Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: August 20, 2009
Publication Date: September 7, 2009
Citation: Locke, M.A., Bingner, R.L. 2009. Effects of Conservation Practices on Sediment and Chemical Runoff. Water Quality Research to Evaluate the Effects of Agricultural Conservation Practices Utilized in the United States and India Workshop Proceedings. Allahabad Agricultural Institute–Deemed University, Allahabad, India. p. 10-11. Interpretive Summary: Abstract Only - interpretative summary not required.
Technical Abstract: Row crop agriculture was introduced on a wide scale in the Southern United States (USA) as populations migrated westward during the 18th and 19th centuries. The trend was for areas predominantly covered by woodlands to be clear-cut, tilled, and cropped intensively, and then abandoned once native soil fertility was exhausted. The resulting erosion and soil productivity loss has fortunately been mitigated to some extent by improved management of these lands. In spite of steps forward, the development, assessment, and adaptation of management methodologies to conserve and improve natural resources such as soil and water continues to be a national priority of the Agricultural Research Service (ARS) of the United States Department of Agriculture (USDA). Alluvial plain watersheds derived from sediment deposition during intermittent flooding and shifting of riverine channels over the millennia. The resulting soil strata in these areas are heterogeneous, topography is relatively flat, and soils tend to be highly productive. The Mississippi Delta Region in the south central USA is an excellent example of an alluvial plain. Like much of the southern USA, the Mississippi Delta has historically been a major producer of cotton. In recent years, other crops such as corn, soybeans, and rice have supplanted cotton as the primary cash crop. All of these crops require significant inputs of fertilizer, pesticides, and irrigation water, and, traditionally, several tillage operations for bed preparation and weed management. As indicated earlier, these management inputs have taken their toll on the quantity and quality of soil and water resources. Various approaches have been used to evaluate the impact of agriculture on the landscape and to assess the benefits derived from conservation practices. These approaches range in scale from laboratory microcosms to watershed studies. This paper summarizes some of the research at various scales by USDA-ARS National Sedimentation Laboratory scientists studying the effects of conservation management on sediment and chemical runoff. Beasley Lake Watershed in the Mississippi Delta was one of 14 watersheds selected to be part of a U.S. national research effort described as the Conservation Effects Assessment Project (CEAP). As an oxbow lake watershed, Beasley is representative of the U.S. Mississippi Delta Region. In 2004, approximately one-third of the Beasley Lake watershed (ca. 280 ha) was converted from cropped land to the Conservation Reserve Program (CRP), a USDA program designed to conserve water and soil resources by removing land from crop production. The remainder of the watershed is still managed for soybean, cotton, or corn production. Sub-drainage areas (1.2 to 6 ha) with similar topography and soil types but different management were selected for study following GPS-based surveys of the Beasley Lake watershed. Sub-drainage areas were either cropped (three sites under reduced tillage soybean production) or CRP (three CRP sites) and were instrumented in late 2005 to collect water samples from field drainage slotted-inlet pipes during all surface runoff events. Runoff samples were analyzed for sediments and nutrients. A large-plot research study was established on the Delta Branch Experiment Station, Stoneville, MS. The experimental area (ca. 2.5 ha) was designed to evaluate various combinations of tillage and cover crop management. Each plot is 150-m long by 8-m wide and equipped with automated surface runoff sampling equipment. Composite runoff samples were collected following runoff events to determine water, sediment, and nutrient losses. Rainfall simulation studies with small erosion trays were conducted to determine benefits of a bahia grass (Paspalum notatum) buffer strip in mitigating herbicide and sediment loss in runoff. Fluometuron (1.68 kg ai ha–1) and atrazine (2.24 kg ai ha-1) were applied to the surface of runoff trays (2.73 m2 area, 1.2% slope) containing Dundee silt loam soil. Herbicide was applied only to the upslope half of each tray 24 h before rainfall simulation. Treatments included either bare soil or a 1-m bahia grass strip at the downslope outlet end of the tray and were replicated four times. Simulated rainfall was applied to the soil surface (2.5 cm in 20 min; Vee-Jet oscillating nozzles). Runoff was collected in fractions and processed for sediment and herbicide concentrations.