Field-Scale Nitrogen Balances Associated with Long-Term Continuous Corn Production
1998
Karlen, D. L. (Douglas L.) | Kramer, Larry A. | Logsdon, Sally D.
Excessive residual soil NO₃-N indicates economic inefficiency for producers and increases the potential for nonpoint leaching of N to water resources. Our objective was to construct an approximate fieldscale N budget for continuous corn (Zea mays L.) grown on deep loess soils in four 30- to 60-ha field-scale watersheds in western Iowa. Preplant and postemergence soil NO₃-N levels were determined for the 0- to 30-cm, 30- to 60-cm, and 60- to 90-cm depths in April before N fertilizer was applied and again at the V6 growth stage. A simple root-zone water balance and N removal by corn grain were determined. The 4-yr average showed approximately 100 kg ha⁻¹ of NO₃-N in the upper 90 cm of the root zone before an average of 168 kg of fertilizer N ha⁻¹ was applied. Grain removal accounted for 30 to 70% of the fertilizer N. There were significant differences in grain yield and N removal among the four watersheds. Factors contributing to those differences included different fertilizer rates, tillage practices, and application times. During the four study years, an average of 50% of the applied N was available for leaching, denitrification, and/ or NH₃ volatilization. High levels of residual soil NO₃-N following continuous corn production coupled with steady percolation of precipitation that infiltrated but was not used by the corn crop appear to be the two major factors supplying NO₃-N to groundwater baseflow that enters streams draining the watersheds. Based on the seasonal water balance, the most successful N management strategies will be those that minimize the amount of residual NO₃-N remaining in the soil profile at the end of the growing season.
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