The seasonal pattern of radiocaesium partitioning within swards of Agrostis capillaris at two defoliation intensities

Many semi-natural ecosystems with potentially high soil-plant transfer of r adiocaesium are grazed by domestic animals. This paper investigates effects of grazing intensity over time on the partitioning of Cs-137 in the grass Agrostis capillaris. Two levels of defoliation were simulated in a pot expe riment by frequent clipping to sward heights of 3 and 6 cm, respectively. T he swards showed characteristics similar to field swards, but may not have reached equilibrium with the 6-cm cutting regime. Between June and December the pool of Cs-137 in the standing biomass increased markedly. Twice as mu ch Cs-137 was removed from the 3-cm compared to 6-cm swards through clippin g. However, the total Cs-137 activity incorporated into standing biomass pl us clippings did not differ between defoliation regimes. The partitioning o f Cs-137 between green and dead leaves varied with defoliation intensity, t ime and leaf age. The pool of Cs-137 in the standing biomass reached a maxi mum in December equivalent to 1.3% of that applied to the organic soil. A f urther 0.5% had been removed overall through clipping. The results are disc ussed in the context of controlling grazing intensity as a countermeasure. (C) 1999 Elsevier Science Ltd, All rights reserved.