Submitted to: Soil and Tillage Research
Publication Type: Peer reviewed journal
Publication Acceptance Date: 9/5/2006
Publication Date: 9/20/2007
Citation: Pappas, E.A., Patterson, J., Smith, D.R., Huang, C. 2007. Effects of Tilling No-Till Soil on Losses of Atrazine and Glyphosate to Runoff Water under Variable Intensity Simulated Rainfall. Soil and Tillage Research. 95(1-2):19-26. Interpretive Summary: Chemicals used to control weeds in crops such as corn and soybeans may sometimes run off farm land and enter surface water bodies such as lakes and streams. If a surface water body that is used as a drinking water supply receives excess amounts of these herbicides, then the municipal water treatment plant must filter them out in order for the water to be safe to drink. This added filtration process can be expensive. Farmers can help control excess herbicides in runoff by choosing chemicals that bind with soil more readily, are less toxic, or degrade more quickly. Additionally, selecting the best tillage practice can help minimize herbicide pollution. In this study, we examined two different herbicides under two tillage systems for herbicide runoff potential. Experimental corn plots were treated with atrazine and glyphosate and either conventionally tilled or not tilled. We discovered that the use of glyphosate to control weeds in corn resulted in runoff water that had herbicide levels below the level that was safe to drink, while the use of atrazine resulted in runoff water that had herbicide levels in excess of that which is safe to drink. Additionally, runoff herbicide levels were generally higher in the no-till system than in the conventionally tilled system, although this difference was not important where glyphosate was used. Use of atrazine in the no-till system caused very high levels of herbicide in runoff water. The impact of this study is that farm managers and those making management recommendations to farmers have a new basis for selecting herbicide and tillage management regimes that will help minimize herbicides in runoff water. Minimizing herbicides in runoff water will result in safer drinking water and a lower cost of water treatment.
Technical Abstract: Herbicides released through agricultural activities to surface waters and drinking water systems represent a risk to human and environmental health, as well as a cost to municipalities for removal. This study focuses on the viability of glyphosate tolerant cropping systems as an alternative to atrazine based systems, and the impact of tillage practices on the runoff pollution potential of these systems. Variable intensity field rainfall simulations were performed on 3 first-year conventionally tilled (CT) and 3 long-term no-tilled (NT) plots treated with atrazine and glyphosate according to label. Runoff from plots was collected at regular time intervals during two simulated rainfall events and analyzed for herbicide concentration, sediment content, and volume. Maximum glyphosate concentration in runoff was approximately 20% of the maximum contaminant limit (MCL) for glyphosate (700 'g/L), while atrazine concentrations in runoff consistently exceeded the atrazine MCL (3 'g/L). Atrazine concentration and loading were significantly higher in runoff from NT plots than from CT plots, whereas glyphosate concentration and loading were impacted by tillage treatment to a much lesser degree. Results suggest that glyphosate - based weed management may represent a lower drinking water risk than atrazine - based weed management, especially in NT systems.