Upland Soybean Production: Surface and Shallow Groundwater Quality as Affected by Tillage and Herbicide Use

Abstract

Information on the effects of tillage practices on pesticide transport in runoff and shallow groundwater is lacking for much of Mississippi, particularly the uplands of northern Mississippi. Therefore, herbicide transport in surface runoff and shallow groundwater was determined in no-till (NT) and conventional-till (CT) soybean [Glycine max (L.) Merr.] watersheds (about 2 ha each) in these loessial uplands (fragipan soils). For the 1991 crop year, runoff losses of the preemerge herbicides metribuzin (4-amino-6-tert-butyl-4,5-dihydro-3-methylthio-1,2,4-triazin-5-one, Lexone) and metolachlor [2-chloro-6-ethyl-N-(2-methoxy-1-methylethyl)acet-o-toluidide, Dual] were about 20 and 9%, respectively, of that applied to the NT watershed and about 23 and 11%, respectively, of that applied to the CT watershed. Greater than 90% of these losses occurred as a result of the first runoff event. Although sediment concentrations from the NT watershed were reduced by two orders of magnitude compared with the CT watershed, herbicide losses in runoff, as well as runoff volumes, were about equal. Herbicide losses in runoff in crop years 1992 and 1993 were lower for both watersheds due to the longer time interval between herbicide application and first runoff. Herbicide movement into the soil profile was greater in the NT watershed.