PRIMISULFURON AND RIMSULFURON DEGRADATION IN AQUEOUS-SOLUTION AND ADSORPTION IN 6 COLORADO SOILS

Hydrolysis and adsorption of the sulfonylurea herbicides rimsulfuron a nd primisulfuron were investigated under laboratory conditions, Degrad ation in aqueous solutions was determined between pH 3 and 8 and betwe en 5 and 35 C, Rimsulfuron degraded faster than primisulfuron. Half-li ves at different temperatures at pH 4 ranged from 0.16 to 5.8 d for ri msulfuron and from 0.47 to 16.1 d for primisulfuron, Primisulfuron hyd rolysis at 30 C decreased with increasing pH, but rimsulfuron decrease d up to PH 7, then increased, suggesting rapid degradation in alkaline conditions, Adsorption, measured in six Colorado soils, was complete within 2 h in all soils, Adsorption isotherms were determined by batch equilibration of 75 to 600 mu g L(-1). Rimsulfuron was adsorbed in am ounts 3.7 to 7 times higher than primisulfuron, with adsorption distri bution coefficients (K-d) ranging from 0.1 to to 1.18 for primisulfuro n and from 0.71 to 5.1 for rimsulfuron. Adsorption of both herbicides was slightly correlated with soil clay content, and primisulfuron adso rption was also correlated with organic matter content.