Sediment Loss and Runoff from Cropland in a Southeast Atlantic Coastal Plain Landscape

Abstract

<abstract> <bold><sc>Abstract.</sc></bold> Widespread implementation of conservation tillage systems during cotton (Gossypium hirsutum L.) and peanut (Arachis hypogea L.) production in the Atlantic Coastal Plain region of the U.S. has substantially reduced erosion and sediment loss. However, the benefits of conservation tillage in these cropping systems are being threatened by weather shifts that include increased frequency of high-intensity rainfall, policies that encourage the removal of crop residues as cellulosic feedstocks for energy production, and increased herbicide resistance in weeds. Long-term integrated studies are needed to quantify potential impacts. We evaluated runoff and sediment loss from six 0.2 ha fields located on a gently sloping hillslope in a Southern Atlantic Coastal Plain landscape over ten years (2000-2009) during rotational cotton-peanut production, with a rye (Secale cereale) winter cover crop. Half of the fields were in conventional tillage (CT; inversion tillage with cover crop residue incorporation prior to planting), and half were in strip tillage (ST), which is a commonly used conservation tillage practice in the region. Fields were laid out as contrasting tillage pairs at upper, middle, and lower landscape positions and irrigated as needed. Runoff and sediment load from CT fields was significantly greater than from ST fields at each landscape position. Over the 10-year study period, mean annual total sediment load was 1823 kg ha^-1 year^-1 from CT fields and 237 kg ha^-1 year^-1 from ST fields (an 87% difference), and runoff was reduced by 41%. A soil tolerance value (T) of 2,200 kg ha^-1 year^-1 was exceeded in three out of ten years in CT fields and never exceeded in ST fields. On a monthly basis, extreme events (>90th percentile; 10%) accounted for 61% to 72% of the 10-year total sediment load for the CT system (341 to 2,828 kg ha^-1 month^-1) and 73% to 84% for the ST system (49 to 593 kg ha^-1 month^-1). The rainfall and irrigation total was above the normal monthly rainfall in 83% of these extreme monthly periods (mean 179 mm, range 81 to 316 mm). Sediment load was greatest in summer and spring, and during cotton production. The study results improve estimates of the increase in rainfall event size tolerated by CT vs. ST cropping systems, demonstrate the benefits of conservation tillage management during cotton and peanut production, and are expected to guide management decisions that focus on reducing sediment loss in this landscape. Specifically, the results point to the use of cover crops and strip tillage as essential best management practices for this purpose.