum and nitrogen fertilizers together for nonlegume crops requiring molybdenum and legumes together with phosphorus-potassium fertilizers on soils with a lack of this element.
According to the data of field experiments, the average increase in pea yield from the use of molybdenum fertilizers on sod-podzolic, gray forest soils and leached chernozems is 0.26 t/ha, hay and clover seeds on sod-podzolic soils – respectively, 1.30 t/ha and 0.08 t/ha.
Table. Average yield gains of legume crops from molybdenum application (data of the All-Russian Institute of Fertilizers and Agrochemistry), t/ha
| Peas (grain) | ||||
| Veatch: | ||||
| - grain | ||||
| - green mass | ||||
| Soybeans (grain) | ||||
| Fodder beans (grain) | ||||
| Clover: | ||||
| - hay | ||||
| - seeds | ||||
| Alfalfa (seeds) | ||||
High efficiency of molybdenum fertilizers with a sufficient supply of other nutrients is achieved when the molybdenum content in the soils of the Non-Black Earth zone is less than 0.15 mg per 1 kg of soil, in the Black Earth zone – less than 0.15-0.30 mg per 1 kg. The application of molybdenum fertilizers in legume-grass hayfields and pastures increases the number of legumes in the herbage, the protein content in the forage and the overall productivity of the lands.
Table. Action and effect of molybdenum on yield and botanical composition of herbage (by Sharov)
| Without molybdenum | |||||
| Molybdenum foliar feeding (150 g/ha) | |||||
The average yield increase in pea grains is 0.2-0.3 t/ha, clover hay – 0.8-1 t/ha, vetch hay – 0.7-0.9 t/ha, cauliflower – up to 3 t/ha, tomatoes – 7 t/ha, potatoes – 2.5 t/ha, beets forage – 5 t/ha. Molybdenum contributes to an increase in protein content in peas, in hay clover, vetch, alfalfa, sugar content and vitamin content in vegetables are increased.
Molybdenum content in soil
The gross content of molybdenum in the soil varies in the range of 0.20-2.40 mg per 1 kg of soil, the mobile forms – from 0.10 to 0.27 mg per 1 kg of soil. As a rule, in the arable soil horizon the share of mobile forms of the gross content is 8-17%. Most poor in molybdenum are soils of light granulometric composition with low content of organic matter, in sod-podzolic, sandy soils, which contain 0.05 mg/kg of soil. Higher content of bulk and mobile forms is in black earth soils.
Molybdenum is contained in the soil in oxidized form as calcium molybdates. Mobility and availability to plants is affected by the reaction of the environment. In soils with pH < 5.5, molybdenum forms poorly soluble compounds with aluminum, iron, manganese, in alkaline soils – well soluble sodium molybdate. Liming promotes the transition of molybdenum from soil reserves in the mobile state, so molybdenum fertilizers on limed sod-podzolic soils reduce efficiency. At pH 7.5-8.0 even on calcareous soils mobility begins to decline due to an increase in carbonates.
Molybdenum deficiency can appear on sod-podzolic, gray forest, chernozem soils, dried acidic peatlands.
Table. Effects of manganese on crop yields (by P.A. Vlasyuk), t/ha
| Sugar beet (roots) | ||
| Winter wheat (grain) | ||
| Spring wheat (grain) | ||
| Corn (grain) |
Molybdenum fertilizers
Ammonium molybdenum (ammonium molybdate, ((NH4)2MoO4) is mainly used as molybdenum fertilizer. In some regions, waste from the electric tube industry is used.
Molybdenum is a part of some industrial wastes. Thus, slags from ferroalloy plants contain 0.2-0.6% of molybdenum, wastes from molybdenum enrichment plants contain 0.002-0.05%, wastes from electric lamp factories contain 5-6%.
A promising form of fertilizer is molybdenized superphosphate designed for row application at a dose of 50 kg/ha, which corresponds to 50-100 g/ha of molybdenum.
Table. Assortment of molybdenum fertilizers
| Ammonium molybdate | ||
| Waste from the light bulb industry | ||
| Simple granulated superphosphate with molybdenum | ||
| Double granulated superphosphate with molybdenum | ||
Application of molybdenum fertilizers
Among the ways of applying molybdenum fertilizers the pre-sowing treatment of seeds is effective and economically justified. For the treatment of 100 kg of large seeds 25-50 kg of ammonium molybdate or ammonium-sodium molybdate is used, for 100 kg of clover or alfalfa seeds – 500-800 grams.
Molybdenum fertilizers are used on sod-podzolic, gray forest soils, dried peatlands, leached chernozems and other soils, poor in available forms of molybdenum for plants. Application on calcareous sod-podzolic soils is less effective because lime promotes the transition of soil reserves of molybdenum in available forms. The efficiency increases with a good phosphorus-potassium background.
Molybdenum fertilizers can be used to apply to the soil, the pre-sowing treatment of seeds, foliar feeding of plants. The method depends on the type of fertilizer and culture. Doses of application are calculated at the rate of 1 kg of molybdenum per 1 hectare. Slags of ferroalloy plants in a finely ground bring in 50-60 kg / ha, the slag processing of oxidized ores and poor concentrates with a content of 3-8% bring in a finely ground in a dose of 12-30 kg / ha. Low-percentage wastes from enrichment plants are expedient to use in the area of their location due to insufficient transportability.
Molibdenized granulated superphosphate is introduced into the rows with the seeds of clover, alfalfa, peas and other crops at a dose of 50 kg/ha. The use of phosphorus and molybdenum increases with row application, as they contribute to a more complete mutual absorption. Molybdenum in the background of phosphorus increases the yield more than without it.
Table. Application of molybdenum microfertilizers for various crops[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Molybdenum superphosphate (0,2% Mo) | Leguminous | 50 kg per hectare in rows when sowing | Soil application |
| Molybdenum ammonium (50% Mo) | Peas, vetch, soybeans and other large-seeded crops | 25-50 g in 1.5-2.0 L of water per 100 kg of seeds | Pre-sowing seed treatment |
| Clover, alfalfa | 500-800 g in 3 liters of water per 100 kg of seeds | Pre-sowing seed treatment | |
| Peas, fodder beans, clover, alfalfa, and other legumes grown for grain; vegetable, fruit-berry | 200 g per 100 liters of water (air treatment) | Non-root fertilization during budding - beginning of flowering | |
| Long-term cultivated pastures | 200-600 g in 100 liters of water (air treatment) | Non-root fertilization during budding - beginning of flowering |
Seeds are powdered or moistened before sowing. This method is the most promising because it is less labor-intensive and requires less fertilizer consumption. Seed pre-treatment is the most effective method of molybdenum application. Seed treatment is carried out before sowing or a few days or months in advance. Seeds are dried well after treatment. It is recommended to combine presowing treatment with seed dressing. Consumption is 25 g of molybdenum per 100 kg of seeds, or 50 g of molybdenum ammonium or 80 g of molybdenum-sodium ammonium per 1.2-2 liters of water. This amount of solution treats 100 kg of seeds of peas, vetch, soybeans, and other large-seeded crops. For 100 kg of clover and alfalfa seeds 500-800 g of ammonium molybdenum, which is dissolved in 3-5 liters of water, is used. The treatment is carried out evenly so that all the solution is absorbed by the seeds. For a hectare rate of vegetable seeds, depending on the size and seeding rate 60-100 grams of ammonium molybdenum, with a larger dose corresponding to the finer seeds.
For foliar feeding, 100-150 g per 1 ha of sowing is used. For long-term cultivated pastures, 200-600 g per 1 ha. For aerial spraying, a hectare standard is dissolved in 100 liters of water; when ground spraying of row crops – in 300-400 liters. Foliar feeding of legume grasses, peas and other crops grown for seeds or grains is carried out during the budding – blooming period. Fertilizing perennial grasses – clover and alfalfa in hay – is carried out in autumn in the year of sowing after removal of cover crop with well developed leaf surface. On natural meadows with a large proportion of legume component in the herbage, foliar feeding is carried out at the beginning of grass regrowth. In the absence of legumes in the grass mixture or a small amount, a good result is obtained by seeding meadows with a small amount of clover (6-8 kg/ha) with seeds pre-treated with molybdenum. In this case foliar feeding is not carried out.
When applying molybdenum fertilizers on seed crops of legume crops, boric fertilizers are applied together, which usually increases the efficiency of joint application.
In orchards, berry and vineyards, spraying in spring with 0.01-0.05% solution of molybdenum ammonium.
Phosphate fertilizers increase mobility of molybdenum in the soil and its availability to plants, as molybdate ions are replaced with phosphate ions. All processes that enhance mineralization of organic matter increase the mobility of soil molybdenum.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Manganese fertilizers
Manganese fertilizers are microfertilizers that meet the needs of crops for the trace element manganese.
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- Mineral fertilizers
- Microfertilizers
- Boron fertilizer
- Copper fertilizer
- Manganese fertilizers (Русская версия)
Manganese in plant life
The presence of manganese in plant organisms was discovered in 1872; for a long time it was considered unnecessary for plant nutrition. K.K. Giedroytz established that manganese acts better on a lime background. The necessity of manganese for plant life was noted by F.V. Chirikov.
Cereals, beets, fodder root crops and potatoes have higher requirements for sufficient content of available forms of manganese in soil. With the harvest of various crops from 1 ha 1000-4500 g of manganese is removed.
Table. Manganese content in plants and its removal with the yield of crops on different soils (by Katalymov)
| Sugar beet: | ||||
| - roots | ||||
| - leaves | ||||
| Oats: | ||||
| - grain | ||||
| - straw | ||||
| Spring vetch (hay) | ||||
| Potatoes: | ||||
| - tubers | ||||
| - haulm | ||||
| Barley: | ||||
| - grain | ||||
| - straw | ||||
Manganese is an essential element for all plants. Its average content in plants is 0.001%, or 10 mg per 1 kg of weight. It is mainly concentrated in leaves and chloroplasts.
Manganese is a metal with high redox potential and can participate in biological oxidation reactions.
The participation of manganese in photosynthesis has been established: after addition of manganese to plants that were deficient in it, restoration of photosynthetic rate was observed after 20 minutes. Manganese is involved in the system of oxygen release during photosynthesis and in reductive reactions of photosynthesis. It increases the content of sugars, chlorophyll and its bonds with protein, improves outflow of sugars, and enhances respiration rate.
Manganese is a member of hydroxylamine reductase, which carries out the reduction of hydroxylamine to ammonia, as well as an assimilation enzyme that reduces carbon dioxide during photosynthesis. It is involved in the activation of many reactions, including the conversion of di- and tricarboxylic acids during respiration. It is assumed that manganese is part of the enzyme that synthesizes ascorbic acid, as well as malate dehydrogenase, isocitrate dehydrogenase, hydroxylamine reductase, glutamintransferase, ferredoxin. About 30 metalloenzyme complexes activated by manganese are currently known.
Manganese is involved in the mechanism of action of indolylacetic acid on cell growth. Manganese has been shown to be necessary as an auxin oxidase cofactor for the enzymatic degradation of indolylacetic acid. Calcium and manganese contribute to the selective absorption of ions from the external environment. With the exclusion of manganese from the nutrient medium in plant tissues, there is an increase in the concentration of the main elements of mineral nutrition, their ratio in the nutrient balance is disturbed. There is evidence of the effect of manganese on the movement of phosphorus from the aging lower leaves to the upper and reproductive organs. It increases water-holding capacity of tissues, reduces transpiration, and affects fructification of plants.
Under acute manganese deficiency, cases of lack of fructification in radish, cabbage, tomato, pea, and other crops have been noted. Manganese promotes and accelerates development of plants. Under deficiency, chlorosis, gray spotting of cereals, and spotting yellowing of sugar beet can be observed.
Manganese fertilizers increase the yield of sugar beet by 0.9-1.6 t/ha on average, increase the sugar content of roots by 0.1-0.6%, the yield of cereal crops – by 0.15-0.35 t/ha on average, silage mass of corn with lactiferous cobs – by 4.0-7.0 t/ha, potatoes – by 2.5-3.5 t/ha, tomatoes – by 3-4 t/ha, as well as cotton, vegetable, fruit and berry crops. The content of protein, sugars, crude protein, gluten, fats and vitamins increases.
Manganese content in soil
There are significant reserves of manganese in soils: in yellow soils – more than 1%, in sod-podzolic and chernozem soils – 0.1-0.2%. However, most of it is in the form of hard-soluble oxides and hydroxides. In soil, manganese is mainly in a divalent form, in silicates and oxides can replace Fe2 + and Mg2 +, which leads to their leaching. In acidic soils, manganese forms ferromanganese nodules with iron hydroxides.
Plants can absorb divalent manganese compounds. Manganese compounds of other valences are unstable, especially the trivalent form. Mn4+ is present in a reducing environment, forming compounds that are hardly soluble. Under conditions of excessive moisture, anaerobic conditions are created, which intensify reducing processes, increasing the content of available manganese. On irrigated lands manganese is not applied. In dry weather, especially on carbonate soils with an alkaline reaction of the environment, divalent manganese transforms into trivalent and quadrivalent forms unavailable for plants. Under these conditions, the effectiveness of manganese fertilizers increases. Manganese mobility increases when ammonia forms of nitrogen fertilizers are applied.
Lime and alkaline forms of fertilizer reduce manganese mobility and its entry into plants. Sod-podzolic soils tend to contain the highest amounts of manganese. Sugar, fodder and table beets, wheat, corn, barley, alfalfa, vegetable and fruit crops especially suffer from manganese deficiency.
As a result of high content of manganese in soil, its amount in the soil solution can reach 2200 μg/l with the formation of complexes with fulvic acids. When the reaction of soil solution is close to neutral, plants may experience a lack of manganese due to transition to hard-soluble compounds. In practice, to prevent the binding of metal ions by soil and improve their availability to plants use chelates of manganese and iron, which are brought with irrigation water and at foliar feedings.
Micronutrient chelates are widely used. For example, in Sweden foliar feedings of sugar beet are carried out with chelate containing 6 % of manganese, EDTA is used as a ligand. In experiments conducted in the UK, treatment of spring wheat crops increased yields from 2.8 to 4.7 t/ha.
Manganese fertilizers are used in Ukraine. A positive effect of their use is noted on chernozem, carbonate, saline and chestnut soils with low content of manganese available for plants. On soils of the Non-Black Earth zone manganese is effective at its content of 25-55 mg / kg soil, Black Earth – 40-60 kg/kg soil, on gray soils – 10-50 mg per 1 kg of soil.
Manganese fertilizers are applied to gray forest soils, weakly leached chernozems, saline and chestnut soils for oats, wheat, fodder crops, potatoes, sugar beets, corn, alfalfa, sunflowers, fruit and berry, citrus and vegetable crops.
Soils that require the use of manganese fertilizers include carbonate black soils, chestnut and brown semi-desert soils of the Volga region, the North Caucasus, the Urals and Western Siberia. On northern sod-podzolic soils these fertilizers most often do not give a positive effect, in some cases have a negative effect on plants.
K.K. Gedroyts and O.K. Kedrov-Zikhman pointed out the positive effect of manganese on calcareous soils. Manganese fertilizers do not always have a positive effect on various soils in the south of European Russia. Probably, the use of these fertilizers should be paid attention to alkaline, neutral and carbonate soils, light on granulometric composition.
On chernozems, an increase in sugar beet yield from the application of manganese fertilizers is 1.0-1.5 t/ha, root sugar content increases by 0.2-0.6%, cereal yield, including winter wheat, increases by 0.15-0.30 t/ha.
Таблица. Effects of manganese on crop yields (by P.A. Vlasyuk), t/ha
| Sugar beet (roots) | ||
| Winter wheat (grain) | ||
| Spring wheat (grain) | ||
| Corn (grain) |
Manganese fertilizers
As manganese fertilizers are used waste from manganese-ore enterprises, the content of manganese in which is 10-18%. They also contain about 20% of calcium and magnesium, 25-28% of silicon oxide, 8-10% of halides and a small amount of phosphorus.
Table. Assortment of manganese fertilizers
| Marganized superphosphate | ||
| Sulfuric manganese |
Manganese sulfate because of its high cost is mainly used in greenhouse vegetable production. Given that manganese is effective against phosphate fertilizers, it is advisable to produce superphosphate enriched with manganese.
Marganized superphosphate is a pellet of light gray color containing 1.0-2.0% manganese and 18.7-19.2% P2O5. It is obtained by adding 10-15% manganese sludge to powdered superphosphate during granulation.
Manganese sulfate or manganese sulfate (MnSO4) is a finely crystalline salt, the content of manganese is 32.5%, well soluble in water.
Manganized nitrophoska contains nitrogen, phosphorus, potassium, 0.9% of manganese, well available to plants.
Methods of use
Manganese fertilizers are applied to the soil, used for seed pre-sowing and foliar dressing. Organized superphosphate at a dose of 200-300 kg/ha is used to apply to the soil for sugar beets, cereals, corn, vegetables, oilseeds and other crops with the plow at plowing or pre-sowing cultivation. It is also introduced into the rows during sowing in a dose of 50-100 kg/ha. Superphosphate can be replaced by nitrophosphate, the dose is calculated by the content of nitrogen, phosphorus and potassium. Before sowing it is also possible to apply manganese slime in a dose of 50-200 kg/ha.
When applied to the soil, the dose of manganese per element is 2.5 kg/ha. About a third of manganese fertilizers for agriculture is needed in the form of manganese sulfate for foliar feeding and seed pre-sowing treatment.
To powder the seeds use 50-100 g of manganese sulfate mixed with 300-400 g of talcum powder to process 100 kg of sugar beet, wheat, barley, corn, peas, sunflower seeds. Sprinkling can be combined with seed dressing. For foliar fertilization of field crops, the application rate is 200 g of sulfuric manganese per 1 ha; for spraying of fruit and berry crops, the application rate is 600-1000 g/ha. When aerial spraying, 150-200 grams dissolved in 100 liters of water per 1 ha; when ground spraying, 30-50 grams per 100 liters.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Copper fertilizer
Copper fertilizer – microfertilizer that meet the needs of crops in the trace element copper.
Copper in plant life
On average, plants contain 0.0002% copper, or 2 mg per 1 kg of weight, varies depending on the species and soil conditions. With the harvest of different crops carried 7-27 g of copper per 1 hectare.
In the plant cell about 2/3 of copper is insoluble, bound state. The largest amount of copper is concentrated in seeds and the most viable growing parts of plants. 70% of copper in the leaf is concentrated in chloroplasts. Physiological role of copper is determined by its incorporation into copper-containing proteins and enzymes catalyzing oxidation of diphenols and hydroxylation of monophenols: orthodiphenol oxidase, polyphenol oxidase and tyrosinase.
Table. Copper content in plants grown on sod-podzolic soil and powerful black earth (according to Katalymov)
| Spring wheat: | ||||
| - grain | ||||
| - straw | ||||
| Oats: | ||||
| - grain | ||||
| - straw | ||||
| Spring vetch (hay) | ||||
| Potatoes: | ||||
| - tubers | ||||
| - haulm | ||||
| Sugar beet: | ||||
| - roots | ||||
| - leaves | ||||
The copper-containing enzyme cytochrome oxidase has been well studied. It is assumed that the active center of cytochrome oxidase includes copper and iron. Almost half of all copper contained in leaves is in the copper-containing protein, plastocyanin. Copper deficiency has a negative effect on the activity of copper-containing enzymes.
Copper performs certain functions in nitrogen metabolism as a part of nitrite reductase, hyponitrite reductase and nitric oxide reductases. Due to the effect of copper on the biosynthesis of leghemoglobin and the activity of enzyme systems, these enzymes enhance the process of binding molecular atmospheric nitrogen and the assimilation of soil and fertilizer nitrogen.
There is evidence of an increase in the strength of the chlorophyll-protein complex under the action of copper, a decrease in the destruction of chlorophyll in the dark and a positive effect on the greening process in all plants.
As a result of inactivation by the copper-containing enzyme polyphenol oxidase auxins, copper inhibits the effect on growth of high doses of these substances. The copper-containing enzyme tyrosinase regulates the oxidation of the amino acid tyrosine to the black pigment melanin. Lack of this enzyme leads to albinism, the lack of green coloration in plants. The darkening of broken potatoes, apples, etc. is also caused by tyrosinase.
Ethylene inhibits tissue differentiation and inhibits cell division, DNA synthesis, and plant growth. Ethylene synthesis is regulated by a copper-containing enzyme. Reduction of phenolic inhibitors in plants leads to elongation of stems and lodging of plants. Probably by regulating the content of phenolic growth inhibitors in plants, copper increases lodging resistance of plants. It increases the drought, frost and heat tolerance of plants.
Copper deficiency leads to growth retardation, chlorosis, loss of turgor and wilting of plants, delayed flowering and death of crops. Cereal crops in acute copper deficiency have no ear development (white plague or processing disease), fruit crops have dryness.
Copper content in soils
The gross content of copper in soils ranges from 0.1 to 150 mg/kg of soil. In the arable layer in the mobile form is mainly divalent copper cation in the exchange-absorbed state. Copper is a part of soil minerals and organic matter. The greatest quantity of copper is connected with montmorillonite and vermiculite, iron and manganese oxides, iron and aluminum hydroxides. Stable complexes of humic and fulvic acids may form with copper, so upper peatlands, sod-carbonate, bog, swamp, sandy and sandy loam soils are poor in copper. Liming of acidic soils reduces the availability of copper to plants because it promotes fixation in the soil. Lime acts as an adsorbent for copper, and by alkalizing creates conditions for the formation of stable complexes with organic compounds.
Plants are deficient in copper, and soils are considered poor, when the content in the soils of the Non-Black Earth zone – less than 1.5-2.0 mg, in the Black Earth zone – less than 2.0-5.0 mg per 1 kg of soil.
The need for copper fertilizers is mainly observed in the North-West, Central, Volga-Vyatka regions of Russia.
Copper fertilizers are effective on peaty, light sandy and sod-gley soils. On drained peatlands, even with the application of full mineral fertilizer, a full harvest of grains and other crops can be obtained only with the application of copper. According to experiments, the application of copper fertilizers on peat bog and light loamy soils increases the yield of cereals by 0.2-0.5 t/ha.
Mobility of copper in the soil increases with acidification of the reaction of the soil solution, reducing the content of organic matter and clay fraction. Fixation of copper is promoted by the high content of organic substances and carbonates, alkaline reaction and fine granulometric composition of soil, with a large proportion of silt.
