inorganic substances, primarily salts, containing nutrients required by plants. Mineral fertilizers greatly affect the soil (its physical, chemical, and biologic properties) and plants. In soil, mineral fertilizers undergo various changes that influence the solubility of their nutrients, their permeability, and their availability to plants. The nature and intensity of these changes are dependent on properties of the soil. At the same time, mineral fertilizers have a great effect on the soil; for example, they enrich the soil with nutrients, alter the reaction of the soil solution, and influence microbiological processes. Because plants receive nutrients through their roots, the addition of mineral fertilizers to soil can actively affect plant
|Table 1. World production of mineral fertilizers (thousands of tons)|
|Nitrogen (N)||Phosphorus (P2O5)||Potassium (K2O)||Total (NPK)|
|1970....................||31 911||21 286||17,564||70,761|
growth and development and, consequently, the general productivity of a field or meadow.
When correctly used, mineral fertilizers are the most efficient means of increasing crop yields and quality (technological properties of fiber plants; sugar content of beets, fruits, and berries; protein content of grain; oil content of sunflowers). The amount of mineral fertilizers applied per hectare (ha) of crops is one of the main indicators of the productivity of agriculture, particularly of its most important branch, crop cultivation.
Almost all mineral fertilizers are produced by the chemical industry. They are obtained by processing agronomic ores or by synthesis. Comparatively small quantities of industrial wastes and such natural salts as potassium and Chile saltpeter are used in agriculture.
There are direct and indirect mineral fertilizers. The first type, which contains plant nutrients (N, P, K, Mg, B, Cu, Mn), is subdivided into single and mixed fertilizers. Single fertilizers generally contain one nutrient; they include nitrogen fertilizers (ammonium, sodium, and calcium nitrates; ammonium sulfate; urea), phosphorus-supplying fertilizers (superphosphate, ground rock phosphate, dicalcium phosphate), potassium fertilizers (potassium chloride, 30 and 40 percent potassium salt, potassium sulfate), and micronutrient fertilizers. Mixed fertilizers (double and triple) contain two or more nutrients (nitrophos, ammophos, nitrophoska).
Indirect mineral fertilizers are used to improve the agrochemical and physiochemical properties of soil and to activate its nutrients (for example, lime fertilizers and gypsum). Some fertilizers are marked by both direct and indirect activity. For example, the application of basic slag or ground rock phosphate not only provides phosphorus for plants but also neutralizes soil acidity. Mineral fertilizers are solid (powdered or, more commonly, granulated) or liquid (aqueous ammonia, liquid ammonia, ammoniates).
According to their effect on the soil solution, mineral fertilizers are distinguished as being acid, alkaline, or neutral. In acid fertilizers the cations are absorbed by the soil; the anions, which are not absorbed as readily, acidify the soil solution. In alkaline fertilizers the anions are easily absorbed by the plants, while the cations gradually accumulate and alkalize the soil. Neutral fertilizers do not affect the soil solution.
Commercial mineral fertilizers have been widely used only since the 19th century. Until that time, manure, ash, feces, and natural fertilizers were used. In the first half of the 19th century, farmers began to use bone meal. In 1840 the German chemist J. von Liebig proposed treating bones with sulfuric acid to convert the main part, the poorly soluble tribasic calcium phosphate, into the water-soluble monobasic calcium phosphate readily assimilated by plants. This fertilizer, known as superphosphate, was soon produced by decomposing natural rock phosphate with sulfuric acid. By the end of the 19th century, the production and use of superphosphate were widespread in a number of countries. In Russia the first superphosphate plant was established in 1868 in Kovno (Kaunas). Experiments carried out by the Russian agricultural chemist A. N. Engel’gardt between 1860 and 1880 demonstrated the effectiveness of ground rock phosphate on acid podzols and helped to further the extraction and use of rock phosphate. In the 20th century the assortment of phosphorus-supplying fertilizers was substantially broadened.
Natural sodium nitrate, deposits of which were discovered in Chile, was first used as a fertilizer in the 1830’s. The production of nitrogen fertilizers increased after the industrial synthesis of ammonia from hydrogen and atmospheric nitrogen (1914—18) was developed. Potassium fertilizers were first used in the 1860’s, after the discovery of the Stassfurt potassium salt deposits in Germany. Potassium fertilizers came into wide use with the discovery of new deposits, including the world’s richest deposit, the Solikamsk in the USSR (1920’s).
Numerous Russian and Soviet scientists, including A. N. Engel’gardt, D. I. Mendeleev, P. A. Kostychev, K. A. Timiriazev, P. S. Kossovich, K. K. Gedroits, D. N. Prianishnikov, P. A. Baranov, S. I. Vol’fkovich, V. M. Klechkovskii, and A. V. Sokolov, made great contributions to the study of the role of mineral fertilizers in increasing crop production. Since the mid-20th century the manufacture and use of mineral fertilizers has increased rapidly throughout the world (see Table 1). In 1972 the major foreign producers were (in millions of tons of NPK [nitrogen-phosphorus-potassium]): United States, 16.4 (78 kg per capita); Federal Republic of Germany, 4.6 (78 kg); France, 4.7 (91 kg); German Democratic Republic, 3.3 (193 kg); Japan, 2.8 (26 kg); Poland, 1.9 (57 kg); Italy, 1.7 (32 kg); Great Britain, 1.3 (22 kg); Rumania, 1.2 (58 kg); Czechoslovakia, 0.8 (52 kg); Hungary, 0.6 (53 kg); and Bulgaria, 0.4 (51 kg). In 1971 the supply of mineral fertilizers per hectare of arable land was (in kg of NPK): United States, about 110; Federal Republic of Germany 350; France, 140; German Democratic Republic, 332; Japan, about 390; and Czechoslovakia, 254.
