DEGRADATION OF THE SULFONYLUREA HERBICIDE [C-14] AMIDOSULFURON (HOE-075032) IN SASKATCHEWAN SOILS UNDER LABORATORY CONDITIONS

The degradation of the herbicide [C-14]amidosulfuron (HOE 075032) was studied in three Saskatchewan soils at 0.1 mug/g under controlled temperature and moisture conditions. At 85 % of field capacity, degradation approximated to first-order kinetics at soil temperatures of 10, 20, and 30-degrees-C, with half-life values ranging from 14 +/- 2 days (mean and standard deviation) in a loamy sand incubated at 30-degrees-C to 231 +/- 41 days in a clay at 10-degrees-C. In a clay at 20-degrees-C, herbicide degradation followed first-order kinetics and was directly correlated with soil moisture, with half-life values varying from 246 +/- 21 days at 50 % of field capacity to 63 +/- 17 days at 100 %. There was negligible herbicide breakdown in air-dried soils incubated at 30-degrees-C for 70 days. During the study period, solvent-extractable 14C degradation products accounted for up to 48 % of the applied radioactivity. Solvent-nonextractable radioactivity associated with the soils incubated at 20-degrees-C ranged from 4 to 11 % of the initial treatment.