Wheat, oats, barley, grasses, flax, hemp, root crops, meadow clover, millet, sunflowers, mustard, sugar and fodder beets, fodder beans, peas, vegetable and fruit crops respond well to copper fertilizers. The need for copper increases under conditions of high doses of nitrogen fertilizers. Peas, vetch, lupine, hemp, flax, beets, vegetables, and fruit crops suffer from copper deficiency in soil.
Copper fertilizer application
Agricultural demand for copper fertilizers is mainly met by copper sulfate, copper-potassium fertilizers and copper-containing industrial waste.
Table. Assortment of copper fertilizers
| Copper sulfate | ||
| Powder containing copper | ||
| Pyritic burns | ||
Sulfuric copper or copper sulfate pentahydrate, copper sulfate (CuSO4⋅5H2O) is a blue-blue crystalline salt containing 25.4% of copper, well soluble in water.
Pyrite cinders are copper fertilizers of local importance, containing 0.2-0.7% of copper, an industrial waste product for production of sulfuric acid. They contain impurities of iron, manganese, cobalt, zinc and molybdenum. The disadvantage of pyrite slag is the presence of arsenic, lead and other heavy metals, so their use requires systematic control of the potential pollution of soil, plants and agricultural products. It is applied once in 4-5 years at a dose of 500-600 kg/ha in the fall under the autumn plowing or spring under the pre-sowing cultivation.
Slags from zinc-electrolyte and copper-smelting plants containing 0.2-0.5% copper are used as copper fertilizer. Also – low percent oxidized copper ores containing about 0.9%.
Seed pre-sowing treatment is carried out by spraying with 0.1-0.2% copper sulfate solution or by powdering. Consumption of the solution by spraying is 6-8 liters per 100 kg of seeds. To sprinkle 100 kg of seeds you should use 50-200 g of well dried and ground copper sulfate. Sprinkling is combined with seed dressing. Sprinkling with copper sulfate is convenient for flax, the seeds of which soak when soaked. Covering foliar dressing rate is 200-300 g per 1 ha of seeds or 0.02-0.05% solution. When ground spraying of row crops – 300-400 l/ha, when aerial application – 100 l/ha.
Pyrite slag, copper-containing slag, and low-percentage oxidized copper ore are used to apply to the soil. Pyrite slag and slags are applied in an amount of 500-600 kg/ha once every 4-5 years, and low percent oxidized copper ore – 200-300 kg/ha. Fertilizer is applied with a plow when plowing the fallow land, or with a cultivator.
Copper fertilizers increase the yield of spring wheat by 0.2-0.5 t/ha, barley by 0.2-0.3 t/ha, oats by 0.4-0.6 t/ha, corn green matter by 2.1 t/ha, and cobs by 9-13%. Copper fertilizers improve product quality: protein content in cereal grains, vitamins in vegetables, fruits and berries increase, fiber quality of flax and hemp improves.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Boron fertilizer
Boron fertilizer is a microfertilizer that meets the needs of crops for the trace element boron.
- Mineral fertilizers
- Microfertilizers
- Boron fertilizer (Русская версия)
Boron in plant life
Boron was discovered in plant ash in the 1950s. Boron is abundant in nature in the form of the oxygen-containing minerals boric acid (H3BO3) and sodium tetraborate, or borax (Na2B4O7⋅10H2O).
The average content of boron in plants is 0.0001%, or 1 mg per 1 kg of weight. Dicotyledonous plants need this element the most. Significant content is noted in flowers, especially in stigmas and stolons. In plant cells, most of the boron is concentrated in cell walls. Boron enhances pollen tube growth, pollen germination, and leads to increased number of flowers and fruits. Boron deficiency impairs the process of seed ripening. It reduces the activity of oxidative enzymes, affects the synthesis and movement of growth stimulants.
Plants have a lifelong need for boron. It is not reutilized, so when it is deficient, young growing organs suffer. Disease and die-off of growth points occur.
In plants, boron is involved in carbohydrate, protein and nucleic acid metabolism. Its deficiency leads to disruption of synthesis, transformation and movement of carbohydrates, formation of reproductive organs, fertilization and fruiting.
According to M.Y. Shkolnik’s concept, boron deficiency in dicotyledonous plants leads to disturbances in physiological processes:
- accumulation of phenols occurs;
- phenolic auxin oxidase inhibitors increase accumulation of auxins;
- nucleic metabolism and protein synthesis are disrupted;
- cell wall structures and cell division processes are disrupted;
- tissue turn browning occurs due to increased permeability of tonoplast vacuoles and penetration of polyphenols into cytoplasm under the influence of phenols.
The main physiological role of boron is to participate in the exchange of auxins and phenolic compounds. Boron is not a part of enzymes, but it activates auxin oxidase and p-glucosidase.
Boron deficiency leads to plant damage by dry rot (root crops), brown rot (cauliflower), hollowness (turnips and rutabaga), bacteriosis, yellowing (alfalfa), drying tops (tobacco), broken fertilization in flax, sunflower growing point dies off.
Sunflowers, alfalfa, fodder crops, flax, rice, sauerkraut, vegetable crops, and sugar beets are sensitive to boron deficiency.
Application of boric fertilizers provides an average increase in sugar beet root crops yield of 2,5-5,0 t/ha and sugar yield of 0,4-0,8 t/ha. Increase of flax seed yield – on average 0.08-0.15 t/ha. On sierozem soils of Central Asia boron fertilizers increase the yield of raw cotton by 0.15-0.45 t/ha.
Boron improves product quality: the content of protein, sugars, starch, vitamins increases, the oil content of seeds increases, their germination and germination energy improves. Thanks to the fact that boron improves photosynthesis and carbohydrate exchange, it favors outflow of sugars from leaves and their inflow to reproductive organs.
Sugar beet, fodder root crops, flax, clover, alfalfa, potato, corn, sunflower, buckwheat, legumes, cotton, vegetable and fruit crops are the most responsive to boron fertilizers. Grain spiked crops respond poorly. Boron fertilizers used for sugar beet seeds increase the yield of seeds, improve their quality, increase their germination and germination energy. In all experiments boron fertilizers resulted in an increase in sugar content by 0,3-2,15%.
Excess of boron causes plant toxicosis, and boron is primarily accumulated in the leaves. It appears as a peculiar burn of lower leaves, marginal necrosis appears, leaves turn yellow, die off and fall off.
Effectiveness of boric fertilizers
Different crops respond differently to elevated boron content in the soil. For example, grain crops suffer from excess at mobile boron content of 0.7-8.8 mg/kg soil, alfalfa and beets tolerate boron concentration in the soil above 25 mg/kg soil. The content of boron in mobile form of more than 30 mg/kg of soil can cause severe diseases of plants and animals.
The toxicity of boron is influenced by the amount and ratio of other nutritional elements. A good supply of calcium and phosphorus increases the demand for boron in crops.
The importance of boron increases under conditions of liming acidic podzolic soils, as liming reduces the availability of boron, fixes it in the soil and delays its arrival in plants. Application of boric fertilizers on limed soils eliminates diseases of root rot of heart and potato scab.
High efficiency of boron fertilizers is noted on sod-gley and calcareous sod-podzol soils. It can be explained by transition of boron on calcareous soils in the hard-to-reach form. Partly it is fixed by biological way, as liming stimulates biological processes.
On light soils the crops need boron fertilizer at 0.2 mg/kg of soil, on loamy soils – 0.3 mg/kg of soil. It increases in dry years and decreases in wet ones.
Boron is poor in sod-podzolic, sod-gleyey, waterlogged soils of light granulometric composition, red earth, humus-carbonate, leached chernozems, gray soils, peaty soils. In tundra soils the gross boron content is 1-2 mg/kg, mobile – up to 0,1 mg/kg, in sod-podzolic soils – 2-5 and 0,04-0,60 mg/kg, respectively.
For the Non-Black Earth zone boron application is advisable when the content of mobile forms less than 0,2-0,5 mg/kg of soil, in the Black Earth zone – 0,30-0,65 mg/kg of soil.
Boron application on poor soils increases the yield of flax straw by 0,2-0,3 t/ha, sugar beet – an average of 4.5 t/ha and an increase in sugar content by 0,3-2,1%. On sod-podzolic, sod-gley, peat-bog and grey forest soils the yield of flax seeds from application of boric fertilizers increases on the average by 80-100 kg/ha, fiber – by 70-80 kg/ha. Quality of fiber improves.
Positive effect of boric fertilizers is shown on seed plants of perennial leguminous grasses, first of all, on sod-podzol soils with limestone. This is explained by the fact that liming in combination with organic and mineral fertilizers develops vegetative mass, but at the same time, even on well limed soils, there is a deficiency of boron for development of buds and flowers. For this reason, when boron is lacking, the development of the mass is delayed. Boric fertilizers increase the clover seed yield by 50-100 kg/ha.
Table. Efficiency of boric fertilizers on sod-podzolic soils[1]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Sugar beet | ||
| Sugar beet (peat-bog soils) | ||
| Flax (seeds) | ||
| Potatoes | ||
| Carrots | ||
| Cabbage | ||
| Tomato |
Boron fertilizer
Boron is included in boric fertilizers in the form of water-soluble boric acid. Of boron-enriched basic fertilizers, boron-superphosphate and boron-magnesium fertilizers are used in agriculture:
| Boric acid technical | |
| Boron-magnesium fertilizer | |
| Boron-superphosphate granulated |
Granulated borosuperphosphate is a light gray granule containing 18.5-19.3% P2O5 and 0.2-1% boric acid (H3BO3).
Double borosuperphosphate contains 40-42% P2O5 and 1.5% boric acid.
Borosuperphosphate is mainly used in beet-growing and flax-growing areas. It is used for sugar beet, flax, fodder root crops, grain legumes, buckwheat, sunflowers, cucumber, vegetables, fruit and berries. It is necessary to apply a 200-300 kg/ha dose for main application and 100-150 kg/ha dose for sowing in the rows. Under flax, cucumber, vegetables, fruits and berries – 150 kg/ha, under the flax in the rows – 50 kg/ha.
Boron-magnesium fertilizer is a gray powder, which is a waste product of boric acid production. It contains up to 13% boric acid, or 2.2% B, and 1520% magnesium oxide. It is used for sugar beet, fodder root crops, grain legumes, buckwheat and flax; in mixture with other fertilizers it is applied at the rate of 20 kg/ha.
Boric acid is a fine crystalline powder of white color. It contains 17% of boron and is well soluble in water. It is used for foliar dressing at a dose of 500-600 g/ha for perennial grasses and vegetable crops, for fruit and berry crops – 700-800 g/ha; for pre-sowing seed treatment – 100 g boric acid per 100 kg of seeds.
Table. Application of boric fertilizers for various crops[2] Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Borosuperphosphate (0,2% B) | Sugar beets, forage root crops, cereals, pulses, buckwheat | In the soil, with the main application of | |
| In the rows, when sowing | |||
| Flax | In the soil, with the main application of | ||
| In the rows, when sowing | |||
| Cucumber, vegetables, fruit and berries | In the soil, with the main application of | ||
| Boric acid (17% B) | Sowing perennial grasses and vegetable crops to produce seeds | For pre-sowing tillage | |
| Fruit and berries | Non-root fertilizing | ||
| Boron-magnesium fertilizer (2,2% B) | Sugar beets, forage root crops, leguminous crops, buckwheat, flax | In the soil in a mixture with mineral fertilizers |
Borax, or sodium tetraboric acid, a crystalline salt of boric acid (Na2B4O7⋅10H2O), contains 11% boron.
Boron-containing nitroammonium phosphate is a compound fertilizer containing 0.15 percent boron. It is applied to all crops during primary tillage.
Boron-datolite fertilizer is made from datolite rock (2CaO⋅B2O3⋅2SiOy⋅2H2O) by decomposition with sulfuric acid, with which boron transforms into boric acid (H3BO3). The boron content is about 2% or 12-13% boric acid. Boron-datolite fertilizer is a light gray powder with good physical properties. It is primarily used for soil application, and can be used for seed treatment.
Boracite meal (CaO⋅MgO⋅3B2O3⋅6H2O) contains about 10% B. It is ground boron ores without any preliminary treatment. In finely ground form, boron is converted to a plant-available state.
Application of boron fertilizer
Boron fertilizers are used for soil application, seed pre-sowing treatment and foliar dressing. Boron superphosphate and bormagnesium fertilizer are mainly used for soil application. The latter can be used for seed sprinkling. For pre-sowing application to the soil for sugar beets, buckwheat, vegetable crops, peas, corn, cotton, seed crops of clover, alfalfa and other crops a dose of 1 kg/ha of boron is recommended, for flax, strawberries and cucumbers – 0.5 kg/ha.
Boron-magnesium fertilizer is more effective on light sandy soils where plants are responsive to magnesium. Dose of spreading with embedding in the soil before sowing is up to 100-150 kg/ha. It is better to mix the fertilizer and apply it together with mineral mixtures. The dose when applied to the rows at sowing is 30-35 kg/ha.
Seed treatment before sowing is carried out by spraying or powdering. Spraying is carried out by solution of boric acid with concentration not more than 0.05% (1 g of boric acid per 2 liters of water). Consumption is 2 liters of solution per 100 kg of seeds. When seeds are powdered with boric-magnesium fertilizer consumption is 300-500 g per 100 kg of seeds. It is advisable to combine the powdering with treatment.
Root feeding is carried out by a solution of boric acid at the rate of 100-150 g per 300-400 liters of water by ground tractor sprayers. During aerial feeding – 100-150 g per 100 liters of water. Cultures are fertilized by a solution of boric acid when vegetative mass is well developed: sugar beet – before the tops close in rows, corn – in the phase of panicles; clover, alfalfa, pea and other cultures – during budding and early flowering. Spraying is carried out in windless dry weather, in the morning or evening hours.
For plants, the content of mobile, water-soluble boron depends on the soil-forming rock and granulometric composition of the soil. The heavier the granulometric composition, the higher the boron content. The assimilable form of boron (boric acid) is poorly fixed by the soil and can be washed out by precipitation. Therefore, soils with sufficient and excessive moisture are poor in mobile forms of boron. The content of available forms is influenced by the content of aluminum and iron hydroxides.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Microfertilizers
Microfertilizers – chemical substances and their mixtures used in agriculture as a source of micronutrients for plant nutrition.
Micronutrients are chemical elements that are in plants in thousandths to hundredths of a percent and perform functions in the processes of life.
The theoretical basis of the use of trace elements in agriculture became possible after the establishment of the physiological role of trace elements in plant life. Y.V. Peyve, M.V. Katalymov, P.A. Vlasyuk, R.K. Kedrov-Zikhman, M.Y. Shkolnik made a significant contribution to solving theoretical and practical problems related to plant micronutrients.
- Mineral fertilizers
- Microfertilizers (Русская версия)
Importance of microelements in plant life
The positive effect of trace elements is due to their participation in redox processes, carbohydrate and nitrogen metabolism. They increase plant resistance to diseases and adverse environmental conditions. Under the influence of trace elements in the leaves increases the content of chlorophyll, photosynthetic processes improve, assimilating activity of the whole plant increases. Many trace elements are part of the active centers of enzymes and vitamins.
Micronutrients can form complexes with nucleic acids, influence physical properties, structure and physiological functions of ribosomes. They influence the permeability of cell membranes and nutrient supply to plants.
Thus, when micronutrients are disrupted in corn, the intake of ammonium and nitrate nitrogen decreases. The greatest decrease in the absorption of ammonium nitrogen is noted with a deficit of zinc, molybdenum and an excess of cobalt, manganese. Nitrate nitrogen absorption rate decreases with copper and manganese deficiency. With an excess of zinc in the nutrient medium, the absorption of ammoniacal nitrogen decreases, with copper deficiency – increases. Molybdenum and zinc nutrition disorder results in increased difference in ammonium and nitrate nitrogen absorption.
In general, when micronutrient nutrition is disturbed, nitrate nitrogen intake decreases first of all. When cobalt and zinc nutrition is disturbed, the rate of ammonium nitrogen incorporation into proteins decreases.
In a number of soil and climate zones, crops are responsive to various microfertilizers. This is most often observed with prolonged application of high doses of mineral fertilizers, especially on drained peaty soils, irrigated lands and on light soils with a granulometric composition.
Table. Crop micronutrient requirements (according to scientific institutions, 1988)
| Cereals: | |||||
| winter wheat | |||||
| winter rye | |||||
| spring wheat | |||||
| spring rye | |||||
| barley | |||||
| oats | |||||
| Leguminous: | |||||
| peas | |||||
| beans | |||||
| lupine | |||||
| Oilseeds: | |||||
| winter rape | |||||
| spring rape | |||||
| mustard | |||||
| flax | |||||
| Vegetables: | |||||
| cauliflower | |||||
| cucumber | |||||
| carrots | |||||
| radish | |||||
| raphanus | |||||
| tomato | |||||
| white cabbage | |||||
| onion | |||||
| Row crops: | |||||
| potato | |||||
| sugar beet | |||||
| Fodder: | |||||
| meadow clover | |||||
| alfalfa | |||||
| lupine | |||||
| corn for silage and green mass | |||||
Note. – low need for the element; + – medium need; ++ – high need.
Legumes have a higher molybdenum content and accumulate 2-10 times more iron than cereals. Legumes have a greater need for cobalt fertilizers.
Plants also accumulate trace elements differently, which becomes important in the use of crop products.
When the content of trace elements above or below the threshold concentrations, the body loses the ability to regulate metabolic processes, which is manifested by the development of endemic diseases. In modern conditions of intensification and chemicalization of agriculture, knowledge of the threshold concentrations of trace elements in plants and fodder is especially relevant.
Table. Threshold concentrations of chemical elements in the feed for farm animals[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
Note. *Limits at normal regulation of functions in animals of different species in different biological states
Introduction of micronutrients provides a significant increase in crop yields.
On average, microfertilizers can increase crop yields by 10-12%. The greatest effect is achieved in regions where soils are depleted in certain micronutrients. There are many such soils. According to large-scale agrochemical survey of soils, low and medium provision with mobile boron 37,3%, molybdenum – 85,5%, copper – 64,9%, zinc – 94,0% cobalt – 86,9%, manganese – 52,5% of the total arable area.
Table. Influence of microelements on the yield of crops in the main areas of their application[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
| Sugar beets: roots | |||
| seeds | |||
| Flax: straw | |||
| seeds | |||
| Clover: hay | |||
| seeds | |||
| Cabbage, seeds | |||
| Vicia-oat mixture, hay | |||
| Barley, grain | |||
| Wheat, grain | |||
| Sugar beets: roots | |||
| Winter wheat, grain | |||
| Sunflower, seeds | |||
| Corn, grain | |||
| Wheat, grain |
Currently, the supply of micronutrients in agricultural production has decreased, while the need of agriculture in Russia in the near future is estimated at 12 thousand tons.
Table. Agricultural demand of the Russian Federation for microfertilizers (tons of nutrients) (according to VNIPTIHIM, 1999)
| Russian Federation | ||||||
| Central: | ||||||
| Bryanskaya | ||||||
| Vladimirskaya | ||||||
| Ivanovskaya | ||||||
| Kaluzhskaya | ||||||
| Moskovskaya | ||||||
| Ryazanskaya | ||||||
| Smolenskaya | ||||||
| Tulskaya |
Content of microelements in soil
The criteria for plant microelements requirements are their content in plants and the level of their content in the soil. It does not matter the total (gross) amount in the soil, but the presence of mobile forms, which to some extent determine the availability of plants. Most often the content of trace elements in mobile form for copper, molybdenum, cobalt and zinc is 10-15% of the gross content in the soil, for boron – 2-4%.
Table. The content of trace elements in plants, mg/kg dry matter[3] Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill..
| Winter wheat (grain) | ||||||
| Spring wheat | ||||||
| grain | ||||||
| straw | ||||||
| Rye (grain) | ||||||
| Barley: | ||||||
| grain | ||||||
| straw | ||||||
| Oats: | ||||||
| grain | ||||||
| straw | ||||||
| Peas (grain) | ||||||
| Vetch (grain) | ||||||
| Timothy | ||||||
| Clover | ||||||
| Corn (green mass) | ||||||
| Alfalfa (hay) | ||||||
| Sugar beet: | ||||||
| roots | ||||||
| leaves | ||||||
| Potatoes (tubers) | ||||||
| Fodder cabbage | ||||||
The degree of mobility of trace elements in soil depends on: environmental reaction, composition of parent rock, vegetation, microbiological activity, carbonate, redox properties, granulometric and mineralogical composition, humus content, haloxides, application of a set of agrotechnical measures, especially water and chemical soil amelioration, application of organic and mineral fertilizers.
The influence of soil conditions is specific and may differ for different trace elements. For example, acidification increases the mobility of manganese, copper, boron, zinc, but reduces the availability of molybdenum.
The concept of “mobility” in modern science does not have a precise definition. In most cases, the mobility refers to all forms of trace elements that can move in water, salt extracts, solutions of strong and weak acids and alkalis. Often no distinction is made between mobile and plant-accessible forms.
The mobile forms of trace elements in the soil are divided into:
- weakly mobile – pass into solutions of strong acids;
- slightly mobile – pass into solutions of weak acids and alkalis; – acid-buffered solutions;
- readily soluble – pass into water and carbonic acid extracts.
It is important that the selected extract when determining the mobile form is the most appropriate for the assimilating ability of a particular plant. Assessment of the suitability of extracts to determine the provision of soils with microelements carry out field experiments with microfertilizers, which establish a correspondence between the content of mobile forms of trace elements and efficiency of microfertilizers.
In our country a differentiated approach to the choice of methods for determining mobile forms of trace elements in the soil depending on soil type, properties and agrochemical characteristics is applied.
The system of extracts proposed by J.V. Peyve and G.J. Rinkis is used for sod-podzolic soils. The scale of soil provision with microelements is developed.
When analyzing forest, chernozem, chestnut, carbonate and saline soils for determination of mobile forms of manganese, zinc, copper, cobalt acetate-ammonium buffer solution pH 4.8 (by Krupsky-Alexandrov) is used; boron is determined in a water extract after boiling, molybdenum in oxalate extract (by Grigg).
When analyzing carbonate and saline, brown, swampy-meadow soils and gray soils, zinc, copper, and cobalt are extracted using 1 n acetate-sodium buffer solution with pH 3.5 (according to Kruglov); molybdenum is extracted by oxalate buffer solution with pH 3.3 (according to Grigg); boron is determined in an aqueous extract.
