Monitoring pesticide movement into subsurface drains

Pesticide losses to subsurface drains were monitored in field trials on an agriculturally important loamy silt soil in the "Soester Börde", a typical crop growing area in Germany. Over a one year period, the drainflow was measured and the drain water was analysed for four applied herbicides. Significant differences were observed comparinng spring and autumn applications. The herbicides applied in spring 1992 were only found in concentrations equal or smaller than 0.15 myg/l (chloridazon, metamitron) in the drain water; pendimethalin was not detected in the drains during this spring/summer period. Following the autumn application, maximum concentrations of about 62 myg/l for isoproturon and 0.7 myg/l for pendimethalin were observed. Between 0.09 percent and 0.4 percent of the applied isoproturon, but less than 0.001 percent of pendimethalin leached to the drains from November 1992 to April 1993. The experimental results indicate that both preferential flow and nonequilibrium sorption we re occuring on a field-scale.