DRAINAGE SYSTEM IMPACTS ON SURFACE RUNOFF, NITRATE LOSS, AND CROP YIELD ON A SOUTHERN ALLUVIAL SOIL

Abstract

Excess rainfall and subsequent surface runoff is a challenge to farmers of the Lower Mississippi River Valleyregion. In 1993, we established an experimental field site in Baton Rouge, Louisiana, consisting of 16 hydraulically isolatedplots (0.2 ha) on a Commerce soil (Aeric Fluvaquents). Our objective was to determine drainage system impacts on surfacerunoff, subsurface drainage effluent, nitrate loss, and corn (Zea mays L.) yield. We evaluated the following drainage systems(four replications) in 1995 and 1996: surface drainage only (SUR), controlled subsurface drainage at 1.1 m below the soilsurface (DCD), and shallow water table control at a 0.8 m depth via controlled -drainage/subirrigation (CDSI). Planting date,fertility management, and minimum tillage were consistent across treatments. When compared to SUR, DCD and CDSI didnot reduce surface runoff or nitrate loss in runoff. This is in contrast to previous research showing that subsurface drainagesystems decreased runoff on this soil, the difference being that we did not use deep tillage. Our results suggest that subsurfacedrainage systems should be coupled with deep tillage to reduce nutrient loss in runoff from this alluvial soil. DCD and CDSIcontrolled the shallow water table, but the increased annual effluent from subsurface drainage increased nitrate losscompared to SUR. DCD and CDSI had no affect on corn yield under these rainfall conditions. With respect to nitrate lossand crop yield in this region, typical SUR drainage may be the best management practice (BMP) in the absence of effectiverunoff mitigation, such as deep tillage.