Solute Transport in Eroded and Rehabilitated Prairie Landforms. 2. Reactive Solute

Authors: Schneider, Sharon; Koskinen, William; Yates, Scott

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/23/2009
Publication Date: 8/4/2009
Citation: Papiernik, S.K., Koskinen, W.C., Yates, S.R. 2009. Solute Transport in Eroded and Rehabilitated Prairie Landforms. 2. Reactive Solute. Journal of Agricultural and Food Chemistry. 57:7434-7439.

Interpretive Summary: In hilly landscapes, soil properties change with slope position. Soil erosion exaggerates these differences. Soil-landscape rehabilitation is the movement of soil from the lower slope to eroded areas in the upper slope. Soil-landscape rehabilitation makes the soil more uniform and increases crop yields in areas of soil addition. Information regarding the impact of varying soil properties, topography, and climate conditions on the transport of pesticides is critical to the development of improved pesticide management practices. We quantified the rate of dissipation of the commonly-used herbicide S-metolachlor (trade name Dual) after fall and spring application to eroded and rehabilitated landforms. Although slope position and bulk soil movement within the landform had a large impact on soil properties, we observed no differences in metolachlor dissipation between different slope positions and between eroded and rehabilitated landforms. Most of the fall-applied metolachlor was depleted from the root zone during the winter (presumably by runoff and leaching out of the root zone). At the beginning of the growing season, only 20% of the fall-applied metolachlor remained in the soil. During the spring, half of the remaining S-metolachlor was depleted from soil in 24 to 29 days. In these trials, fall-applied metolachlor dissipated prior to spring planting to such an extent that it provided no control of grassy weeds. The results of this research suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination. This information enables better pesticide management decisions for the northern Corn Belt. Results will be used to improve models to predict pesticide transport in hilly landscapes, cropped soils, and soils that are frozen for significant periods.

Technical Abstract: Information regarding the impact of varying soil, landscape, and climate conditions on the off-site transport of pesticides is critical to the development of improved pesticide management practices. We quantified the rate of S-metolachlor dissipation after fall and spring application in eroded and rehabilitated landforms in which topsoil was moved from the lower slope to the upper slope. Despite large differences in soil properties, including soil organic carbon contents that varied by up to a factor of 4, the rate of metolachlor dissipation from the top 1 m was essentially the same at all landscape positions. Most of the fall-applied metolachlor was depleted from the root zone during the winter (presumably by leaching and runoff), so that only 20% of the applied metolachlor remained in the top 1 m of the soil profile at the beginning of the growing season. S-metolachlor dissipated in the spring with a half-life of 24 to 29 d. Bromide and metolachlor were depleted from the root zone at nearly the same rate during most of the growing season, suggesting that metolachlor degradation and plant uptake acted together to result in a dissipation rate similar to that for a non-reactive tracer, which was primarily dissipated through plant uptake. In these trials, fall-applied metolachlor dissipated prior to spring planting to such an extent that it provided no control of annual grasses. The results of this research suggest that fall-applied metolachlor may not provide economic weed control and presents an increased risk of water contamination. Although landscape position and bulk soil movement within the landform had a large impact on soil properties, we observed no significant differences in metolachlor dissipation between different landscape positions and between eroded and rehabilitated landforms.