Аннотация:Land use changes (LUC) significantly affect the carbon balance in ecosystems. The study was aimed to determine the dynamics of soil organic carbon (SOC) under anthropogenic LUC using the RothC model. Field data was obtained at experimental plots (Luvic Phaeozem) in Moscow region. The research consisted of two parts. 1. The solution of the direct problem of modeling: to calculate SOC losses after recultivation of abandoned lands with standard parameters of transformation. Input data included both own experimental and literature data. It was shown that SOC is accumulated only under perennial grasses because their biological features and agrotechnology are similar to native grasslands (fig. 1). The highest losses of SOC were common for annual grasses and barley due to the short vegetation period, small amount of plant residues, and inputted fertilizers. SOC losses were minimal under pasture crop rotations with perennial grasses and maximal under rotations with row crops through intensive tillage (fig. 2). The rate of SOC losses from old abandoned lands was higher than from young ones due to low content of decomposable carbon in the last one. 2. The solution of the inverse problem: to correct coefficients in the model’s formulas if field data on SOC sequestrated during the reforestation of arable lands is known. Carbon pools in abandoned lands of different ages were determined in our previous studies. The average values and the medians for all carbon pools were calculated: input plant residues (IPR), СО2 emission, microbial biomass (Cmic), decomposable (DPM) and resistant (RPM) plant materials, and SOC. Using this data, the annual carbon balance in soils was calculated. The input parameters to simulate the SOC dynamic in abandoned lands during the reforestation were also corrected (table). This study was supported by RFBR grant 18-04-00773а and fundamental research theme of IGRAS 0148-2019-0009.