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Complicated fertilizers

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Complicated fertilizers – mineral salts containing several plant nutrition elements, such as potassium nitrate (KNO3), ammonium hydrophosphate ((NH4)2NPO4). As a rule, they do not contain impurities (ballast), so they have a high content of nutrients.

Complicated fertilizers have advantages:

  1. High concentration of nutrients, no or little impurities such as sodium, chlorine.
  2. Fertilizer storage, transportation and application costs are lower. Often these costs are higher than fertilizer preparation costs. According to calculations, the costs for shipping, storage and application of complicated fertilizers compared to simple fertilizers are 10% lower.
  3. Due to the presence of several nutrients in a single granule of solid complex fertilizer allows for a more uniform distribution of nutrients on the soil surface.
  4. The absence of impurities allows you to apply in conditions where high concentrations of salts is undesirable, such as arid conditions, or when fertilizing crops that are sensitive to high osmotic pressure of the soil solution (flax, cucumbers).
  5. Higher fertilizer efficiency due to the presence of nitrogen, phosphorus and potassium in common foci.

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Fertilizers

Complicated fertilizer production

Production of complicated fertilizers in the USSR was started in the 60’s. Their share in total supplies to agriculture in 1980 was 20.2%. 

Ammophos dominates in the range of complicated fertilizers in Russia. Of the three-component fertilizers with a ratio of nutrients 1:1:1, nitrophoska and nitroammophoska are mainly used, of the two-component – nitrophos and nitroammophos. Later in the range appeared azophoska, diammonium phosphate, liquid complex fertilizers, diammophoska, ammophosphate, crystalline. In different regions the efficiency of carbamomophoska and carboammophos application was studied.

It is promising to expand the range of concentrated solid and liquid complex fertilizers through the use of polyphosphoric acids, as well as enriching them with trace elements, magnesium, etc.

An important property of complicated fertilizers is the solubility of their constituent components in water and solutions.

Technological methods of producing complicated fertilizers can be divided into two groups:

  • production on the basis of nitric acid decomposition of phosphate raw materials – nitrophos, nitrophosky;
  • production with the use of phosphoric acids – nitroammophos, nitroammophoski, diammonitrophoski, diammophoski, carboammophoski, ammophoski.

Complicated fertilisers were originally based on nitric acid decomposition of phosphate raw materials. Currently, phosphoric acid processes are used. Ammonium nitrate, urea and ammonium sulphate are used as nitrogen components.

Phosphoric acid derived from apatite and phosphate rock, as well as phosphate-containing products are used as phosphoric components. High-grade phosphate raw materials with high phosphorus content and small amounts of impurities, primarily oxides such as R2O3, are used for production. Phosphate ores usually contain a large amount of impurities, so almost all of them are subject to enrichment. Phosphate ores with a ratio of Fe2O3 : P2O5 more than 8-10, are not used for the production of water-soluble phosphate and complicated fertilizers.

Phosphate rock, with a high content of aluminum and iron oxides, little suitable for sulfuric acid processing for the production of phosphoric acid, as insoluble iron and aluminum phosphates are formed, and part of the phosphoric acid is lost. In practice, for the extraction phosphoric acid is used phosphate raw materials with a content of Fe2O3 not exceeding 8% of the mass of P2O5. The obtained wet-process phosphoric acid with a content of P2O5 28-32% for the production of complicated fertilizers is evaporated, increasing the concentration of P2O5 to 52%.

For the production of complicated fertilizers also use polyphosphoric (superphosphoric) acid acid containing 75-77% P2O5. Over half of the phosphorus in the acid is in polyphosphoric form (42% – in pyrophosphoric form H4P2O7, 8% – in tripolyphosphoric H5P3O10, 1% – in tetrapolyphosphoric H6P4O13), 49% of P2O5 – in orthophosphoric form.

Of the potassium-containing components for complicated fertilizers, mainly potassium chloride is used.

Complicated fertilizers based on nitrogen-acid decomposition of phosphate raw materials

The idea of decomposition of phosphate raw materials by nitric acid was first proposed in 1908. D.N. Pryanishnikov. However, it was realized much later when production of nitric acid from synthetic ammonia increased.

