Micronutrient Fertilizers

fertilizers that contain trace elements (such as boron, copper, manganese, zinc, and cobalt)—that is, substances that plants require in small quantities. They are distinguished according to trace element; there are also polymicronutrient fertilizers, which contain two or more trace elements. Salts of trace elements, industrial wastes (slag or slurry), frits (alloys of salts with glass), and chelates (compounds of organic substances with metals, such as zinc and copper) are used as micronutrient fertilizers.

The first experiments in Russia and abroad that showed the beneficial effect of micronutrient fertilizers on the growth and development of plants were performed in the second half of the 19th century. However, they were not studied in detail until after 1930, although a great deal of data had been collected earlier on their importance for increasing crop yields. Among the countries that have made extensive use of micronutrient fertilizers (mainly after 1940) are the USA, Great Britain, France, Sweden, the Federal Republic of Germany, the German Democratic Republic, Poland, Bulgaria, Italy, and Japan.

Soviet micronutrient fertilizersBORON. Boron fertilizers include boron-datolite (boron content, 2.0–2.5 percent), magnesium borate (1.5–2.0 percent), boron superphosphate (0.1–0.5 percent), boric acid (16–17 percent), and borax (11.3 percent). They are most effective on carbonate and sandy soddy podzolic soils, on soddy gley soils under sugar beets (for which they increase the tuber yields by 20–40 quintals per hectare [ha]), flax (yield increased by 1–2 quintals per ha), clover, alfalfa, buckwheat, sunflower, legumes, vegetables, and fruits. They improve the quality of produce (increasing the sugar content of beets, the fiber yield of flax, and the oil content of seeds) and are a means of controlling plant diseases, such as beet rot and flax bacteriosis, that result from a boron deficiency.

COPPER. Copper fertilizers are used in the form of pyrite cinders (copper content, 0.3–0.5 percent) and copper sulfate (about 23 percent), mainly on peaty and sandy soddy podzolic soils under grains (wheat, barley, and oats; increased grain yields of 2–3 quintals per ha), vegetables, flax, and legumes. They accelerate the ripening of crops and improve their quality, increase the quantities of sugars and vitamins that accumulate in vegetables, and make flax fibers finer and stronger.

MANGANESE. Manganese fertilizers include manganese superphosphate (2–3 percent MnO), a preparation containing manganese (3.5–4.5 percent MnO), manganese slurry (12–22 percent MnO), open-hearth slag (3.2–17.6 percent MnO), and manganese frits (7–21 percent MnO). They are used mainly on chernozem, soddy carbonate, and gray forest soils. They increase the yields of grains, vegetables, berries, and sugar beets by approximately 8–10 percent.

ZINC. Zinc fertilizers include zinc sulfate (zinc content, about 25 percent), slag (2–7 percent), zinc slurry, wastes from copper smelters, and zinc chelates and frits. They are effective on carbonate and calcareous soils with a neutral or alkaline reaction of the soil solution. They increase yields and improve the quality of sugar beets, beans, peas, flax, and oats and eliminate plant diseases caused by a zinc deficiency in the soil—for example, resetting of leaves and top drying.

MOLYBDENUM. Molybdenum fertilizers include powder containing molybdenum (a mixture of ammonium tnolybdate and a filler, with at least 10 percent molybdenum), ammonium-sodium molybdate (at least 36 percent), and molybdenum superphosphate (0.05–0.1 percent). They are used on acid soddy podzolic and gray forest soils and leached chernozems for legumes (clover and alfalfa) and cereals and legumes (peas, vetch, and beans). They increase hay and grain yields by 20–25 and 15–20 percent, respectively, and the amount of protein and carotene in the produce is increased.

COBALT. Cobalt sulfate is effective when used under legumes on soddy podzolic soils, particularly of the sandy type, and on boggy soils. It greatly increases yields and stimulates the fixation of atmospheric nitrogen by rhizobia (nodule bacteria). The use of micronutrient fertilizers containing vanadium, iodine, and other trace elements is now under study.

The requirement of crops for micronutrient fertilizers is determined by their biological characteristics and quantity of available trace elements present. The fertilizers are usually applied to the sow rows before sowing, together with the seeds and macronutrient fertilizers, or in the form of top dressing (a 0.01–0.05 percent solution of the micronutrient is sprayed on the crops). They may also be used to treat the seeds before they are sown (the seeds are soaked in a 0.02–0.05 percent solution). They are applied at the rate of 0.5–5.0 kg of trace element per ha.