The influence of degradation processes on enzymatic activity and the content of forms of mineral nitrogen in agricultural soils

The purpose of the work was to study the concentration of various forms of mineral nitrogen and nitrogen cycle enzymes in farmland soils. The objectives of the research included studying the content of ammonium and nitrate forms of nitrogen, as well as the activity of urease and nitrate reductase in soils of farmland on the territory of the Donetsk People's Republic (DPR). To study the soils of agricultural lands, model sites located in the southern part of the Shakhtersky district of the DPR were selected and represented by moderately washed-out chernozems with low, low and medium humus. The control was an area with steppe vegetation (ordinary chernozem, thick, with medium humus content). The results of the researches allow us to draw conclusions about the development of degradation processes in a number of model sites and their impact on the content of ammonium and nitrate nitrogen in agricultural soils. Growing crops removing substantial amount of mineral nutrients, the slope of the sites surface, and the duration of cultivation of grain crops in the same sites lead to a significant decrease in the concentration of ammonium and nitrate nitrogen. Thus, the most significant decrease in the concentration of nitrogen of ammonium compounds (by 77–82%) was recorded in model slope areas under maize and sunflower. Analysis of the data showed that exchange ammonium is confined to the underlying genetic horizons. The minimum concentration of nitrates in the arable horizon was recorded under the joint influence of such unfavorable factors as: unreasonable layout of fields along the relief elements; violation of crop rotation conditions; use of precursor crops with a significant level of removal of nutrients (wheat, maize). When studying the activity of urease, it was found that a low number of soil microorganisms associated with the cultivation of maize and sunflower, as well as with the development of degradation processes of various genesis, led to the suppression of the functioning of the urease of soils in model areas. The maximum urease activity was observed in areas under winter wheat and amounted to 68–72% in relation to the control indicators. As a result of studies of nitrate reductase activity, a decrease in its values was also found in areas used to grow crops that form a large phytomass (maize and sunflower).