Quantifying and managing corn water use efficiencies under irrigated and rainfed conditions in nebraska using the hybrid-maize simulation model

This study used the Hybrid-Maize model to quantify corn (Zea mays L.) water use and water use efficiencies (WUEs) under irrigated and rainfed conditions at Mead and North Platte in Nebraska. Water use efficiency is quantified using both evapotranspiration (ET) and transpiration (T), respectively, based on 20 yr of simulations. Across-year variations of crop total ET and T and WUE are greater in rainfed fields than irrigated fields. When crop growth is limited by water, crop biomass and grain yield depend strongly on seasonal total ET, while the dependence becomes much weaker or even insignificant once water limitation is eliminated. Seasonal total T is about 81% of total ET under irrigated conditions and 76% under rainfed conditions. Seasonal dynamics of ET and T follows the pattern of crop biomass growth. Evapotranspiration-based WUE is low in the spring when plants are small and the canopy is open, while WUE reaches its plateau shortly before silking. Evapotranspiration-based WUE for total biomass at a plateau ranges from 45 to 55 kg ha^-1 mm^-1, while T-based WUE ranges from 55 to 65 kg ha^-1 mm^-1 in Nebraska. Evapotranspiration-based WUE for grain filling ranges from 50 to 70 kg ha^-1 mm^-1. Eliminating non-water-related crop growth constraints is critical to the improvement of WUE, and meeting crop water demand during the reproductive stage is important for maximizing grain yield in deficit irrigation.