Effects of soil moisture and treatment volume on bentazon mobility in soil

Soil moisture affects the leaching behaviour of pesticides by inducing their physical entrapment in the soil structure. Columns containing soil aggregates were dampened to specific initial moisture levels. Bentazon was dripped onto surface aggregates in different volumes. The columns were then percolated after an equilibration period. Soil water from the columns was divided arbitrarily among mobile and immobile regions in order to describe the herbicide redistribution processes in the soil. When the soil was dry before treatment, bentazon losses by mass flow were 1.5 to 4 times higher than in wet conditions. Between application time and percolation, any water present in the porous matrix might favour pesticide diffusion towards immobile water regions as well as adsorption into and onto soil aggregates, preventing its leaching. The use of large solution volumes of the pesticide modifies surface soil moisture, suppressing any difference in behaviour between dry and wet soil application conditions