EVIDENCE FOR THE ACCELERATED DEGRADATION OF ISOPROTURON IN SOILS

The herbicide isoproturon was degraded rapidly in a sandy loam soil un der laboratory conditions (incubation temperature, 15 degrees C; soil moisture potential, -33 kPa). Degradation was inhibited following trea tment of the soil with the antibiotic chloramphenicol, but unaffected by treatment with cycloheximide, thus indicating an involvement of soi l bacteria. Rapid degradation was not observed with other phenylurea h erbicides, such as diuron, linuron, monuron or metoxuron incubated in the same soil under the same experimental conditions. Three successive applications of isoproturon to ten soils differing in their physicoch emical properties and previous cropping history induced rapid degradat ion of the herbicide in most of them under laboratory conditions. Ther e were, however, no apparent differences in ease of induction of rapid degradation between soils which had been treated with isoproturon for the last five years in the field and those with no pre-treatment hist ory. A mixed bacterial culture able to degrade isoproturon in liquid c ulture was isolated from a soil in which the herbicide degraded rapidl y.