HERBICIDE LOSSES IN RUNOFF FROM CONSERVATION TILLED WATERSHEDS IN A CORN/SOYBEAN ROTATION

Authors: Shipitalo, Martin; Edwards, William; Owens, Lloyd

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/12/1996
Publication Date: N/A
Citation: N/A

Interpretive Summary: The planting of corn and soybean in rotation can increase yields of both crops and help alleviate problems that may occur when these crops are grown in monoculture. In steeply sloping farmlands of Appalachia, however, conservation tillage practices, such as minimum and no-tillage, must be used to keep soil losses at acceptable levels. Residue cover during the soybean year, however, may be insufficient to adequately protect the soil surface from erosion. Therefore, we planted a rye cover crop following soybean harvest to further protect the soil. Soil, nutrient, and herbicide losses in runoff all appear to be at tolerable levels under this management practice. Average losses of the herbicides alachlor, atrazine, linuron, and metribuzin during a 4-year period were all less than 0.5% of the amounts applied. Generally, only during the first few runoff events after application were the concentrations of the herbicides in the runoff at levels that might cause concern.

Technical Abstract: In areas with steeply sloping farmlands concern that soybean does not produce enough residue to control erosion under conservation tillage has favored production of corn in monoculture, although yields of both crops can be higher when grown in rotation. Previous research at our location has demonstrated that soil and nutrient losses in runoff from a corn\soybean rotation were tolerable when a rye cover crop following soybean harvest was used to provide additional residue cover. Herbicide losses in runoff under this cropping sequence, however, have not been evaluated. Therefore, runoff from two chisel and two no-till watersheds was monitored for 4 yr to determine the effect of the rotation on losses of four herbicides and to compare the behavior of atrazine and linuron, which control a similar spectrum of weeds. As a percentage of applied chemical, average losses were small with atrazine (0.31%) > linuron (0.20%) > metribuzin (0.14%) > alachlor (0.05%). Atrazine concentrations, however, consistently exceeded the lifetime Health Advisory Level\Maximum Contaminant Level (HAL\MCL) of 3 ug/L in the first few runoff events after application and atrazine was detectable in the runoff during the soybean years, at times above the HAL\MCL. Linuron was rarely detected in runoff following corn harvest or during the soybean years. The 2 ug/L MCL for alachlor was only exceeded during the first few events after application, whereas metribuzin concentrations never exceeded the HAL of 200 ug/L.