INFLUENCE OF DIFFERENT FIELD SITES ON PESTICIDE MOVEMENT INTO SUBSURFACE DRAINS

Pesticide movement to subsurface drains was monitored in two typical crop production areas in Germany. Field trials were conducted on two subsurface-drained soils, a silt loam and a poorly structured sandy soil, under different climatic conditions. Over a period of one year, the drainflow was measured and the drain water was analysed for all applied herbicides. Different leaching behaviour was observed at the two field sites. Following autumn application of pendimethalin and isoproturon to the Soester Borde soil maximum concentrations of about 62 mug litre-1 for isoproturon and 0.7 mug litre-1 for pendimethalin were observed in drainflow from this silt loam. The early occurrence of both herbicides in the drain water only two days after application is consistent with fast flow through macropores. In contrast, on the subsurface-drained sandy soil in Brandenburg, isoproturon did not reach the drains until two months after autumn application and was found at maximum concentrations of only 1.4 mug litre-1; pendimethalin was not detected in the drain water. Pesticide movement after spring application seemed to be of minor importance. At both locations, spring application led to low concentrations of pesticides in the drainflow (pendimethalin < 0.01 mug litre-1; metolachlor less-than-or-equal-to 0.05 mug litre-1; chloridazon less-than-or-equal-to 0.15 mug litre-1; metamitron less-than-or-equal-to 0.02 mug litre-1; terbuthylazine less-than-or-equal-to 1.4 mug litre-1).