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Monitoring Tile Systems in Iowa: Overview and Results

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan www.asabe.org

Citation:  2016 10th International Drainage Symposium Conference, 6-9 September 2016, Minneapolis, Minnesota  .(doi:10.13031/IDS.20162490464)
Authors:   Christopher H. Hay, Adam Kiel, Anthony Seeman, Peter Kyveryga
Keywords:   nitrate, nutrients, subsurface drainage, water quality.

Abstract. The Iowa Nutrient Reduction Strategy calls for target load reductions of 41% for nonpoint sources of nitrogen. Nitrate from agricultural subsurface drainage systems is a major contributor of nitrogen loading to Iowa surface water. The Iowa Soybean Association tile monitoring program was established to inform farmer and stakeholder decisions on strategies for reducing nitrogen loading from subsurface-drained landscapes in Iowa. In 2015, there were 250 subsurface drainage monitoring sites and 1,740 water samples collected. Management data were collected for 110 fields associated with monitoring sites. Mean nitrate-nitrogen concentrations across all samples were 15.4 mg L–1. Nitrogen load from the drainage systems was highly correlated with discharge and moderately with concentration. Nitrate-N concentrations were greatest from the Des Moines Lobe region of Iowa. Both nitrate-N concentrations and nitrogen loads were greatest from corn-corn systems than from corn-soybean rotations. Nitrate-N concentrations were greater from fields with full width tillage, but nitrogen loads were similar to those from no till or strip till. Fields that used cover crops in the previous non-growing season had reduced nitrate-N concentrations compared to those without cover crops; however, nitrogen loads were greater from the cover crop fields. Despite the limitations of this one-year observational data set, the data provide a picture of nitrate-nitrogen concentrations and nitrogen loading from drainage systems in Iowa under current practices. Additional years of data collection will further contribute to our knowledge of nitrogen losses from subsurface drainage systems.

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