Maximizing Grain Sorghum Water Use Efficiency Under Deficit Irrigation.

Development and evaluation of sustainable and efficient irrigation strategies is a priority for producers faced with water shortages resulting from aquifer depletion, reduced base flows and reallocation of water to non-agricultural sectors. Under a limited water supply, yield maximization may not be attained by allocating all available water to fully irrigated crops on a fraction of the land base. Deficit irrigated (DI) crops may exhibit equal or greater water use efficiencies (WUE) compared with full irrigation (FI). Managed deficit irrigation (MDI), whereby additional water is allocated during critical growth stages with reduced applications at other periods, may further increase WUE. We evaluated the influence of three irrigation strategies on soil water use, yield and WUE of grain sorghum [Sorghum bicolor (L.) Moench] during three growing seasons on a Torrertic Paleustoll in the High Plains of Texas, USA. Irrigation water was applied with an overhead, lateral move sprinkler with low pressure, mid-elevation nozzles. Soil water contents were measured weekly throughout each growing season from 0.10 to 2.30 m depth at 0.20-m intervals using a neutron moisture meter (NMM). Water contents were also measured at selected locations at high temporal resolution using time domain reflectometry (TDR). Irrigation timing of the FI treatment was determined by managed allowed depletion as determined by measured water contents. The DI sorghum was irrigated at 50% of FI. MDI sorghum was irrigated at 75% of FI during full bloom and 50% at all other stages except prior to differentiation where additional water was withheld compared with DI. Early season soil water evaporation was estimated using TDR-microlysimetry. Crop water use was estimated as the change in stored soil water plus measured precipitation and irrigation assuming negligible runon/runoff and drainage beyond 2.3 m. The FI sorghum exhibited significantly (P<0.0001) greater grain yields than DI and MDI sorghum in all study years. The influence of irrigation strategy on WUE was year dependent; WUE’s of MDI exceeded or equaled FI sorghum WUE in two of the three years.