ИСТИНА

RothC model was used for simulation soil organic carbon (SOC) stocks in 7 Russian long-term experiments founded in 1933-1980 with mineral and organic fertilization. Crop sequences include alternation of cereals, row crops and grasses, four experiments have crop rotations with bare fallow field. Actual weather data and yearly carbon input through crop residues estimated from crop yield and above ground biomass production were used as input data. RothC satisfactorily simulated the observed changes in SOC on Podzol, Albeluvisols and Chernozem,as evaluated through the root mean square error, coefficient of determination and the mean difference. However, in the absence of clear trend, RothC turns out to be less sensitive to the observed interannual SOC dynamics. For sandy Podzol 1.1-1.3 Mg C ha -1yr-1 annual C input was required to maintain initial C level, while for loamy Albeluvisols necessary rates were 1.4-2.0 Mg C ha -1yr-1. Inputs of 2.6-2.9 Mg C ha -1yr-1 were required to maintain soil C on Chernozem. If C input in long-term was inadequate to maintain SOC it leads to consistent decrease of resistant plant material. Preferable effect of agronomic practices on active C pools leads to possibility of C sequestration only in a short-term and makes it highly yield-dependent. Simulation of SOC dynamics for plots with no fertilization and the lowest SOC stock revealed that above ground NPP input is sufficient for maintaining constant SOM stocks after conversion to a grassland for forage production and returning FYM in the same plot.