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 radiocaesium are grazed by domestic animals. This paper investigates effects of grazing intensity over time on the partitioning of 137Cs in the grass Agrostis capillaris. Two levels of defoliation were simulated in a pot experiment by frequent clipping to sward heights of 3 and 6 cm, respectively. The 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 137Cs in the standing biomass increased markedly. Twice as much 137Cs was removed from the 3-cm compared to 6-cm swards through clipping. However, the total 137Cs activity incorporated into standing biomass plus clippings did not differ between defoliation regimes. The partitioning of 137Cs between green and dead leaves varied with defoliation intensity, time and leaf age. The pool of 137Cs in the standing biomass reached a maximum in December equivalent to 1.3% of that applied to the organic soil. A further 0.5% had been removed overall through clipping. The results are discussed in the context of controlling grazing intensity as a countermeasure.