Abstract <p>The research was conducted in 2010‒2022 in Belgorod oblast, which is part of the Central Chernozem Economic Region and located on the southwestern and southern slopes of the Central Russian Upland. The aim of the research was to analyze the results of the monitoring of the organic carbon content in the soils of agroecosystems under conditions of large-scale biologization of agriculture. The study found that the typical and leached chernozems lost 40.0‒42.0% of organic carbon during long-term use in agriculture compared to their counterparts in natural ecosystems. On average, for the studied subtypes of slightly washed-out chernozems, the decrease in the content of this parameter was 14.5‒16.4% compared to unwashed arable soils. The organic carbon content was 1.87‒2.22 and 5.30‒6.98 times lower in the genetic B horizon and the upper layer of the C horizon, respectively, than in the plow horizon. As a result of the implementation of comprehensive measures aimed at increasing the supply of organic matter to the soil and reducing its losses, the weighted average С_org content in the arable soils of the region increased by 0.174%, which corresponds to the accumulation of 19.1 carbon units/ha. A direct linear relationship has been established between the levels of organic carbon and easily hydrolyzable nitrogen in soils.</p>