Dynamics of 137Cs transfer factors to plants and the effects of protective measures on this radionuclide accumulation in the agricultural production is estimated on the example of the south-western regions of Bryansk District. Three periods in decreasing the 137Cs content in plants during 20 years after the Chernobyl accident are identified. The contribution of radionuclide decay, natural biogeochemical processes and protective measures aimed at reduction of the 137Cs accumulation in agricultural plants during various periods after radioactive fallout is shown. Maximum permissible levels of 137Cs contamination of cultivated lands, where crop products meeting current standards may be obtained, at different scopes of protective measures on radioactive-contaminated territories are forecasted. Periods after radioactive fallout, when crop and forage products meeting radiological standards are obtained, are assessed.