Contemporary Trend in Erosion of Arable Ordinary Chernozems (Haplic Chernozems (Pachic)) within the Volga Upland (Saratov Oblast, Russia)

The current trend in erosion rate of ordinary chernozems in Saratov oblast has been assessed. Detailed studies have been performed in a small catchment area of the Bolshoi Kolyshley River (Medveditsa River basin) using the radiocesium and soil-morphological methods. Data of long-term hydrometeorological observations in the region, reported results of observations of water runoff and soil loss on the runoff plots of the South-Eastern Research Institute of Agriculture (Saratov oblast), results of analysis of the grain size and mineral composition of stratozems developed on the catchment valley bottom were also used for analysis. The quantification of sedimentation rate in the valley bottom during two time windows (1963–1986 and 1986–2017) based on the sediment dating using ¹³⁷Cs as a chronomarker indicates their decrease at least in 4–6 times after 1986, which points to a proportional reduction in erosion rate on the plowed slopes of the catchment area. The analysis of the temporal variability of suspended yields in the regional rivers (Medveditsa and Khopyor) during the period from 1940 to the present time allows us to draw an analogous conclusion for the Volga Upland within Saratov oblast. The decrease in the erosion rate of ordinary chernozems could be mainly caused by the reduction in water runoff from slopes during the spring snowmelt because of reduction in soil freezing depth against the background of rising air temperature in winter and spring. This decrease in erosion rate during the snowmelt period was not balanced by the regional increase in rainfall erosion related to some increase in the rate of runoff-forming rainfalls. In the part of Saratov oblast, located within the Volga Upland, where the studied catchment is situated, on the contrary, even a reduction in the frequency of rains with a rainfall depth of more than 30 mm occurred over the last decades. The reduction in the cultivated land area since the late 1980s because of the abandonment of plowlands on the steepest slopes also contributed to the decrease in total soil loss by erosion at the river basin scale. Within the studied small catchment, the share of perennial grasses in crop rotations increased after 1986, which also led to reduction of the rate of erosion of ordinary chernozems.