Submitted to: Soil and Water Conservation Society
Publication Type: Abstract Only
Publication Acceptance Date: October 13, 2006
Publication Date: October 13, 2006
Citation: Tomer, M.D., James, D.E., Green, C.H., Moorman, T.B. 2006. Conservation Practices and Water Quality in the Iowa River's South Fork Watershed [abstract]. Soil and Water Conservation Society. p.39. Technical Abstract: The Iowa River’s South Fork drains 87,000 ha under intensive, high-production agriculture. Corn-soybean rotations occupy about 85% of the watershed. About 100 swine CAFOs generate manure applied onto about a quarter of the watershed annually. Artificial drainage is extensive because the young glacial terrain is poorly dissected; hydric soils cover 54% of the watershed. In this CEAP Benchmark watershed, the SWAT model has been calibrated for hydrologic flows, considering tile drainage. Nutrient load calibrations are being initiated for SWAT (not reported here). Measured E. coli populations in the stream frequently exceed the recreational-contact standard of 125 cells/100 ml, with multiple sources suspected. Water quality monitoring data also show seasonal NO3-N concentrations often exceed 20 mg L-1. Loads during 2002-2004 were 16-26 kg NO3-N ha-1yr-1, but only 0.4-0.7 kg P ha-1yr-1. However, concentrations typically exceed EPA’s suggested water quality standards for the region for both nutrients. A conservation-practices inventory conducted in 2005 by NRCS was combined with a sequence of annual crop cover imagery to identify dominant management systems in the watershed. About 8% of the agricultural land is in no-tillage or zone-tillage. On remaining fields, inadequate residue (<30%) often follows soybeans, indicating that maintaining residue when applying manure into bean residue is a key management challenge in the watershed. While spatial analysis tools can be applied to prioritization of practices to assist farm-scale conservation planning, alternative management systems that can reduce risk of runoff as well as NO3 leaching in this situation need to be developed and encouraged. Future research also needs an explicit focus on developing approaches to establish linkages between management practices and water quality at the watershed scale.