Fate of the herbicide cinosulfuron in rice plant-grown lysimeters over twoconsecutive years

The fate of the herbicide cinosulfuron in rice paddies was elucidated by us ing lysimeters. Rice plants were grown on lysimeters treated with [C-14]cin osulfuron by the conventional method. During the growing period, the volati le chemicals, (CO2)-C-14 evolved from the soil surface, and the leachate C- 14-radioactivity were measured. After harvest, the C-14- radioactivity dist ributed in straw, ear without rice grains, chaff, and brown rice grains was also measured. When rice plants were cultivated for two consecutive years, the C-14-radioactivity in straw was 47 similar to 116 times higher than th at in brown rice grains in the first year, whereas in the second year, the amount decreased considerably, being still 38 similar to 51 times larger in the former than in the latter. The C-radioactivity distributed down to the 30-cm soil depth was 89 similar to 92% of the original amount in the first year, and 60 similar to 71% in the second year. The C-radioactivity leache d gradually with time, totaling 0.5 similar to 0.6% of the original amount.