Fertilizers

Importance of Fertilizers

In connection with the multifunctional role of fertilizers in the agrocenosis, their importance increases with the productivity of agriculture, as confirmed by the experience of farming in many highly developed countries of the world.

Organic and mineral fertilizers affect soil structure, the reaction of the soil solution, the rate of microbiological processes, actively participate in the reproduction of fertility, affect plant nutrition, growth and development, resistance to adverse external factors, and, in general, yield and its quality. Fertilizers affect plant resistance to diseases.

When crops are cultivated, nutrients are removed with the harvest, lost with surface runoff and infiltration into deep layers, and through erosion. As a result, the nutrient balance changes, fertility, crop yields, and product quality decrease. To mitigate the deficiency of biogenic elements in the soil, fertilizers are applied.

In the process of their life activity, plants form dry matter by absorbing carbon dioxide from the air, water, and mineral substances from the soil. As a result, plants accumulate certain substances that characterize the chemical composition of plants. The most important, so-called biophilic, nutrients are nitrogen, phosphorus, and potassium. The amount of nutrients absorbed by plants, contained in all organs and in the entire mass of the harvest, allows determining their need for nutrients. Nutrient consumption is expressed in kg per 1 ha or in kg per 1 t of marketable products, including by-products. The optimal content and ratio of nutrients in the soil, provided other factors of plant life are sufficient, allows obtaining the maximum possible crop yields with high quality.

D. N. Pryanishnikov noted: the countries of Western Europe needed 100 years to increase the yield of wheat from 0.7 to 1.6 t per 1 ha through crop rotation and improved soil tillage, and 25 years to increase yield from 1.6 to 3 t with the help of fertilizers. In Russia, up to half of the total increase in crop yield is provided by the use of fertilizers. For example, applying fertilizers on the soils of the Non-Chernozem Zone, characterized by low natural fertility, or on southern soils with limited moisture supply, allows obtaining yield increases of up to 75%.

The use of fertilizers in most cases is economically profitable. According to calculations, 1 ruble spent on mineral fertilizers provides an increase in yield worth an average of 2.2 rubles. The share of economic costs for the purchase and use of mineral fertilizers in the country as a whole until 1990 was 15–17% of all crop production costs. The economic return of fertilizers depends on natural soil fertility. For example, in the Non-Chernozem Zone with high moisture supply but low natural fertility, with a yield of grain crops of 3 t/ha, the application of fertilizers produces 70–80% of the yield increase. In the dry steppe, fertilizers account for 50% of the increase.

Fertilizer as the Main Factor in Increasing Yields

World agricultural practice shows that yield is related to the amount of fertilizers applied.

The relationship between grain production and the use of mineral fertilizers is clearly seen in the example of Russia, where a sharp decline in the application of mineral fertilizers and soil fertility occurred.

According to data from field experiments of the agrochemical service of Russia, the yield increase from the application of mineral fertilizers is: winter wheat — 0.49–1.27 t/ha; winter rye — 0.48–1.08 t/ha; spring barley — 0.32–1.29 t/ha; maize (grain) — 0.65–2 t/ha; potato — 4.9–9.1 t/ha; sugar beet — 5–14.4 t/ha; maize for silage — 2.3–18.1 t/ha; natural grasses for hay — 0.6–3 t/ha.

The intensification of agriculture leads to further growth of yields and accelerates the removal of nutrients from the soil and the mineralization of humus. Regulation of these processes becomes possible through the application of fertilizers. In the 1980s, about 60% of nutrients were applied to the soil with mineral fertilizers, and the use of organic fertilizers was over 4 t per 1 ha per year. In the 1990s, the application of organic fertilizers decreased more than 5 times, and of mineral fertilizers — 10 times. The humus deficit was 0.52 t per 1 ha of arable land; the need for manure to cover the deficit was 6.5 t/ha.

