Herbicides in surface runoff: A rainfall simulation study on small plots in the field

Abstract

The transport of the herbicides isoproturon, dichlorprop-p, and bifenox via surface runoff was investigated on small field plots with simulated rainfall at an intensity of about 70 mm/h. Isoproturon and dichlorprop-p, with water solubilities of 65 and 700 mg/l respectively, were transported mainly in the runoff water phase. Their runoff concentrations primarily depended on the preceding cumulative rainfall. Concentrations of runoff water and sediment decreased with increasing cumulative rainfall according to a power function. Total isoproturon and dichlorprop-p losses in runoff mainly depended on the time of runoff initiation as well as on total runoff and soil loss. Factors like soil type, vegetation, slope, or rainfall intensity affected total herbicide losses by influencing the time of runoff initiation as well as total water and soil losses. In most cases isoproturon losses were higher than losses of dichlorprop-p. Interflow resulted in increased herbicide concentrations in the runoff water. The increase was more pronounced for dichlorprop-p than for isoproturon. Bifenox, with a water solubility < 1 mg/l, was strongly adsorbed to the eroded sediment and moved of the plot almost exclusively in the sediment phase. Its concentration in the sediment mainly depended on the amount of preceding soil loss. For all runoff experiments the bifenox concentrations in the sediment of the first runoff litres were similar. The time of runoff initiation did not influence the bifenox concentration.