Organic Fertilizers

fertilizers containing nutrients in the form of organic compounds of plant or animal origin. Organic fertilizers have varied agronomic effects on soil properties. When they decompose as a result of the vital activity of soil microorganisms, they form humus and compounds of nitrogen, phosphorus, potassium, calcium, sulfur, and other elements that are accessible to plants. The carbon dioxide given off during decomposition fills the soil air and the ground layer of the atmosphere, improving the carbon nutrition of plants. Systematic application of organic fertilizers improves the physicochemical and chemical properties and the water and air conditions of the soil and stimulates the vital activity of useful microorganisms, such as nitrogen-fixing bacteria and ammonia producers. Organic fertilizers serve mainly to implement the soil-plants-animals-soil cycle of nutrients. The use of organic fertilizers makes possible the application of mineral (inorganic) fertilizers in large quantities and high crop yields.

Organic fertilizers include most indigenous fertilizers (manure, liquid manure, peat, compost, and poultry manure), green manure, urban wastes (garbage and garbage composts, sludge, and fecal matter), wastes from the food and tanning industries, sapropel (silt), straw, and guano. The nutrient content of the most common organic fertilizers is given in Table 1.

Organic fertilizers have been known since the beginning of farming. They were used in China, Korea, and Japan 3,000 years ago. In the 13th and 14th centuries, manure was already in use in the countries of Western Europe and in what is now the European part of the USSR; green manure has been used in Middle Asia since ancient times. In the second half of the 20th century, annual world consumption of organic fertilizers was 3–4 billion tons, which corresponds to 15–20 million tons of nitrogen, 3–4 million tons of P₂O5, and 18–24 million tons of K₂O. In the USSR, 360 million tons of organic fertilizer was applied to the fields in 1965, 468 million tons in 1970, and more than 500 million tons in 1973.

Organic fertilizer is applied during plowing (sometimes during cultivation), placed in seed furrows during planting of such crops as potatoes and cabbage, or applied as top dressing. It is also used as a fuel, for making soil mixtures and mixtures with mineral fertilizers, and for mulching planted areas. The amounts of organic fertilizer applied range from 15 to 60 tons per hectare (ha), or up to 80–100 tons per ha for vegetables and hemp, and 5—10 tons per ha for application in furrows. The amounts applied in combination with mineral fertilizers are much lower.

Organic fertilizers are most effective on soddy-podzol soils. The gain in yield, in quintals per hectare, is 50–60 for potatoes, 30 for sugar beets, 60–100 for vegetables, and 6–7 for cereal crops.