In the middle of the 20th century, the so-called “Green Revolution” occurred, the foundations of which were laid by Norman Borlaug. Countries with a high level of chemicalization of agriculture are distinguished by higher yields, the increase of which is based on new intensive varieties and progressive agronomic practices. According to summarized data of Academician of the Russian Academy of Agricultural Sciences V. F. Ladonin (1999), world grain production grew 3 times: from 630 million t in 1950 to 1970 million t in 1990. Over the same period, the use of mineral fertilizers grew 10 times: from 14 to 140 million t. At the same time, grain production increased due to the intensification of agriculture, not the expansion of sown areas. The yield of grain crops in the second half of the 20th century increased 2.5 times, on average by 2.1% per year.

In developed countries from 1970 to 1990, fertilizer use increased from 26 to 83 kg/ha, in the countries of East Asia and the Pacific — from 36 to 190 kg/ha, in Europe — from 88 to 142 kg/ha, in the CIS and DPRK — from 46 to 110 kg/ha. In 1990, the grain yield in the DPRK was 4.2 t/ha. World records for wheat were over 16 t/ha, for maize — over 22 t/ha.

The increase in crop yield is 50% determined by fertilizers, the remaining 50% by other factors. According to studies conducted in the USA, the growth of yield in the post-war years in the USA was 41% due to mineral fertilizers, 15–20% — herbicides and chemical plant protection products, 15% — agronomic practices, 8% — hybrid seeds, 5% — irrigation, 11–18% — other factors.

The growth of yield leads to an increase in the consumption of nutrients by plants, therefore the higher the planned crop yield, the more fertilizers are needed. However, yield increases in direct dependence on increasing fertilizer doses up to a certain level, at which the maximum return per unit of fertilizer by the resulting agricultural product is achieved.

Increasing fertilizer doses is economically justified until the costs of applying an additional amount of fertilizer are fully compensated by the yield increase.

Effective use of fertilizers is possible under the condition of high agronomic practices.

Numerous experiments in various soil-climatic conditions have proven the influence of doses and forms of nitrogen fertilizers on grain quality, primarily the protein content of winter wheat grain.

The chemicalization of agriculture does not replace organic fertilizers. D. N. Pryanishnikov believed: an incorrect attitude to manure is an incorrect attitude to the nutrient elements of mineral fertilizers. Organic fertilizers are one of the main elements of the fertilizer system. Thus, in the Non-Chernozem Zone, 20–30 t of manure per 1 ha give a yield increase of grain crops of 0.6–0.7 t/ha, potato 6–7 t/ha, root crops up to 15 t/ha, silage crops 15–20 t/ha. The aftereffect of manure persists for 4–5 years. During this time, one ton of manure gives 0.1 t of additional production in grain equivalent.

In experiments of the Dolgoprudnaya station, the application of 36 t/ha of manure on four crops of the crop rotation allowed obtaining 3.4 t/ha of additional production in grain equivalent.

Negative environmental consequences are especially acute in the production of vegetable crops, which are distinguished by the greatest ability to accumulate nitrates and other residual chemicals. Therefore, vegetable growing needs biologization, that is, an increase in the share of organic fertilizers in the fertilizer system, perennial grasses in crop rotations, and the use of biological plant protection agents.

Excessive concentration of livestock waste poses a great environmental danger. The main way of their use is the fertilization of perennial grasses.

The uneven application of organic and mineral fertilizers is a serious economic and environmental problem. Uneven application leads to an uneven stand, uneven ripening, reduced product quality, and increased leaching of nutrients. Losses from infiltration increase with increasing fertilizer doses. According to data of T. N. Kulakovskaya, in Belarus in years with excessive moisture, nitrogen losses from leaching on sandy soils reach 60 kg/ha, on sandy loam — 20–25 kg/ha, on loam — 10 kg/ha. In years with normal moisture, these indicators decrease approximately 2 times. Nitrogen losses in the form of gaseous compounds constitute 10–30% of the applied amount (Mineev, 1984).

