ИСТИНА

Climate change in Russia will lead to an increase in the SOM content in general. This scenario is associated with the intensification of peat formation in shallow peat bog soils in the north and an increase in the accumulation of humus in soils in the south. However, climate aridization and expansion of arctic and subtropical deserts appear to be the most unfavorable scenarios for climate change. In the case of expansion of arid territories, a significant degradation of soil organic matter will occur. Currently, this scenario remains unexplored. The most massive cropland abandonment was caused by the farming system collapse in the former Soviet Union in the early 1990s when about 59 million ha of former arable lands withdrawn from agricultural use. It was the largest land use change of the 20th century in the northern Hemisphere. The withdrawal of land area from cultivation led to substantial carbon sequestration in former arable soils and can mitigate the current climate changes. A small positive carbon balance occurs in the arable soil horizons with a net negative carbon balance in arable soils in general. This feature is determined by the stabilization of agricultural production and, accordingly, by the stabilization of the influx of root detritus. The carbon balance of pasture soils is negative, which is due to insufficient attention to pasture management, overgrazing, etc. The average C sequestration rate in the upper 20 cm of mineral soil was 0.96 t C per ha per year for the first 20 years after abandonment and it was 5 times higher than over next 30 years.