Review of best management practice reduction efficiencies in the Lower Mississippi Alluvial Valley

Abstract

Agricultural best management practices (BMPs) can help reduce nutrient and sediment concentrations and loads leaving farm fields, which in turn can reduce negative impacts on downstream aquatic systems. For nearly three decades, significant federal investment in technical and financial assistance has been provided to implement farm BMPs. Of the conservation programs, only a few attempt to estimate the amount of nutrient and sediment reduction resulting from cost-shared practices, let alone potential positive effect on local or regional water quality. The current study provides a review of the scientific literature to determine nutrient reduction efficiency percentages for BMPs in row-crop agriculture within the Lower Mississippi Alluvial Valley (LMAV), an area with high delivery of both nitrogen (N) and phosphorus (P) to the Gulf of Mexico. The review consisted of multiple agricultural and biological database searches, a BMP effectiveness tool, and outreach to scientists. Only 18 articles (9 BMPs) provided BMP efficiencies that met specific criteria of (a) row-crop agriculture, (b) clay/silt loam soils, (c) slopes of 0% to 5%, and (d) occurrence within the LMAV. Best management practices included tillage management, wetlands, winter rice field management, subsurface drainage, and vegetated drainage ditches. The majority of the nine key BMPs for the LMAV provided significant nutrient reductions ranging from 15% to 100%. For seven BMPs that had total nitrogen (TN) and total phosphorus (TP) reduction efficiencies, the range was between 17% and 76%. Given the limited availability of BMP efficiency estimates within this physiographic region, these estimates should be used with caution. Significant resources should be committed to conducting replicable studies in the LMAV to provide the most reliable estimates possible of BMP effectiveness under a wide-range of realistic cropping, hydrological, and weather conditions in order to inform program and policy development and analysis.