Humus balance under major agricultural crops in Russia – a criterion for the transition to regenerative agriculture

The study was conducted to assess the annual humus budget (HB) formed under major crops in agroecosystems of the Russian Federation’s agricultural zone in 2022. This year was characterised by favourable weather conditions and a relatively high crop yield, which contributed to the formation of adequate biomass for humus formation. A national model for managing the humus/carbon budget in soils of Russian agroecosystems was used in the study. In arable soils, the HB was positive and amounted to 4.911 million tons, which corresponds to the production of 10.607 million tons of carbon units, or 9% of greenhouse gas emissions from agriculture in the country in 2022. A positive HB confirms the possibility of a transition to regenerative agriculture, in which crop production will make a significant contribution to the promotion of lowcarbon development in the Russian Federation. Under individual crops, the HB ranged from -1.582 to +0.958 t/ha. The highest values of this indicator (from +0.923 to +1.463 t/ha) were found in soils under perennial grasses, grain crops, cultivated hayfields, and pastures. The lowest humus formation (from -0.117 to 0.213 t/ha) was observed in rowcrop forage roots, melons, potatoes, and vegetables. Grain crops and perennial grasses made the most significant contribution to humus accumulation (carbon absorption) by soils of agroecosystems. Among the crops whose cultivation was accompanied by humus loss from soils, the leading ones were oilseeds (especially sunflower, to a lesser extent soybeans), corn for green fodder, and potatoes. Differences in HB values depend on agricultural technologies used to cultivate them. An inverse relationship was observed at the trend level between an increase in soil humus content and the number of tillages during crop cultivation. The highest humus mineralisation in soils (1.653-1.705 t/ha) was observed under potatoes, melons, forage root crops, vegetables, and corn for green fodder. The lowest (0.473-0.505 t/ha) was observed in soils under cultivated hayfields, pastures, and perennial grasses.