In the field stationary experiment, the dynamics of the general biological activity of chernozem, depending on the biomass of plant residues, maximum saturation with sunflower, methods of the basic soil tillage under different hydrothermal conditions was studied. The issue of arable layer differentiation at different methods of the basic soil tillage in the crop rotation on fertility and biological activity and dynamics of these parameters depending on the intensity of mechanical action on the soil and the cycle of organic matter is a very important aspect for the theoretical study of innovative soil protecting technologies of growing of field crops. The research was carried out at the State Enterprise "Experimental Farm of Dnipro" of the State Institution of the Institute of Grain Cultures of the National Academy of Sciences of Ukraine in the stationary field experiment of laboratory of the crop rotation and environmental protection systems of soil tillage in five-year crop rotation: peas - winter wheat - sunflower - barley spring - corn according to generally accepted techniques of experimental work, during 2010-2019. The soil of the experimental site is common chernozem heavy-clayey loam with content in the arable layer: humus – 4.2%, nitrate nitrogen – 13.2 mg / kg, mobile phosphorus and potassium compounds, respectively 145 and 115 mg / kg. According to the results of the research, the minimization of soil tillage causes the significant changes in the differentiation of the arable layer (0-30 cm) relative to the positional disposition of nutrients, the concentration of potential humus substances in the aerobic zone and the intensification of microbiological activity, as evidenced by the volumes of carbon dioxide releases. The largest organic mass in crop rotation naturally left itself corn, and the minimum - barley spring and sunflower. Substantial redistribution of the projective coverage of the surface of the field with plant residues and their mixing with the soil in the profile of the arable layer was carried out by various methods and systems of basic soil tillage. For example, after harvesting of corn and carrying out of soil tillage on the surface of the field, the minimum number of plant residues remains for the moldboard soil tillage system - 0.61 t/ha. The intermediate position was occupied by the differentiated (discing) cultivation system – 3.12 t/ha, and the maximum amount of vegetative substrate was logically marked for zero soil tillage – 4.34 t/ha. The intensity of the decomposition of organic matter in the soil is a heterogeneous process, which primarily depends on the determining factors - moisture, temperature and aeration level of the treated layer of chernozem. The intensity of the processes of breathing of soil microorganisms makes it possible to estimate the total biological activity of the soil, which is based on the amount of carbon dioxide released, depending on the different methods of soil tillage per unit area of the field surface. As our studies have shown, the biological activity of the soil depended on the phases of development of plants of field crops and had a sufficiently wide amplitude of variation. Thus, as an example of the mouldboard plowing, it is evident that insufficient soil warming at normal humidification at the time of corn sowing has led to the decrease in biological activity to 35.0 mg CO2/kg of soil/day. The maximum intensity of soil respiration (49.2 mg СО2 /kg of soil /day) occurred at 30 days after sunflower sowing, when the optimal combination of temperature and humidity of the soil was noted. Similar regularities and tendencies in the release of СО2 from the soil during certain phases of sunflower development are also noted for differentiated and zero cultivation systems, but with somewhat lower overall CO2 release, respectively, by 0.3-5.3 mg СО2/kg ha/day (10-12%) and 5.5-7.2 mg СО2/kg ha/day (12-22%) compared to the mouldboard soil tillage system. Generally, this tendency took place both in the maximum and at the minimum amplitude of the activity of respiration processes, that is, the indicators of the general biological activity of the soil were higher in the background of plowing and prevailed other systems of mechanical cultivation of chernozem (differentiated, zero system). Thus, the biological activity of the soil is the derived indicator, which depends on the features of the technology of growing of cultures in the crop rotations, the presence of organic matter of plant residues in the chernozem, the level of compaction of arable layer and the methods of basic soil tillage. The use of deep plowing due to the creation of favorable conditions for the expansion of the root system of crops with sufficient aeration and moisture absorbtion properties provides maximum biological activity under all crops of crop rotation, decomposition of residues and intensive mineralization processes. However, methods of unploughed treatment of the soil contributed to increasing the antierosion stability of the surface of chernozem from the shock energy of rain drops, as well as providing more favorable conditions for the humification of organic residues instead of undesirable intensive mineralization.
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