Water productivity of maize in the US high plains

Maize water production functions measured in a 4-year field trial in the US central high plains were curvilinear with 2.0 kg m(-3) water productivity at full irrigation that resulted from 12.5 Mg ha(-1) grain yields with 630 mm of crop evapotranspiration, ETc. The curvilinear functions show decreasing yield but relatively constant water productivity up to 25% ETc reduction. Water productivity declined rapidly with ETc reductions greater than 25% and was zero at about 40% of full ETc because about 270 mm of ETc was required to produce the first unit of grain yield. These results corroborate those of previous studies that show reduction in irrigated area rather than deficit irrigation will usually provide higher net returns if water consumption (ETc) is limited. Water balance techniques adequately estimated ETc when precision irrigation was carefully scheduled and seasonal precipitation was low. Water productivity relationships based on ETc are more transferable than those based on irrigation water applied.