Submitted to: Journal of Environmental Quality
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/3/2007
Publication Date: 5/1/2008
Citation: Potter, T.L., Truman, C.C., Strickland, T.C., Bosch, D.D., Webster, T.M. 2008. Herbicide Incorporation by Irrigation and Tillage Impact on Runoff Loss. Journal of Environmental Quality 37:839-847. Interpretive Summary: Intense thunderstorms commonly occur at times when crops like peanut and cotton are planted. Growers also frequently apply herbicides at or soon after planting for weed control. Because these storms often produce surface runoff, there is a substantial risk for herbicide residue transport to streams and rivers. Increasingly growers are encouraged select practices which will minimize runoff of herbicides and other pest control products. A practice that has potential is irrigation of fields soon after application. To quantify impacts in crop production areas of the Atlantic Coastal Plain region of the eastern USA, we conducted rainfall simulations in a field in a cotton-peanut rotation in south central Georgia (USA). We found that herbicide runoff was up to two times less from plots that were irrigated prior to a rainfall event compared to those that were not. Studies also showed that the practice’s efficacy was strongly impacted by tillage management and herbicide properties. When a commonly used conservation-tillage practice, strip-tillage, was used, whether plots were irrigated or not had little impact on runoff of an herbicide that has low water solubility and high capacity for adsorption by soil. These findings will be useful to growers, since it will help them determine when irrigation will be most useful to reduce herbicide runoff losses. Our studies also indicated that the accuracy of herbicide runoff estimates made using simulation models may be improved if tillage and other management practices are taken into account when describing herbicide adsorption by sediment and washoff from cover crop mulch. Improved model accuracy is general goal of all stakeholders involved with pesticide management and registration.
Technical Abstract: Runoff from farm fields is a common source of herbicide residues detected in surface waters. Soil incorporation by post-herbicide application irrigation has the potential to reduce runoff risks and improve weed control efficacy. To assess runoff impacts, we conducted rainfall simulations following preemergence metolachlor (2-chloro-N-(2-ethyl-6-methylphenyl)-N-[(1S)-2-methoxy-1-methylethyl]-acetamide) and pendimethalin (N-(1-ethylpropyl)-3,4-dimethyl-2,6-dinitro-benzenamine) application to plots located in a peanut (Arachis hypogaea L.) field in the Atlantic Coastal Plain region of Georgia (USA). Runoff, sediment, and herbicide loss as function of tillage, strip (ST) versus conventional (CT), were compared on plots with and without irrigation after herbicide application. On CT plots irrigation reduced metolachlor runoff two-fold. Pendimethalin runoff from CT- and metolachlor runoff from ST-plots was also reduced although differences between irrigated and non-irrigated plots were less. Irrigation had no impact on pendimethalin runoff from ST plots. Results indicate that use of the practice will likely reduce edge-of-field herbicide loads in runoff and protect surface water quality; but impacts will be limited when conservation practices like ST and herbicides like pendimethalin are used. During the study we also observed that herbicide washoff from cover crop residue was 2-fold less than predicted amounts using default parameters in an equation commonly used to estimate washoff. In addition we found that tillage and irrigation prior to rainfall simulations significantly impacted Koc of both herbicides on sediment entrained in runoff. Confirmatory work is needed to determine if these observations may be generalized to other pesticides and agronomic settings.