DEGRADATION OF THE FUNGICIDE DIFENOCONAZOLE IN A SILT LOAM SOIL AS AFFECTED BY PRETREATMENT AND ORGANIC AMENDMENT

Degradation of the fungicide diffenoconazole was examined in a silt lo am soil under controlled conditions (60% WHC, 30 degrees C) in the lab oratory. Difenoconazole was applied at 0.1 and 1.0 mg kg(-1) dry soil, respectively. The experiments Mere run with non-pretreated and pretre ated field soil, respectively, partly mixed with easily decomposable o rganic matter (leaf powder). In all experiments, degradation curves sh owed a sigmoidal shape with clear acclimation phases. Pretreatment wit h difenoconazole in the field decreased the acclimation phases, DT50- and, in some cases, DT90-values. The incorporation of easily decomposa ble organic matter decreased both DT50- and DT90-values and increased the general microbial activity significantly. We conclude that difenoc onazole is metabolized by an acclimated part of the soil microflora. H owever, the degradation seems to be stimulated in the presence of suit able co-substrates. (C) 1997 Elsevier Science Ltd.