Changes in land use affect significantly the amount of organic carbon stored in the soil and vegetation. Since 1990, the land use system in Russia has been considerably changing and more than 10 Mha of croplands were abandoned. The carbon balance of cultivated soil under fallow was compared with that of soils abandoned 4, 8, 13, and 28 years ago and converted naturally to permanent grassland (Moscow region, Russia, 54°50’N 37°37’E). The carbon balance in the abandoned ecosystems varied from –116 to –392 g C/m² · yr depending on the period of abandonment. The average net ecosystem productivity of abandoned lands in Russia was –236 g C/m² · yr. Since the 90s, the total C-sink for the Russian territory may be estimated to 231–802 Tg C per year due to the conversion of former croplands to permanent grasslands. Based on own field studies and literature analysis, the carbon accumulation rates (R_CA) for the main soil types have been estimated. The mean values of R_CA were 132 ± 21 and 70 ± 8 g C/m² · yr for the periods 0–15 and 15–30 years of abandonment, respectively. Due to the land use change from croplands to permanent grasslands, the total C accumulation in Russian soils amounted to 184–673 Tg C during 1990–2004 and can reach 282–1030 Tg C by 2020.

Keywords: land use change, net ecosystem production, CO2 emission, carbon balance, soil organic carbon, C accumulation rate, abandoned lands