Potassium Fertilizers

inorganic substances used as a source of potassium nutrition for plants; usually salts of hydrochloric, sulfuric, and carbonic acids dissolved in water—often combined with other compounds containing potassium—in a form accessible to plants.

Natural deposits of potassium salts are the primary source of potassium fertilizers. The first major deposit was discovered in Stassfurt in the 1840’s. In subsequent years industry began to produce potassium chloride, potassium nitrate, and potassium sulfate. Deposits of potassium salts were discovered in France, Canada, and the United States. By 1913 world production of potassium fertilizers was 1.19 million tons (in terms of K₂O); in 1967, 14.7 million tons; and in 1970, 19 million tons. There were no known deposits of potassium salts in prerevolutionary Russia, and potassium fertilizers were not produced. preparation of potassium chloride. Potassium chloride is used as a potassium fertilizer and as a raw material for the preparation of other potassium salts and potassium hydroxide.

The creation of the potassium industry in the USSR began in 1929, after the discovery (in 1925) of potassium deposits in the Northern Urals (Solikamsk and Berezniki). In 1931 the country’s agriculture received 210, 000 tons of potassium fertilizers (in terms of K₂O); in 1940, 219, 000; in 1960, 766, 000; in 1965, 1, 891,000; in 1967, 2, 136, 000; in 1968, 2, 210, 000; and in 1971, 2, 804, 000 (that is, 12.7 kg of K₂O per hectare of arable land).

Potassium fertilizers are divided into raw potassium salts, which are produced by mechanical processing (sorting, crushing, and pulverization) of natural potassium salts, and concentrated, or high-analysis, potassium fertilizers, such as potassium chloride, potassium sulfate, and 30-percent and 40-percent potassium salts (a mixture of finely ground natural kainite or sylvinite with potassium chloride), as well as potash, potassium-magnesium sulfate, potassium electrolyte, and ash. A description of the main potassium fertilizers is given in Table 1.

Potassium fertilizers are usually used against a background of phosphorus or nitrogen and phosphorus fertilizers. The greatest gains in yield are achieved on soils that are poor in free potassium: peaty, floodplain, sandy-loam, and light loamy soddypodzolic soils. Plants growing on gray forest loams, podzolized and leached-out chernozems, and terra rossa in the humid subtropics, where there is extensive cultivation of tea plants and citrus crops, also need potassium fertilizers. Plants that require large quantities of potassium, such as potatoes, vegetables, sugar beets, fodder root crops, tobacco, and rustic tobacco, are most responsive to it. Although flax and hemp absorb a small amount of potassium from the soil, they assimilate it poorly; therefore, their cultivation involves the application of potassium fertilizers. Under soil conditions in the nonchernozem zone of the European part of the USSR, legumes, perennial leguminous grasses, corn, winter grain crops, buckwheat, and fruit and berry plantings respond well to potassium fertilizers.

Potassium has a positive effect on the quality of products: there is an increase in the sugar content of root crops, the starch content of potatoes, the production and quality of fiber in textile crops, and the protein content in feed plants, particularly against a background of nitrogen-ammonia fertilizers. In addition, potassium fertilizers strengthen plant resistance to certain fungus diseases and increase the cold and drought resistance of winter grains, leguminous grasses, and perennial plantings.

The effectiveness of potassium fertilizers depends on their content of accompanying elements, such as sodium and chlorine. For example, in potatoes, tobacco, grapes, lupines, and other crops that are sensitive to chlorine, the quality of the harvest is usually improved merely by application of potassium nitrate or potassium carbonate. Sugar beets and certain other plants respond favorably to the sodium in raw and mixed potassium salts. Therefore, in the primary zones of sugar beet planting, sylvinite (which contains sodium in addition to potassium) produces a considerable gain in root yield and increases the sugar content much more than does pure potassium chloride. Raw potassium salts are undesirable for grapes, buckwheat, tobacco, beans, and potatoes. If these crops are fertilized with potassium chloride it is applied only during fall plowing so that there will be time for the chlorine that is not absorbed by the soil to be leached out of the tilled layer to a significant degree during the fall and early spring. The use of potassium-magnesium sulfate, potassium sulfates, potassium nitrates, and furnace ash for these crops is even better. The use of potassium fertilizers (ideally, together with phosphorus fertilizers) increases the productivity of meadows and improves hay quality.

The dosages of potassium fertilizers depend primarily on soil conditions, the physiological characteristics of the crop being fertilized, and the properties of the fertilizers. On soddy-podzolic soils the dosage of K₂O is 30–60 kilograms per hectare (kg/ha), and for hemp the dosage is increased to 120; on gray forest soils and chernozems, 30–60 and 30–45 kg/ha, respectively (for hemp, up to 90 kg/ha); on terra rossa and sierozems, 30–60 kg/ha. Potassium fertilizers are usually used as the primary fertilizer for fall or spring plowing or cultivation. Top-dressing of plants with potassium (if an insufficient quantity was applied during plowing) has become common in the cultivation of sugar beets, potatoes, corn, and certain vegetable crops. In this case it is better to use potassium fertilizers together with nitrogen and phosphorus fertilizers, applying them in the in terrow spaces with plant feeders at a depth of at least 10–12 cm (calculating 20–30 kg of K₂O per hectare). Shallow placement of potassium fertilizers in the soil during top-dressing of plants does not produce favorable results. Therefore, the use of potassium for top-dressing of solidly planted crops (grains, legumes, and grasses) is not advisable. Each centner of K₂O applied in the form of potassium fertilizer provides the following average gains in yield (in centners): raw cotton, 1–2; sugar beets, 35–40; potatoes, 20–33; flax fiber, about 1.5; winter grains, 3–5; spring crops, 2–3; hay from sown grasses, 20–33; meadow hay, 8–18. The aftereffect of potassium fertilizers lasts three to four years.