TRANSFER OF RADIOCESIUM IN SENSITIVE AGRICULTURAL ENVIRONMENTS AFTER THE CHERNOBYL FALLOUT IN SWEDEN .1. COUNTY OF GAVLEBORG

In 1986, 15 farms in the Chernobyl-affected area of the county of Gavl eborg were investigated for radiocaesium transfer to grass and cereal grain. The soil surface layer (0-5 cm) in 1986 and the crop products i n 1986-1994 were analysed. The aim was to study the impact of site and soil characteristics on sensitivity of Cs-137 transfer in a long-term perspective. The transfer was much higher to grass than to cereal gra in. For both crop products, however, there was a considerable annual r eduction. For grass, and especially in the fallout year 1986, the tran sfer 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 gr ass was reduced by a factor of 2 to 100. Both ploughing through the su rface layer and the mixing of radiocaesium with soil contributed to a decreased transfer of radiocaesium to crops. Thick stubble and grass s ward on the grassland sites was the main reason for a lag period of hi gh persistent transfer. The annual reduction was less on organic than on mineral soils. Measures to decrease the transfer to crops are discu ssed in relation to a new concept to evaluate the long-term behaviour of Cs-137 in agricultural environments.