Extensive agrochemical studies of soils have shown that soils of certain biogeochemical provinces are often poor in mobile forms of some trace elements. For example, in the Moscow region up to 80% of the studied lands need boric fertilizers; molybdenum deficiency is found in 60% of areas, copper – in 50-60%.
B.A. Yagodin and I.V. Vernichenko summarized the data on the provision of soils of the main biogeochemical zones with mobile forms of trace elements obtained from soil and plant analysis, field and vegetation experiments.
Table. Gradations of soil sufficiency of Russian soils with mobile forms of trace elements
The range of extracts used is wide, from strong acids to aqueous solutions. Much of it is aggressive and is unlikely to extract only the trace elements available to plants. When comparing the values of consumption of trace elements by plants with their content in the soil, extracted by aggressive extracts, it was found that plants assimilate less than 1% of trace elements extracted from them.
When assessing the provision of soils with available forms of trace elements and developing practical recommendations, changes in the content of mobile forms depending on the time of sampling should be taken into account. These fluctuations can be so significant that in different periods of vegetation the soil is both well and poorly supplied with trace elements.
Fertilization changes the mobility of trace elements by changing the reaction of the environment, synergism and antagonism. Thus, phosphorus reduces the intake of zinc and copper, sometimes increasing the intake of manganese. The introduction of magnesium increases the intake of phosphorus to plants. Organic matter changes the adsorption of all mineral elements. Therefore, along with soil analysis of the content of mobile trace elements, it is possible to more accurately assess the availability of plants with the help of the plants themselves.
Depending on the amount of trace elements in the soils of the Non-Black Earth zone, the following levels of their provision with trace elements have been established (table).
Table. Grouping of soils of the Non-Black Soil Zone by the provision of plants with microelements [4] Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill. [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
Note. The first group – crops of low micronutrient removal and with comparatively high assimilative capacity: cereals, corn, legumes, potatoes. The second group – crops with high and medium microelement removal, with high and medium assimilating ability: root crops, vegetables, grasses (legumes, cereals, grasses), orchards. The third group – crops of high micronutrient removal – all above mentioned crops in conditions of good agrotechnical background: irrigation, high doses of fertilizers, use of the best varieties, good soil treatment and plant care.
The grouping of soils according to the availability of manganese, copper, zinc, and cobalt extracted from soils by acetate-ammonium buffer solution with pH 4.8 (according to Krupsky-Alexandrova) is shown in the table below.
Table. Grouping of soils according to the provision of plants with trace elements (extractant: acetate-ammonium buffer with pH 4.8 according to Krupsky-Alexandrova)[6]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.
The content of mobile manganese in soils extracted by acetate-ammonium buffer solution with pH 4.8 is about 3-4 times lower than in the 0.1 n H2SO4 extract (according to Peiwe-Rinkis). In contrast, the zinc content in the acetate-ammonium extract is 2-4 times higher than in 1 n KCl. The extraction of copper and cobalt in the buffer solution is, on average, 6-8 times less (with the variation from 3 to 15 times) than in 1 n HCl and 1 n HNO3.
The Don State Agrarian University has developed a scale of zinc availability for carbonate chernozem and chestnut soils (table).
Table. Scale of zinc availability in carbonate black soils and chestnut soils (E.V. Agafonov, 2012)
For carbonate soils of Uzbekistan (sulfur soils), “limit values” of normal provision of cotton with mobile forms of microelements in sodium acetate extract with pH 3.5 were developed.
Table. Limits of normal provision of cotton with mobile forms of trace elements for carbonate soils of Uzbekistan (sulfur soils) (sodium acetate (sodium acetate) extract with pH 3.5).
| Manganese | |
| Copper | |
| Zinc | |
| Cobalt | |
| Boron (water-soluble) | |
| Molybdenum (oxalate-soluble) |
Classification of microfertilizers
Microfertilizers are usually classified according to the main microelement:
- boron fertilizers;
- copper fertilizers;
- manganese fertilizers;
- molybdenum fertilizers;
- zinc fertilizers;
- cobalt fertilizers;
- selenium-containing fertilizers;
lithium fertilizers.
Application of microfertilizers in agriculture
The results of research on promising types and forms of microfertilizers show the feasibility of production and application of microelement-enriched fertilizers, including complex ones. Tests of experimental and pilot batches of basic fertilizers enriched with microelements have shown that, for example, at the expense of boron in nitroamphoska applied to leached chernozem and sod-podzolic soils, additional yield increases are obtained: 3-4 t/ha of sugar beet roots, 0.23-0.29 t/ha of cabbage seeds, 0.21-0.37 t/ha of pea seeds.
Addition of molybdenum-enriched superphosphate to sod-podzolic soils provides additional 0.5-0.6 t/ha of legume grass hay. Under conditions of severe copper deficiency, for example, on drained peat-bog soils of lowland type, against the background of basic fertilizers, spikelets almost do not yield grain, whereas potassium chloride enriched with copper allows to receive 2.5-3.0 t/ha of barley grain, 15-18% increase grass yield and 20% increase vegetable yield.
According to forecasts, the demand of agriculture in microelements must be provided by 60-70% by basic fertilizers enriched with microelements and by 30-40% by technical salts used for foliar dressing and pre-sowing seed treatment.
Some industrial wastes, such as metallurgical slags, pyrite slag, sewage sludge, etc., can be used as a source of trace elements. Fertilizers of this type do not always contain nutrients in a form accessible to plants and often contain toxic impurities.
Micronutrient fertilizers “MiBAS” developed on the lignin base and made from the wastes of pulp and paper industry, printing, electronic, machine-building and other industries can be promising. The technologies developed for utilizing this waste allow us to extract microelements in a pure form and obtain environmentally safe fertilizers. At the same time, lignin-containing waste from pulp and paper production and metal-containing waste are utilized.
The distinctive feature of the new fertilizers is the lignin base, which creates a polymer film on the surface of, for example, seeds, and reliably adheres to this surface. The composition of microfertilizers “MiBAS” includes copper, zinc and cobalt-containing components. Fertilizers “MiBAS” are technologically advanced in use, they are not dusty and are compatible with plant protection products. The effectiveness of these microfertilizers has been established by field and production experiments.
Lignin-based microfertilizers are available in a granular form with a prolonged action for basic application and a liquid concentrate for pre-sowing seed treatment. The content of trace elements in granular form is 10±5%, in the concentrate, which is diluted 3-fold before treatment, 1.3±0.3%. Consumption of granular fertilizer is 50-150 kg/ha, liquid concentrate in diluted form – 10-20 kg/t seed.
Timing and methods of microfertilizer application
It is better to apply microfertilizers to the soil as part of the main mineral fertilizers. It is promising to introduce microelements as part of slow-acting fertilizers, as well as to apply them with irrigation water.
Based on the information about the content of trace elements in the soil and plants to determine the doses of trace elements needed for application. Doses of microfertilizers vary depending on soil and climatic conditions, biological characteristics of crops. Approximate doses for individual crops are given in the table.
Table. Doses and applications of microfertilizers for different crops (CINAO, 1987)
*For potatoes.
Table. Doses and methods of application of various microfertilizers for major crops[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
For the conditions of the North Caucasus region, recommendations on the rates of microfertilizers for field crops depending on the methods of application and the content of trace elements in the soil (Podkolzin, Demkin, Burlay, 2002) were developed.
Table. Doses and methods of microfertilizers for field crops depending on the content of trace elements in the soil[8]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.
Microelements (boron, molybdenum, copper, manganese, zinc, cobalt) are important in protected ground conditions. Methods of application: pre-sowing application to soil, pre-sowing seed treatment and foliar feeding. You should use 2-3 liters of solution per 100 kg of seeds. Seedling watering at the rate of 10 liters per frame. Soaking the seeds – up to 24 hours at a ratio of seed weight to solution 1:2. Non-root feeding is carried out at the rate of 300 liters per 1 ha.
Table. Doses of microfertilizers for vegetable crops in protected ground (greenhouses)[9] 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.
Doses of microfertilizers are much lower than macrofertilizers, and the requirements for uniformity are higher. Therefore, it is more rational to use basic fertilizers enriched with micronutrients. For example, under buckwheat, sugar beets, vegetables, peas, corn, cotton, seed clover, alfalfa make boric superphosphate 300-350 kg/ha. For flax, strawberries and cucumber doses of boron superphosphate are reduced by 2 times. Bormagnesium fertilizer is best made in rows – 30-55 kg/ha or scattered – 100 kg/ha in conjunction with other mineral fertilizers.
Molybdenum superphosphate is introduced into the rows with the seeds of clover, alfalfa, peas and other legumes at a dose of 50 kg/ha.
Copper fertilizers are pyrite (pyrite) pellets (0.2-0.3 Cu), which are applied in doses of 500-600 kg/ha under autumn tillage once in 4-5 years.
Effectiveness of microfertilizers
Effective use requires:
- Knowledge of the requirements of crops for micronutrients, their content in the soil in a form accessible to plants. Optimization of nutrition should be carried out in a balanced macro- and micronutrients.
- Improving the range of microfertilizers.
- Strengthening of agrochemical and sanitary control over the use of industrial waste as fertilizer.
- Study of the influence on the formation of product quality in a balanced plant nutrition by macro- and microelements, the role of microelements in the formation of individual quality indicators.
- Study of transformation, reutilization, balanced optimization of metabolism of organic compounds in plants that characterize the quality of products and the role of microelements in these processes.
Currently, production of microfertilizers is developing in two directions: production of unilateral microfertilizers in the form of individual salts, chelates and frits; production of complex and unilateral macrofertilizers enriched with microelements.
Unilateral microfertilizers are used for crops with severe deficiency of any microelement. The disadvantage of using one-sided microfertilizer is the difficulty of application in small doses, especially in the soil, when it is difficult to achieve uniform distribution over the surface. Unilateral microfertilizers are used in the form of chelates and frits, which is especially important when applying boron, because this eliminates the impact of locally high concentrations of boron on sensitive crops.
Enriched macrofertilizers reduce application costs, have less danger of toxic effects when applying excessive doses of fertilizers, and reduce environmental pollution.
For foliar fertilization, individual salts are mainly used, e.g. manganese, zinc, iron sulfates.
The use of trace elements in combination with macronutrients in complex fertilizers or nutrient mixtures should be limited, and used in conditions of absolute nutrient deficiency in the cultivation of plants on low fertile sandy and sandy loam soils, in hydroponics or protected ground, in horticulture and ornamental floriculture.
Tasks of microfertilizer agrochemistry
In the field of agrochemistry of microelements of primary importance for practical application in agriculture, ensuring high agrochemical and economic efficiency, are the tasks on:
- development of methods for predicting the effectiveness of microfertilizers on the basis of agrochemical analysis of soils for the content of available forms of microelements and plant diagnostics;
- studying the effect of microfertilizers on the value and quality of crop yields in a network of geographical field experiments, carried out according to a single method and program, on the background of increasing doses of basic mineral fertilizers
- studies of the macro- and microelements balance in long-term field experiments with fertilizers in crop rotation in different soil and climatic zones, including fertilizer systems
- studying the interaction of macro- and microelements in the processes of nutrition and metabolism, the impact of microfertilizers on the use and uptake of major nutritional elements from soil and fertilizers.
Researches on development of methods of efficiency forecasting include definition of limiting values of the maintenance of microelements in soils and plants, development of perfect methods of definition of accessible forms in soils, establishment of scientifically proved gradations of security of soils by microelements for concrete soil-climatic zones, taking into account features of cultures, type and granulometric composition of soils, a level of application of organic and mineral fertilizers and methods of regulation of a water mode.
It is important to develop methods of rational use of industrial waste containing microelements and search for raw materials suitable for microfertilizer production.
Studies of macro- and microelements balance in long-term field experiments with crop rotations should be accompanied by research on the impact of applying high doses of organic and mineral fertilizers, methods of chemical melioration and chemical means of plant protection on the content and availability of soil and fertilizer microelements to plants.
It is promising to study agrochemical value of microelements: iodine, lithium, aluminum, vanadium, titanium, selenium, rubidium, bromine and fluorine, as well as determine the negative impact of copper, fluorine, arsenic, chromium, lead, cadmium, nickel as a result of man-made environmental pollution.
It is also necessary to study the hidden lack of trace elements without external manifestation of signs, which leads to a decrease in yield and product quality.
At the present stage of development it has become possible to take into account many factors determining the norms of macro- and microfertilizers application with the help of computer technology.
Sources
Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry/Under ed. B.A. Yagodin. – M.: 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.
Sulfur fertilizers
Sulfur fertilizers are mineral fertilizers that contain sulfur in a form accessible to plants and meet the needs of plants in this element.
- Mineral fertilizers
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Sources of sulfur supply to the soil
When developing the system of fertilization of crops and in crop rotation, sulfur as an element of plant nutrition has not been given due attention before, since the range of mineral fertilizers produced by the domestic chemical industry contains a sufficient amount of sulfur as a co-element or in the form of impurities. Significant amounts of sulfur also enter the soil as a result of technogenic pollution, mainly in industrial areas, and due to volcanic activity.
From the atmosphere sulfur enters the soil with precipitation: in large industrial areas – more than 100 kg/ha, in rural areas – 2-3 kg/ha. In the European part of Russia with atmospheric precipitations falls down to 5-10 kg/ha of sulfur, in separate regions – to 15-17 kg/ha, in Eastern Siberia and Far East – 2-3 kg/ha, near large industrial centers – up to 25-45 kg/ha. In Pre-Urals with precipitation came 16 kg/ha of sulfur, in Donbass – 54 kg/ha, in Moscow suburbs – 17-136 kg/ha per year. With precipitation of more than 10 kg/ha of sulfur per year, plants are usually provided with this element, so, according to calculations, the overall balance of sulfur in agriculture is positive.
Plants can absorb gaseous sulfur compounds from the atmosphere through their leaves. The foliar uptake accounts for up to 30% of total uptake.
In the future, sulfur may become an element limiting yields and product quality. It depends on the introduction of progressive cultivation technologies, the use of high doses of mineral fertilizers, aimed at the realization of the potential productivity of plants and accompanied by an increase in the removal of nutrients from the soil, including sulfur. A large amount of sulfur can be washed out with precipitation beyond the root layer, since SO42- anion is poorly absorbed by the soil, especially by light soils with a granulometric composition.
With sulfur-containing fertilizers some amount of sulfur enters the soil. For example, ammonium sulfate contains 24% S, potassium sulfate – 17.6% S, potassium magnesia – 18.3% S, schoenite – 15.9% S, magnesium sulfate – 28-30% S. However, they do not play a significant role in providing sulfur for sod-podzolic soils, as they are used in limited quantities. Sulfur is included in the nitrophoska sulfate and superphosate.
Phosphogypsum contains 22% S, is a waste product of chemical plants producing double superphosphate, similar in composition to gypsum, but contains impurities of phosphorus and some other elements. It can serve as a sulfur fertilizer of local importance. The disadvantages of phosphogypsum – high humidity up to 30-35%, an impurity of fluorine and strontium. Therefore, when using it, it is necessary to constantly monitor the accumulation of these elements in the soil, plants and products, not allowing them to exceed the maximum allowable concentration (MAC).
Gypsum contains 18.6% S, is a fast-acting, well available to plants neutral sulfuric acid salt of calcium. It is used mainly for reclamation of saline soils.
Elemental sulfur as a fertilizer is used little. It becomes available to plants only after conversion into sulfate form by microorganisms. The rate of this process is influenced by the fineness of grinding, temperature and humidity of the soil, microflora activity, soil type, and the content of other elements. Elemental sulfur is less susceptible to leaching from the arable layer and has a longer persistence than gypsum and sulfate forms.
Sulfur is contained in manure up to 1 kg SO42- per 1 ton. However, the proportion of areas fertilized with manure is small.
Application of sulfur fertilizers
The effect of sulfur and sulfur-containing fertilizers on crop yields and product quality depends on the sulfur content in the soil, fertility, biological characteristics of the crop, and weather conditions.
Features of sulfur fertilizer application:
- In soil, up to 85-90% of sulfur is in organic form as part of humus and other organic compounds, 10-15% – in the form of SO42-, which is assimilated by plant roots. Sulfur of soil organic compounds as a result of mineralization due to microbiological activity is converted into mineral sulfur. This process is called sulfification, which has a seasonal character with a minimum in spring, maximum in summer, and attenuation in autumn. The release of nitrogen and sulfur occurs in the same ratio as they are in humus and organic residues. At present, there are no criteria for assessing the availability of sulfur in plants. For example, legumes and crucifers are not deficient in sulfate when the sulfate content is more than 11-14 mg/kg, and cereals – more than 7 mg/kg.
- When applying sulfur-containing fertilizers, consider the critical levels of sulfur in plants and the ratio N:S, by which you can estimate the lack of sulfur. The critical sulfur content in wheat grain is 0.17%, in potato tubers 0.11%, in alfalfa – 0.2%, in cotton during the phase of budding – 0.5%. The critical N:S ratio in wheat grain is 14.8, in barley 13.1-16.4, in clover 15-18.5.
The efficiency of sulfur fertilizers is influenced by weather conditions, especially in early spring. Yield gains from application of sulfur were higher in years with low spring temperatures and abundant rainfall, i.e. when sulfification processes slowed down and mineral sulfur reserves were washed into the lower soil layers and became unavailable for plants. - Therefore, in early spring on sod-podzolic soils mineral sulfur, as well as mineral nitrogen, is in short supply. Regardless of the total sulfur content in the soil, spring crops respond well to sulfur fertilizer applied before sowing. Overwintering plants, especially clover and alfalfa, also respond well to sulfur fertilizer applications in the spring.
- Neutral forms of sulfur-containing fertilizers – gypsum, phosphogypsum and simple superphosphate – are most effective on sod-podzolic soils. By the action of gypsum and phosphogypsum are of equal value. Sulfate forms of nitrogen and potassium fertilizers, as well as elemental sulfur are inferior in effectiveness as they have an acidifying effect on the soil solution. Phosphogypsum increases yields of intensive crops such as corn, fodder rutabaga, and fodder sprouts that take out large amounts of nutrients, including sulfur, as well as leguminous grasses and lupine. Yield gains from applying phosphogypsum and other sulfur fertilizers increase in years with high yields and in years with cold springs.
- The timing and methods of sulphur fertilizer application depend on the biological characteristics of crops: under winter cereals – preplanting, spring cereals – under pre-sowing cultivation, clover – in early spring on the regrowing plants, row crops equally respond to the pre-and post-sowing application.
- Most crops respond well to sulfuric fertilizers with a sufficiently fertilized background and the systematic application of nitrogen, phosphorus and potassium fertilizers in the rotation. Yield gains from the use of sulfuric fertilizers are: winter wheat grain – 0.2-0.4 t/ha, winter rye – 0.15-0.3 t/ha, barley – 0.2-0.3 t/ha, oats – 0.15 t/ha, clover hay – up to 1.5 t/ha, Potato tubers – up to 3.0 t/ha, rutabaga roots – 3.0-5.0 t/ha, turnip hay – up to 3.0 t/ha, green mass of fodder cabbage – up to 4.0 t/ha. The quality of plant products increases – the content of protein, dry matter, starch in potato tubers, the share of marketable products.
- Sulfur-containing fertilizers contribute to the absorption of other nutrients.
For the majority of cultures the optimum dose of sulfur is 50-60 kg/ha on sandy soils, for cruciferous crops on loamy soils – 100-120 kg/ha of sulfur. It is applied in fall for autumn autumn plowing, in early spring for pre-sowing tillage, and in spring during grass growth. If there is a shortage of sulfur, sulfur fertilizer is added to rows during planting and foliar feeding with 0.5-2% sulfate solution.
Sources
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.
Magnesium fertilizers
Magnesium fertilizers are mineral fertilizers that meet the magnesium requirements of crops.
- Mineral fertilizers
- Nitrogen fertilizers
- Phosphate fertilizers
- Potassium fertilizers
- Magnesium fertilizers (Русская версия)
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- Magnesium fertilizers (Русская версия)
Raw materials for the production of magnesium fertilizers
The main source for the production of magnesium fertilizers are natural compounds and minerals of this element. Magnesium is part of more than 200 minerals, many of which are used directly as a source of magnesium or processed into magnesium fertilizers: sulfates, chlorides, carbonates, silicates, hydroxides, aluminosilicates.
Ways to provide magnesium to plants
Ways of providing magnesium to plants:
- Liming of soils with magnesium-containing lime fertilizers. This simultaneously achieves the supply of all crops of the rotation with magnesium and calcium and eliminates excessive acidity of the soil.
- Application of magnesium mineral fertilizers for crops in the rotation, taking into account their biological needs.
- The application of organic fertilizers, which contain magnesium in an amount of 0.01-0.09%.
Classification of magnesium fertilizers
Lime-magnesium and potassium-magnesium fertilizers account for the largest share in the range of magnesium fertilizers. Magnesium fertilizers are classified by solubility into:
- water insoluble – milled natural minerals and rocks, such as dunite, serpentinite, vermiculite, dolomite, magnesite, brusite and dolomitized limestone. When interacting with acidic soils, magnesium available to plants is released into the soil solution;
- water-soluble – raw salts and products of their processing – epsomite, kainite, carnallite;
- soluble in citric acid and available to plants – magnesium fused phosphate.
By composition, magnesium fertilizers are divided into:
- simple – magnesite, dunite;
- complex ones containing several nutrients:
- nitrogen-magnesium – ammoshenite, dolomite-ammonium nitrate;
- phosphorus-magnesium – magnesium fused phosphate;
- Potassium-magnesium – potassium-magnesium concentrate, potassimagnesia, polyhalite, cainite, carnallite;
- bormagnesium – magnesium borate;
- lime-magnesium – dolomite, dolomitized limestone and products of their processing;
- containing nitrogen, phosphorus and magnesium – magnesium-ammonium phosphate.
Magnesium-containing lime fertilizers
Magnesium-containing lime fertilizers simultaneously enrich the soil with mobile magnesium compounds and neutralize excessive acidity, are practically the most effective and cheapest way to supply sandy and sandy loam soils with magnesium.
Dolomite flour (CaCO3⋅MgCO3) contains about 20% MgO and 30% CaO; carbonic calcium and magnesium account for at least 85%. It is used to lime acidic soils at a dose of 3-4 t/ha. In this case the soil is enriched with magnesium in amounts sufficient to provide the plants on one to two rotations of crop rotation. The most effective on the light soils.