Losses of fertilizers during transportation and storage may be related to their ability to stratify — segregation (for mixed fertilizers), vapor pressure and viscosity (for liquid forms), bulk density and angle of repose (for powdery forms). The organization of transportation and storage of fertilizers is also related to fire- and explosion-hazard properties, residual acidity, rate and conditions of decomposition, and toxicity. For example, potassium nitrate when mixed with sawdust can form fire- and explosion-hazard mixtures, and liquid ammonia or its aqueous solutions have a strong asphyxiating odor.

The properties of fertilizers can vary widely depending on the technical features of production, raw materials, and their composition, and are regulated by technical specifications. Thus, for urea the permissible moisture is not more than 0.2–0.3%, calcium nitrate — not more than 14%, powdered superphosphate — not more than 12%, potassium fertilizers — from 1 to 6%. Non-compliance with the requirements entails changes in the physical-mechanical properties of fertilizers, making them unsuitable for use.

One of the properties of fertilizers that strongly affects their use is hygroscopicity — the ability to absorb moisture from the air. Highly hygroscopic fertilizers include calcium (9.5 points out of 10 possible) and ammonium (9.3 points) nitrate, potassium chloride 3.2–4.4 points, potassium sulfate 0.2 points. The conditions of storage, transportation, and packaging of fertilizers are determined by this property. Highly hygroscopic fertilizers are stored and transported in sealed containers, more often in polyethylene bags.

Flowability — the suitability of fertilizers for mechanical application using fertilizer sowing units — depends on moisture capacity. The maximum moisture capacity of mineral fertilizers corresponds to the maximum moisture content at which the ability to be dispersed by fertilizer seeders is preserved.

During storage or prolonged transportation, fertilizers may cake. The use of caked fertilizers involves high costs for grinding before application to the soil. Caking depends on hygroscopicity, moisture, particle size distribution, conditions, and duration of storage. Caking is assessed on a 7-point scale and determined by the resistance to destruction of caked fertilizer. Simple powdered superphosphate (7 points) and fine-crystalline potassium chloride (6 points) are prone to strong caking; ammonium sulfate cakes weakly (2–3 points), potassium sulfate and potassium magnesia are resistant to caking (1 point).

The physical-mechanical properties of mineral fertilizers are related to particle size distribution, that is, to particle size. It is determined by the sieve method. Particle size distribution affects the uniformity of application over the field area. A uniform particle size distribution when spread by centrifugal spreaders ensures uniform distribution across the width of the implement. With a nonuniform particle size distribution, segregation is observed, that is, fertilizer particles of different sizes and masses are thrown different distances from the fertilizer sowing unit: larger and heavier particles fly farther, creating uneven distribution.

The preservation of particle size distribution during storage, transportation, and application to the soil depends on granule strength, which is characterized by mechanical strength to crushing (in kgf/cm³) and abrasion (in %). Granule strength is related to moisture, size and shape of particles, the presence of hydrophobic additives, the packing density of fertilizers, and the duration of storage.

Dispersibility, or flowability, is the mobility of fertilizer particles during application by fertilizer seeders. Dispersibility is assessed on a 12-point system.

When transporting fertilizers and calculating the size of storage facilities, the density of fertilizers is taken into account, that is, the volume of a unit mass (1 t/m³) and the mass of a unit volume. The least dense include ammonium chloride and urea (0.58–0.65 t/m³), heavy — Thomas slag, limestone and phosphorite flour (2.01–1.62 t/m³).

Some fertilizers with good physical-mechanical properties, for example ammonium sulfate and potassium sulfate, may be transported and stored in bulk — in bulk. During their storage, the angle of repose is taken into account, which is formed by the horizontal plane (surface) and the slope line of the fertilizer heap.

Classification of Fertilizers

According to the nature of their effect on the soil and the nutrient regime of plants, fertilizers are divided into direct and indirect.

Direct-action fertilizers are fertilizers that improve plant nutrition with nutrients. This group includes all types of mineral fertilizers, respectively nitrogen, phosphorus, potassium, etc., and organic fertilizers.

Indirect fertilizers improve soil properties and mobilize existing nutrient reserves. Indirect fertilizers include chemical soil ameliorants (lime, gypsum) and bacterial fertilizers.

