One of the biggest issues facing agriculture is the problem of soil degradation due to an increased demand for agricultural products. The issue is important because during prolonged use in agriculture, especially with its low agronomic culture, the physical properties of soils, such as density, porosity, structural state, and water permeability, deteriorate. At the same time, there is a deterioration in the closely related water properties of soils, on which the moisture regime, moisture balance, air regime, moisture-supplying ability, and ultimately fertility, depend. The most informative indicators of purely hydrological degradation of soils are a decrease in the total moisture capacity of the soil and a reduction in the lowest moisture capacity of the soil, which characterizes the retention of moisture in the soil after draining its excess and its optimal content. Also included is an increase in soil moisture at which plants wilt, that is, an indicator of soil drought and a decrease in the range of active humidity. The corresponding parameters of virgin soil under natural soil degradation are taken as the norm.
A sign of soil degradation is not only a negative change in the magnitude of the above indicators but also the duration of their presence in the soil. Thus, long-term existence at humidity corresponding to moisture capacity worsens the air regime of the soil and the use of moisture by plants. A decrease in the soil residence time at a moisture content corresponding to the minimum moisture capacity, and an increase in the duration of soil existence when plants wither, indicate a deterioration in the moisture-supplying ability, moisture regime, moisture supply and crop productivity (Samaniego et al., 2018). The issue is also important because low agronomic farming culture, which does not provide replenishment of stocks of organic and mineral elements of soil nutrition, which are alienated when harvesting crops, observing optimal terms for agricultural work, as well as the use of heavy agricultural machinery, lead to soil degradation and impaired fertility.
When plowing soils, hydrological degradation is caused by changes in the ecosystem in which the soil is formed. The destruction of natural vegetation causes a change in the temperature regime of the soil, moisture conditions, and even water conditions. Compared to natural soil degradation, the open surface of the arable land holds less snow, the soil freezes earlier, is more susceptible to the formation of ice crusts and interlayers during thaws that impede the absorption of melt water, and the unproductive surface runoff of the latter. As a result, arable land is not sufficiently recharged during spring snowmelt. This is also facilitated by the fact that, in contrast to the lands of natural soil degradation, arable land leaves in winter with a surface layer moistened with autumn rainfall, poorly absorbing melt water coming in spring.
Absorption of the latter is impeded by the thawing frozen layers remaining in the soil stratum since the melting of snow on the arable land usually begins before it is completely thawed. Non-thawed layers serve as water resistance and cause surface run-off of melt water and soil erosion (Gomiero, 2016). Under crops, soil moisture is used faster and more intensively than under natural vegetation, including due to the participation of physical evaporation in its consumption, especially before the development of crops and after harvesting as a result of all of the above soil on arable land than under natural vegetation. The ecological functions of soils, due to their chemical and physicochemical properties, provide the absorption capacity of soils such as sorption of mineral and organic substances, microorganisms. This also includes the destruction and mineralization of organic residues, the re-synthesis of mineral and organic substances such as humus and enzymes, the return of nutrients in an accessible form to plant roots.
Such saturation of the soil with life is explained by the heterogeneous structural organization of the soil as a natural body, which at the same time consists of a solid, liquid, and gas phase of substances, is a polydisperse loose mass consisting of mineral, organic and organo-mineral components. All this creates an exceptional variety of environmental conditions for the life of organisms living in the soil. It should be noted that each type of organisms and type of soil is characterized by well-defined and specific species and communities of plants, animals, and microorganisms. The reason why the given issue is important is the fact that most important ecological function of soils is their role as a connecting geochemical link in the biological and geological cycles of substances in terrestrial ecosystems. As a result of selective sorption by plants and soil biota of biophilic elements in the soil, they accumulate and are kept from being carried out into the ocean by land denudation processes (Yang, Wagg, Veresoglou, Hempel, & Rillig, 2018). There is a large number of biophilic elements held in soils in the overall balance of the biological and geological cycles of matter between land and ocean.
In conclusion, biochemical processes in soils have no less influence on the composition of surface and even higher layers of atmospheric air. Soil respiration is a powerful factor in the composition of atmospheric air, including the content of carbon dioxide, methane, nitrous oxide, and other greenhouse gases (Carey et al., 2016). The effect of biochemical soil processes on the soil degradation of the upper layers of the lithosphere becomes more and more obvious. Continental weathering crusts are now considered not only as parent rocks of soils but also as a direct result of the influence of soil-forming processes on the underlying soil layers of rocks.
References
Carey, J. C., Tang, J., Templer, P. H., Kroeger, K. D., Crowther, T. W., Burton, A. J., … Tietema, A. (2016). Temperature response of soil respiration largely unaltered with experimental warming. Proceedings of the National Academy of Sciences of the United States of America, 113(48), 13797-13802.
Gomiero, T. (2016). Soil degradation, land scarcity and food security: Reviewing a complex challenge. Sustainability, 8(3), 1-41.
Samaniego, L., Thober, S., Kumar, R., Wanders, N., Rakovec, O., Pan, M., … Marx, A. (2018). Anthropogenic warming exacerbates European soil moisture droughts. Nature Climate Change, 8, 421-426.
Yang, G., Wagg, C., Veresoglou, S. D., Hempel, S., & Rillig, M. C. (2018). How soil biota drive ecosystem stability. Trends in Plant Science, 23(12), 1057-1067.