Vertical and horizontal spatial variability in the biodegradation of the herbicide bentazone was compared in sandy-loam soil from an agricultural field using sieved

Vertical and horizontal spatial variability in the biodegradation of the herbicide bentazone was compared in sandy-loam soil from an agricultural field using sieved soil, which represents the method most widely used to investigate biodegradation rates, and intact soil cores. An initial experiment compared degradation at 5 depths between 0 and 80 cm using sieved soil. Degradation was shown to follow first order kinetics, and DT50 declined progressively with soil depth from 56 days at 0-10 cm to 520 days at 70-80 cm. DT50 was significantly correlated with organic matter, pH and dehydrogenase. In a subsequent experiment, degradation rate was compared after 127 days in sieved soil and intact cores from 0-10 and 50-60 cm depth from 10 locations across a 160 x 90 m portion of the field. Method of incubation significantly affected mean dissipation rate, although there were relatively small differences in the amount of pesticide remaining in intact cores and sieved soil, ranging between 4.6 and 10.6 %. Spatial variability in degradation rate was higher in soil from 0-10 cm depth relative