Transfer of radiocaesium in sensitive agricultural environments after the Chernobyl fallout in Sweden. I. County of Gävleborg

In 1986, 15 farms in the Chernobyl-affected area of the county of Gävleborg were investigated for radiocaesium transfer to grass and cereal grain. The soil surface layer (0–5 cm) in 1986 and the crop products in 1986–1994 were analysed. The aim was to study the impact of site and soil characteristics on sensitivity of 137Cs transfer in a long-term perspective. The transfer was much higher to grass than to cereal grain. For both crop products, however, there was a considerable annual reduction. For grass, and especially in the fallout year 1986, the transfer depended on interception capacity of the stubble and grass sward, on soil fertility and K-fertilization as well as on dilution by crop growth. In the following years, the annual reduction in transfer to grass was reduced by a factor of 2 to 100. Both ploughing through the surface layer and the mixing of radiocaesium with soil contributed to a decreased transfer of radiocaesium to crops. Thick stubble and grass sward on the grassland sites was the main reason for a lag period of high persistent transfer. The annual reduction was less on organic than on mineral soils. Measures to decrease the transfer to crops are discussed in relation to a new concept to evaluate the long-term behaviour of 137Cs in agricultural environments