SOIL DEGRADATION OF FLUMETSULAM AT DIFFERENT TEMPERATURES IN THE LABORATORY AND FIELD

The degradation rate of the herbicide flumetsulam was examined in Hoytville clay soil at five temperatures and optimal moisture. Half-lives were 246 days at 7.5-degrees-C, 115 days at 15.0-degrees-C, 49 days at 26.1-degrees-C, 34 days at 35.9-degrees-C, and 27 days at 44.0-degrees-C. Construction of an Arrhenius diagram (ln k = -E(a)/RT+ln A) allowed the rate constant k to be calculated for any temperature T. When k was inserted into the first order rate equation (c = c0e(-kt)), the concentration of flumetsulam could be calculated on a monthly basis for any soil. Predictions from this theoretical model were compared with data from three US field locations and found to accurately predict soil residues of flumetsulam under favourable moisture conditions, but not during periods of drought.