ASSESSING WHEAT YIELD, BIOMASS, AND WATER PRODUCTIVITY RESPONSES TO GROWTH STAGE BASED IRRIGATION WATER ALLOCATION

Increasing irrigated wheat yields is important to the overall profitability of limited-irrigation cropping systems in western Kansas. A simulation study was conducted to (1) validate APSIM's (Agricultural Production Systems sIMulator) ability to simulate wheat growth and yield in Kansas, and (2) apply the model to assess the response of wheat yield, biomass, and water productivity to irrigation allocation based on growth stage. The methodology involved combining short-term experimental data, long-term historical weather data (1950-2013), and mechanistic crop growth simulation to determine optimum irrigation management strategies. The model adequately simulated measured soil water in the profile. The goodness-of-fit test between the observed and simulated values for phenology, yield, biomass, and ET of the experimental cultivar in 2008-2009 in our study site agreed well with the 'Batten winter' wheat cultivar in APSIM. Results indicated that, on average, an irrigation allocation of 100 mm increased wheat yield by 14% to 46% compared to rainfed (dryland) production. Application of an additional 100 mm of irrigation did not improve wheat yield substantially (on average < 0.26 t ha(-1)). Higher water productivity for grain yield was obtained when irrigation was applied at booting and heading. Overall, irrigation water use efficiency for grain decreased with an increase in irrigation allocation. The highest irrigation water use efficiency was simulated for wheat grown with a limited irrigation allocation of 100 mm applied at booting and heading. This study demonstrates that limited irrigation targeted at sensitive growth stages could enhance wheat yields and improve water productivity of water-limited cropping systems.