The process of decomposition of natural phosphate raw materials by nitric acid proceeds according to the reaction: 

Ca5(PO4)3F + 10HNO3 = ЗН3РО4 + 5Ca(NO3)2 + HF.

Released hydrogen fluoride interacts with silicon dioxide to form silicon fluoride, the latter reacts with hydrogen fluoride again to form silicic fluoric acid. From the decomposition of phosphate raw materials with nitric acid in the extract contains large amounts of calcium nitrate, which is an undesirable impurity in the finished fertilizer because of high hygroscopic properties and deterioration of the physical properties of complicated fertilizer.

The high calcium content of phosphoric acid leads to insoluble calcium phosphate, whose phosphorus is difficult for plants to access. Therefore, in the production of complicated fertilizers by nitric acid decomposition of phosphate raw materials, it is important to remove excess calcium from the system by reducing the CaO:P2O5 ratio. This production technology uses crushed apatite concentrate and 47-55% nitric acid. Technological schemes differ in the way of extraction of excess calcium from the solution.

Nitrophos and nitrophosks

Nitrophos and nitrophosks are produced by treating phosphate raw materials with nitric acid. The interaction produces calcium nitrate and calcium monophosphate with an admixture of dicalcium phosphate. The following methods are used to remove excess calcium:

1. Production of nitrophoska with freezing of excess calcium nitrate.

Partial freezing of calcium nitrate and its separation from the solution, followed by treatment with ammonia and simultaneous evaporation produces a mixture containing ammonium phosphate, dicalcium phosphate and ammonium nitrate:

H3PO4 + Ca(NO3)2 + NH3 = NH4H2PO4 + CaHPO4 + NH4NO3.

When potassium chloride or sulfuric acid is added to the mixture, nitrophoska is formed, including nitrogen, phosphorus, and potassium. The final products are nitrophoska and calcium nitrate.

Nitrophoska can contain up to 40-50% nutrients. The scheme has the ability to change the ratio of nutrients and receive granular fertilizer, in which up to 60% of P2O5 is water soluble. To obtain nitrofoska with 50-60% water-soluble phosphorus by this method, 70% of CaO is removed from solution in the form of Ca(NO3)2⋅4H2O. The fertilizer has shown high efficiency in all regions where plants are deficient in nitrogen, phosphorus and potassium.

2. Production of nitrophoska by binding excess calcium with carbon dioxide (carbonate scheme):

H3PO4 + Ca(NO3)2 + NH3 + CO2 = CaHPO4 + NH4NO3 + CaCО3.

When calcium nitrate and phosphoric acid are treated with ammonia and carbon dioxide, a mixture consisting of dicalcium phosphate, ammonium nitrate and calcium carbon dioxide is obtained. After mixing with potassium chloride, the mixture is pelleted, dried, separated into fractions and crushed without separating the calcium salts. Carbonate nitrophoska contains 35-37% nutrients. The scheme is the most economical in terms of production, but agrochemical production of carbonate nitrophoska in granular form is inexpedient because phosphorus is in it in citrate-soluble form. Powdered carbonate nitrophoska can be used for main application.

3. Production of nitrophoska and nitrophos by binding excess calcium with ammonium sulfate (sulfate scheme).

Ammonium sulfate is introduced into a hot mushy mixture of calcium nitrate and phosphoric acid (pulp), which reacts with calcium nitrate to form ammonium nitrate and anhydrous calcium sulfate. The mixture is dried and pelletized.

Depending on the consumption of ammonium sulphate you can get a product with different content of water-soluble P2O5.

To obtain a triple fertilizer, the necessary amount of potassium chloride is added to the hot pulp, which partially interacts with ammonium nitrate to form ammonium chloride and potassium nitrate:

KCl + NH4NO3 = NH4Cl + KNO3

After drying and granulation, sulphate nitrophoska is obtained. It is characterized by good physical properties and can be used for most crops on all types of soils. The mixture contains CaHPO4⋅2H2O, Ca(H2PO4)2⋅H2O, NaNO3, NH4Cl, KNO3, CaSO4.

