|Smith Jr, Sammie|
Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/1/1998
Publication Date: N/A
Interpretive Summary: Alternative cropping systems that require less tillage than conventional plowing can reduce erosion and reduce tillage cost. These reduced tillage systems require more herbicide for weeds. Thus, a genuine concern for landowners and other stake holders is whether reduced tillage contaminates shallow groundwater even though it greatly reduces erosion. This study in north Mississippi from 1991 to 1996 showed that conservation tillage practices for corn did not significantly increase chemical contamination of the shallow groundwater; however, the increased water infiltration during the summer contributed to an increased herbicide level following runoff events early in the growing season. Even though groundwater was near saturation during the winter months for all tillage practices, no residual chemical effect resulting from tillage practices was found. The research points to using pre-emergence rotating herbicides and post-emergence Roundup in resistant corn to effectively control weeds in conservation tillage systems. These research results are important because they show that distribution and varying amounts of rainfall throughout the different seasons of the year may alter the effects tillage practices have on groundwater contamination. Information from this study provides the NRCS and extension personnel with additional guidance for making pesticide management recommendations to farmers.
Technical Abstract: Water quality and hydrology of a six-year study near Holly Springs,MS, showed conservation tillage had minor detrimental effects on the water quality in runoff and shallow groundwater and promoted more soil water for crop use during the growing season than conventional tillage. Agrichemical transport and losses were evaluated in runoff and shallow groundwater from no-till (NT), conventional-till (CT), and reduced-till (RT) corn plots on sloping soils possessing fragipan. With adequate weed control, NT produced higher yields than CT on these Loring soils due to soil moisture conservation. However, inadequate weed control occurred in several years of study along with above normal rain resulting in lower NT corn yields as compared to CT yields. Significant differences in corn yield due to available soil moisture and weed control were found for type of tillage, year, and tillage-year interaction. Other results included low sediment concentrations found from NT corn plots and insignificant free water quantities at the fragipan's surface during the cropping season for all tillage systems with limited downward or lateral water movement and thus no agrichemical movement. Maximum groundwater movement within the fragipan occurred in the non-cropping season under soil profile saturation. Amount, timing, and distribution of rainfall primarily influenced agrichemical movement from these corn systems.