Submitted to: Soil Conservation and Water Quality Symposium Proceedings
Publication Type: Proceedings
Publication Acceptance Date: August 3, 2005
Publication Date: November 28, 2005
Citation: Nepple, J., Tomer, M.D., Karlen, D.L. 2005. Assessing soil fertility in the south fork watershed of the Iowa river. Soil Conservation and Water Quality Symposium Proceedings. Available: http://www.swcs.org/en/swcs_international_conferences/2005_annual_conference/index.cfm?nodeID=7456&audienceID=1 Technical Abstract: The South Fork Watershed of the Iowa River in north-central Iowa has been selected for intensive monitoring for the inter-agency Conservation Effects Assessment Project (CEAP). Intensive swine, corn, and soybean production occur within the watershed and local streams have shown elevated levels of nitrate and phosphorus. Discussions with local stakeholders revealed the lack of baseline soil fertility data for this 220,000-acre watershed. This information is needed to help determine the appropriate practices and to identify where scarce resources should be targeted to provide the greatest environmental benefit. The Iowa NRCS and National Soil Tilth Laboratory (NSTL) cooperated to assist local stakeholders to obtain this information. Two transects were run across the watershed and 80-acre tracts were sampled every mile (legal section), given landowner permission. Soil samples were collected by soil type and previous management history. Soil analyses included soil pH, phosphorus, potassium, organic carbon and total nitrogen. A total of 221 soil samples collected from 23 sites showed that 69% of the samples tested high or very high in phosphorus. Potassium levels were more normally distributed with 30% of the samples testing in the optimum soil test class. Organic carbon averaged 1.92% and total nitrogen averaged 0.22% of the soil by mass. Additional analysis will examine variation by subwatershed, landscape position, and manure history. Overall, the study was successful and provides important baseline information for the South Fork CEAP project.