Mineral fertilizers are highly effective. Of the total increase in yield, 50 percent is considered to result from fertilizers, 25 percent from the quality of the variety, and 25 percent from the method of cultivation. Every kg of NPK fertilizers used in correct proportions produces an average of 10 kg of grain or the equivalent amount of other crops.
The mineral fertilizer industry in prerevolutionary Russia consisted of small superphosphate plants. Almost no potassium and nitrogen fertilizers were produced. In the USSR, large plants (Berezniki Nitrogen Fertilizer Plant, Novomoskovsk Chemical Combine, Voskresensk Chemical Combine) were built during the first five-year plans for the production of nitrogen and phosphorus
|Table 2. Production of mineral fertilizers in the USSR (thousands of tons)|
|Nitrogen (N)||Phosphorus (P2O5)||Potassium (K2O)||Total (NPK)|
|Table 3. Use of mineral fertilizers in the USSR|
|Nitrogen (N) (tons)||Phosphorus (P2O5) (tons)||Potassium (K2O) (tons)||Total (NPK) (tons)||NPK per 1 ha arable land (kg)|
|Notes: (1) In Russia in 1913, 0.21 kg of NPK was available per 1 ha of arable land. (2) In 1913, NPK production totaled 0.1 kg per capita, in 1940, 3.9 kg, and in 1972, 64 kg.|
fertilizers, and a potassium industry was established (Solikamsk Potassium Plant). At the end of the second five-year plan (1937), 703,000 tons of mineral fertilizers were produced; in 1913 this figure was 17,000 tons. In the years that followed, particularly after the Great Patriotic War (1941–45), the production of mineral fertilizers in the USSR and their use in agriculture increased steadily (see Tables 2 and 3).
In 1972 the USSR produced 66.1 million tons of standard mineral fertilizers (nitrogen fertilizers containing 20.5 percent N, phosphorus-supplying fertilizers containing 19.6 percent P2Os, and potassium fertilizers containing 41.6 percent KaO). The output was expected to increase substantially by 1975; most of the fertilizers were to be highly concentrated (double superphosphate, urea, potassium chloride) and mixed (ammophos, diammophos).
In the USSR mineral fertilizers are most widely used in the cotton-growing republics of Middle Asia and Transcaucasia, the tea-growing regions of Georgia, Azerbaijan, and Krasnodar Krai, and the beet-, flax-, and hemp-growing regions of the RSFSR and the Ukraine. Such irrigated agricultural regions as the Volga Region, the Northern Caucasus, the southern Ukraine, Middle Asia, and Kazakhstan, where rice and high-quality varieties of wheat are grown, are major users of mineral fertilizers. These fertilizers are being used increasingly in the cultivation of potatoes and other vegetables and on meadows and pastures.
The great variety of soil and climatic zones in the USSR is responsible for the differences in effectiveness of mineral fertilizers (increase in yield per kg of fertilizer or per ha). In the European USSR the effectiveness of fertilizers decreases from west to east and from north to south, and in Siberia from east to west. These variations are determined primarily by the amount and range of precipitation during the year. Mineral fertilizers are most effective in zones with soddy-podzolic, gray forest, and leached chernozem soils. Potassium fertilizers ensure the maximum yield on arid peaty and light, sandy soils. Mineral fertilizers, except phosphorus, are less effective on ordinary and southern chernozems and chestnut soils. Average increases in crop yields in the USSR from optimum amounts of mineral fertilizers are as follows (in centners per ha): grains (on soddy podzols and forest-steppe chernozems), 5–8; fiber flax (on soddy podzols), 1.5 (fiber); sugar beet (on chernozems), 40–70; potatoes (on soddy podzols and gray forest soils), 35–60.
The effectiveness of mineral fertilizers is increased by irrigation and the use of advanced cultivation technology. They are also most effective when combined with organic fertilizers and when applied at rates that take into account plant requirements and the properties of the soil and of the fertilizers themselves. The cultivation of varieties responsive to a particular fertilizer ensures an increase in crop yield. Mineral and organic fertilizers are used within a specific fertilizer system specifying their rate, range, frequency, and method of application. The choice of a given fertilizer system is based on an agrochemical analysis of the soil and results of field experiments. The average rates in the USSR (in kg/ha) are 30–100 N, 30–60 P2O5, and 45–90 K2O; higher rates are used for industrial crops (cotton, sugar beets) and vegetables (cucumbers, tomatoes). Mineral fertilizers are applied in the fall or spring (basic fertilization), at planting time (presowing fertilization), and during the growing season (supplementary feeding). Methods of application include broadcasting (by fertilizer distributors, from an airplane), working the fertilizers into the soil with a plow, cultivator, or harrow (the fertilizers are mixed with the plowed soil), and local application in drill rows or holes (fertilizer drill) during sowing and when bulbs or seedlings are planted. Mineral fertilizers are also used to treat seeds before they are sown (by spraying or soaking them in a solution).
Incorrect use of mineral fertilizers, for example, applying excessive amounts or uneven dressings, may reduce soil fertility, kill plants and animals, and pollute rivers and other bodies of water.
REFERENCESPrianishnikov, D. N. Ob udobrenii polei i sevooborotakh (collection of articles). Moscow, 1962.
Koren’kov, D. A. Mineral’nye udobreniia iikh ratsional’noe primenenie. Moscow, 1969.
Spravochnaia kniga po khimizatsii sel’skogo khoziaistva. Edited by V. M. Borisov. Moscow, 1969.
Avdonin, N. S. Nauchnye osnovy primeneniia udobrenii. Moscow, 1972.
I. I. SINIAGIN