CROP ROTATIONS WITH FULL AND LIMITED IRRIGATION AND DRYLAND MANAGEMENT

Irrigated cropping systems need to maximize the economic value of both rainfall and irrigation water, especially in areas of declining groun dwater. This study compared water management systems in a winter wheat (Triticum aestivum, L.)-corn (Zea mays, L.)-soybean (Glycine max, L.) (W-C-S) and continuous corn (CC) rotation in west central Nebraska fo r dryland, limited irrigation (150 mm/yr), and full irrigation. Crop y ield, evapotranspiration, and soil water storage were determined from field studies conducted at North Platte, Nebraska, on a Cozad silt loa m (Fluventic Haplustoll) soil. Dryland corn used 21.5% more evapotrans piration (ET) in the W-C-S rotation compare to CC. ET for the limited and full irrigation corn was 4.6% and 4.9% more for the W-C-S rotation compared to the CC and was statistically significant at the P > 0.08 level. Water use efficiency, defined by the slope of the linear relati onship between grain yield and ET (partial derivative Y partial deriva tive ET-1), was the same for corn in the W-C-S and CC rotations. Corn grain yield response to irrigation and ET was more than the yield resp onse of winter wheat and soybean. The W-C-S rotation increased corn gr ain yields in two out of three years at this location for dryland mana gement and increased the seasonal ET of corn compared to continuous co rn. Full irrigation management did not consistently increase winter wh eat and soybean grain yields above the limited irrigation treatments. Soil water storage for the full irrigation management was greatly redu ced compared to dryland and limited irrigation management for both rot ations.