Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/15/2007
Publication Date: 3/3/2008
Citation: Nangia, V., Gowda, P., Mulla, D.J., Sands, G.R. 2008. Water quality modeling of fertilizer management impacts on nitrate losses in tile drains at the field scale. Journal of Environmental Quality. 37:296-307. Interpretive Summary: Tile drained row cropland in the Midwest United States is one of the major contributors to the hypoxia in the Gulf of Mexico. This is because tile lines expedite the movement of nutrients from agricultural systems to streams and rivers. Strategies to reduce nitrate loadings to the Gulf of Mexico require better understanding of effects of spacing and depth of tile lines. This study evaluated the effect of tile spacing and depth on tile flow and nitrate losses in two commercial fields in south-central Minnesota. A water quality simulation model was used for this purpose. Results indicated that reductions in nitrate losses are possible by decreasing tile depth or increasing tile spacing.
Technical Abstract: Subsurface tile drainage system is one of the major carriers of nitrate-N from cropland to river systems. Consequently, tile drained row cropland in the upper Midwest United States is one of the major contributors to the hypoxia in the Gulf of Mexico. Strategies to reduce nitrate-N loadings to the Gulf of Mexico require better understanding of effects of tile spacing and depth on flow and nitrate-N losses from tile drained field. This paper evaluates the sensitivity of nitrate-N losses to changes in the spacing and depth of subsurface tile drainage systems. For this purpose, the Agricultural Drainage and Pesticide Transport (ADAPT) model was calibrated and validated using monthly flow and nitrate-N losses measured in tile drains during 1999-2003 from two commercial (west and east) fields in south-central Minnesota. For the calibration period, there was good agreement between observed and predicted flow and nitrate-N losses with r2 values of 0.87 and 0.85, respectively. During validation, there was excellent agreement between observed and predicted flow and nitrate-N loads with r2 values of 0.92 and 0.91 for the west field, and 0.94 and 0.90 for the east field, respectively. The calibrated model was used to evaluate the effects of tile drain spacing and depth with a 50 yr record (1954-2003) of daily precipitation. Simulation results indicated that reductions in nitrate-N losses are possible by decreasing depth or increasing spacing of tile drains. For instance, for a spacing of 40 m, reducing tile depth from 1.5 to 0.9 m reduced nitrate-N losses by 31%, while for a tile depth of 1.5 m, increasing spacing from 27 to 40 m reduced nitrate-N losses by 50%.