If ammonium sulfate is replaced with potassium sulfate, the latter is dissolved in nitric acid and phosphate raw material is treated with this solution. The suspension is neutralized with ammonia, the product is pelletized and dried. Currently, this is the main way to produce nitrophoska with a 33-36% nutrient content.

4. Production of nitrophoska by binding excess calcium with sulfuric acid (sulfuric acid scheme).

Excess calcium is bound with sulfuric acid in the process of nitric acid decomposition of phosphates followed by treatment of the solution with ammonia. Potassium chloride is added to the resulting mixture to produce the finished product – sulfuric nitrophoska containing 35% of nutrients, the composition and properties are similar to sulfate nitrophoska. Bound excess calcium remains in the fertilizer as an impurity of calcium sulfate.

Ammonia may cause retrogradation of the formed soluble salts of phosphoric acid due to local alkalization of the medium.

The method allows to change the ratio of nutrients in a wide range and to produce a product containing up to 50-60% P2O5 in a water-soluble form.

5. Production of nitrophoska by binding excess calcium with phosphoric acid (phosphate scheme).

Phosphate raw materials are decomposed by a mixture of nitric and phosphoric acids in the ratio determined by the specified ratio of N:P2O5 in the finished product and the content of water-soluble phosphorus. The resulting solution after decomposition contains Ca(NO3)2 and free phosphoric and nitric acids. It is subjected to ammonization, in which the calcium of the solution is converted into dicalcium phosphate (CaНPO4). Calcium chloride is then added, granulated, and dried.

Under this scheme, the fertilizer with the highest content of water-soluble phosphoric acid (up to 80%) is obtained, in sulfate and sulfuric acid methods – about 55%. The introduction of potassium chloride produces phosphorus nitrophoska. The content of nitrogen, phosphorus and potassium is 17% each.

Several brands of granulated nitrophosks are produced in Russia.

Table. Characteristics of nitrophosphates

Nitrophosphates
N, %
P2O5 (assimilable), %
K2O
Water-soluble P2O5 content, % (of total content)
Nitrophos grade A
23,5
17
-
50
Nitrophos grade B
24
14
-
50
Nitrophoska grade A (16:16:13)
16-17
16-17
13-14
55
Nitrophoska grade Б (13:10:13)
12,5-13,5
8,5-9,5
12,5-13,5
55
Nitrophoska grade В (12:12:12)
11-12
10-11
11-12
55

Nitrophosks granule size is 1-4 mm, quite strong, when conditioned by adding small amounts of mineral oil and powdering with talc or milled limestone, they do not cake during transportation and storage. Nitrophosks are used as a main fertilizer, pre-sowing in rows and in top dressing. The effectiveness is the same as equivalent amounts of mixtures of simple fertilizers.

Nitrophosks are used as the main fertilizer for many crops and for local application, especially for potatoes.

The production technology of nitrophosks, based on the decomposition of raw materials by nitric acid or its mixture with other acids, is used in foreign countries: Germany, Austria and France. In Germany, nitrophosks are produced without chlorides, some contain magnesium. France produces a large range of nitrophosks for various crops. Chlorine-free nitrophoska is produced for grapes and fruit crops.

In recent years, technological schemes for the production of nitrophosks with 80-95% P2O5 in water-soluble form have been developed, among which the Norwegian method is widespread. Phosphorite by this method is treated with excess nitric acid, followed by crystallization of calcium nitrate at a temperature of -50 °C. This method or its variants are used in Russia, England, Germany, France and the Netherlands. In France, a technology has been developed to produce 54 grades of nitrophosks with a ratio of nitrogen from 8 to 20%, P2O5 – from 7 to 35% and K2O – up to 29%.

Nitroammophos

Nitroammophos is a mixture of NH4H2PO4 + NH4NO3. It is produced by neutralizing mixtures of nitric and phosphoric acids with ammonia. The content of nitrogen and phosphorus is 23% of each. When potassium salts are added, nitroammonium phosphate is produced. The content of N, P2O5 and K2O is 16-17% each. They almost do not contain ballast. The amount of water-soluble phosphates is over 90%. Nitrofoski can be used by the same methods as nitrofoski. The efficiency is comparable to mixtures of simple fertilizers.

