Evolution of Chernozems in the southern forest-steppe of the Central Russian upland under long-term cultivation examined in the agro-chronosequences

Chernozems are the major component of soil cover in the forest-steppe of the Central Russian Upland. They underwent the most significant anthropogenic transformation in terms of duration and scale of development in profiles, due to ploughing. Despite the long list of experimental works, the obtained conclusions are often contradictory. From our point of view, the best way to observe the effect of ploughing on Chernozems is the examination of soils with different durations of cultivation based on an agrochronosequence approach which was used in this study.The most appreciable changes occurred in the arable Chernozems for the first period after the beginning of cultivation. In the soils with 16 and <100 years duration of cultivation, the following changes are observed: 5–7 to 9 cm decreasing of the humus profile, compacting of the plough-layer and its initial enrichment by clay, 15–30% decreasing of the soil organic carbon (SOC) content and stocks in the 0–30 and 0–50 cm depths, about 40 cm uplift of carbonate accumulation, and increasing of soil inorganic carbon (SIC) content and stocks in the 0–100 and 0–200 cm depths. These changes occurred due to abrupt decreasing of the plant residues in agriculture, influence of machinery treatment resulting in destruction of the plough-layer structure and this layer compaction, and changes of water regime. In the arable soils with 100–150 and 150–200 years of cultivation, the further compaction of soil mass, loss of SOC and uplifting of carbonates are not observed. There is backfilling of the SOC along the cracks in the middle part of a profile, high activity of burrowing animals, and continuing redistribution of clay fraction in the deeper horizons. These processes resulted in stabilization of SOC stocks in the profile of the arable soils on the “new” reduced level and shifting of carbonates back to the initial (before cultivation) or even lower level of location, concentrations, and stocks in a profile. After 220–240 years of cultivation, high instability of the studied indicators of the humus and carbonate status can be emphasized. Relatively rapid changes occur in Chernozem properties after the beginning of ploughing, with subsequent slowing. The activity of burrowing animals introduces an ambiguity in the trends of development of the long-ploughed Chernozems in the agrochronosequences we studied. This factor was previously underestimated.