Identification of Priority-based Variable Deficit Irrigation Strategies for Grain Sorghum Production in the Texas High Plains under Increasing Climate Variability

Abstract

Agriculture accounts for 70% of global freshwater usage, majority of which is used for irrigation. Irrigated agriculture in the Texas High Plains (THP) region of the United States highly depends on groundwater availability in the Ogallala Aquifer. Rapidly declining groundwater levels, recurring droughts and increasing climate variability are primary concerns for crop production in the THP, and they necessitate the adoption of efficient irrigation strategies. The objective of this study is to identify efficient growth-stage-based variable deficit irrigation (GS-VDI) strategies for grain sorghum (Sorghum bicolor L.) production using a prioritization scheme that assigns different priority weights for yield, crop water productivity (CWP), and irrigation under different climate variability classes. The Decision Support System for Agrotechnology Transfer Cropping System Model (DSSAT CSM) CERES-Sorghum model was used to simulate a total of 257 GS-VDI strategies, including a control scenario with 100% evapotranspiration (ET)-replacement and 256 combinations of scenarios developed by implementing four levels of ET-replacement (30%, 50%, 70%, and 90%) in four growth stages of sorghum: (i) emergence to panicle initiation, (ii) panicle initiation to boot, (iii) boot to early grain filling, and (iv) early to late grain filling. A prioritization index was developed to analyse the outcomes of these strategies under three prioritization scenarios: (i) equal priority on yield, CWP, and irrigation (PS-1), (ii) higher priority on yield and CWP (PS-2), and (iii) higher priority on CWP and irrigation (PS-3). All three prioritization schemes identified S-61 (30-90-90-30% ET replacement levels during growth stages one through four) and S-29 (30-50-90-30) strategies as the ideal GS-VDI strategies during dry and wet years, respectively. During the normal years, S-62 (30-90-90-50) was identified as the ideal strategy under PS-1 and PS-2 schemes, whereas S-61 strategy was identified as ideal in the PS-3 scheme. These ideal strategies could save 26% to 42% of irrigation water at the expense of 10% to 20% loss in yield in different years. Results from this study would be useful for producers, farm managers, and natural resource conservationists in their efforts to adopt or promote GS-VDI to maximize cropland productivity and reduce irrigation water usage from the Ogallala Aquifer.