Impact of cover crop and season on nutrients and sediment in runoff water measured at the edge of fields in the Mississippi Delta of Arkansas

Abstract

Improved understanding of water quality at the edge-of-field (EOF) from production-size fields is needed to better inform agriculture and resource managers regarding sustainable farming practices and environmental stewardship. We measured runoff water quality at EOF of paired commercial fields in Mississippi and Craighead counties (total of four fields) in the Mississippi Delta region of eastern Arkansas, an understudied agricultural region. The paired fields had similar size, soil properties, and crop (cotton [Gossypium hirsutum L.] or corn [Zea mays L.]). Runoff water quality (nitrate [NO₃], nitrite [NO₂], total nitrogen [TN], phosphate [PO₄], total phosphorus [TP], and suspended sediment concentration) and quantity (discharge) were measured using sensors and automated water samplers installed in surface drainage pipes at the EOF and laboratory analysis. We monitored both precipitation and irrigation events for three years, with the first two years in cover crop and the third year in baseline study. We used the data to evaluate (1) the effectiveness of cover crops in reducing nutrients and sediment losses, (2) differences in growing season and nongrowing season losses, and (3) changes in runoff water quality from irrigation tailwater compared to rainfall event runoff during the growing seasons. We also compared variations in pollutant loadings in the paired fields under identical crop and management practices for baseline monitoring. Cover crops effectively reduced concentrations of NO₃-N and PO₄-P from one field pair at the Caraway location. Generally, concentrations of pollutants were lower in the growing period (May through October) than in the nongrowing period (November through April), suggesting the need for practices such as cover crops to reduce winter loads. Runoff water quality after irrigation was not different from that after rainfall. These findings support the need for baseline studies before actual evaluation of conservation practices, and practices including cover crops at the field in winter.