Spatial Variation In Sorption-Desorption of the Herbicide Saflufenacil In An Eroded Prairie Landscape.

Herbicide interactions with soil determine their availability for plant uptake, transport, and degradation. The kinetics and extent of herbicide partitioning and transformation in soil are affected by properties of the herbicide and of the soil. The herbicide saflufenacil was registered in the US in 2009 and is labelled for the control of broadleaf weeds in corn, soybean, and other crops. Information regarding the environmental fate of this new herbicide is needed to evaluate its potential for weed control, carryover, leaching, and runoff considering the field scale spatial variability of soils in which it may be used. We conducted a series of laboratory studies to evaluate saflufenacil partitioning and degradation in soils from an eroded prairie landscape. In the study landform, soil organic carbon concentrations in the upper slope are about 11 g kg^-1 in the surface soil and decline sharply with depth to <4 g kg^-1 at depths >25 cm. In contrast, the lower slope is an area of deep topsoil accumulation and soil organic carbon concentrations are >20 g kg^-1 throughout the top 40 cm. We determined sorption-desorption and dissipation of the herbicide saflufenacil in surface and subsurface soils collected from the upper slope and lower slope positions of this landscape. Results indicate the potential for spatial variability in saflufenacil dissipation and bioavailability and provide a basis for more detailed studies of saflufenacil fate and transport in soils of the US Corn Belt.