Dolomites are insoluble in water, so their effect depends on the fineness of grinding. The largest increase in crop yields provides dolomite flour with a particle size of less than 1 mm.
Semi-fired dolomite (CaCO3⋅MgCO3) is a product of dolomite firing and contains approximately 27% MgO, 2% CaO, 57% CaCO3. Magnesium is well available to plants. It is used to lime the soil.
Magnesium carbonate, or magnesite, (MgCO3) contains 45% MgO – the most concentrated magnesium fertilizer. It is a natural mineral and burnt magnesite (up to 89% MgO), obtained in the manufacture of refractories. It has an alkaline reaction with a high neutralizing power superior to that of lime. However, high doses of magnesium carbonate cause calcium and boron starvation of plants. Therefore, its use is combined with the introduction of boron for crops that require it, such as sunflowers, beets, and clover, and for the neutralization of excessive acidity it is combined with calcium carbonate.
Burnt magnesia is packed in bags of waterproof material and stored in a dry room.
Main magnesium fertilizers
The Russian Federation industrially produces potassium magnesia and kainite. The share in the total assortment of potassium-magnesium fertilizers is insignificant.
Dunite flour and magnesium serpentine
Dunite flour and magnesium serpentinite, or serpentinite, are wastes of the mining and asbestos industry. According to their chemical composition they are magnesium silicates in a poorly soluble form, so they are used in advance in large doses. These magnesium-containing fertilizers are used as raw materials for the production of complex magnesium fertilizers, as well as a local fertilizer. They decompose slowly under the influence of soil acids. The finely ground dunite contains 41-47% MgO. Serpentinite consists of magnesium metasilicate and contains 32-43% MgO.
Ammoshenite
Ammoshenite ((NH4)2SO4⋅MgSO4⋅6H2O) is a double salt of ammonium sulfate and magnesium sulfate. It is a crystalline mineral of light brown to gray color. Used as a nitrogen-magnesium fertilizer; contains at least 7% N and 10% MgO. It is transported in multi-layer bags impregnated with bitumen.
Magnesium sulfate
Magnesium sulfate (eleonite and kieserite) is a one-sided magnesium fertilizer containing at least 84% MgSO4⋅7H2O and no more than 6% NaCl (17.7% MgO). It is well soluble in water. Used in intensive agriculture in a deficit of magnesium in weakly acidic and neutral soils. In this case, the high yield is a constant need for readily soluble sources of magnesium. It is also used in intensive meadows, in greenhouses, in vegetable growing in the open ground. Magnesium sulfate is used to eliminate acute magnesium starvation by foliar feeding. When entering the soil, most of the magnesium is converted into the metabolized state.
Calimagnesia
Calimagnesia (K2SO4⋅MgSO4⋅6H2O) is a semi-product in the production of potassium sulfate from kainite. It mainly contains the mineral schoenite.
It shows high efficiency on sandy sod-podzolic soils due to good solubility and potassium-magnesium ratio.
Table. Composition of granular species of potassium permanganate, in terms of dry product (%).
Potassium-magnesium concentrate
Potassium-magnesium concentrate is obtained from cainite-langbeinite rock by flotation. The fertilizer mainly contains the mineral langbeinite (K2SO4⋅2MgSO4), in small amounts – polyhalite, halite, gypsum, etc. On average, it contains 30-38% K2SO4, 39-40% MgSO4, 4-5% KCl, and 8-10% NaCl.
Potassium-magnesium concentrate is produced in two grades: grade 1 contains at least 19% K2O and 9% MgO, grade 2 contains at least 17.5% K2O and 8% MgO. The content of chlorine is not regulated, but in the 1st grade – no more than 8%.
Polyhalite salts
Polyhalite salts (K2SO4⋅MgSO4⋅CaSO4⋅6H2O) contain 10-11% K2O, 8-12% MgO, are poorly soluble in water, but potassium and magnesium are available to plants. Polyhalite salts showed effectiveness on different crops, especially on meadows and pastures.
Kainite
Kainite (KCl⋅MgSO4⋅3H2O) – with an admixture of sodium chloride up to 45-47% of the total mass. It contains 10-12% K2O, 22-25% Na2O; 6-7% MgO, 15-17% S and 32-35% Cl. It is a low-percentage fertilizer, so it is mainly used in grasslands and pastures, where it has advantages over potassium chloride because of the presence of magnesium.
Industrial waste
The wastes of potassium and magnesium plants can be used as potassium and magnesium fertilizers – dewatered carnallite containing 23-24% K2O, 18-20% – MgO, 0.9% – Na2O, 50-51% Cl, and potassium chloride electrolyte containing 39-42% K2O, 4% – MgO, 50% – Cl. The negative effect of chlorine is eliminated by advance application. Dehydrated carnallite is effective for various crops on sandy loam soils.
Phosphorus-magnesium fertilizers
Thermophosphates and tomato slag are phosphorus and magnesium fertilizers, a byproduct of metallurgy. The nutrients are contained in citric-soluble forms and are available to plants.
This group of fertilizers includes fused magnesium phosphate, which contains phosphorus and magnesium available to plants (Ca3(РO4)2 + MgSO4⋅SiO3). It is obtained by fusion of natural phosphates and magnesium raw materials (dunite, kieserite, serpentinite, olivinite) at 1350-1400 °С, followed by rapid cooling of the melt with water. It is vitreous transparent granules of different shapes and sizes. The color of the granules varies from bright green to black, depending on the initial raw material.
Fused magnesium phosphate contains 19-21% available citric-soluble P2O5 and 8-14% MgO. Phosphorus in fused magnesium phosphate is contained as a modification of tricalcium phosphate, soluble in 2% citric acid. The production does not require the use of sulfuric acid, and does not require large amounts of energy and water, and allows the use of low percent natural phosphates without prior enrichment. Fertilizer has good physical properties, does not flake, does not contain free acidity.
Finely ground molten magnesium phosphate shows high efficiency for main application on all types of soils. On acidic sandy and sandy loam soils fused magnesium phosphate to some extent neutralizes soil acidity. In humid tropical climates, the fertilizer is more promising than water-soluble forms, as it does not caked and loses less nutrients from leaching with precipitation.
Thermal phosphates are effective when they are finely milled, but in this state they are very dusty. One way to solve this problem is to pellet finely ground fused magnesium phosphate with potassium chloride.
Magnesium ammonium phosphate (MgNH4PO4⋅nH2O) is a concentrated fertilizer containing phosphorus, nitrogen and magnesium. It is produced from phosphoric acid, ammonia and magnesium hydroxide or magnesium chloride, sulfate, carbonate. It can be in the form of crystalline hydrate, containing one (MgNH4PO4⋅H2O) or six (MgNH4PO4⋅6H2O) water molecules. The latter is unstable during storage, releasing ammonia at 30-50°. Single-water magnesium ammonium phosphate is non-hygroscopic, stable up to 230 °C, does not release ammonia during storage. Because of the smaller amount of water, one-water salt contains 35% more nutrients than six-water salt. Nitrogen in the magnesium-ammonium phosphate is poorly soluble in water, which reduces its leaching on light soils and does not increase the osmotic pressure of the soil solution. One-water magnesium-ammonium phosphate contains 45.7% P2O5, 10.9% N and 25.9% MgO.
Phosphorus in magnesium-ammonium phosphate is contained in a citric-soluble form, so this fertilizer is applied as a powder. When used at a dose of 45-60 kg of P2O5/ha, it introduces the amount of magnesium that can meet the needs of all crops on sandy and sandy loamy-sandy ashy soils. Magnesium-ammonium phosphate on such soils is used as the main pre-sowing fertilizer.
Magnesium-ammonium phosphate can also be used as a concentrated nitrogen-phosphate fertilizer. In this capacity it is used in irrigated agriculture, where before sowing phosphorus and nitrogen is added in small doses, and then in the form of top dressing.
Magnesium ammonium phosphate due to its good physical properties can be used to prepare concentrated fertilizer mixtures or compound fertilizers. It is enriched with nitrogen and potassium to the usual ratios.
Organic fertilizers
The source of replenishment of exchangeable forms of magnesium is organic fertilizers. Systematic application increases the accumulation of absorbed magnesium in the soil, especially on sod-podzolic sandy and sandy loam soils.
The application of manure reduces the effectiveness of mineral forms of magnesium fertilizers. On sandy loamy soils with magnesium deficiency, maximum yields can be obtained by the combined application of organic fertilizers and mineral forms of magnesium.
Importance of magnesium fertilizers
Increase of cereal crops yield from application of magnesium fertilizers is 0.2-0.6 t/ha, potato tubers – 1.5-3 t/ha, sugar beet root crops – 2-4 t/ha, corn green mass – 2-6 t/ha, perennial grass hay – 0.4-0.7 t/ha, tea leaf – 0.5-1.0 t/ha. Magnesium-containing fertilizers increase the level and quality of yield. The content of starch, sugar, protein, vitamin C increases in plant products. The quality of seed material is improved – germination and germination energy increase, resistance to adverse environmental conditions and fungal diseases strengthens.
Magnesium requirements of plants
To ensure optimal conditions of magnesium nutrition of crops in the crop rotation and application of rational doses of fertilizers is required:
- determine the magnesium requirements of crops for the planned yield;
- to provide soils with available forms of magnesium;
- use of diagnostic methods;
- determination of the state of the balance of magnesium in the system soil-plant rotation.
The need of plants for magnesium depends on the crop and the size of the crop. The table shows the average long-term data on removal of magnesium with crops of crops obtained on sod-podzolic loamy sand soils, where the lack of magnesium is the most common.
The total removal of magnesium by crops for rotation depends on the specialization. With an increase in the share of grain legumes, vegetables, potatoes and other row crops in the structure of sowing areas magnesium removal increases. Between the need of crops in magnesium and their responsiveness to magnesium fertilizers there is a relationship: more demanding to magnesium crops give a higher increase in yield when it is applied.
Таблица. Magnesium removal with crop yield, kg/t of main products
| Barley | Winter rye | ||
| Clover | Spring wheat | ||
| Flax fiber | Oats | ||
| Winter wheat | Sugar beet | ||
| Vicia-oat mixture | Lupine (grain) | ||
| Potato |
Cereal crops are characterized by less demand for magnesium compared to vegetable, technical and row crops. However, the lack of magnesium, especially at the beginning of the growing season, on cereals leads to magnesium starvation. This is due to the shallow root system of cereal crops at the beginning of the growing season, which can not use nutrients from deeper soil layers. Oats react strongly to magnesium deficiency, while wheat and barley are less sensitive.
Magnesium supply diagnostics
You can assess the availability of magnesium in plants by the appearance of the plant, which in deficiency or excess changes due to disruption of biochemical processes. The main outward sign of magnesium starvation is spotted necrosis: leaves become mottled, areas between veins are pale, veins retain their color. These manifestations are due to the fact that the tissues adjacent to the conductive system are richer in chlorophyll and have a more intense green coloration. Since magnesium moves from the lower leaves to the upper leaves, the signs of starvation from deficiency appear predominantly on the lower leaves. An excess of magnesium causes the leaves to become darker, and abnormal curling and wrinkling is noted.
Soil and plant diagnostics are used to assess magnesium nutrition more accurately and objectively and to optimize magnesium fertilizer doses.
Low magnesium content is often inherent in light soils of granulometric composition. Fertility of sandy soils in terms of magnesium reserves is determined by the degree of weathering of primary magnesium-bearing minerals – feldspars, biotite, serpentine, augite, etc.
The need for magnesium fertilizers is determined by the content of magnesium available to plants, which is determined in the soil extract of 1 n potassium chloride solution (KCl).
For most farming zones, the division of soils by magnesium content is proposed:
- less than 1.0 mg/100 g of soil – very low;
- 1.1-2.5 mg/100 g of soil – low;
- 2.6-5.0 mg/100 g of soil – medium; 2.6-5.0 mg/100 g of soil – medium;
- more than 5.0 mg/100 g of soil – good.
For simultaneous determination of magnesium and other cations, extracts with sodium chloride solution and 1 n acetic acid ammonium are also used. However, each extraction and element requires determination of a different scale of soil elements availability.
The degree of magnesium availability in plants during the growing season can be determined by plant diagnostics based on the magnesium content in individual plant organs (table).
Table. Levels of magnesium content in plants, %/dry matter
| Oats | |||||
| Barley | |||||
| Winter rye | |||||
| Winter wheat | |||||
| Corn | |||||
| Potato | |||||
| Red clover | |||||
| Sugar beet | |||||
| Tomato | |||||
| Cucumber | |||||
| Cottonwood | |||||
| Apple trees | |||||
| Blackcurrant | |||||
| Citrus | |||||
| Tea bushes |
For some crops excessive magnesium level with visual signs of toxicity is established: for corn – more than 0.55% in pre-budding leaf, for alfalfa – more than 2.0% before flowering, for plum – more than 1.1% in leaves in July, for soybean – 1.5%.
For an objective assessment of the magnesium nutrient regime, a number of factors determining the amount, condition, and mobility of magnesium in the soil must be taken into account. An approximate model of these factors was proposed by Hungarian scientists.
Doses of magnesium fertilizer
To determine the needs of an individual farm in magnesium fertilizers, as well as for other elements, carry out balance calculations, taking into account the items of receipt, such as receipt with lime, mineral and organic fertilizers, precipitation and seeds, and consumption, such as removal with crops, losses from leaching and erosion.
Intensive chemicalization, in particular, the use of high doses of mineral fertilizers, leads to increased tension of the magnesium balance, primarily on light sod-podzolic and peat-bog soils, as a result of removal and leaching.
On soils of light granulometric composition with average magnesium content it is recommended to apply 30-40 kg MgO/ra for grain crops and 60-70 kg/ha for potatoes, corn and root crops. On soils with low and very low supply, the dose is increased, with high and high supply – reduced by 15-25%. The lower the magnesium content and the higher the soil acidity, the more the dose of magnesium fertilizer is increased.
Forms and timing of application
Soil liming with dolomites allows the plants to be fully supplied with magnesium.
Calimagnesia, potassium-magnesium concentrate, potassium salt on kainite, applied in doses of potassium fertilizers, provide the plants with the need for magnesium. Under root crops – sodium-loving crops – as potash fertilizers use kainit and potassium salt from kainit. Crops in this case are provided with potassium, magnesium, sodium and sulfur.
Soluble magnesium-containing fertilizers are applied in the spring during tillage. Low soluble magnesium-containing fertilisers are superior to highly soluble ones under conditions of excessive moisture, heavy precipitation and irrigation. Magnesium ammonium phosphate is promising for hydroponics. Magnesium sulphate is used indoors.
If magnesium fertilizers were not applied in the spring before sowing and if magnesium starvation is detected, supplementation is carried out. Well soluble magnesium fertilizer is used for this purpose. Half a dose of the basic fertilizer is given as a top-up, if it is carried out early and if magnesium starvation is severe, full doses are used.
Features of application of magnesium fertilizers for crops
Cereal crops
Features of application of magnesium fertilizers for cereal crops:
- Crops should respond well to magnesium and lime fertilizers. Doses of magnesium more than 40-60 kg/ha for winter cereal crops usually do not lead to further growth of yields.
- Signs of magnesium starvation in spring cereals appear at the beginning of growth, as the root system develops, magnesium nutrition improves and signs disappear. However, due to the low reutilization of magnesium, its deficiency at the beginning of the growing season can negatively affect the final yield and grain quality.
- When applying high doses of potassium fertilizer and liming, the ratio of calcium, potassium and magnesium must be maintained. Violation of this ratio leads to increased crop requirements for magnesium.
- Magnesium fertilizer increases grain yield and improves its quality: increases grain protein content, completeness and weight of 1000 grains.
- Sufficient supply of magnesium increases resistance to lodging, to fungal diseases such as rust.
Potato
Features of magnesium fertilizer application for potatoes:
- Potatoes respond well to the application of magnesium fertilizers, especially on sod-podzolic soils.
- The optimal forms for potatoes are magnesium sulphate, magnesium-containing potash and phosphate fertilizers. Magnesium carbonate can lead to boron starvation of potatoes. In this case, additional boric fertilizer is added.
- Magnesium fertilizers for potatoes are made at the same time as the basic fertilizer in rows during planting at 8-10 cm below the tubers, in the reserve for a number of years, such as a row of rotation or crop rotation, as well as top dressing during the growing season by spraying the tops during budding.
Sugar beet
Features of application of magnesium fertilizers for sugar beet:
- In determining the doses of magnesium fertilizers are based on the amount of magnesium needed to form the planned yield, and losses due to migration through the soil profile.
- The best form for sugar beet is dolomite. From mineral magnesium-containing fertilizers, sodium-containing ones are preferable, as beet is a sodium-voluble crop.
- If the soils are poorly supplied with magnesium, magnesium fertilizers increase the yield of sugar beet and sugar content of root crops.
Corn
Corn for silage with a lack of available forms responds well to magnesium. This is observed more often on light soils, despite a well-developed root system capable of consuming magnesium from the subsoil layers.
On light sandy loam soils, magnesium-containing carbon dioxide lime fertilizers are more effective for corn than pure lime.
Corn for silage is a valuable fodder crop, so the quality of green mass is no less important than the size of the crop. Systematic use of fertilizers worsens cationic composition of green mass, which affects quality of feed, its nutritive value and digestibility by animals. In addition to the usual methods of application of magnesium fertilizers, spraying corn leaves with 2% magnesium sulfate solution has a positive effect.
Grasses, hayfields and pastures
As a result of intensification of cultivation technologies of grasses, natural meadow hayfields and pastures there was a need to use magnesium fertilizers on these lands. When fertilizing perennial grasses to create a balanced content of nutrients in the green mass. Thus, the low content of magnesium in the feed leads to the disease of animals pasture tetany because of the delayed metabolism of mineral nitrogen into organic forms. Large doses of potassium fertilizers aggravate this process by preventing the entry of magnesium into plants due to ion antagonism.
Sources
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.
Potassium fertilizers
Potassium fertilizers are mineral fertilizers that meet the potassium requirements of crops.
- Mineral fertilizers
- Nitrogen fertilizers
- Phosphate fertilizers
- Potassium fertilizers (Русская версия)
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- Mineral fertilizers
- Nitrogen fertilizers
- Phosphate fertilizers
- Potassium fertilizers (Русская версия)
Raw materials for potassium fertilizer production
Natural potassium salts are used as raw materials for the production of potassium fertilizers, whose deposits are located in Russia, Germany, France, USA, Canada, Israel, Italy, Poland, England, Ukraine, Belarus, Kazakhstan and other countries.
Of the 120 potassium-containing minerals, only a small portion is of industrial importance.
Table. Minerals used to produce potassium fertilizers
| Silvinite - nNaCl + mKCl | |
| Carnallite - KCl⋅MgCl2⋅6H2O | |
| Cainite - KCl⋅MgSO4⋅3H2O | |
| Shenith - K2SO4⋅MgSO4⋅6H2O | |
| Langbeinite - K2SO4⋅2MgSO4 | |
| Alunite - (K, Na)2SO4⋅Al2(SO4)3⋅4Al(OH)3 | |
| Polygalite - K2SO4⋅MgSO4⋅2CuSO4⋅2H2O | |
| Nepheline - (K, Na)2O⋅Al2O3⋅Al2O3⋅2SiO2 |
One of the largest potash deposits in Russia is Verkhnekamskoye (over 12 billion tons), located near the cities of Solikamsk and Berezniki on the left bank of the Kama River on the western slope of the Northern Urals. It was formed as a result of the drying up of the ancient Perm Sea. The development of the deposit began in 1925 and the production of fertilizers began in 1929. The upper part of the deposit is represented by carnallite with an admixture of NaCl, CaSO4⋅2H2O, clay, K2O content – up to 17% (10-25%). Carnallite has a mottled color from a combination of yellow, orange, brown and red colors due to the admixture of iron oxide Fe2O3 (iron luster). Below the carnallite lies a thick layer of sylvinite, containing potassium and sodium chlorides in various ratios.
Sulfate potash is obtained from the minerals kainite, langbeinite, mixed langbeinite-kainite rocks and alunite. The deposits of polyhalite, kainite and glaserite (3K2SO4⋅Na2SO4) are available in the Saratov and Orenburg regions and in Bashkiria (Zavolzhskoe deposit).
There are large deposits of potassium minerals in Ukraine in Ivano-Frankovsk and Lvov regions. These deposits are dominated by langbeinite (K2SO4⋅2MgSO4), kainite (KCl⋅MgSO4⋅3H2O), polyhalite (K2SO4⋅MgSO4⋅2CaSO4⋅2H2O), schoenite (K2SO4⋅MgSO4⋅6H2O). The raw materials of these deposits are processed at the Stebnikovsky and Kalushsky combines. The share of impurities is up to 30%, mainly in the form of silt.
Belarusian deposits of potassium salts are located in Polesie (Soligorsk), which is probably an extension of the Carpathian deposits. They are represented by the minerals sylvinite, carnallite and halite.
Zhilyansk deposit in the Aktobe region of Kazakhstan is represented mainly by polyhalite. Carnallite, sylvinite, and glaserite are also present. Polyhalite minerals are the raw material for the production of potassium sulfate, potassium-magnesium sulfate and complex mineral fertilizers. After milling, it can be used as a sulfate form of potassium-magnesium fertilizer, containing 13-15% K2O and 6-7% MgO.
Other minerals containing potassium can be used as fertilizer. For example, an aluminosilicate of potassium and sodium, nepheline (Na, K)2O⋅Al2O3⋅2SiO2, is found in apatite deposits, for example, in the Khibiny deposit. Its potassium content is 5-6%. It is poorly soluble in water, and in acidic soils, it partially decomposes. It also contains 10-13% Na2O and 8-10% CaO, therefore it has a neutralising effect in sour soils. As a rule, it is used as a local fertilizer on acidic and peaty soils.
In the production of aluminum from nepheline as a waste product is obtained potassium carbonate, containing 63-67% K2O, which is a valuable potash fertilizer.
Classification of potassium fertilizers
Potash fertilizers are classified into raw potassium salts and concentrated potassium fertilizers.
Raw potash salts are sylvinite and kainite.
Concentrated potash fertilizers – potassium chloride, potassium salt, potassium sulfate, potassium magnesium sulfate.