The division of fertilizers into direct and indirect is conditional, since each of them can have both a direct and an indirect effect. Once in the soil, fertilizers improve mineral nutrition of plants and influence agrochemical properties. For example, lime or gypsum eliminate excessive acidity or alkalinity of the soil and are simultaneously a source of calcium for plant nutrition.

According to chemical composition, or origin, fertilizers are divided into:

• mineral;
• organic;
• microbiological.

Mineral fertilizers, depending on composition, are divided into:

• single-component, or simple, or one-sided, — containing only one nutrient;
• complex — containing two or more nutrients.

According to the types of nutrients, mineral fertilizers are divided into nitrogen, phosphorus, potassium, zinc, etc. In turn, each type can be divided depending on forms; for example, nitrogen fertilizers include nitrate, ammonium, ammonium-nitrate, and amide forms.

Depending on the main component, fertilizers are divided into macro- and microfertilizers.

According to their effect on the reaction of the soil solution, mineral fertilizers are distinguished as:

• physiologically acidic;
• physiologically alkaline;
• physiologically neutral.

Physiologically acidic fertilizers include fertilizers whose cations are absorbed by plants to a greater extent than anions. Accordingly, physiologically alkaline are fertilizers whose anions are absorbed to a greater extent. Physiologically neutral mineral fertilizers do not affect the reaction of the soil solution.

According to the method of production, fertilizers are divided into:

• industrial;
• local;
• non-traditional.

Industrial fertilizers are mineral fertilizers produced at chemical plants.

Local fertilizers are fertilizers obtained at the places of their use, directly on farms or near them. Local fertilizers include manure, manure slurry, poultry manure, composts, peat, ash, calcareous tuffs, green fertilizer.

According to aggregate state, fertilizers are divided into:

1. solid:
2. powdery, with a particle size less than 1 mm;
3. crystalline, with a crystal size more than 0.5 mm;
4. granulated, with a granule size more than 1 mm;
5. liquid;
6. gaseous.

Mineral Fertilizers

Mineral fertilizers are industrial substances or minerals that contain one or several plant nutrients, more often in mineral form, less often in organic form. Currently, mineral fertilizers account for about 60% of the nutrients applied to the soil.

The active ingredient is the nutrient contained in the fertilizer. The content of the active ingredient in the fertilizer is expressed as a percentage by mass: for nitrogen fertilizers — calculated as N, for phosphorus — as P₂O₅, for potassium — as K₂O, for magnesium — as MgO, for calcium — as CaO or CaCO₃, for microfertilizers — as the corresponding microelement.

The composition of complex fertilizers is usually expressed as the content of active ingredients by numbers separated by dashes or colons. The first number, as a rule, denotes the percentage content of nitrogen (N), the second — phosphorus (P₂O₅), the third — potassium (K₂O). For example, N:P:K — 17:17:17.

The ratio of active ingredients in complex fertilizers is usually denoted by numbers, with the nitrogen content taken as unity. For the above example, the ratio will be 1:1:1.

The application rate or dose of fertilizers is usually denoted in active ingredient (kg/ha) as a subscript: N₆₀P₉₀K₃₀.

Organic Fertilizers

Main page: Organic fertilizers

Complex Fertilizers

Main page: Complex fertilizers

Microfertilizers

Main page: Microfertilizers

Microbiological and Bacterial Fertilizers

Main page: Microbiological and bacterial fertilizers

References

1. Yagodin B. A., Zhukov Yu. P., Kobzarenko V. I. (2002). Agrochemistry. Edited by B. A. Yagodin. Moscow: Kolos.
2. Mineev V. G., Sychev V. G., Gamzikov G. P. et al. (2017). Agrochemistry. Textbook. Edited by Mineev V. G. Moscow: Publishing House of VNIIA named after D. N. Pryanishnikov.
3. Niklyaev V. S. (2000). Fundamentals of Agricultural Production Technology. Agriculture and Crop Production. Moscow: “Bylina”.
4. Evtefeev Yu. V., Kazantsev G. M. (2013). Fundamentals of Agronomy: textbook. Moscow: FORUM.