Nitroammophoska 17:17:17 is produced by the introduction of potassium chloride, and with the introduction of potassium sulfate – mark 16:16:16. The fertilizer is universal and is used on all types of soils as the main fertilizer, for sugar beets and potatoes – also at sowing.

Complicated fertilizers produced by neutralizing phosphoric acids with ammonia

Ammonium phosphates (ammophos and diammophos)

Н3РO4 + NH3 = NH4H2PO4 – monoammonium phosphate (ammophos),

H3PO4 + 2NH3 = (NH4)2HPO4 – diammonium phosphate (diammophos).

Ammophos contains 10-12% N and 46-50% P2O5. Diammophos, produced from apatite, contains 18% N and 50% P2O5, from Karatau phosphorites – 16-17% N and 41-42% P2O5. Ammophos is characterized by good physical, chemical and mechanical properties without the use of conditioning additives during granulation. Ammophos and diammophos are physiologically acidic fertilizers.

Ammophos is mainly used as a row fertilizer for crops and as the main fertilizer, for example, for cotton. It is a good component for the preparation of mixed fertilizers, as it is compatible with many fertilizers. The disadvantage is the unbalanced ratio of nitrogen to phosphorus (1:4), while the optimal ratio of nitrogen to phosphorus should be close to one or less (most plants consume nitrogen than phosphorus).

Diammophos has this ratio of nitrogen to phosphorus (1:2.5), but its physical properties are worse. It can also be used for row application and as a top dressing for technical and vegetable crops. Because of its high cost, its application is limited; it is used in livestock production as a feed additive. It is the most concentrated of all complicated fertilizers.

By adding potassium chloride to ammophos and diammophos, triple fertilizers are produced, which are common in the United States, England, Japan and India, because these countries have large reserves of sulfur and large production of sulfuric acid, which provides phosphoric acid and complicated fertilizers based on it. The United States leads the world in the production and use of mono- and diammonium phosphate. Because of the unbalanced nitrogen to phosphorus content in the U.S., a large volume of these fertilizers are used to make mixed fertilizers.

Comparative tests of these fertilizers with equalized K doses under major crops and on major soil types have shown their equal effectiveness to an equivalent mixture of simple fertilizers.

Ammonium phosphates are convenient for local application as a pre-sowing or pre-sowing fertilizer. They do not contain large amounts of ballast, do not create a high concentration of the solution and do not increase its osmotic pressure.

Ammonium polyphosphates

Until recently, the production technology for superphosphate, precipitate and ammonium phosphate was based on the use of orthophosphoric acid (H3PO4), which in pure form contains no more than 54% P2O5. Mixtures of polyphosphoric acids contain from 70 to 83% P2O5, which allows to obtain more concentrated complex fertilizers.

Preparation of polyphosphoric acids requires heating and vacuum:

2H3PO4 —(heating, vacuum)→ H4P2O7 + H2O;

H3PO4 + H4P2O7 —(heating, vacuum)→ H5P3O10 + H2O;

H5P3O10 —(heating, vacuum)→ 3HPO3 + H2O etc.

In these reactions, phosphate groups are condensed, which is why polyphosphoric acids are called condensed acids. In the chemical industry, they are also called superphosphoric acids, which is more of a commercial term.

Polyphosphoric acids: HPO3 – metaphosphoric, H4P2O7 – pyrophosphoric, H3P3O10 – tripolyphosphoric, H6P4O13 – polyphosphoric. In the USSR polyphosphates were produced in 1964.

For transportation of polyphosphoric acids they use special stainless steel truck and railroad tanks.

Initial product for production of polyphosphates is mixture of polyphosphoric acids, obtained from concentrated orthophosphoric acid or phosphorus. The most concentrated polyphosphoric acids are derived from thermal orthophosphoric acid.