Raw potassium salts
Raw potassium salts (sylvinite, kainite) are produced by crushing and grinding natural potassium salts. As a rule, concentrated layers of the deposit are used for production, less concentrated ones are used for processing. Initially raw potassium salts were mainly used as fertiliser, later on they were substituted by concentrated potassium salts due to the fact that they contain a lot of ballast substances that increase transportation and application costs.
Because of the expensive transportation of raw potassium salts are used in the areas of their extraction on a limited scale. The main part is used to produce concentrated potash fertilizers.
Sylvinite
Sylvinite is a mineral that is a mixture of potassium and sodium chlorides and contains 12-18% K2O and 35-40% Na2O. According to the technical specifications, sylvinite from the Solikamsk deposit must contain 15% K2O. It is hygroscopic and cakes when stored.
It is offered in rough milling with the size of crystals of 1-5 mm. It has a pinkish-brown color with inclusion of blue crystals. It is transported in bulk. It is applied to sodium-loving crops.
Kainite
Kainite (KCl⋅MgSO4⋅3H2O) is a mineral of cainite-langbeinite rock, representing large pinkish-brown crystals, with mechanical admixtures of rock salt (NaCl), CaSO4, MgSO4, etc. It contains about 10-12% K2O, 6-7% MgO, 32-35% Cl–, 22-25% Na2O, 15-17% SO42-. When potash and potassium chloride are mixed, they make potassium salt, which contains 30-40% K2O. Humidity not more than 5%. It does not cake, it is transported in bulk.
It is a good fertilizer for sugar beets on chernozems. It is extracted in Stebnik (Western Ukraine), the composition of kainite of these deposits is close to Solikamsk sylvinite.
Concentrated potassium fertilizers
In terms of potassium content, the most concentrated fertilizer is potassium chloride, the most used potassium fertilizer in Russia.
Potassium chloride
Potassium chloride (KCl) is the main potassium fertilizer. Production accounts for 80-90% of the total production of potash fertilizers. It is received from sylvinite. Chemically pure potassium chloride contains 63% K2O. Depending on the method of production, the potassium chloride used as fertilizer contains 50-60% K2O. It is a fine crystalline powder of pink or white color with a grayish tint. It has a small hygroscopicity, often caking.
In the industry different methods of production are used, for example, halurgical, flotation, gravitational.
The halurgical method splits potassium and sodium chlorides on the basis of their different solubility. Solubility of KCl doubles when the temperature rises from 0 °C to 100 °C, while the solubility of NaCl almost does not change. Grinded sylvinite is dissolved at 110°C in a solvent lye – saturated NaCl solution, and only KCl of sylvinite dissolves, while NaCl remains insoluble as a precipitate.
When the resulting solution is cooled, a crystalline precipitate of KCl falls out, and the mother saturated solution of NaCl is used to process new batches of sylvinite. The production waste is up to 95% NaCl, which is used to produce soda, technical and table salt.
The flotation method of separating the minerals sylvin (KCl) and halite (NaCl) on the basis of the different ability of the surface of the particles of these minerals to wetting by water. Preliminary crushed ore is agitated in an aqueous solution with addition of alkylsulfates as a reagent-collector at the rate of 100-200 g of the reagent for 1 ton of ore. The reagent is adsorbed on the surface of potassium chloride particles. Then air is blown through the pulp in the form of small bubbles. Particles of hydrophobized sylvin are carried with the air bubbles to the surface in the form of foam. The KCl foam concentrate is dehydrated by centrifugation and dried. The halite particles are collected at the bottom of the flotation machine.
The flotation potassium chloride has larger pink crystals. Hydrophobic additives reduce hygroscopicity and caking. The advantage of the method is that no high temperatures are required and the product has better physical properties. The flotation method is used at Berezniki potassium plant; the produced potassium chloride contains 60% K2O.
The flotation method is the most widespread in Russia.
The gravity method is relatively new in France and other countries, based on the different densities of KCl (1.987 g/cm3) and NaCl (2.17 g/cm3). In Russia the method has been improved. Hydrocyclones are used to separate small particles of KCl and NaCl. The method is used at Solikamsk combine.
Methods of in-situ leaching of ore (salvinite) with subsequent processing of solution by evaporation and crystallization are also used.
The use of coarse-crystalline and granular potassium is more preferable, as fine-crystalline has poor physical properties, is not convenient for the preparation of fertilizer mixtures with granular superphosphate and granular ammonium nitrate. Introduction of such fertilizer mixtures with centrifugal spreaders leads to separation (segregation) of fertilizers and uneven application. Coarse-crystalline potash is 30% less absorbed by the soil and remains in a form accessible to plants for a longer time, which increases the effectiveness of coarse-crystalline potash.
Potassium salt
Potassium salt contains 40-44% K2O, 20% Na2O and 50% Cl. It is obtained by mixing potassium chloride with crude potassium salts, most often with crushed sylvinite, less often with kainite. Its appearance is that of small mottled crystals. According to technical specifications it must contain not less than 40% of K2O.
The 30% potassium salt is a mixture of sylvinite and kainite, suitable for magnesium-demanding crops on sandy and sandy loam soils poor in magnesium.
Mixed potassium salts are the most suitable fertilizer for beets, cruciferous vegetable crops, carrots and others that respond favorably to sodium and magnesium on light soils.
Potassium sulfate
Potassium sulfate is a concentrated chlorine-free potash fertilizer containing 45-52% K2O. It is a fine crystalline powder of white color with yellow or gray tint, moisture content 1.2%. It is not caking and may be transported in bags or in bulk. It is received by treatment of polymineral potash ores, for example langbeinite, shenite, or by exchange reaction with potassium chloride:
2KCl + MgSO4 = K2SO4 + MgCl2.
In saturated solution, due to low solubility, potassium sulphate precipitates first, which is filtered and dried.
Potassium sulfate is produced in the Western Ukraine by the processing of langbeinite salt. Fertilizer has good physical properties, non-hygroscopic, does not caked.
The advantage of potassium sulfate is that it does not contain chlorine. Compared with chlorine-containing fertilizers, potassium sulfate provides an increase in yields of grapes, buckwheat, tobacco and other chlorophobic crops. It is widely used in vegetable growing, especially in protected ground. Sulfur also has a positive effect on cruciferous crops, legumes and some other crops.
However, in cost terms, potassium sulfate is one of the most expensive potassium fertilizers.
Calimagnesia, potassium-magnesium sulfate
Calimagnesia, potassium-magnesium sulfate (K2SO4⋅MgSO4) contains 26-29% K2O and 9% MgO. It is obtained from cainite-langbeinite rock. It is a dehydrated mineral of schoenite, that is why it is sometimes called so. It is a white, strongly pulverized powder with a grayish or pinkish hue, or grayish-pink irregularly shaped granules. It does not cake and is transported in bags or in bulk.
Primarily used for chlorine-sensitive crops or on light soils.
Kalimag
Kalimag contains 16-20% K2O and 8-9% MgO. It is produced from langbeinite (K2SO4⋅2MgSO4) after grinding and leaching of sodium chloride. Approximate composition: K2SO4 – 39%, MgSO4 – 55%, NaCl – 1%, insoluble residue – 5%. Available in the form of gray granules. It does not cake and can be transported in bulk. Its efficiency is close to that of potassium permanganate.
Potassium-chloride electrolyte
Potassium-chloride electrolyte is potassium chloride with admixtures of sodium and magnesium chlorides. It is a by-product of magnesium production from carnallite. It contains 34-42% K2O, 5% MgO, 5% Na2O and up to 50% Сl. Highly dusty fine crystalline powder with yellow tint. It does not cake and is transported in paper bags or in bulk. The effect is similar to potassium chloride, and is more effective than potassium chloride on magnesium-poor soils. It is produced in Solikamsk.
Potassium-containing cement dust
Potassium-containing cement dust contains 14-35% K2O and is a waste product of cement production. Includes carbonate (K2CO3), hydrocarbonate (KHCO3) and potassium sulfate (K2SO4). It also contains CaCO3, MgO (3-4%), silicic acid, semi-oxides, and some trace elements. It has an alkaline reaction does not contain chlorine, so it can be used for potatoes, buckwheat, grapes, tobacco, citrus.
In Netherlands, Norway, Finland, potassium-containing cement dust is used as potash and lime fertilizer. It is well soluble in water and accessible to plants. The calcium carbonate it contains makes it hygroscopic. Cement dust can be used to produce potassium phosphate and granulated.
Furnace ash
Furnace ash is used as a local potassium-phosphate-lime fertilizer. It is effective for all crops and on all types of soils. Potassium is contained in the form of potassium carbonate (K2CO3, potash). Phosphorus ash is assimilated by plants in the same way as precipitate and tomas slag, unlike superphosphate, it does not bind in hard-soluble phosphorus compounds. Lime eliminates the negative effect of potash on soil structure.
K2O content depends on the fuel burned. For example, hardwood ash contains 10-14% K2O, 7% P2O5, 36% CaO, and softwood ash contains 3-7% K2O, 2.0-2.5% P2O5, and 25-30% CaO. From young trees, more ash is produced and the content of nutrients is higher.
The ash contains micronutrients. The dose of ash for plowing or cultivation is 5-6 cwt/ha. Peat ash and ash to neutralize excessive acidity is applied in an amount of 1.5-3 t/ha, better under plowing.
Interaction of potassium fertilizers with soil
Potassium fertilizers are well soluble in water. When applied to the soil are dissolved in the soil solution and enter into an exchange (physical and chemical) interaction with the soil absorbing complex (SAC), partially in non-exchange interaction.
The exchange absorption of potassium cations is a small part of the whole absorption capacity. The exchange reaction is reversible:
[SAC]Ca2 + 2KCl ⇔ [SAC](K2, Ca) + CaCl2;
[SAC](Al, H) + 4KCl ⇔ [SAC]K4 + AlCl3 + HCl.
In the exchanged-absorbed state, potassium loses mobility, which prevents leaching outside the arable layer, except for light soils with low absorption capacity. The exchange-absorbed potassium remains available to plants.
Secondary processes of interaction between soil solution and soil absorbing complex gradually displace potassium cations from it. The root system of plants takes an active part in this exchange at the expense of root excretions.
Potassium cations displace an equivalent amount of calcium, magnesium, ammonium, hydrogen, aluminum cations from the SAC. On slightly acidic and neutral soils with high absorption capacity and buffering, exchange processes almost do not affect the reaction of the soil solution. On acid and highly acidic soils, especially on light granulometric composition, with exchangeable hydrogen and aluminum in the SAC, the application of potash fertilizers leads to acidification of the soil solution. Therefore, on such soils the efficiency of potash fertilizers decreases.
Additional acidification of the soil solution occurs as a result of physiological acidity of potassium salts, but it is much less than that of ammonium salts, and appears only with long-term application for potassium-loving crops.
Non-exchange (fixed) potassium is much less mobile than exchange-absorbed, practically not available to plants. Non-exchangeable absorption (fixation) of cations with ion radius of 0.130-0.165 nm (K+, NH4+, Rb+, Cs+) is typical for clay minerals of montmorillonite group and hydromica group with three-layer swelling crystal lattice. Therefore, the value of non-exchange potassium uptake depends on mineralogical composition: the more minerals of montmorillonite group and hydromica, the more pronounced is the fixation of potassium.
Fixation occurs due to penetration of cations into the interstitial spaces of minerals in the state of swelling, occupy hexagonal voids in the grid of oxygen atoms of the tetrahedral layers, pull down both negatively charged oxygen layers, as a result of which they appear in a closed space. Variable wetting and drying of the soil intensify the process of fixation. Potassium fixation also occurs in damp soil, but to a lesser extent.
The share of fertilizer potassium fixation in different soils depending on mineralogical composition and fertilizer dosage is from 14 to 82% of the applied amount.
According to the results of experiments conducted at the All-Russian Institute of Fertilizers and Agrochemistry, the form of potassium fertilizer does not affect potassium fixation by the soil. This process is influenced by the size of fertilizer particles: when applying coarse-crystalline or granular fertilizers, the fixation is reduced by 20-30% due to less contact between the fertilizer and the soil.
The size of non-exchangeable absorption also depends on the fertilizer dose: the absolute amount of fixed potassium increases with increasing dose, in percentage terms – slightly decreases. The potential capacity of the soil to fix potassium is high. In V.U. Pchelkin’s laboratory experiment at a potassium dose of 1000mg/100g the slightly leached black earth fixed 147.3 mg/100g, which is equivalent to 4420 kg/ha of soil.
With a systematic application of potassium fertilizers and a positive balance of potassium in the soil increases the content of mobile forms (water-soluble and exchangeable) and fixed forms.
With a negative balance of potassium the opposite process takes place. As the available water-soluble and exchangeable forms of potassium are consumed, there is a gradual transition of fixed potassium and part of the crystal lattice potassium to more mobile forms. Thus, in the experiment on a loamy soil (England) for 101 years, plants took out with crops 3-4 times more potassium than it was contained in the soil in the exchangeable form. In the experiments of Kobzarenko (1998), plants on control variants took out from sod-podzolic light loamy soil (Moscow region) 583 kg/ha of potassium for 17 years that in 2,9 times more than the initial content of exchangeable potassium in the soil. At the same time, there were no significant changes in the content of exchangeable potassium during the reference period. These studies confirm the possibility of gradual replenishment of exchangeable potassium by other forms.
Experiments also confirm the weak migration of fertilizer potassium along the soil profile, except for sandy and sandy loam. In lysimetric experiments annual leaching of potassium outside the root-containing layer was 0.4-7.0 kg/ha in the Non-Black Earth zone on loamy soils, and up to 12 kg/ha on sandy loamy soils.
Effectiveness of potassium fertilizers
Potassium (2.5-4.5:1:3.5-6) predominates in the ratio N:P:K for potassium-loving crops, and nitrogen (2-3:1:1:1.5-3.5) for grain crops.
Average removal of potassium with crops per 1 ton of marketable products and the corresponding amount of by-products is 25-30 kg for cereals, potatoes – 7-10 kg, sugar beets – 6,7-7,5 kg, vegetable crops – 4-5 kg, perennial grass in hay – 20-24 kg.
Crop sufficiency with potassium can be judged by its content in the soil in the exchangeable form. Methods of determination differ for types of soils:
- for sod-podzolic soils – Kirsanov method (0.2 n. HCl), Peyvet method (1 n. NaCl), Maslova method (1 n. CH3COONH4);
- for gray forest soils and chernozems (except for carbonate ones) – Chirikov’s method (0,5 n. CH3COONH4);
- for carbonate chernozem, chestnut soils and gray soils – Machigin’s method (1%-m (NH4)2CO3).
All methods of determining potassium in the soil available to plants are based on the extraction of the exchange form, adsorptionally held by colloidal particles. This amount also includes water-soluble potassium.
The effectiveness of potassium fertilizers depends on:
- soil type and granulometric composition;
- availability of available potassium in the soil;
- the needs of the crops in the crop rotation;
- the amount of precipitation;
- temperature;
- organic matter content in the soil;
- nitrogen and phosphorus fertilizers;
- the method of incorporation;
- forms of potash fertilizers.
Potassium fertilizers are highly effective on sod-podzolic soils, red soils, gray forest soils, and northern chernozems. Especially poor in mobile (exchangeable) potassium are sod-podzolic sandy and sandy loam soils, dried peatlands and peat-bog soils.
Potassium fertilizers have a positive effect when the content of mobile potassium in the soil at the level of 1st-3rd classes. With a higher supply, the effectiveness of potassium fertilizers decreases and is determined primarily by crop rotation, doses of nitrogen and phosphorus fertilizers and agronomic practices.
The efficiency of potassium fertilizers, as well as phosphorus and nitrogen fertilizers, is higher on slightly acidic and neutral soils than on strongly acidic ones. Therefore, liming of acidic soils is a condition for increasing efficiency. However, due to the antagonism of potassium and calcium ions in limed soils, the doses of potassium fertilizers are increased.
Table. Effectiveness of potash fertilizers depending on the acidity of sod-podzolic soils (by Mineev)
The application of manure, which itself is a good source of potassium, usually reduces the effect of mineral potash fertilizers.
The greatest efficiency of potash fertilizers is achieved in an optimal ratio with nitrogen and phosphorus. One-way application of potash fertilizers is carried out on drained peatlands and peat-bog soils, with sufficient content of other nutrients.
Timing, methods and forms of potassium fertilizer application
On soils of medium and heavy granulometric composition chloride-containing potash fertilizers in full dose, except for row application in small doses for some crops, it is advisable to make under autumn autumn autumn autumn tillage. This allows you to place fertilizers in a wetter layer of soil, where the bulk of the roots develop, and the chlorine is washed from the arable layer during the fall and spring. Only on light, peat-bog and floodplain soils, potash fertilizer is made in spring. Under row crops and vegetable crops, a portion of the total dose of potassium is appropriate to give as a top-up.
In the rotation of potassium fertilizers made in the first place for potassium-loving crops, which give a significant increase in yield.
Flax and hemp consume relatively little potassium, but because of the weak root system, which under normal conditions can not provide plants with sufficient potassium, for these crops make increased doses of potash fertilizer.
For chlorophobic crops, it is advisable to apply fertilizers with minimal chlorine content. When using chlorinated potassium fertilizers for potatoes, the amount of starch is reduced by 7-15% compared with chloride-free fertilizers.
Application of potassium fertilizers on different soils
In Russia, more than 1/3 of the arable land areas are characterized by low and medium levels of exchangeable potassium and need to apply potash fertilizers. Their use is most effective on sandy, sandy loam sod-podzolic, peat-bog, floodplain soils and red soils. They also have a positive effect in the zone of sufficient moisture on loamy sod-podzolic, gray forest soils, podzolized and leached chernozems with low and medium potassium supply.
Sod-podzolic soils
Sod-podzolic soils have relatively small reserves of available potassium. Non-exchangeable potassium is part of the prevailing in these soils of secondary clay minerals – kaolinite and montmorillonite, which can not provide restoration of stocks of exchangeable potassium. This explains the positive effect of potash fertilizers on sod-podzolic soils.
According to data from many years of experience, the annual introduction of potassium fertilizers in an amount of 30-90 kg K2O per 1 ha increases the yields of root crops, particularly potatoes, and cereal crops. The largest yield increases of up to 30-50% are obtained on light loamy and sandy soils, where potassium reserves are extremely low. In shorter experiments with nitrogen-phosphorus background, potash fertilizers also provide an increase in yields of all crops in the first rotation of the rotation: the increase in grain yields averaged 10-20%, root crops – over 30%.
With the depletion of soil reserves of potassium and the improvement of nitrogen-phosphorus nutrition of plants the need for potash fertilizers increases, increasing their effectiveness, which is especially manifested in heavy soils with a granulometric composition. Because of the small stocks of mobile potassium sod-podzolic soils moderate doses of up to 90 kg/ha K2O does not provide a positive balance. However, the content of exchangeable potassium in the soil due to dynamic equilibrium between forms of potassium in the control is maintained at the initial level, which is associated with the mobilization of natural soil potassium caused by physiological acidity of fertilizers, biological accumulation by plants due to their better development on fertilized variants as well as by inclusion of potassium of subsoil and underlying soil layers. Mobilization of unexchangeable potassium under the influence of fertilizers provides an increase in mobile forms of potassium and is accompanied by a decrease in its reserves.
Gray forest soils
Gray forest soils are characterized by a low content of exchangeable potassium in the arable layer. However, in comparison with sod-podzolic soils, the effect of potassium fertilizers on the yield of various crops is weaker. It is connected with the fact that unexchangeable potassium of silt fraction is a part of hydromica of loess-like loam – the main soil-forming rock of gray forest soils. Hydromica have a high fixing ability in relation to monovalent cations and the ability to easily release unexchangeable absorbed potassium, which either passes into the exchange state or is directly used by plants.
The study of the potassium regime of gray forest soils in long-term experiments has shown that during one rotation of the crop rotation when making low doses of fertilizers is a negative balance of potassium. But, despite this, there is an increase in the content of available forms of potassium (exchangeable and readily hydrolysable) while maintaining the level of non-exchangeable form in fertilized variants. Under the influence of plants and fertilizers all reserve forms of potassium are mobilized and their transition into the exchangeable state occurs.
With prolonged use of nitrogen-phosphorus fertilizers in the rotation of gray forest soils potassium effect increases from rotation to rotation.
Black soil of the forest-steppe and steppe zones
Black earth soils (chernozems) of forest-steppe and steppe zones contain sufficient reserves of potassium available to plants. Soil-forming rocks and clay minerals of chernozems are rich in non-exchangeable potassium, which actively passes into mobile forms, so the effectiveness of potash fertilizers on these soils is small. Even potassium-loving crops (row crops and technical), little response to the application of potassium fertilizers. It is especially noted on soils of heavy granulometric composition.
Over time, the effectiveness of potassium fertilizers increases, which is especially noticeable when growing sugar beets and other potassium-loving crops, as well as when applying potassium on the background of nitrogen-phosphorus fertilizers, which is explained by the depletion of soils not potassium due to the removal of crops.
Systematic fertilization does not lead to a significant increase in the content of mobile forms in chernozems even with a positive balance, which is due to the high saturation of the absorbing complex of chernozems with divalent bases that prevent the absorption of potassium.Favorable conditions for potassium fixation in chernozems: mineralogical composition of the silty fraction – hydromica and highly dispersed minerals of the montmorillonite group, which are characterized by a high ability to fix univalent cations, as well as high saturation of the soil absorbing complex (SAC) with bases, increased soil acidity, high content of organic matter, absence of potassium competitor – absorbed ammonium, irreversible coagulation of colloids with periodic drying of the top layer. These conditions contribute to non-exchangeable absorption of potassium in the arable and subsoil layers. At negative balance on fertilized variants increase non-exchange potassium is explained with mobilization of less mobile forms under the influence of plants and fertilizers, as well as the release of secondary minerals potassium – hydromica.
Potassium has a positive effect under adverse weather conditions. With an abundance of precipitation, it reduces lodging of crops in dry years helps to combat floods caused by drought. Proper use of potassium fertilizers on chernozems, that is, on the background of nitrogen-phosphorus fertilizers in wet and dry years, increases the yields of major crops, especially potassium-loving.
Chestnut soils and gray soils
The content of mobile potassium in chestnut soils of dry steppe and grey soils of Central Asia is high, reaching 40-60 mg K2O/100 g of soil. Potassium reserves are huge, as it is a part of hydrosols and is easily released, so the efficiency of potassium fertilizers is insignificant.
