Maize evapotranspiration, yield production functions, biomass, grain yield, harvest index, and yield response factors under full and limited irrigation

South-central Nebraska is one of the most extensively irrigated areas in the U.S., with over 65,000 active irrigation wells, and maize is the major agronomical crop produced. Maize production in this region requires supplementary irrigation for maximum productivity. Effective on-farm implementation of full and limited irrigation practices for potential improvements of crop productivity requires knowledge of locally developed crop yield response to water functions. In this study, the effects of full and limited irrigation practices on maize (Zea mays L.) plant height, leaf area index (LAI), grain yield and biomass production, actual crop evapotranspiration (ETa), yield production functions, yield response factors (Ky), and harvest index (HI) were investigated. Field experiments were conducted in 2009 and 2010 under center-pivot irrigation at the University of Nebraska-Lincoln, South Central Agricultural Laboratory near Clay Center, Nebraska. Four irrigation regimes [fully irrigated treatment (FIT), 75% FIT, 60% FIT, and 50% FIT] and a rainfed treatment were evaluated each year. Maize ETa, LAI, biomass production, grain yield, and HI were significantly affected by the irrigation regimes. Maize yields varied from 9.05 Mg ha-1 for the rainfed treatment to 15.5 Mg ha-1 for FIT in 2009 and from 11.7 to 15.5 Mg ha-1 for the respective treatments in 2010. HI ranged between 0.49 for rainfed and 0.57 for FIT with an all-treatment average of 0.54. ETa ranged from 481 mm for rainfed treatment to 620 mm for FIT in 2009 and from 579 to 634 mm for the same treatments in 2010. Strong yield vs. irrigation relationships (R2 ≥ 0.98 in both years) and yield vs. ETa relationships (R2 = 0.94 in 2009 and R2 = 0.97 in 2010) were measured. There was a strong linear increase in ETa with increasing irrigation amounts (R2 ≥ 0.97). The yield-irrigation and yield-ETa relationships showed variation between the two years due to the impact of weather variability on these relationships, indicating the importance of accounting for weather variability impact on the slopes of crop yield production functions. Based on the slopes of the ETa vs. grain yield relationships, 1.2 Mg ha-1 (in 2009) and 1.7 Mg ha-1 (in 2010) of grain yield was produced per 25.4 mm of ETa beyond 280 mm (in 2009) and 403 mm (in 2010) of ETa that was used by maize to start producing grain yield, which is also called the amount of ETa required for establishing grain yield. Yield response factors varied between treatments and with year for the same treatment and averaged 1.65 in 2009 and 2.85 in 2010, with a two-year average of 1.82. No statistically significant difference (p \u3e 0.05) in grain yield was found between 75% FIT and 100% FIT. In terms of crop response to water performance, the 75% FIT and 60% FIT treatments were very comparable to the fully irrigated treatment and are viable practices in increasing crop water productivity of maize with supplementary irrigation under these experimental, soil and crop management, and climatic conditions