Polyphosphoric acids are used to make triple superphosphate containing 55% P2O5. When polyphosphoric acids are saturated with ammonia under pressure, ammonium polyphosphates are produced.

Table. Characteristics of some ammonium polyphosphates[1]Yagodin B.A., Zhukov Yu.P., Kobzarenko V.I. Agrochemistry / Edited by B.A. Yagodin. - Moscow: Kolos, 2002. - 584 p.: ill.

Fertilizer
Formula
N, %
P2O5, %
N:P2O5
N+P2O5, %
Diammonium pyrophosphate
(NH4)2H2P2O7
13
66,9
1:5
79,9
Triammonium pyrophosphate
(NH4)3HP2O7
18,3
62,0
1:3,4
80,3
Tetraammonium pyrophosphate
(NH4)4P2O7
22,7
57,7
1:2,5
80,4
Pentaammonium tripolyphosphate dihydrate
(NH4)3P3O10⋅2H2O
18,4
56,2
1:3,1
74,6

For practical purposes, the second and third of these ammonium polyphosphates are valuable, characterized by high phosphorus and nitrogen content and an acceptable ratio. These fertilizers are used in solid form or introduced as the main component in liquid and suspended fertilizers.

Ammonium polyphosphates are highly soluble in water. Ammonium polyphosphates can be partially replaced with potassium, calcium or trace elements (zinc, copper, iron). The latter with orthophosphates form insoluble salts, while with polyphosphates they are chelated and remain available for plants, which is promising for the creation of new types and forms of fertilizers.

The physical properties of ammonium polyphosphates are good, the granules are strong, are a good component for mixed fertilizers. Thus, by adding ammonium nitrate or urea and potassium chloride, you can get a triple fertilizer with a total content of the active substance of 60%.

In the USA, solid mixtures are prepared from polyphosphoric acid and solid ammonium polyphosphate with the addition of potassium salt, magnesium oxides, zinc, and molten sulfur. This makes it possible to produce fertilizers that are more complex in composition and intended use.

Polyphosphates in the soil are less mobile than orthophosphates, as more active interact with soil minerals. Hydrolysis of polyphosphates occurs in the soil, the intensity of which increases with increasing biological activity of the environment. At 7-12 °C, they are slow, with increasing temperature – increased. The optimal temperature for hydrolysis is 30-35 °C. Polyphosphate hydrolysis reactions:

HPO3 + H2O → Н4Р2О7;

Н4Р2О7 + H2O → 2Н3РО4;

H5P3O10 + 2H2O → 3Н3РО4.

Plant uptake of phosphorus by polyphosphates is slower than by orthophosphates, due to hydrolysis of the latter to the orthophosphorus form. During the growing season, the advantage in phosphorus uptake is retained by polyphosphates, since retrogradation is less pronounced than for orthophosphates. Ammonium polyphosphates are used for all crops on all types of soils.

Phosphoammonium-magnesia

Phosphoammonium-magnesia, or magnesiumammonium phosphate (MgNH4PO4⋅H2O) is a low-soluble complicated fertilizer containing 10.9% N, 45.7% P2O5 and 25.9% MgO. Nitrification of ammonium under soil conditions is as fast as that of ammonium fertilizers. Nitrogen is represented by water-soluble form, phosphorus and magnesium by citric-soluble form. Therefore, these fertilizers belong to the long-term fertilizers. It is advisable to use them on light sandy soils as the main fertilizer for potatoes, root crops and vegetable crops, as well as in irrigated agriculture, greenhouses when growing vegetables on hydroponics.

Magnesium-ammonium phosphate is formed by the interaction of a solution of monoammonium phosphate with an aqueous suspension of magnesium oxide or its salts or phosphoric acid, ammonia and magnesium hydroxide with its salts (chloride, sulfate or carbonate). For example:

MgCl2 + (NH4)2HPO4 + NH4OH → MgNH4PO4 + H2O + NH4CI.

Carboammophos and carboammophosks

Carboammophos is produced by the interaction of urea synthesis intermediates (ammonia and carbon dioxide) and phosphoric acid. The ratio of nitrogen and phosphorus is – 25:30; 34:17; 33:20, etc.

