Modeling for Best Management of the Effects of Irrigation Frequencies, Initial Water, and Nitrogen on Corn

Crop water and nitrogen production functions (CW-NPF) used in irrigation (I) management need to integrate the effects of climate, initial soil water levels at planting (Iw), amounts and frequencies of irrigations, and N levels. Field experiments integrating these factors and their interactions on crop responses are lacking as they are expensive to conduct. The objective of this modeling study was to study the effects of these factors and explore ways of enhancing the corn (Zea mays L.) irrigation water use efficiency (IWUE) and nitrogen use efficiency (NUE) and minimizing residual soil and leached N. The study was an extension of the corn experiments conducted in a sandy loam soil near Greeley, CO from 2008 to 2011, using the Root Zone Water Quality Model (RZWQM2). We simulated corn response to varying Iw, I amounts and frequencies, and N levels. For each of four levels of Iw (low, medium, high, and average), irrigation was applied at frequencies of 3, 7, 10, and 14 d to supplement rainfall to meet the potential crop ET demand from 0 to 100% at 10% intervals. N rates were 0 to 300 kg ha−1 at 50 kg ha−1 intervals. The simulated grain yield was higher at higher I frequencies and Iw. NUE increased with I up to 60% ET replacement but plateaued thereafter. For higher IWUE and NUE with minimum soil residual N, optimum N rates for grain yield for I levels of 40, 50, 60, 70, 80, 90, and 100% ET replacement were 50, 100, 100, 150, 200, 200, and 200 kg N ha(−1), respectively. For optimum grain yield, 3- to 7-d irrigations to replace 90% ET losses and N at 200 kg ha(−1) were the best management choices simulated. The results demonstrate the value of validated process-based crop system models in developing site-specific irrigation and N recommendations for enhanced IWUE and NUE in corn production.