Increasing water and N use efficiency and lowering environmental pollution are primary concerns for both agricultural production and environmental quality in northwestern China. A 2-yr field experiment was conducted to assess and model the effects of irrigation, N, and plant density on maize ( Zea mays L.) when N fertilizer and irrigation were separated in an alternating furrow irrigation system. Regression modeling (a ternary quadratic equation) showed that N fertilization positively affected yield, water use efficiency, N uptake, soil NO 3-N, and NH 3 volatilization. Irrigation improved yield, N uptake, and increased soil NO 3-N in the deeper soil layer (0.6-2.0 m) but reduced water use efficiency, NH 3 volatilization, and soil NO 3-N in the 0- to 0.6-m soil layer. Planting density positively affected yield, water use efficiency, and N uptake but negatively influenced NH 3 volatilization and soil NO 3-N. The combination of 255 kg N ha -1 N fertilizer, 100 mm of irrigation water, and 59,467 plants ha -1 in 2010 and 245 kg N ha -1 N fertilizer, 98 mm of irrigation water, and 58,376 plants ha -1 in 2011 resulted in maximum income for maize yield (7245 kg ha -1 in 2010 and 6972 kg ha -1 in 2011). However, environmental and agronomic objectives did not match. Specifically, the combination of N, irrigation rate, and plant density with maximum yield increased N leaching and NH 3 losses, whereas the combination lowering environmental pollution due to N losses caused a reduction in yield. Therefore, the trade-off in management of N, irrigation, and planting density was emphasized for both environmental and agronomic benefits in our study.
