Effect of Cropping Cycles and Repeated Herbicide Applications on the Degradation of Diclofopmethyl, Bentazone, Diuron, Isoproturon and Pendimethalin in Soil

The influence of wheat, corn, oilseed rape, and soybean cropping cycles on the degradation of five herbicides in soil was studied. Microbial biomass carbon was markedly higher in planted soils relative to bulk soil, especially with wheat and corn, after several cropping cycles. Biomass in soils planted with soybean and corn was adversely impacted by bentazone but recovered after three cropping cycles. Diclofop-methyl application in wheat-planted soils resulted in a persistent increase of the amount of microbial biomass; two applications were sufficient to enhance its degradation. Mineralization rates of isoproturon, diuron, and pendimethalin were not affected after the first cropping cycle but were increased in planted soils after five cropping cycles.