Irrigation Quantity and Uniformity and Nitrogen Application Effects on Crop Yield and Nitrogen Leaching

The combined effects of irrigation and N management on crop yield and NO₃⁻ leaching have not been extensively investigated. The objective of this study was to quantify the relationships between irrigation management (including uniformity) and N management on corn (Zea mays L.) yield and NO₃⁻ leaching. Yield and N leaching were simulated using the CERES-Maize (version 2.10) model for various combinations of irrigation amounts and uniformity and N amount and timing of split N applications for semiarid conditions typical of Tulare County in California. Simulated grain yield increased, reached a plateau, and then decreased with increase in applied water under uniform irrigation. The amount of applied water above which yield decreased was higher for the higher N application rate and the later simulated split N application. The simulated amounts of N leached were consistent with the yield results. The higher water applications that lead to reduced yields were associated with higher N leaching for a given N application amount. The effects of irrigation were simulated assuming Christensen's Uniformity Coefficient (CUC) of 100, 90, and 75. The results were only slightly affected by CUC = 90 compared with 100. A CUC of 75 caused a reduction in yield and increase in N leaching compared with uniform irrigation. The lowest CUC required a higher N application to achieve the same yield as uniform irrigation. Under nonuniform irrigation, it is impossible to manage either water or N application in a manner to achieve high yields without considerahle NO₃⁻ leaching. High yield and low NO₃⁻ leaching are compatible goals and can be achieved by appropriate irrigation and fertilizer management for irrigation systems that have a CUC of 90 or greater. Research supported by California Fertilizer Research and Education Program.