On old-fallow, long used irrigated grey soils with the systematic application of nitrogen and phosphorus fertilizers the content of mobile forms is small, so the yield and product quality of crops, especially cotton, increases.
Soils of steppe and arid-steppe regions
Soils of steppe and dry-steppe regions, most often, are well supplied with potassium. Due to the variability of moisture conditions, on typical, ordinary, southern chernozems, chestnut soils and gray soils the effect of potash fertilizers is small or does not appear at all. Application of potassium fertilizers is justified only for potassium-loving crops – sugar beet, sunflower, vegetable crops, on chestnut soils and sierozem under irrigation.
The process of potassium depletion in soils of arid steppe and desert zones due to large reserves of non-exchangeable potassium, mineralogical composition of soils and soil-forming rocks proceeds slowly. It is important to periodically replenish potassium reserves by adding it with irrigation water during irrigation. Reducing the content of potassium in the soil with prolonged use and systematic use of nitrogen and phosphorus is manifested by signs of potassium starvation of plants and the growth of efficiency of potash fertilizers.
On solonets, as a rule, rich in potassium, potash fertilizers are not used, as they increase solonetzation and do not bring the expected effect.
Application of potassium fertilizer and liming
Application of potassium fertilizers on sandy soils that need liming increases the need to neutralize soil acidity, as potassium displaces ions of hydrogen, aluminum, manganese, which reduce pH, from the soil absorbing complex. When liming acidic soils, the need for potassium fertilizers increases. Additions of potassium on the background of lime increases in absolute and relative values. The effect of lime, in addition to improving the physical and chemical properties of soils, is also manifested in the improvement of nitrogen-phosphorus nutrition of plants and a slight decrease in the availability of potassium for plants due to its increased fixation by soil colloids. With increasing yields at liming also increases removal of potassium from the soil, and the transition to available forms goes less intensively than in acidic soils.
Because of the antagonism of potassium and calcium, there is a need to increase the dosage of potash fertilizers in liming and soils with a neutral reaction. Liming of soils in such cases significantly increases the effectiveness of potash fertilizers.
On the other hand, the improvement of the potassium regime increases the benefits of liming. The use of manure reduces the effect of potash fertilizers, as it affects the nutrient regime of soils, while being a good source of potassium.
Increasing the efficiency of potash fertilizers
The main ways to increase the efficiency of potash fertilizers:
- Application taking into account natural and economic conditions and the provision of soils with mobile forms of potassium.
- Increasing the culture of farming, cultivation of soils, optimal provision of crops of rotation with other fertilizers, i.e. balanced nutrition of crops.
- Liming of acidic soils.
- Introduction of potassium in the rotation in the first place for crops with high responsiveness to potassium.
- Selection of forms of potash fertilizers, taking into account the biological features of crops. For example, potassium sulfate and potassium chloride have the same effect on the yield of most crops. Chloride-free forms contribute to increased yield of buckwheat, millet and some varieties of tobacco, increase the sugar content in berries of certain grape varieties, the starch content in the tubers of late varieties of potatoes, improve the quality of flax fiber.
- Proper selection of the timing and methods of application. In most regions of the country potash fertilizer is made in autumn under autumn plowing, except for sandy soils and floodplains. This contributes to the uniform distribution of potassium in the arable layer and leaching of chlorine into the underlying horizons during the fall-winter and spring periods.
- Optimization of potassium fertilizer doses taking into account meteorological conditions. Thus, the application of 80 kg/ha of K2O against the background of N60P60 increased winter wheat yields by 240 kg/ha, by 660 kg/ha and by 1190 kg/ha, compared with the background at an average temperature of 16.5°C during May-July, at 15.2°C and at 13°C. This is due to the difficulty in getting potassium into the plants at low temperatures. Potassium fertilizers improve the physical properties of grain, especially with excess precipitation of more than 80 mm in July, during ripening and ripening. For example, in the Non-Black Earth zone during this period, a lack of potassium produces small and puny grain.
- Full provision of optimum doses of potassium fertilizers in combination with other nutrients peat (developed and old), peat-bog soils, which are poor in this element (0,02-0,3 of gross content). In these soils, potassium is mobile, not accumulated in the arable horizon and is almost completely used by plants in the first year of application. The effect of fertilizers increases with double regulation (irrigation and drainage) of these soils. The greatest effect is achieved under vegetables and root crops, which pay back the application of potassium by an increase in yield.
Several groups of soils are distinguished by the availability of exchangeable potassium.
Table. Gradations of soil provision with mobile (exchangeable) potassium, mg/kg of soil (Methodological Guidelines for Comprehensive Monitoring of Soil Fertility of Agricultural Lands, 2003)
| Very low | |||||
| Low | |||||
| Medium | |||||
| Increased | |||||
| High | |||||
| Very high |
Generalization of data from long-term stationary experiments of the geographical network has shown that the content of 10-15 mg K2O/100 g of soil and application of 60-90 kg K2O/ra on sod-podzolic, gray forest soils and leached chernozems ensures the productivity of the crop rotation of 3-5 t/ha of grain units. However, significant reserves of potassium and dynamic equilibrium between its forms make the index of exchangeable potassium content, which characterizes the ability of the soil to provide potassium nutrition to plants, less reliable. In the process of plant nutrition all forms of soil potassium participate, therefore mobile forms (soil solution and exchangeable) and unexchangeable potassium of primary and clay minerals, as well as mobility, ability and recovery rate of exchangeable potassium from reserve forms should be taken into account.
The provision of soils with unexchangeable potassium depends on the type of clay minerals, genetic features and the granulometric composition of soils. The greatest quantity is bound by mica minerals (hydromica, illite, vermiculite), less – by montmorillonite, the least one absorbs non-exchangeable kaolinite.
According to the degree of provision of unexchangeable potassium soils are divided into groups:
- low 10-20 mg K2O/100 g of soil,
- medium 20-50 mg K2O/100 g of soil,
- increased 50-100 mg K2O/100 g soil,
- high 100-150 mg K2O/100 g soil.
With prolonged use of potassium fertilizers increases the amount of exchangeable potassium, its mobility and share in easily hydrolyzable and non-exchangeable fractions increase. With the increase of these indicators, the effectiveness of “freshly applied” potassium decreases and the effect of “residual” potassium accumulated as a result of fertilizer application increases. However, these data do not allow us to establish common criteria for all soils potassium availability.
There are different methodological approaches to determine the degree of supply of mobile potassium. Thus, it is possible to determine this index by saturation of absorbing complex with exchange potassium, taking 1.8-3.0% as an active level. However, the saturation value of the soil absorbing complex exchangeable potassium must be established for each type of soil, depending on the mineralogical composition of the silt fraction of the soil and the underlying soil-forming rock, biological characteristics of cultures, the conditions of nitrogen-phosphorus nutrition and moisture supply. In each case, the less saturation of the absorbing complex of potassium, the higher the effectiveness of fertilizers.
Optimal concentrations of potassium in the soil are established, although they need to be clarified.
- Potassium in the soil is in various interrelated forms. When applying potassium fertilizers, its reserves are replenished, but due to differences in the composition of clay minerals in sod-podzolic soils more increases the content of the exchange form, and on chernozems – non-exchange. In all cases, during plant nutrition available forms of potassium are replenished at the expense of non-exchangeable forms. Therefore, when determining the potential reserves of available potassium is taken into account.
- Potassium in the soil is less mobile than nitrogen, but more mobile than phosphorus. Therefore, when trying to create an optimal potassium level by periodic application of high doses on heavy clay soils, potassium is fixed by minerals, and on light sandy and sandy loam soils migrates along the soil profile beyond the root layer.
- The application of higher doses of fertilizers and chemical meliorants changes the availability of potassium to plants. For example, when liming acidic soils, even with high potassium content its availability due to the antagonism of calcium and potassium decreases. Therefore, optimal doses of potassium fertilizers on calcareous soils are increased by 1.5-2 times. Antagonism and synergy exist between potassium and other cations and anions.
- Cultivated plants respond differently to potassium nutrition. A group of potassium-loving crops has been identified for which the optimal level of exchange potassium should be higher than, for example, cereals, legumes, annual and perennial grasses.
- Chlorophobic crops react negatively to excess chlorine in the soil. This negative phenomenon can be eliminated by adjusting the doses, timing and application methods. For example, the early application of chloride-containing potash fertilizers in autumn under autumn plowing.
Doses of potassium fertilizers
Optimal doses of potash fertilizers in crop rotations depend on the location, frequency and sequence of lime and manure applications. With liming of sod-podzolic soils and the corresponding increase in yields, the need for potash fertilizers increases particularly strongly.
According to long-term field experiments on sod-podzolic soils with initial pH of 4,2, when potassium fertilizers were made in parallel on the background of lime and without it, showed that after the first rotation (6-8 years) the amount of exchangeable potassium in limed soils with pH 5,0-5,6 compared with unlimed with pH 4,0-4,3 decreased in 2 times and is associated with increasing potassium fixation. At the application of 35-50 kg K2O/ha, this ratio was maintained, although the content of exchangeable potassium in both backgrounds increased by 10%. When increasing the dose of potassium to 70-100 kg/ha, the difference between the backgrounds was 20% and disappeared at doses of more than 100 kg K2O/ha. This explains the fact that higher doses of potassium fertilizer were effective on the limed background, as the same level of exchangeable potassium content (11 mg K2O/100 g) was achieved without liming at a dose of 60 kg K2O/ha, and with liming – 100 kg/ha of potassium.
Thus, the effectiveness of potassium fertilizers on sod-podzolic soils is related to acidity: the lower it is, the higher is the effect of K2O application. On acid sod-podzolic soils increasing of potassium doses more than 60 kg/ha on the average across the crop rotation does not lead to significant growth of productivity with reduced payback. On calcareous soils with the application of nitrogen and phosphorus in doses of 100-120 kg/ha efficiency of potassium fertilizers is significant, not reduced with the increase of doses of potassium to 140 kg/ha and averages 20-25%. Payback of increased doses of potassium is not less than 5 grain units/kg.
Application of organic fertilizer without liming reduces the effectiveness of potassium fertilizer the stronger the higher doses of manure.
On black soils, especially in the steppe areas, the effect of potassium fertilizers is weaker, which is explained by the high content of mobile forms of potassium. However, with the systematic application of high doses of nitrogen-phosphorus fertilizers, the role of potassium increases. Therefore, in determining the effectiveness of potassium fertilizers take into account the intensity of crop rotation, saturation with potassium-loving crops and optimization of plant nutrition with macro- and microelements.
Relationship of crops to potassium nutrition
There are peculiarities of potassium fertilizer application by crops. For example, for sugar beets the need for potassium remains during all periods of growth and development, the lack is especially undesirable in the second half of the growing season with intensive sugar accumulation. Lack of potassium during this period delays protein synthesis and contributes to the accumulation of nitrate nitrogen. Potassium starvation, as well as excess nitrogen, increases “blooming”, which reduces yields and sugar content. Under the sugar beet optimum time of application of potassium fertilizer is considered the main under the plowing. Along with this application is used in the rows and in top dressing.
Potatoes are a typical potassium-loving plant. By the time of harvesting, up to 96% of the potassium contained in the potato crop is concentrated in the tubers. It is sensitive to chlorine: its excessive potassium reduces the starchiness of the tubers. The best potassium fertiliser for potatoes is potassium sulphate. Chlorinated fertilizers cause physiological diseases, the external signs of which are blackening of the stem and leaves. With the autumn application of potassium fertilizers, due to the washout of chlorine, the negative effect is eliminated. Kalimag and kalimagnesia are also applied under potatoes, especially on light soils. Potassium fertilizers additionally increase yield when applied to the fertilized background. On chernozem with the application of manure, the need for potash fertilizer is reduced. Doses of fertilizers for potatoes are determined by the planned yields, fertilized background fertilizer doses are lower.
Optimal provision of cereals with potassium increases the strength of straws, reducing lodging. Potassium combined with phosphorus increases winter hardiness of winter crops. Forms of potash fertilizer for crops are equal. Of legumes, lupine is sensitive to chlorine.
Flax responds to the introduction of potassium, improving fiber quality: the length and number of elementary fibers increases, flexibility and fiber strength increase.
Potassium fertilizers are effective for fruit trees on all soils, especially on light soils: the percentage of flowering branches in apple trees increases, the marketability of fruits increases, the period of their preservation lengthens.
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.
Phosphate fertilizers
Phosphate fertilizers are mineral substances that contain phosphorus in a form accessible to plants, or in a form that becomes accessible to plants when released into the soil, and serve to provide phosphorus to crops.
- Mineral fertilizers
- Nitrogen fertilizers
- Phosphate fertilizers (Русская версия)
Raw materials for the production of phosphate fertilizers
The raw material for phosphate fertilizers is natural phosphate-bearing ores – apatite and phosphorite. Waste products from the metallurgical industry are also used as phosphate fertilizers. The main global reserves of phosphate ores are located in Morocco, the USA and Russia.
According to the content of phosphorus ores are divided into rich ores up to 35% and poor ores containing 5-10%. Most often due to the large amount of impurities are subject to enrichment.
Apatite
Apatite is a mineral present in a dispersed state in soils and parent rocks. Deposits are rare. The world’s largest deposit was discovered in 1925 in the Khibiny on the Kola Peninsula. Smaller deposits of less valuable provenience are to be found in Russia, in the Urals and South Baikal region, in Brazil, Spain, Canada, the United States, and Sweden.
Apatites are rocks of endogenous origin. Pure apatite is a colorless, greenish or yellow-green mineral, the content of phosphorus is up to 42% in terms of P2O5. Apatite crystals are hexagonal prisms with high strength. Its empirical formula is [Ca3(PO4)2]3⋅CaF2. Fluorine can be replaced by chlorine, carbonate or hydroxyl groups. Accordingly, fluorapatite, chlorapatite, carbonatapatite, hydroxylapatite are distinguished.
In the Khibiny, apatite is represented as apatitenepheline rock. Nepheline is an aluminosilicate of (K, Na)2O⋅Al2O3⋅SiO2 composition, containing up to 5-6% of K2O. Apatite and nepheline account for about 90% of the ore mass, the rest being feldspar, hornblende and other minerals.
Nepheline on acidic soils can be used as a potash fertilizer. It is insoluble in water, but in an acidic environment, potassium passes into a plant-accessible form.
The apatitenepheline ore is extracted by open-pit and underground mining methods. According to its external signs it is sorted, and in this case commercial ore is obtained with up to 30-31% P2O5 content. Further the ore is subjected to enrichment by flotation, due to which nepheline is almost completely removed. The resulting apatite concentrate contains 39-40% P2O5 and is used to produce phosphate fertilizers.
Phosphorites
Phosphorites are sedimentary rocks, usually of marine origin, consisting of amorphous or crystalline calcium phosphate with an admixture of quartz, lime, clay particles and other minerals.
Phosphorites are the result of the activity of marine plant and animal organisms in the past geological periods. The biological origin is confirmed by the content of organic matter (up to 0.5-1.0% carbon). Deposits are found in sedimentary rocks in the form of nodules of various sizes and shapes (nodule phosphorites), less often – in the form of beds of solid masses (layer phosphorites).
Phosphorites are characterized by greater particle strength than apatites; they can be amorphous and finely crystalline.
A distinction is made between nodular (nodule) phosphorites in the form of rounded stones and layered (massive) phosphorites, which are a fused mass. The latter are less common. There are also granular varieties of shell-forming rocks.
According to the geotectonic position, the phosphate deposits can be platform deposits, i.e. horizontally occurring in large areas of the crust with a low thickness of the layer, and geosynclinal, i.e. located in folded mountain areas. An example of a geosynclinal deposit is Karatau.
Most Russian phosphorite deposits are of the jugular type. Such phosphorites as a rule do not have a pronounced crystalline structure, are easier to decompose and therefore are of interest for direct (without chemical treatment) use as a fertilizer.
The crystalline structure is more pronounced in phosphorites of older geological age.
The disadvantage of most of the phosphate deposits is a low concentration of phosphorus with a high content of oxides such as R2O3 in the raw material, which complicates the processing and production of superphosphate. The impurity of oxides such as R2O3 leads to additional consumption of acid in the production of fertilizers and retrogradation, that is, the reverse transition of phosphate in low-soluble compounds. Thus, to obtain 1 ton of P2O5 in superphosphate, the decomposition of apatite concentrate requires 1.89 tons of sulphuric acid, whereas for phosphate rock with impurities – 2.5 tons.
Deposits of phosphate rock are quite widespread in the world, but, for example, in Western Europe, they are small and almost not suitable for development. The largest phosphorite deposits are in North Africa. In the United States, there are deposits in Florida, Tennessee and some other states.
Large reserves of phosphorites are concentrated in Russia, but most of them are poor in phosphorus and contain large impurities of oxides such as R2O3. Most of the deposits are concentrated in the European part of Russia.
Table. Chemical composition of phosphorites and apatites, % on dry matter[1]Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Vyatsko-Kamskoe | ||||||
| Yegoryevskoye (Portland horizon) | ||||||
| Seshchinskoe | ||||||
| Shchigrovskoe | ||||||
| Khibinskoe: | ||||||
| apatitenepheline rock | ||||||
| apatite concentrate | ||||||
The Vyatsko-Kamskoe deposit is located in the northeast of European Russia, of the jugular type, with a phosphorus content of 24-26% P2O5.
The Egoryevskoye deposit is located in the Moscow region. The deposits are represented by two horizons, separated by a layer of loose glauconite sand: the upper is Ryazan and the lower is Portland. The quality of the latter is higher than the Ryazan sand: it contains 25-26% P2O5 and 4-5% semi-reductive oxides. The Ryazan layer contains, on average, 21-23% P2O5 and 10-12% semi-reactivated oxides.
The Seshchino deposit is located in the Dubrovskii district of the Bryansk region. Phosphorites lie in three horizons of sandy nodules, sometimes cemented into a plate. The upper layer is about 0.5 m thick and contains 14% P2O5, and the middle layer is 0.53 m thick and contains 16% P2O5. Between these horizons there is a layer of glauconite sand about 1 m thick.
The Shchigrovskoe deposit in the Kursk Region refers to sandy phosphorites. The crystals are of various sizes and shapes, cemented with sandy rock into a continuous slab (“nugget”). Sometimes these slabs contain clusters of gallstones, loosely embedded in loose sandy rock. This type of phosphorites occurs in the Voronezh, Tambov, Orel, Bryansk, Kaluga, and Smolensk Regions. The content of phosphorus is 14-19% P2O5, is of little use for processing and is used in the form of phosphate meal.
Phosphorites Karatau formed in the mobile areas of the earth’s crust, in place of which later emerged mountain formations. A distinctive feature of the deposit is the presence of thick phosphate-bearing layers of complex occurrence with high phosphorus content. The layers alternate with phosphate-siliceous and phosphate-carbonate rocks. In the main horizon of the deposit, the content of P2O5 is 26-29%. The greatest value are layer thicknesses up to 7 m, the content of P2O5 in them reaches 30-35% with 2-2.5% of semi-reductive oxides. A disadvantage of Karatau phosphorites is an increased content of magnesium, which gives them hygroscopicity. For elimination of this property additional processing is required that entails increase in cost of production.
Classification of phosphate fertilizers
Phosphate fertilizers, depending on solubility and availability to plants, are classified into three groups:
- containing phosphorus in water-soluble form, include simple and double superphosphate, phosphorus is well available to plants;
- containing phosphorus in a water insoluble form, but soluble in weak acids, such as 2% citric acid; these include precipitate, tomas slag, open-hearth phosphate slag, defluorinated phosphate; phosphorus is accessible to plants;
- containing phosphorus that is insoluble in water, poorly soluble in weak acids, and soluble in strong acids; include phosphate meal, bone meal. These fertilizers are not available to most crops, but can be assimilated by some plants (lupine, buckwheat) under the influence of acidic root secretions.
Due to the fact that most soils have a near-neutral reaction, the most effective phosphorus fertilizers are considered water-soluble, which are widely used in the world. The technology for processing raw materials for the production of phosphate fertilizers is aimed at converting phosphorus into a form that is accessible to plants.
Fertilizers containing phosphorus in water-soluble form
Phosphate fertilizers containing phosphorus in water-soluble form include superphosphates.
According to the method of production and the content of P2O5 are divided into:
- simple;
- double;
- triple.
By output form:
- powdered;
- granular.
Water-soluble forms are applicable on all types of soils, under all crops and in different methods. To increase their effectiveness, techniques are carried out aimed at reducing chemical absorption by the soil, i.e. introduction of granular forms, row and local introduction.
Simple superphosphate
Simple superphosphate, or calcium dihydroorthophosphate, one-substituted calcium phosphate, monocalcium phosphate, – Ca(H2PO4)2 – phosphate fertilizer, P2O5 content 16-20%. It is well soluble in water and weak acids.
The production technology was proposed by J. Libich. The first plant for the production was built in 1843 in England by Loose – the founder of Rotamsted agricultural experiment station.
Thanks to the simple and cheap production technology superphosphate is the main phosphate fertilizer used all over the world.
The technological scheme of production is of a continuous type. Raw materials are natural phosphates – apatite concentrate or phosphate rock. The treatment of phosphate rock with concentrated sulphuric acid produces one-substituted calcium phosphate and anhydrous calcium sulphate (gypsum):
[Ca3(PO4)2]3⋅CaF2 + 7H2SO4 + 3H2O = 3Ca(H2PO4)2⋅H2O + 7CaSO4 + 2HF.
The resulting gypsum remains as part of the fertilizer, accounting for up to 40%.
In addition to the formation of calcium dihydroorthophosphate, side reactions occur with the formation of free phosphoric acid:
[Ca3(PO4)2]3⋅CaF2 + 10H2SO4 = 6H3PO4 + 10CaSO4 + 2HF.
The impurity of phosphoric acid in the final product may be 5.0-5.5%, which gives superphosphate an acidic reaction and hygroscopicity.
If there is a local deficiency of sulfuric acid in the reaction mixture, the formation of calcium hydroorthophosphate occurs:
[Ca3(PO4)2]3⋅CaF2 + 4H2SO4 + 12H2O = 6CaHPO4⋅2H2O + 4CaSO4 + 2HF.
Since the resulting gypsum is not separated, the phosphorus content in the product is about 2 times lower than in the feedstock. For this reason, phosphate rock with low P2O5 content is almost unsuitable for the production of superphosphate. Superphosphate with at least 19% of citrate-soluble phosphorus is obtained from apatite concentrate, and not less than 19.5% in the highest grade.
