Fertilizers replenish stocks of nutrients in the soil in an accessible form and supply them with plants. At the same time, they have a great influence on the properties of the soil and thereby affect the yield also indirectly. Increasing the yield of plants and the mass of roots, fertilizers enhance the positive effect of plants on the soil, contribute to the increase in its humus, improve its chemical, water-air and biological properties. Organic fertilizers (manure, composts, green manure) have a great direct positive effect on all these soil properties.
Acid mineral fertilizers, if they are systematically applied without organic fertilizers (and on acidic soils without lime), can have a negative effect on the properties of the soil (Table 123). Prolonged use of them on acidic, unrecognized soils leads to a decrease in soil saturation with bases, increases the content of toxic aluminum compounds and toxic microorganisms, degrades the water-physical properties of the soil, increases the bulk weight (density), reduces soil porosity, aeration and water permeability. As a result of the deterioration of the soil properties, the yield increase from fertilizers is reduced, the “negative effect” of acid fertilizers on the crop is manifested.
The negative effect of acidic mineral fertilizers on the properties of acidic soils is associated not only with the free acidity of fertilizers, but also with the effect of their bases on the absorbing complex of the soil. Displacing exchangeable hydrogen and aluminum, they convert the exchangeable acidity of the soil into an active one and at the same time strongly acidify the soil solution, dispersing the colloids fastening the structure and reducing its strength. Therefore, when applying large doses of mineral fertilizers, it is necessary to take into account not only the acidity of the fertilizers themselves, but also the magnitude of the exchangeable acidity of the soil.
Lime neutralizes the acidity of the soil, improves its agrochemical properties and eliminates the negative effect of acid mineral fertilizers. Even small doses of lime (from 0.5 to 2 t / ha) increase soil saturation with bases, lower acidity and drastically reduce the amount of toxic aluminum, which in acidic podzolic soils has an extremely strong negative effect on the growth and yield of plants.
In long-term experiments with the use of acidic mineral fertilizers on chernozem, there is also a slight increase in soil acidity and a decrease in the amount of exchangeable bases (Table 124), which can be eliminated by adding small amounts of lime.
Organic fertilizers have a great and always positive effect on all soils. Under the influence of organic fertilizers - manure, peat composts, green manures - the content of humus increases, soil saturation with bases increases, including calcium, the biological and physical properties of the soil (porosity, moisture capacity, water permeability) improve, and acidity and content decrease in soils with acid reaction. toxic aluminum compounds and toxic microorganisms. However, a significant increase in the content of humus in the soil and the improvement of its physical properties are observed only with systematic introduction of large doses of organic fertilizers. A single application in acidic soil together with lime improves the qualitative group composition of humus, but does not lead to a noticeable increase in its percentage in the soil. Similarly, peat introduced into the soil without composting does not have a noticeable positive effect on the properties of the soil. Its effect on the soil increases dramatically if it is pre-composted with manure, slurry, faeces or mineral fertilizers, especially alkaline, as the peat itself decomposes very slowly and in acidic soils forms many highly dispersed fulvic acids supporting the acidic reaction of the medium.
A large positive effect on the soil has a joint application of organic fertilizers with mineral. At the same time, the number and activity of nitrifying bacteria and bacteria fixing atmospheric nitrogen — oligonitrophils, free-living nitrogen fixers, etc. — especially increase. In acidic podzolic soils, the number of microorganisms on the Aristovskaya environment decreases, which, in her opinion, produce a large number of strong acids, podzolizing soil.