FATE OF THE NEW SULFONYLUREA AMIDOSULFURON IN SOIL

Degradation and phytotoXiCity of C-14-labelled amidosulfuron influenced by the experimental factors soil texture and soil pH were investigated in 6 lysimeters under outdoor conditions during a 2-year test period. The results showed that the experimental factors did not clearly affect the fate of amidosulfuron in soil. A rapid loss of radioactivity in both test years was observed 3-5 months after application. At the end of the experimental period, approx. 30% of the total activity applied was still found in the 0-30 cm soil layers. The radioactive balance sheet prepared at the end of the experiment indicated that only small amounts of radioactivity were localized in plant material and percolate (in total 0.5% of the C-14 applied). Most of the radioactivity determined in the soil was not extractable. Only in the 0-10 cm soil layer traces of intact amidosulfuron were detected at the end of the experiment. The calculated initial half-life time mean value for the active ingredient was 14 days. The highest active ingredient (a.i.) concentration determined 3 months after application (2.3 mug/kg) did not damage rape the following sensitive crop seeded in the lysimeters. A bioassay system using lentil as test plant was established. Residue concentrations could be determined in a range from 0.5 to 1.7 mug/kg. Differences in bioavailability were found for freshly added a.i. in a concentration range of < 1 mug/kg and for a.i. in the same concentration after aging under practical field conditions.