88-98% of phosphorus in superphosphate is contained in the form accessible to plants: water-soluble – calcium dihydroorthophosphate and phosphoric acid, and citrate-soluble – calcium hydrophosphate, which accounts for 10-25% of available phosphorus.
Ready superphosphate contains small impurities of calcium, iron and aluminum phosphates.
Free phosphoric acid in superphosphate prevents saturation of gypsum (CaSO4⋅2H2O) with water, so the calcium sulfate remains anhydrous or CaSO4⋅0,5H2O.
The end product is powdery superphosphate, which is a light gray substance. Free phosphoric acid leads to hygroscopicity and humidity, which should not exceed 12-15%. During storage and transportation powdered superphosphate cakes, loses its flowability and spreadability. When applied to soil, powdered superphosphate is subjected to rapid chemical absorption, and phosphorus becomes unavailable to plants.
These disadvantages are eliminated by granulating powdered superphosphate.
Granulated superphosphate does not clump, does not caked, has a reduced moisture content. Due to the slow dissolution of granules in the soil moisture and reducing the contact area of the fertilizer particles with the soil reduces the chemical binding, which is especially important when applied to acidic soils with a high content of H2O. Granulated superphosphate allows for more uniform dispersion.
Granulated superphosphate contains up to 1-2.5% free phosphoric acid and up to 1-4% moisture.
The granulation process is carried out in long (7.5 m) rotating drums, in which powdered superphosphate is moistened to 16%, while the rotation of the drum is pelletized, taking the form of round small granules of different sizes. After drying, the granules are sorted to remove particles smaller than 1 mm and larger than 4 mm. A fraction of 1 to 4 mm in diameter is obtained. The larger pellets are crushed and together with the smaller ones (“retur”) are returned for re-pelletizing. The retur act as pelletizing centers.
During granulation, free phosphoric acid is neutralized by adding ammonia, lime or phosphorite. When ammonia is used in the process, ammoniated superphosphate is produced, which contains 1.5-3% nitrogen. When neutralized with phosphate meal phosphorus content in the finished fertilizer increases to 20-22%, but at the same time decreases the relative content of water-soluble phosphorus.
The quality of superphosphate is estimated by the content of phosphoric acid and phosphorus soluble in water and citrate solution – aqueous solutions of ammonium citrate and ammonia.
Simple superphosphate is used on all types of soils. The main disadvantage is its low phosphorus content, which reduces its economic efficiency, especially in transportation.
Double superphosphate
Double superphosphate is a concentrated phosphate fertilizer that is obtained from apatite or phosphorite by treatment with phosphoric acid. It contains phosphorus in the form of calcium dihydroorthophosphate [Ca(H2PO4)2], like simple superphosphate with an admixture of up to 2.5% of free phosphoric acid. The main difference from simple superphosphate is the absence of gypsum.
There are two phases in the production process: the first is phosphoric acid, and the second is double superphosphate.
Two methods are used to produce phosphoric acid.
At the wet extraction method phosphoric acid is obtained by treatment of phosphorite, including with low phosphorus content, with sulfuric acid, with the formation of phosphoric acid:
Ca3(PO4)2 + 3H2SO4 + 6H2O = 2H3PO4 + CaSO4⋅2H2O.
Extraction of phosphoric acid is made with a 20-25% solution of sulfuric acid, so as not to dissolve a large amount of the contained semi-fluoric oxides. The phosphoric acid is then separated from the precipitate and concentrated by evaporation. The resulting phosphoric acid is used to process phosphorite with high phosphorus content and less contaminated with impurities:
Са3(РO4)2 + 4H3PO4 + Н2О = 3Ca(H2PO4)2⋅Н2О.
The second method of phosphoric acid production is the method of phosphorus sublimation from low-grade phosphorites at a temperature of 1400-1500 °C in electric furnaces or blast furnaces. In this case the separated elemental phosphorus is collected under water, burned and the resulting phosphorus oxide is neutralized with water:
P2O5 + 3H2O = 2H3PO4.
The second step in the production of double superphosphate is the reaction of phosphoric acid with phosphate raw material with a high phosphorus content:
[Ca3(PO4)2]3⋅CaF2 + 14H3PO4 + 10H2O = 10Ca(H2PO4)⋅H2O + 2HF.
The initial raw material for the production of phosphate fertilizers determines the composition of impurities. The best double superphosphate is obtained from apatite, the content in it of P2O5 is 45-49%, free acid not more than 2.5%, the proportion of water-soluble P2O5 – not less than 85%.
Available double superphosphate in the form of pellets of light gray color. The cost of 1 ton of P2O5 double superphosphate by 6-13% higher than in a simple one, but the high concentration of P2O5 causes savings in transportation and storage. The cost of using P2O5 double superphosphate is 8-13% lower than plain.
By the action of double superphosphate in an equivalent dose is not different from the simple. However, due to the lack of sulfur (in the form of gypsum), double superphosphate may be inferior to simple on soils with low sulfur content and under the crops that require sulfur nutrition, such as legumes and cruciferous plants. In these cases, the application of double superphosphate is combined with sulfur-containing fertilizers, such as ammonium sulfate, potassium sulfate, potassium magnesium sulfate.
Superphos
Superphos is a new promising type of concentrated phosphate fertilizer with a long-lasting effect. It is produced by chemical enrichment and treatment with a mixture of sulphuric and phosphoric acids of phosphate meal.
The consumption of acids to produce 1 ton of P2O5 in superphos – 1-1.3 tons of sulfuric and 0.36 tons of phosphoric acid – 2 times less than the production of 1 ton of P2O5 double superphosphate. The use of P2O5 phosphate raw materials reaches 95%.
Superphos is produced in granular form, and contains 38-40% P2O5, 19-20% of which are in water-soluble form. The efficiency of action is not inferior to double superphosphate.
Fertilizers containing phosphorus that is insoluble in water but soluble in weak acids
Semisoluble (citrate-soluble) forms of phosphate fertilizers are used on all types of soils and for all crops, but their effectiveness can strongly depend on the type of soil. On acidic soils, the effect of fertilizers with an alkaline reaction, such as tomaslag and phosphate slag, may be higher than superphosphate.
Precipitate (dicalcium phosphate)
Precipitate, or dicalcium phosphate, calcium hydroorthophosphate, monocalcium phosphate, – CaНРO4⋅2H2O. It is obtained by interaction of orthophosphoric acid and milk of lime (calcium hydroxide solution) or a suspension of calcium carbonate:
2H3PO4 + 2Ca(OH)2 = 2(CaHPO4⋅2H2O);
H3PO4 + CaCO3 + H2O = CaHPO4⋅2H2O + CO2.
Quantities of initial substances are taken in the ratio corresponding to the chemical reaction equation.
The precipitate is separated from the liquid, dried at not more than 100 °C to prevent loss of crystallization water, which contributes to the solubility of the precipitate.
The technology of precipitate production as a fertilizer is not economically justified, so it is mainly used for fodder purposes. As a fertilizer, it is obtained by recycling weak solutions of orthophosphoric acid, which are wastes from other industries, such as the production of gelatin at bone-processing plants.
Fertilizer precipitate is a white or light gray powder that does not cake and is well dispersible. Depending on the initial raw material, it contains 25-35% of the citrate-soluble form P2O5. Feed precipitate contains 44% P2O5, no more than 0.2% P, 0.001% As, 0.002% Pb.
By its effect on the yield is similar to superphosphate, but it is used only for the main application for plowing in the same doses of P2O5 as superphosphate. On soils not saturated with bases and grey soils, the efficiency of precipitate is higher than superphosphate, due to stronger binding of phosphorus by superphosphate. On chernozems the effect of superphosphate is the same or slightly superior to that of precipitate.
Unfluorinated phosphate
Unfluorinated phosphate, or calcium orthophosphate, tricalcium phosphate – Ca3(PO4)2 contain 28-32% of citric-soluble P2O5. The content of P2O5 fertilizer refers to a concentrated phosphate fertilizer.
It is produced by thermal treatment of phosphate raw materials. The process involves steaming water vapor mixture of apatite or phosphate with 2-3% silica (sand) at 1400-1550 °C. Fluorine, contained in apatite, is separated as hydrogen fluoride. The degree of defluorination reaches 94-96%.
Chemical reaction of hydrothermal decomposition of apatite in the presence of silica:
n[Ca3(PO4)2]3CaF2 + mSiO2 + nH2O = 10nCaO⋅3nP2O5⋅mSiO2 + nHF.
The resulting product contains up to 30-32% (from apatite) or up to 20-22% (from phosphorite) of citrate-soluble P2O5, depending on the raw material.
Unfluorinated phosphate has good physical properties. As a basic fertilizer on sod-podzolic and chernozem soils, it is as effective as superphosphate.
Unfluorinated phosphate is mainly used for mineral feeding of animals.
Томасшлак
Thomas slag, or fused magnesium phosphates, contains phosphorus in the form of tetracalcium phosphate (4CaO⋅P2O5 or Ca4P2O9) or silicocarnatite (Ca4P2O9⋅CaSiO3). According to technical specifications, the content of lemon-soluble P2O5 must be at least 14%. They occupy a small part among the used phosphate fertilizers.
It is obtained as a byproduct of the processing into iron and steel phosphoric iron by the method of S. Thomas. As the content of phosphorus reduces the quality of the metal, for its removal Thomas suggested in 1879 that phosphorus should be bound with freshly burnt lime. At 1800-2000 °C, phosphorus was oxidised to P2O5, and the binding of P2O5 resulted in the formation of calcareous salts of phosphoric acid. These compounds with calcium silica and other impurities float to the surface of molten metal in the form of slag, which is separated, after cooling is crushed, milled, and in this form used as phosphate fertilizer.
An excess of SiO2 produces a double salt of tetracalcium phosphate and silica calcium – silicocarnatite, and a lack of SiO2 produces tetracalcium phosphate. Both salts are soluble in 2% citric acid. Thomas slag also contains hard-soluble phosphates.
Thomas slag is a dark, heavy powder, containing from 7-8% to 16-20% of citrate-soluble P2O5. As an impurity it contains calcium silicate, compounds of iron, aluminum, vanadium, magnesium, manganese, molybdenum, and others.
Used as a basic fertilizer. More effective on acidic soils, as it has an alkaline reaction.
When applied to soil, as a result of interaction with soil moisture containing dissolved carbon dioxide (carbonic acid), it gradually breaks down to form freshly precipitated tricalcium phosphate, which is available to plants.
Thomas slag is used on all types of soils, in which phosphorus fertilizers have a positive effect on yield, but its effectiveness on different soils is manifested differently. On chernozems – weaker than superphosphate, on soils of the Non-Black Earth zone, especially acidic peaty and sandy, tomas slag is more effective as it reduces acidity. Neutralizing ability of tomas slag is important when combining phosphorus fertilizers with physiologically acidic forms of nitrogen fertilizers.
Martin phosphate slag
Martin phosphate slag is produced as a by-product of the steelmaking process in open-hearth furnace steelmaking. Lime materials are also used for binding phosphorus.
The content of phosphorus in the open-hearth slag ranges from 8 to 12% P2O5, almost all in a citrate-soluble form. Phosphate slag contains a double salt of calcium tetraphosphate and calcium silicate, impurities of iron, manganese and magnesium compounds.
It is used as a basic fertilizer. Has a strong alkaline reaction, so it is more suitable for acidic soils. Due to the low phosphorus content, it is advisable to use near production sites.
Thermophosphates
Thermophosphates contain 18-34% P2O5, produced by fusion or sintering of natural phosphates with carbonates or silicates of sodium or potassium, as well as metallurgical slags, lime, quartz. In this process, hard forms of phosphorus are converted to a citric-soluble form.
The melting temperature of thermophosphates is 1000-1200 °C. During high-temperature treatment the crystal lattice of phosphate raw materials is broken, fluorine is released in the form of hydrogen fluoride, and phosphorus passes into an amorphous form Ca3(PO4)2, which is accessible to plants. Amorphous form is obtained and remains stable at 1180 ° C. With decreasing temperature, it transforms into crystalline form, which is poorly assimilated. Therefore, the reaction mass is rapidly cooled to reduce this transition.
In composition and properties thermophosphates are similar to tomas slag and can be used on all soils. Thermophosphates obtained by fusion with alkaline salts, soluble in citric acid and ammonium citrate solution, have better accessibility to plants than tomas slag. The advantage of this method of phosphate fertiliser production is that low-percentage phosphate and apatite, which are unsuitable for superphosphate production, can be used as a feedstock.
On acidic soils have a stronger effect than superphosphate, especially on podzolic soils.
Bone meal
Bone meal is a by-product of bone processing. Skimmed bones are treated with steam at 1.5-2 atm, followed by a rinse with water to extract the glue. The result is a degreased and de-glued bone pulp, which is treated with hydrochloric acid. The minerals Ca3(PO4)2, Mg3(PO4)2 are dissolved and the soft bone structure consisting of ossein is separated. When heated with water, ossein yields high-quality gelatin.
A hydrochloric acid solution of phosphates is treated with “lime milk,” in which the phosphates precipitate with the formation of precipitate according to the equation:
Н3РО4 + Са(ОН)2 = СаНРO4⋅2Н2О.
Skimmed and deglazed bone meal contains 30-35% P2O5 and up to 1% nitrogen. The phosphorus in bone meal is in a water insoluble form, but is more available than phosphate meal. The effectiveness of bone meal is affected by the acidity of the soil. Even in slightly acidic environments, bone meal has a good effect on crop yields.
Fused magnesium phosphate
Fused magnesium phosphate contains 20% P2O5 in a citric-soluble form and 12% MgO. It is obtained by fusing phosphorite with silicate olivinite or serpentinite.
It is advisable to use on sandy loam soils, in which crops are well responsive to magnesium.
Red phosphorus
Red phosphorus contains 229% of phosphorus in terms of P2O5. A promising most highly concentrated phosphate fertilizer. To convert it into a plant-accessible form in the soil at the same time a catalyst, such as copper, about 1% of the weight of phosphorus is used.
On sod-podzolic soil, after 3 weeks after embedding, 20% of red phosphorus changes into compounds available for cereal crops. Its efficiency is equal to that of superphosphate, and later it surpasses it.
Fertilizers containing phosphorus that is poorly soluble in weak acids but soluble in strong acids
Hard-soluble fertilizers have a fairly good effect on acidic soils of the Non-Black Earth zone and on soils of the northern part of the Black Earth zone (leached and podzolized chernozems).
Phosphate meal
Phosphate meal (phosphorite flour) is finely ground phosphorite. It is used as a fertilizer on acidic sod-podzolic, gray forest and peaty soils, on podzolized and leached chernozem soils and red soils. On typical, common and southern chernozems the effect of phosphoric flour is weaker and unstable.
Phosphate meal is the cheapest fertilizer. It ranks second after superphosphate in terms of production and use. Its production consists of removing coarse impurities (sand, clay) from phosphate rock, cutting it into 1 to 3 cm pieces and grinding to a fine flour. Grinding fineness of phosphate meal affects its efficiency. According to the requirements of technical specifications at least 80% of the mass of phosphate flour should have a particle size of no more than 0.17 mm.
As raw materials, chelated phosphate rock, often of low percentages, without a pronounced crystalline structure, is used. Grinding of such raw materials yields a flour, suitable for direct application, but it is of little use for chemical processing. Such phosphorites include raw materials from the Egorievskoye, Shchigrovskoye, Seshchinskoye, Krylovetsky, and Kineshemskoye deposits.
Phosphate meal is a powder of gray, dark gray or brown color. The content of P2O5 in the fertilizer of the first grade is 28-30%, the second – 22-24%, the third – 19-21%. Fertilizer is non-hygroscopic, does not caked, well dispersed, a lot of dust.
Phosphorus in phosphate meal is contained in the form of fluorapatite [Ca3(РO4)2]3СaF2, which is insoluble in water and poorly soluble in weak acids, so it is inaccessible to most plants.
The efficiency of phosphate meal is influenced by the origin and composition of phosphate, the fineness of grinding, biological characteristics of crops, soil properties and the acidity of the accompanying fertilizers.
Phosphate meal interacts with the soil, which has actual and potential acidity, with the gradual decomposition of calcium phosphate, its transformation into dicalcium phosphate:
Ca3(PO4)2 +2H2O+ 2CO2 → 2CaHPO4 + Ca(HCO3)2.
According to studies, soils with a hydrolytic acidity of less than 2.5 mg⋅ eq/100 g, poorly decompose phosphorite, so its efficiency on such soils is low. On the contrary, the higher the hydrolytic acidity, the more effective action of phosphate meal. This explains the positive effect of phosphoric flour on degraded and leached chernozems, on which exchange acidity is low and hydrolytic acidity is high.
Soils with a small absorption capacity at hydrolytic acidity of 3-3.5 mmol/100 g of soil and saturation with bases of 50-60%, as a rule, have an acid reaction (5,0-5,5), which is caused by exchange acidity. At high absorption capacity, hydrolytic acidity equal to 6-7 mmol/100 g of soil and saturation degree of 75-85% the reaction is close to neutral (6.0-6.5). Therefore, high effect of phosphate meal will be manifested at high acidity and lower degree of saturation of soils with bases.
The effect of phosphate meal is influenced by the absorption capacity and the degree of saturation of the soil with bases. With the same hydrolytic acidity, the efficiency increases with decreasing absorption capacity.
The total interaction surface of phosphate meal with the soil increases with increasing fineness of grinding.
Table. Increase in potato yield from mineral fertilizers on different soils (All-Russian Institute of Fertilizers and Agrochemistry)
The effectiveness of phosphate meal depends on the biological characteristics of plants. The results of the experiments of D.N. Pryanishnikov, P.S. Kossovich and other scientists allowed to divide crops into groups according to their ability to assimilate phosphorus from hard-soluble phosphates. Plants with a good ability to assimilate difficultly soluble phosphates include lupine, buckwheat, mustard; somewhat less so peas, sainfoin, melil and hemp. All cereals, flax, beets, potatoes, vetch can assimilate phosphorus from phosphate meal only after interaction with acidic soils. Barley, spring wheat, flax, millet, tomato, turnipa do not assimilate phosphate flour.
The ability of plants to assimilate hard-soluble phosphates changes with age. Most plants are poor at assimilating the hard-to-digest forms during the first period of life; later in life, this ability increases.
Most scientists explain the ability to assimilate hard-to-dissolve phosphates by the amount and composition of acidic root excretions of plants. F.V. Chirikov explains this ability by the increased consumption of calcium: plants that absorb more calcium, better assimilate phosphorus.
The assimilation of phosphorus from phosphate meal, as established by D.N. Pryanishnikov, also depends on the accompanying fertilizers: physiologically acid fertilizers increase the availability of phosphorus, physiologically alkaline fertilizers and lime materials – reduce.
Phosphate meal was widely used in the former Soviet Union. Its use is likely to expand in the future. The disadvantage of phosphate meal is that it is very dusty. To reduce dusting, mixtures of phosphate meal can be used:
- Mixtures of phosphorite flour with ammonium chloride in the ratio N:P2O5 = 1:1; in this case the content of each nutrient is 14%, dustiness is eliminated, and the content of citric-soluble phosphorus increases by 1.5 times.
- The impact on the phosphate meal molten potassium disulfate at a temperature of 205-210 °C for 50-60 minutes in a screw mixer: dustiness is eliminated, the content of P2O5 is 16%, of which 70% in lemon soluble form, the content of K2O – up to 17%.
The efficiency of phosphate meal is influenced by the geological age and mineralogical composition of phosphorite. Phosphorites of ancient origin with crystalline structure are characterized by poor availability to plants, especially apatite.
To increase availability, phosphorite meal is composted with topsoil peat or manure. In composts, the effectiveness increases with sour peat at a peat to flour ratio of 100:1. Phosphorite meal is used to prepare peat and manure-phosphate composts.
Phosphorite flour for better decomposition of phosphate meal is made in advance under deep plowing in a moist layer. Application in double or triple doses, has a prolonged effect.
In Russia acidic soils under arable land occupy about 50 million hectares. They are usually characterized by low content of mobile phosphorus.
Vivianite (bog ore)
Vivianite, or bog ore, is phosphoric acid iron oxide – Fe3(PO4)2⋅8H2O. It contains 28% P2O5. It is found under a layer of peat in the form of whitish mass.
A good source of phosphorus for crops on sod-podzolic, gray forest soils and leached chernozems. Vivianite is easily loosened by drying, well dispersed.
Phosphoritization
Phosphoritization is the application of hard-soluble phosphate (phosphorite flour) in the crop rotation for several years ahead and is one of the methods of increasing soil fertility, especially of acidic soils, the effectiveness of mineral fertilizers and increasing crop yields. Phosphate meal is applied in large doses to 1-1.5 t / ha, which provides phosphorus nutrition plants for 6-8 years, improves the nutrient regime and increases the productivity of the rotation.
Improvement of phosphate regime leads to increased efficiency of other fertilizers. Phosphoritization is a reclamation technique to improve the fertility of acidic soils, the effectiveness of which depends on the acidity and the provision of mobile phosphorus. First of all phosphoritization is carried out at pH below 5.5 and the content of mobile phosphorus to 5 mg/100 g soil.
Phosphoritization in the rotation is best done in a pair for winter crops and cereals with undersowing leguminous grasses, which are able to absorb hard-soluble phosphorus, better accumulate nitrogen and increase productivity of subsequent crops in the rotation.
Phosphoritization is used for radical improvement of meadows and pastures. Lime and phosphate meal are applied separately, for example, before and after plowing, in different soil layers.
Phosphoritization is a mandatory method of improving newly developed low fertility lands, drainage, development of peatlands and low fertility acidic meadows on mineral soils. Norms of phosphate meal is not less than 200 kg of P2O5, or 1 ton per meal. For more accurate calculation of the dose use rates of the nutrient to increase mobile phosphorus per 1 mg/100 g of soil.
