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Title:   Author  item
                                            Malone, Robert

                                                         - *Rob*item
                                            HUTH, N - CSIROitem
                                            CARBERRY, P - CSIROitem
                                            Ma, Liwangitem
                                            Kaspar, Thomasitem
                                            Karlen, Douglasitem
                                            Meade, Terryitem
                                            KANWAR, R - IOWA STATE UNIVERSITYitem
                                            Heilman, Philip

                                                         - *Phil*
  Submitted to: Geoderma
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/7/2007
                                    Publication  Date: 7/19/2007
                                    Citation: Malone, R.W., Huth, N., Carberry, P.S., Ma, L., Kaspar, T.C., Karlen, D.L., Meade, T.G., Kanwar, R.S., Heilman, P. 2007. Evaluating and predicting agricultural management effects under tile-drainage using modified APSIM. Geoderma. 140:310-322.Interpretive Summary: Poor nitrogen management in subsurface drained agricultural basins in the U.S. Midwest is one factor contributing to increased nitrate loading in the Mississippi River.  Promising conservation practices to reduce nitrate loading include correct timing of N application and planting cover crops after grain harvest.  In general, however, conservation practices have only been tested over a few years and limited environmental and management conditions.  An accurate and management sensitive simulation model for tile-drained Midwestern soils would help optimize agricultural management practices.  Therefore, we enhanced the Agricultural Production Systems Simulator (APSIM) for tile-drainage, tested the modified model for several management scenarios, and then predicted nitrate leaching with and without winter wheat cover crop.  For the most part, the model accurately predicted yearly drainage, crop yield, and nitrate leaching and responded accurately to treatment differences.  A winter wheat cover crop was predicted to reduce nitrate loading 42% under forty-nine years of corn-soybean rotations and 150 kg N/ha applied to corn.  The modified model APSIM-DRAIN should help agronomists, soil scientists, and agricultural engineers design agricultural systems that reduce nitrate leaching while maintaining crop production goals.
                                Technical Abstract: An accurate and management sensitive simulation model for tile-drained Midwestern soils is needed to optimize the use of agricultural management practices (e.g., winter cover crops) to reduce nitrate leaching.  Our objectives were to enhance the Agricultural Production Systems Simulator (APSIM) for tile-drainage, test the modified model for several management scenarios, and then predict nitrate leaching with and without winter wheat cover crop.  Twelve years of data (1990-2001) from northeast Iowa were used for model testing.  Management scenarios included continuous corn and corn-soybean rotations with single or split N applications.  For 38 of 44 observations, yearly drain flow was simulated within 50 mm of observed for low drainage (<100 mm) or within 30% of observed for high drain flow with minimal calibration.  Corn yield was simulated within 1500 kg/ha for 13 of 24 observations.  For 34 of 45 observations yearly nitrate load was simulated within 10 kg N/ha for low loads (<20 kg N/ha) or within 30% of observed for high loads.  Several of the poor yield and nitrate loading predictions appear related to poorly simulated N-uptake.  The model accurately predicted greater corn yield under split N application (140-190 kg N/ha) compared to single 110 kg N/ha application and higher drainage and nitrate loads under continuous corn compared to corn/soybean rotations.  A winter wheat cover crop was predicted to reduce nitrate loading 42% (324 vs. 557 kg N/ha with and without cover) under forty-nine years of corn-soybean rotations and 150 kg N/ha applied to corn.  These results suggest that APSIM-DRAIN is a promising tool to help estimate the relative effect of alternative management practices under fluctuating high water tables.


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