Effect of Soil Type, Selected Best Management Practices, and Tillage on Atrazine and Alachlor Movement through the Unsaturated Zone

Introduction: Results from groundwater monitoring programs in Wisconsin have shown numerous cases of contamination by agricultural chemicals in areas with sandy soils and/or shallow aquifers (Postle, 1990). The extent and magnitude of this contamination, however, varies greatly between areas with similar landscape conditions and management practices. It appears that a particularly susceptible region is the intensively cropped, irrigated, sandy valley along the lower Wisconsin River (LWRV). Data from soil-column studies suggested that herbicide fluxes through the root zone of LWRV soils are 15 to 100 times 7 greater than those through the similar, well-drained, sandy soils from the Central-Sands (CS) area of Wisconsin (Wietersen, 1991).

We need to understand the link between groundwater contamination and field use of agricultural chemicals in the LWRV, as well as the differences between sandy soils from the LWRV and CS. To address this need, in 1988, we (under the initial direction of Tommy Daniel) initiated a comprehensive study of herbicide and nitrate movement in the LWRV. The effects of soil type, irrigation management, tillage, and a tank mix polymer (that had been noted to reduce herbicide leaching) on agricultural chemical transport through the vadose zone to groundwater are being investigated. The primary goal of this research is to improve our understanding of the relationships between herbicide behavior and both intrinsic (i.e., inherent soil properties) and extrinsic (e.g., pesticide application and irrigation management strategies) variables.