With the introduction of potassium-containing salts get carboamphoska with an aggregate content of nutrients up to 60-65%, for example, grade 20:20:20. Nitrogen in these fertilizers is in amide (70-75%) and ammonia forms, up to 90% of phosphorus – in a water-soluble form.

In field experiments, the use of these fertilizers is equal to mixtures of simple fertilizers. Rice and cotton plants are better affected than mixtures of simple fertilizers with ammonium nitrate. In hayfields and pastures, nitrogen losses were noted with surface application.

Potassium metaphosphate

Potassium metaphosphate (KPO3) contains up to 60% P2O5 and up to 40% K2O, a concentrated complicated fertilizer. Potassium metaphosphate with phosphorus content in citrate-soluble and water-soluble forms is obtained. The most promising method is the decomposition of potassium chloride or carbonic acid with orthophosphoric acid at a temperature of 450 °C. When using extraction phosphoric acid, potassium metaphosphates containing 54% P2O5 (in water-soluble form), 35-40% K2O, and 60% P2O5 (in citrate-soluble form) and 40% K2O are obtained.

In a number of experiments, potatoes, sugar beets, barley, flax showed a good effect from the use of this fertilizer.

Potassium nitrate

Potassium nitrate (KNO3), contains 13% nitrogen and 46% potassium oxide, contains no ballast impurities and has good physical properties. The formation of potassium nitrate is based on the exchange reaction of NaNO3 and KCl: 

NaNO3 + KCl → NaCl + KNO3.

Concentrated solutions of sodium nitrate, which are formed during the alkaline absorption of waste nitrous gases in the production of nitric acid, and potassium chloride are used as feedstock. The fertilizer is non-hygroscopic and well dispersed. It is applied to vegetable crops, especially indoors. Good for crops that are sensitive to chlorine.

A disadvantage of potassium nitrate is the ratio between nitrogen and potassium (1:3.5). Therefore, its application requires the additional application of nitrogen fertilizers, and if it is necessary to apply phosphorus, then phosphorus fertilizers.

Application and efficiency of complicated fertilizers

The effect of complicated fertilizers on crop yields depends on:

  1. presence of water-soluble forms of phosphorus in their composition;
  2. the type and biological characteristics of crops;
  3. soil and climatic conditions;
  4. agronomic technology of application (timing and methods of application);
  5. ratio of nutrients in the fertilizer;
  6. forms of nitrogen, phosphorus and potassium components of fertilizers;
  7. complex of agronomic practices, against which complicated fertilizers are used.

All factors are interrelated. Thus, on sod-podzolic soils citrate-soluble form of P2O5 under direct action and after action is also available for plants, as well as water-soluble, whereas on chernozems, gray soils and chestnut soils more accessible water-soluble form. In complicated granular fertilizers the optimum content of water-soluble P2O5 from assimilated should be at least 50%, on chernozems and gray soils – at least 60-70%.

Sulfuric acid nitrophoska, nitroammophoska and diammonitrophoska with the highest content of water-soluble phosphorus provide the maximum efficiency on sod-podzolic soils. The effect of carbonate granular nitrophosks, which contain almost no water-soluble phosphorus, worse than the equivalent mixtures of simple fertilizers, especially on chernozems. With an increase in the proportion of water-soluble phosphorus in the composition of the fertilizer the coefficient of its use by plants increases. The same pattern is maintained when evaluating the methods of fertilizer application. For example, complicated fertilizers with a high content of phosphorus in water-soluble form are more effective at local application.

