Evaluating Growth-Stage-Based Variable Deficit Irrigation Strategies for Improving Yield and Irrigation Water Use Efficiency of Grain Sorghum

Highlights Four irrigation levels were simulated over four sorghum growth stages, resulting in 256 scenarios. Boot to early grain filling stage was found to be the most sensitive stage to water stress. Maximum irrigation water use efficiency (IWUE) achieved with less irrigation than that required to achieve maximum yield. A strategy with 70% deficit in the first stage and 10% deficit in the remaining stages was found ideal based on yield in normal years. A strategy with 70% deficit in the first and fourth stages and 10% deficit in the remaining stages was found ideal based on IWUE in normal years. ABSTRACT. Recurring droughts, declining groundwater levels in the Southern Ogallala Aquifer, and projected warmer and drier future climate pose major challenges for irrigated grain sorghum [Sorghum bicolor (L.) Moench] production in the Texas High Plains (THP) region. Managed deficit irrigation during different growth stages could improve sorghum yield and irrigation water use efficiency (IWUE). This study aimed to develop and evaluate growth-stage-based variable deficit irrigation (GSVDI) strategies for grain sorghum production in the THP region under different weather conditions (e.g., dry, normal, and wet years). The CERES-sorghum module within the Decision Support System for Agrotechnology Transfer (DSSAT) Cropping System Model that was previously evaluated based on a grain sorghum-cotton rotation experiment at Halfway, TX, was used. Four growth stages of sorghum were considered, namely, emergence to panicle initiation (GS1), panicle initiation to boot (GS2), boot to early grain filling (GS3), and early to late grain filling (GS4). Long-term (1978-2019) simulations were conducted with combinations of four deficit irrigation levels (30%, 50%, 70%, and 90% evapotranspiration [ET] replacements) applied during the aforementioned growth stages, which resulted in 256 GSVDI scenarios. Efficient irrigation scenarios were identified as ones that resulted in both simulated yield and IWUE levels in the 95 th percentile of the 256 considered. Among them, the ideal GSVDI scenarios were identified for each weather category based on simulated sorghum yield and IWUE. The identified ideal GSVDI strategies were then compared with the control scenario (100% ET replacement in all growth stages). The results indicated that implementing GSVDI strategies could lead to significant irrigation water savings while maintaining higher sorghum yields. For example, S-64 (strategy of 30% ET replacement in GS1 and 90% ET replacement in GS2 to GS4) was identified as the ideal GSVDI scenario for normal years, and it saves 12.2% of irrigation water with a minor loss (1% less) in grain sorghum yield as compared to the control scenario. Suggested GSVDI strategies from this study could be very useful to optimize sorghum production while reducing groundwater withdrawals from the Ogallala Aquifer. Keywords: CERES-sorghum, DSSAT, Evapotranspiration, Ogallala Aquifer, Sorghum grain yield, Texas High Plains.