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Title:   Author  item
                                            Malone, Robert

                                                         - *Rob*item
                                            Ma, Liwangitem
                                            Heilman, Philip

                                                         - *Phil*item
                                            Karlen, Douglasitem
                                            KANWAR, R - IA STATE UNIVERSITYitem
                                            Hatfield, Jerry
  Submitted to: Geoderma
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 5/7/2007
                                    Publication  Date: 7/19/2007
                                    Citation: Malone, R.W., Ma, L., Heilman, P., Karlen, D.L., Kanwar, R.S., Hatfield, J.L. 2007. Simulated N Management Effects on Corn Yield and Tile-Drainage Nitrate Loss. Geoderma. 140:272-283.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 loss from agricultural fields include correct N application amount and planting winter cover crops after grain harvest.  In general, however, conservation practices have only been tested over a few years and limited environmental and management conditions.  A thoroughly tested model shown to be accurate and management sensitive for tile-drained Midwestern soils would help optimize agricultural management practices.  Therefore, we tested the Root Zone Water Quality Model (RZWQM) for response to 5 chemical fertilizer and five swine manure treatments with fourteen years of field data and then predicted nitrate leaching and corn yield for 22 different management strategies.  For the most part, the model accurately predicted yearly crop yield and nitrate leaching and responded accurately to treatment differences.  A winter wheat cover crop was predicted to reduce average annual nitrate loss in tile drains 5-6 kg N/ha, which appears consistent with published field studies and may be a treatement to ameliorate agricultural management with potential for elevated N loss such as swine manure application to soybean.  The tested RZWQM can be used to quantify the relative effects of corn production and N loss under several alternative management practices but caution should be used for simulation of fall N application because N loss may be overpredicted in these scenarios.  The tested and calibrated model RZWQM should help agronomists, soil scientists, and agricultural engineers design agricultural systems that reduce nitrate leaching while maintaining crop production goals.
                                Technical Abstract: Thoroughly tested simulation models are needed to help quantify long-term effects of agriculture. Our objectives were to evaluate the Root Zone Water Quality Model (RZWQM) response to different N management strategies and to then use the tested model with observed weather data from 1961-2003 to quantify the long-term corn (Zea mays L.) yield and N loss. Fourteen years (1990-2003) of field data from 30-0.4 ha plots in northeast Iowa were available for model testing. Annual crop yield, nitrate loss, flow weighted nitrate concentration, and drainage for various management scenarios were averaged over plots and years to create five chemical fertilizer and five swine manure treatments. Predicted corn yield and flow weighted nitrate concentration in tile drainage for the 10 treatments were correlated with observed data (R2 > 0.83).  The long-term simulations indicate that average corn yield plateaus and N loss accelerates as quadratic functions of increasing spring UAN-N rates from 100 to 200 kg N/ha. Winter wheat (Triticum aestivum L.) sowed after corn and soybean [Glycine max (L.) Merr.] harvest was predicted to reduce long-term N loss by 5 to 6 kg N/ha, which appears consistent with published field studies and may be a treatment to ameliorate agricultural management with potential for elevated N loss such as swine manure application to soybean. Although RZWQM may overpredict winter nitrification under fall N application, after calibration and thorough testing RZWQM can be used to quantify the relative effects of corn production and N loss under several alternative management practices.


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