Fertility, Soil

the capacity of soil to provide plants with enough assimilable nutrients and moisture to produce crops.

A distinction is made between natural and actual soil fertility. The former is determined by the nutrients and moisture present in the soil and by other environmental conditions. Actual soil fertility is the amount of nutrients and moisture derived from the soil by the plants in a given year. It depends primarily on the farming practices used. High natural fertility does not ensure high actual fertility, and high actual fertility does not necessarily mean that the soil has high natural fertility. With good farming practices it is possible to make unproductive soils highly fertile.

Actual fertility is a very dynamic property of soil, one that can change rapidly under the influence of natural conditions and farming practices. The most important factors affecting soil fertility include the presence of the right quantities and forms of essential nutrients; the availability of moisture and the stability of its level; good aeration, which is important for the development of the root system and for the life processes of microorganisms that break down organic matter and store nutrients in a form available to higher plants; texture and structure; the presence of toxic substances; and the pH. The sum of these properties determines the cultivability of the soil.

All the elements of soil fertility are interrelated. Soil fertility depends on such factors affecting soil formation as climate, parent material, natural and cultivated plants, and topography. The way in which soil is used is particularly important. The principal means of regulating the nutrient supply, especially in mobile forms available to plants, is the addition of mineral and organic fertilizers. The introduction of legumes into crop rotations and the improvement of conditions promoting the activity of nitric bacteria and other organisms that take up nitrogen from the atmosphere are also important. Excessive acidity is corrected by liming, and excessive alkalinity (solonetzes) by the application of gypsum.

An important prerequisite of soil fertility is the absence of excessive quantities of readily soluble salts, chiefly sodium chloride, sodium sulfate, magnesium, calcium, and other cations. An excess of salts is corrected by flushing the soil. The accumulation of salts can be prevented through proper irrigation practices and drainage.

Soil fertility is markedly decreased by the presence of such toxic chemical compounds as ferrous oxide and mobile aluminum compounds, which usually accumulate in waterlogged soils. The moisture supply can be controlled by farming practices and hydraulic-engineering measures (late fall plowing, snow retention, early spring harrowing, interrow cultivation, irrigation, drainage). Soils with good aeration and adequate moisture are the most fertile. Low fertility is often due to pathogenic organisms. Their removal by chemical agents (sterilization, application of fungicides or nematocides) and by farming procedures (crop rotation, cultivation) increases soil fertility sharply. Correct use of soils not only prevents a decrease in their fertility but yields a steady increase.

The history of agriculture, with the increase in crop yields and productivity of livestock raising, refutes bourgeois Malthusian and neo-Malthusian theories concerning the law of diminishing soil fertility. The Marxist-Leninist classical writers revealed the lack of scientific substantiation of this law and showed that soil fertility changes constantly under the influence of both natural and socioeconomic conditions. The latter conditions are responsible, in turn, for scientific and technological advances and for their application to agriculture.