Table. Fertilizer rates for increasing the content of mobile phosphorus by 10 mg P2O5/kg of soil (by Litvak Sh.I., 1990; Sychev V.G., Shafran S.A., 2013)
| Sod-podzolic | sandy and sandy loam | by Kirsanov | ||
| light loam | ||||
| medium loam | ||||
| heavy loam | ||||
| Grey Forest | sandy and sandy loam | by Kirsanov | ||
| loamy | ||||
| heavy loam | ||||
| Podzolized black earth | light loam | by Chirikov | ||
| loamy | ||||
| Leached black earth | heavy loam | by Chirikov | ||
| Typical black earth | heavy loam | by Chirikov | ||
| Common black earth | loamy | by Chirikov | ||
| heavy loam | ||||
| Carbonate black earths | On average | by Machigin | ||
| Chestnut | On average | by Machigin | ||
Example. Initial data: sod-podzolic loamy sand soil; pH 4.5; content of mobile phosphorus 4.6 mg/100 g soil; planned – 9 mg/100 g soil.
The dose of phosphoritic flour is determined by the formula:
D = (P – F) ⋅ C, or
D = (9,0 – 4,6) – 60 = 264 kg P2O5/ha,
where D – dose, kg/ha P2O5; P – planned content, mg P2O5/100 g soil; F – actual content, mg P2O5/100 g soil; C – consumption of P2O5 to increase its content by 1 mg/100 g soil.
Interaction of phosphate fertilizers with soil
The solubility of phosphate fertilizers, including water-soluble ones, is lower than that of nitrogen and potassium fertilizers. When applied to the soil as the phosphate ion dissolves, it transforms into compounds characteristic of a particular soil type and due to the genetic features, physical, chemical and mineralogical properties, the degree of cultivation. The speed of this process is slow, so part of the applied phosphate fertilizers, especially in granular form or in semi-soluble and insoluble forms, remain unchanged for a long time.
Transformation of soluble fertilizer phosphorus can be due to:
- chemical absorption of phosphate ions by cations of calcium, magnesium, oxides and hydroxides of iron, aluminum, manganese and titanium;
- colloid-chemical (exchange) absorption on the surface of the soil solid phase;
- biological absorption by plant root systems and soil microflora.
Exchange absorption (adsorption) of phosphate ions occurs on the surface of positively charged colloidal particles, such as colloids of oxide hydrates, or on positively charged areas of negatively charged colloids, such as the minerals of the kaolinite and montmorillonite groups and hydromica and colloids of the protein group. Exchangeable absorption is stronger in an acidic environment. For example, illite (a mineral of the hydromica group), bentonite (of the montmorillonite group) and kaolinite adsorbed at pH 4-4.5 from 7.7 to 9.7 mg-eq H2PO4– per 100 g of mineral. There were no significant differences in the absorption of anions by minerals of montmorillonite and kaolinite groups, as in the case of exchange absorption of cations. The reaction of the medium leads to a change in the electrical potential of the soil colloids. Acidification of the soil solution promotes better absorption of anions; alkalinization, on the contrary, causes a decrease in absorption. Therefore, for soils with weakly acidic and neutral reaction, exchange uptake is weaker (Antipov-Karataev et al:)
The exchange absorption of phosphate ions on the common chernozem of the Stone Steppe is also confirmed by I.P. Serdobolsky.
According to the All-Russian Institute of Fertilizers and Agrochemistry, adsorption absorption of sod-podzolic soils accounts for 70-80% of the total amount of absorbed phosphates.
Exchange-absorbed phosphoric acid anions can be displaced into solution (desorption) by other mineral and organic acid anions, such as hydrocarbonate-ion, citric, malic, oxalic, formic and humic acids. These anions are always present in the soil solution as a result of plant respiration and root excretions as well as microbiological decomposition of plant residues and organic fertilizers. Thus, there is no shortage of anions for desorption of phosphate. This determines the good mobility and plant availability of exchange-absorbed phosphates. According to the results of studies, the availability of exchange-absorbed phosphate is close to water-soluble. However, the latter are few in the soil solution, so it is the exchange-absorbed phosphates that play an important role in the phosphorus nutrition of plants.
Part of the phosphate of fertilizers dissolved in the soil solution is absorbed by the soil through chemical binding. Peculiarities of chemical absorption are determined by soil type and soil acidity.
The pH value of the soil determines the solubility of calcium, magnesium, aluminum, iron, manganese, titanium salts, which, when interacting with water-soluble phosphate, translate it into hard-soluble compounds. For example, at pH less than 5, the content of aluminum ions in the soil increases, and at pH less than 3 – iron ions. It is generally accepted that the lowest binding of phosphate and the highest mobility occurs in the pH range of 5.0-5.5. In more acidic soils, aluminum and iron oxides are absorbed; in less acidic soils, calcium and magnesium are absorbed.
Thus, in soils with a near-neutral reaction of water-soluble phosphate fertilizers, monophosphate [(Ca(H2PO4)2⋅H2O] after some time by chemical absorption into the two-substituted calcium and magnesium phosphates (CaНРO4⋅2H2O or MgНРO4) and remain long time in a form accessible to plants. Subsequently, the hydrogen of the two-substituted salt is gradually replaced with calcium or magnesium, forming three-substituted phosphates Ca3(РO4)2, Mg3(РO4)2, and subsequently the basic phosphate octacalcium phosphate [Ca4H(РO4)3⋅ЗН2O], with solubility constantly decreasing.
However, while these salts are in a freshly precipitated amorphous state, they retain the ability to dissolve in weak acids, which causes some accessibility to plants. Only as the three-substituted and basic phosphates crystallize (“ageing”), they lose their accessibility. The process of “aging” of phosphates is called phosphate retrogradation.
In sod-podzolic soils with acidic and weakly acidic reaction the chemical binding of phosphate ions is due to mobile semi-hazardous oxides:
Al(OH)3 + H3PO4 → AlPO4 + 3H2O;
Fe(OH)3 + H3PO4 → FePO4 + 3H2O.
Freshly precipitated amorphous aluminum and iron phosphates also remain available to plants for some time, but become insoluble as they “age”. Both water-soluble phosphates of fertilizers and phosphates transferred to the solution from the exchange-absorbed state as a result of desorption are subject to chemical absorption.
The intensity of chemical and colloidal-chemical absorption of phosphate fertilizers is in direct dependence on the content of mobile forms of oxides such as R2O3. Phosphoric acid as a result of biological absorption is able to be fixed in the soil, in the body of microorganisms. In terms of energy of absorption of phosphate of soluble fertilizers soils can be arranged in the following sequence: red soils > podzolic soils > chernozem > gray soils.
The process of phosphate uptake by the soil and further transformation is very slow. Experience of long-term application of high doses of phosphate fertilizers several times higher than P2O5 removal showed that most of the phosphorus is accumulated in soils in easily soluble form in amounts up to 600-1000 mg/kg of soil.
At the same time there is an excessive accumulation of phosphorus in soils. This phenomenon is observed in several European countries, which used phosphate fertilizers for over a century. In the late 80’s excessive accumulation of phosphorus occurred in Russia in the beet-growing zone and some farms of the Moscow region.
Field and vegetation experiments have shown that “residual”, i.e. previously unused phosphorus fertilizers remain available to plants. Thus, the effects of previously applied phosphorus fertilizers at Rotamsted experimental station have been observed for more than 50 years.
These experiments show that significant amounts of phosphate are not permanently fixed in the soil. There is information about the possibility of mobilization of phosphate resources of soils in conditions of deficit of phosphate fertilizers. In this case there is a gradual transformation of hard-soluble phosphates into soluble ones.
However, long-term cultivation of crops in conditions of phosphorus fertilizer deficiency leads to depletion of soil reserves and their gradual degradation.
Effectiveness of phosphate fertilizers
The effectiveness of phosphate fertilizers depends on:
- soil and climatic conditions;
- fertilizer properties;
- zonal peculiarities of soils;
- biological characteristics of crops;
- agrochemical methods to optimize the use of phosphate fertilizers;
- phosphate content;
- moisture availability.
Features of the application of phosphate fertilizers, taking into account their solubility:
- water-soluble phosphates are used on all soils, under all crops and in different ways;
- the effectiveness of phosphates soluble in weak acids depends on soils, for example, on acidic soils their effect is higher than that of superphosphates;
- hard-soluble fertilizers are effective on acidic soils of the Non-Black Earth zone and on northern leached and degraded chernozems.
On all soils, superphosphate and precipitate have a more stable effect on the yield.
Influence of soil phosphorus content on efficiency
Phosphorus fertilizers have a greater effect on yield on soils with low and medium content of mobile phosphorus, while on soils with high and high content the effect is weak or absent.
On sod-podzolic and gray forest soils, the optimum content of mobile phosphorus by Kirsanov’s method is 10-15 mg/100 g. This level of security is considered sufficient to obtain under normal climatic conditions and nitrogen-potassium fertilizers on the background of high yields of field crops, such as grain – to 5.5 t/ha, hay perennial grass – 5,5-7,0 t/ha. The same value of the optimum content of mobile phosphorus according to Chirikov’s method is accepted for non-carbonate chernozems. On carbonate chernozems, chestnut and gray soils, the optimum content according to Machigin’s method is 3-4.5 mg/100 g.
With the content of mobile phosphorus in sod-podzolic soils, 10-12 mg/100 g, yield increases from making phosphorus fertilizers are unstable, and at 15 mg/100 g, the effect is usually absent. Complete rejection of phosphate fertilizers on these soils is not advisable, since it leads to depletion of soil mobile phosphates, so make compensating doses of fertilizers P2O5 removal by plants. Agrotechnically optimal can be considered a combination of making the main fertilizer hard-soluble forms with a row (start) introduction of soluble.
Phosphate fertilizers must be made at high doses of nitrogen-potassium fertilizers to avoid imbalances in the ratio of elements (N:P:K).
Application of fertilizers on soils with a low content of phosphorus should provide a gradual increase in content to optimum levels. To do this, the doses are calculated not only for the planned yield, but also to increase soil fertility. To increase the content of mobile phosphorus in the soil by 1 mg/100 g, you can use the developed All-Russian Research and Design Institute of Agricultural Chemistry nutrient rates.
Table. Consumption of nutrients to increase the content of mobile phosphorus in the soil by 1 mg/100 g[2]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
| Sod-podzolic | Sandy and sandy loam | |
| Light and medium loamy | ||
| Clay and heavy loam | ||
| Grey forests | Sandy and sandy loam | |
| Light and medium loamy | ||
| Clay and heavy loam | ||
| Podsoled and leached black soils | Sandy and sandy loam | |
| Light and medium loamy | ||
| Clay and heavy loam |
Influence of moisture availability
The effectiveness of phosphate fertilizers depends on the moisture availability of crops. As the continental climate increases, which leads to a decrease in moisture availability, the effectiveness decreases. However, phosphate fertilizers contribute to economical consumption of moisture by plants, so they mitigate the effects of moisture deficit.
Efficiency of phosphate fertilizers depending on soil type
On chernozem soils phosphate fertilizers show good efficiency, which is explained by the sufficient supply of nitrogen to the soil and the development of root systems of plants. On phosphorus fertilized background plants spend 10-15% less water to create a unit yield.
On gray forest soils, the effect of phosphorus decreases due to deterioration of nitrogen supply and mobility of organophosphorus compounds in them.
On sod-podzolic soils phosphate fertilizers show a fairly high efficiency if used in combination with other fertilizers, with observance of agronomic and meliorative measures.
Effect of fertilizer properties
To avoid nitrogen losses when applying phosphate and nitrogen fertilizers, observe the following rules:
- Do not mix alkaline forms of phosphate fertilizer with ammonium forms of nitrogen fertilizer.
- Dry superphosphate is mixed with ammonium nitrate before application, as their mixture dries out during long storage.
- Mixing superphosphate and ammonium sulfate leads to the formation of gypsum, the mixture hardens during prolonged storage.
- When you mix acidic superphosphate with nitrate fertilizer leads to the formation of free nitric acid, which quickly volatilizes:
Н3РО4 + NaNO3 = NaH2PO4 + HNO3.
- Before application, excessive acidity of superphosphate, which negatively affects young plants, is eliminated by mechanical mixing with phosphate rock (up to 15%), dolomite flour (up to 10%) or lime.
Methods of phosphate fertilizer application
Phosphate fertilizers, as a rule, are applied in two ways: pre-sowing and main. Given the low mobility of phosphate in the soil with poor root system development in the initial period of growth, the role of pre-sowing application of phosphate fertilizers is important in the formation of high yields.
Even on soils with a high content of mobile phosphorus the concentration of phosphate ions in the soil solution is not sufficient to provide plants with sufficient phosphorus in the early stages of growth. Row (starting) application of phosphate fertilizers is carried out in doses of 7-20 kg/ha of P2O5. At the same time only water-soluble easily accessible forms – granular superphosphates are used. Powdered superphosphates in the spring conditions quickly become damp, clumpy and clog the fertilizers.
According to CINAO data, 1 ton of granular superphosphate at row application gives an increase of 5-6 tons of grain, at main application – 1-2 tons. Phosphate fertilizers also affect the quality of production: increases the protein content of grain, sugar content of sugar beet roots, starchiness of tubers, accelerated ripening.
Water-soluble phosphate fertilizers, often granulated superphosphate, give a good effect, when applied when sowing crops in wells and nests. The fertilizer is applied by combined seeding machines. For sugar beet, potatoes, and other crops superphosphate is made by combined seeding machines simultaneously with nitrogen or nitrogen-potassium fertilizers. According to experimental data, 0.5 kg of granulated superphosphate, or 10 kg P2O5 per 1 hectare provides an additional 250-300 kg/ha of grain. When there is a deficit of phosphate fertilizers, superphosphate application under grain crops during sowing shows good efficiency.
Feeding with superphosphate may be effective:
- when inadequate doses of phosphate fertilizer are applied in the main application, under autumn plowing;
- in areas of sufficient moisture or irrigation;
- on soils with strong chemical absorption in case of prolonged contact of superphosphate with soil, especially on acidic ones with high R2O3-type oxide content.
In other cases, top dressing is less effective than the application of similar doses before sowing or in the rows.
A wide variety of soil types in Russia allows the successful use of all types of phosphate fertilizers for the main fertilizer.
Timing of phosphate fertilizer application
The timing of application is important for hard-to-remove phosphates. They are applied well in advance, in the fall, so that some of the calcium phosphate has had time to transform into more accessible forms by the growing season.
Depth of phosphate fertilizers embedding in the soil
Due to the low mobility of phosphate in the soil, the depth of embedding of the main phosphorus fertilizer is important. Therefore, it is sought to create a supply of available phosphorus in the zone of the location of the active part of the root system of plants. This is especially important in arid conditions, where the upper part of the arable layer dries up in summer. Thus, in the experiment with 32P, surface application of superphosphate on pasture at a dose of 450 kg/ha P2O5 did not lead to penetration of phosphorus deeper than 2.5 cm.
The depth and location of fertilizer depend on the method of embedding.
Table. Placement of fertilizers in the arable soil layer depending on the method of their embedding, %[3]Yagodin B.A., Zhukov Y.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.
From the above data, we can see that the main part of the fertilizer concentrates in the upper (0-9 cm) layer by harrows or cultivators. More uniform embedment is achieved by the plough without skimmer, deeper – plough with skimmer, but in this case in the upper layer of fertilizer remains little. In the latter case, there is a need for row-before-sowing fertilizer. Applied phosphate fertilizers do not migrate along the soil profile and remain in the places of embedding. Only subsequent tillage changes their location in the arable layer.
Therefore, the depth of plowing for a particular crop determines the depth of embedding of the main phosphorus fertilizer.
Optimization of phosphate fertilizer doses
Soils with sufficient reserves of phosphorus through systematic fertilization are able to provide crops with optimal phosphorus nutrition for a long time. Phosphorus mitigates the effect of extreme weather conditions on plants, high yields can be formed even in conditions of drought, low or high temperatures.
In the practice of world farming, especially in Europe, the increase of phosphorus content in the soil in the rotation is achieved by periodic application of high doses of phosphorus fertilizers. Due to the conservation of phosphorus in a form accessible to plants, the weak migration along the soil profile and the absence of losses, as well as data on the optimum levels of mobile phosphorus for crops allows you to calculate the rates of phosphorus fertilizers, which are necessary to achieve optimum phosphate nutrition. The main way to maintain an optimal diet of phosphorus is to apply mineral and organic fertilizers.
Agrochemistry has accumulated enough knowledge about this biogenic element, there are still a number of unresolved problems:
- Low utilization rate of phosphorus fertilizers by individual crops and, in general, in the agrocenosis.
- Systematic application of high doses of phosphorus fertilizers and over-phosphating of soils leads to a violation of the balance of other biogenic elements, which worsens the nutrient regime.
- Various substances contained in phosphate fertilizers in the form of impurities, including heavy metals, have a negative impact on the environment and by getting into plants and agricultural products.
- Immobilization (retrogradation) of phosphorus in the soil as a result of chemical absorption. These processes are particularly intense in carbonate chernozems, red soils, acidic sod-podzolic soils with a high content of aluminum and iron oxides.
- Mobilization of soil phosphates. It is especially important for those farming areas and soils where as a result of systematic application of large doses of phosphate fertilizers created stocks that exceed the optimal phosphate level.
Optimization of phosphorus nutrition of crops depends on the specification of crop rotations in specific soil and climatic conditions. The complexity of optimizing phosphorus nutrition of plants is associated with the binding of a number of biogenic elements, such as zinc, copper and the imbalance of nutrients in the soil.
Development and application of optimal doses of phosphorus is associated with a set of agrotechnical, chemical and biological methods of mobilization of phosphorus accumulated as a result of systematic application of phosphorus fertilizers. Thus, the use of physiologically acidic nitrogen and potassium fertilizers in combination with trace elements mobilizes phosphorus on chernozems, gray and chestnut soils, which were introduced excessive amounts of phosphorus. In this case, it is possible to obtain high crop yields for a long time without making phosphorus fertilizers. Liming of acidic sod-podzolic soils also contributes to the mobilization of soil phosphates associated with halved aluminum and iron oxides.
When solving the problems of optimization of phosphorus fertilization, taking into account the phosphate regime of the soil must be taken into account:
- Objective evaluation of the effectiveness of phosphorus fertilizers is carried out not only on the productivity of individual crops, but also on the crop rotation.
- Methods for assessing the phosphate level and optimization of phosphorus fertilization depend on the ways of determining mobile phosphorus in the soil.
- For objective assessment you should consider both the content of mobile phosphorus by the method adopted for this type of soil, and its mobility in weak salt suspensions.
On sod-podzolic light loamy soils, the optimum content of mobile phosphorus in the arable layer is considered to be 10-15 mg/100 g of soil. On these soils, provided a good agricultural practices and the provision of plants with nitrogen and potassium, the average annual productivity of the field rotation is 45-50 centners of grain units of the main products. A higher content of mobile phosphorus reduces the payback period of phosphorus fertilizers.
Optimal phosphate regime on gray forest soils is close to the regime of sod-podzolic soils when using Kirsanov method. The same value of the optimum content of mobile phosphorus is established for chernozems, when determined by the Chirikov method. On carbonate chernozem, gray and chestnut soils the optimal level is 3-4.5 mg/100 g of soil by Machigin’s method.
To optimize the phosphorus fertilizer in addition to the optimal content use:
1. balance coefficient of utilization, or balance coefficient, removal coefficient. Shows the proportion of nutrient removal from the nutrients applied with fertilizer, calculated by the formula:
where Kb – balance coefficient; R – phosphorus removal with the crop; D – the dose of phosphorus applied.
2. Compensation compensation coefficient, or intensity of balance (Kc), the value inverse to Kb, is equal to:
Balance coefficient – a measure of fertilizer efficiency at the appropriate content of nutrients for given soil conditions.
Increase or decrease in fertilizer dose (Kopt, %) in accordance with the nutrient removal is calculated by the formula:
The optimal dose of fertilizer is calculated by the formula:
Dopt = Ropt ⋅ V%.
Then, the degree of soil supply of phosphorus depending on the content of its mobile form (K) is equal:
К = Dopt – Ropt.
At a low content of soil mobile phosphorus K is 48-55 kg P2O5/ha, at medium – 17-20 kg P2O5/ha, at high – 3-6 kg P2O5/ha.
3. Doses of phosphorus and potassium fertilizers are calculated according to the formula:
DР(К) = R – SO + CР(К),
where DP(K) – the dose of phosphorus or potassium fertilizers, kg a.s./ha; R – phosphorus or potassium removal with the planned yield, kg/ha; SO – phosphorus or potassium content in organic fertilizers, kg/ha; CP(K) – amount of phosphorus or potassium increasing these elements by 10 mg/kg in soils with low content and 5 mg/kg in soils with average nutrient content, kg/ha.
For the optimum level is taken the content of mobile phosphorus in the soil, which achieves at least 90-95% of the maximum yield, and the missing 5-10% is replenished by phosphorus fertilizer to compensate the removal of the planned yield.
Generalization of the results of long-term experiments allowed to develop general principles of differentiation of doses of fertilizers, taking into account specific conditions.
Table. Differentiation of doses of phosphorus fertilizers and phosphorus removal by plants depending on the provision of soils with mobile phosphorus[4]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.
*A single dose (differentiation coefficient of 1) is taken as a dose of P60.
**In a row at sowing.
Doses of P2O5 for pre-sowing application are determined by the crop. Some of them, such as corn and sunflowers, can be inhibited by direct contact of seeds with superphosphate. Therefore you need to create a soil layer between the seeds and the fertilizer; the doses of P2O5 in this case are 7-10 kg/ha.
Cereals and vegetable crops, flax, hemp are less sensitive and respond positively to granulated superphosphate at a dose of about 10 kg/ha, it is acceptable to mix it with the seeds before sowing with an ordinary row seeder. In this case, the seeds and fertilizer must be dry, granules must have good mechanical strength, not to be crushed in the sowing unit and not to clog it. Superphosphate must have a neutral or slightly acidic reaction. Acidic superphosphate even in short contact with seeds (up to 2 hours) reduces the germination of winter rye, barley, spring wheat, flax and beet seeds. If its acidity is less than 1%, it may be mixed with rye and beet seeds not earlier than 2 hours before sowing; with other listed crops – 4-8 hours. Neutralized superphosphate can be mixed with the seeds of these crops one day before sowing.
When sowing sugar beets and potatoes, 20 kg/ha of granulated superphosphate or the same dose of complex fertilizer is applied. The remainder of the total calculated dose of phosphorus (minus pre-sowing dose) is applied in the main fertilizer.
On average, phosphate fertilizer doses vary from 30-45 kg/ha to 90-120 kg/ha of P2O5 and depend on soil fertility, soil and climate conditions, planned yields, forecrop and related fertilizers.
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.