Three-component complicated fertilizers in different soil and climatic conditions show high efficiency. In the zonal aspect, taking into account the biological characteristics of crops the following regularities compared with mixtures of simple fertilizers are noted:

  1. In forest-podzolic and forest-steppe zones on sod-podzolic soils and chernozems three- and two-component fertilizers in crops of cereals, sugar beet, flax and potatoes at basic application are equivalent to mixtures of one-sided fertilizers on efficiency, in some cases exceed them. Chlorine-free nitrophoska is more effective on potatoes.
  2. In the steppe zone on common, carbonate, southern chernozems the efficiency of complicated fertilizers is less than in the forest-log zone. In this zone, the yield increase of grain crops from applying nitroamphoska is higher than from nitrophoska.
  3. On chestnut soils and gray soils irrigation increases the efficiency of fertilizers. The effect of two- and three-component complicated fertilizers on cereal crops, corn and cotton is better than mixtures of simple fertilizers.
  4. Under conditions of rice cultivation as a flooded crop, the efficiency of complicated fertilizers containing nitrate nitrogen is lower than that of fertilizer mixtures containing ammonium or amide nitrogen.
  5. Complicated fertilizers are effective when applied pre-sowing to cereals, industrial, silage crops and annual grasses.

Local application of nitroammophoska on sod-podzolic, gray forest soils and chernozems is more effective than superphosphate. On the background of the main application and the increased content of phosphorus in the soil at row application the effect of mineral fertilizers is reduced. Biological characteristics of crops and diversity of soils determine the need for complicated fertilizers with different ratios of nitrogen, phosphorus and potassium.

On sod-podzolic soils, phosphorus and potassium fertilizers when applied in the fall and spring show about the same effectiveness. Spring nitrogen fertilizer application is more effective than the fall fertilizer, because nitrogen is washed into the underlying soil layers during the winter-spring period, which causes nitrogen starvation of winter and spring crops in the spring. Therefore, on loose sandy soils, complicated fertilizers and equivalent mixtures of simple fertilizers are ineffective when applied in a full dose from autumn. On winter crops, the effect of complicated fertilizers increases with half the dose of nitrogen applied in the spring.

Thus, on sod-podzolic soils, complicated fertilizers with a predominance of phosphorus and potassium in the autumn application for winter and spring crops and the introduction of nitrogen at a full dose in spring are more effective compared with a full dose of fertilizers in an equalized ratio of nutrients, made in autumn.

In the zone of sufficient moisture, especially on light sod-podzolic soils, it is recommended to apply a complicated fertilizer in autumn with less nitrogen (1:2:2, 1:2:1, 1:4:0), followed by the spring application of additional nitrogen to the optimum content. On leached chernozems and sod-podzolic clay soils single application of the whole dose of complex or mixtures of simple fertilizers is not inferior to fractional application during the growing season.

Complicated fertilizers based on urea for basic application to cereals, potatoes, sugar beet, corn and other crops on the soils of the forest and steppe zones are as effective as nitroamphoska and simple fertilizer mixtures. When fertilizing rice on meadow-chernozem soils carbamammofoska and fertilizer mixture with ammonium sulfate showed a greater positive effect on yield than nitroammofoska, because the latter contains nitrogen in nitrate-ammonium form.

In meadows and pastures on sod-podzolic and mountain-meadow soils carboamphoska and carboammophoska inferior in their effect to fertilizers with nitrate-ammonia form of nitrogen, which is associated with nitrogen losses as a result of urea hydrolysis at surface application. On cotton and cereal crops under irrigation conditions on chestnut soils and gray soils urea-containing fertilizers are more effective than mixtures based on ammonium nitrate.

As polyphosphates are just as effective as orthophosphate-based fertilizers, they can be applied to crops under various soil and climate conditions.

In powdered calcium polyphosphate phosphate phosphate is in a citrate-soluble form, which in some cases reduces its effect, for example, on potatoes, a crop that responds better to water-soluble phosphate fertilizers.

Adding micro-nutrients to macrofertilizers improves plant nutrition and increases their effectiveness. A range of complicated fertilizers enriched with micronutrients has been developed. For example, ammophos containing N – 12% and P2O5 – 51%, B – 0.4%, Zn – 1.0% Mn – 3.0%; nitroammophoska containing N – 17%, P2O5 – 17%, K2O – 17%, B – 0.17%, Mo – 0.05%, Mn – 1.5%, Co – 0.05% and I – 0.003%; carboammophoska – N – 21%, P2O5 – 21%, K2O – 21%, I – 0.2%.

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 Research Institute named after D.N. Pryanishnikov, 2017. – 854 с.