Economic return versus crop water productivity of maize for various nitrogen rates under full irrigation, limited irrigation, and rainfed settings in south central Nebraska

Field research was conducted at the University of Nebraska-Lincoln South Central Agricultural Laboratory (SCAL) located near Clay Center, NE, in the growing seasons of 2011 to 2014. A partial economic analysis was conducted for maize (Zea mays L.) at nitrogen (N) fertilizer treatments of 0, 84, 140, 196, and 252 kg ha^-1 under full irrigation (FIT), limited irrigation (75% FIT), and rainfed settings for all growing seasons and then compared to crop water productivity (CWP) measured as crop water use efficiency (CWUE) and irrigation water use efficiency (IWUE). Nitrogen fertilizer increased CWUE and IWUE in all growing seasons. The CWUE values ranged from 0.90 to 2.81 kgm^-3 and the IWUE values ranged from -1.01 to 3.24 kgm^-3. Operational costs and net income varied among treatments and across years. Irrigation and N fertilizer rate had an interacting effect (P_0.05 < 0.05) on both gross and net income in 2011, 2012, and 2013. Net income was maximized under rainfed settings with a N fertilizer rate between 140 (dry year) to 196 kg ha^-1(wet year); in contrast, the optimal N fertilizer rate under irrigated conditions was 196 kg ha^-1. Positive relationships were observed between relative net income (RNI) and CWUE with R² values of 0.72, 0.87, and 0.84 for rainfed, 75%FIT, and FIT, respectively, as well as between RNI and IWUE with an R² value of 0.96 for 75% FIT and 0.86 for FIT. Lower CWUE and IWUE values were associated with lower RNI. With consideration to CWUE, IWUE, and partial factor productivity of N, full irrigation management is recommended under non-water-limiting conditions and limited/deficit irrigation management strategies (e.g., 75% FIT) under water-limiting conditions, with N fertilizer rate not exceeding 196 kg ha^-1 to achieve a high economic return for the study area.