Abstract
The continuous agronomic experiment revealed long-term dynamics of the total humus content and presented a forecast of the change in humus content in typical low humus chernozem under different technologies of till- age till 2050. Aim. To determine the rates of humus accumulation dynamics and mineralization of total humus and to develop the forecast of the change in its content within a continuous agronomic experiment under long- standing application of different technologies of soil tillage to typical low humus chernozem of the Left-Bank Forest-Steppe of Ukraine. Methods. Field, laboratory-analytical, mathematical and statistical. Results. The application of different technologies of tillage to typical low humus chernozem for 42 years resulted only in the delay in dehumifi cation processes and some stabilization of humus mineralization, but it did not promote its preservation and extended restoration to the initial level as of the start of the experiment. The increase in the total humus content for simple and extended restoration of humus in the centennial cycle equaled 20–25 t and 30–33 t per 1 ha respectively. To ensure the increase in content and reserves of humus for 42 years, it is necessary to introduce 10–12 t of humus per 1 ha for simple restoration of total humus content and 14–15 t per 1 ha – for extended restoration annually. Conclusions. Simple restoration of humus in typical chernozem may be stated after achieving its actual (2017) content of at least 90 % from the content as of the beginning of the centennial cycle (92 years), which ensures maximal approximation to the non-decreasing cycle of humus dynamics trends in the centennial cycle. If the humus content is ensured in the actual measurement for the level, exceeding 90 % from the initial content, and dynamics trends are growing, one may state the success of achieving the state of extended restoration of humus. The obtained state of simple and extended accumulation of humus is ensured by the positivity of the trends of humus increase during the continuous experiment (42 years) with simultaneous decrease in dehumifi cation process in the centennial cycle (92 years) which is impos- sible to neutralize completely.
Highlights
Humus content is the most important index of fertility and agroecological state of chernozems
Under the impact of the increasing economic activity of humans involving the use of chernozems, there is a stage in the centennial cycle when its development is directed towards mitigating elementary processes of soil formation, which is related to the development of the processes of dehumi¿cation and agrophysical degradation, and, as a result, the decrease in the level of natural and ef¿cient fertility of chernozems in the conditions of natural-anthropogenic soil formation
Under longterm subsurface tillage, the reserves of detritus in the humus horizon were 1.16–1.4 times higher compared to the long-term ploughing, and the most considerable accumulation of detritus took place in the 0–20 cm soil layer, where the total reserves of detritus increased up to 35–38 % from the reserves of the total humus, which is con¿rmed by the data of other researchers, proving that the content of detritus in the total humus is from 35 % to 40 %, and exceeds 40 % in the virgin analogues of chernozems [26]
Summary
Humus content is the most important index of fertility and agroecological state of chernozems. Numerous studies demonstrate active manifestation of dehumi¿cation during the tillage of chernozems and their further usage in agriculture [15]. The application of fertilizers and different systems of tillage and crop rotations is a powerful factor, impacting the parameters of the humus state of chernozems and the implementation of their potential fertility via its effective form [15, 16]. The fertilizers satisfy the needs related to the decrease in humus reserves [13] and humus balance in chernozems while cultivating some crops only by 50–60 %. Modern studies of humus content dynamics are related to solving rather complicated methodological problems [17], caused, ¿rst of all, by the spectrum of chernozem humus, which changes the actual picture of humus dynamics considerably. The most signi¿cant way of solving these issues is a continuous agronomic experiment – the most realistic way of studying the processes of accumulation and mineralization of humus, forecasting the dynamics for the nearest perspective and working out the agrotechnical technologies of regulating it in chernozems
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