Semi-arid regions are reliant on supplemental irrigation to produce large-yielding and high-quality malt barley (Hordeum vulgare, L.). Current and widespread drought in the western United States is of particular concern as surface and ground water reductions are occurring that affect irrigation water availability. Implementing a seasonal deficit of water compared to evapotranspiration (ET) is a potential mechanism to reduce water usage if yield and quality can be maintained. Research was conducted at the University of Idaho Aberdeen R&E Center, Aberdeen, Idaho on the effects of deficit irrigation on yield, grain quality, and malt characteristics of barley. Five genotypes were selected to represent those used for large-scale adjunct brewing and those targeted at the all-malt craft industry. Irrigation was managed at three rates (100%, 75%, and 50%) of estimated crop evapotranspiration (ETc) using a sprinkler irrigation system. Total aboveground dry matter (TDM) was not affected by irrigation until soft dough (Feekes 11.2; F11.2). Yield was similar within a genotype with irrigation reduction from 100% ETc to 75% ETc. Averaged across genotypes, yields were 6936 kg ha-1 at 100% ETc and 6297 kg ha-1 at 75% ETc. At 75% ETc, protein was just below the adjunct target of 130 g kg-1, excluding Harrington, and no genotype stayed below 120 g kg-1, the all-malt target. Deficit irrigation is promising, particularly for adjunct brewing; however, expected changes to malting quality profiles must be understood and varietal selection, breeding advancements, and/or changes to malting criteria may be needed for successful implementation of deficit irrigation
