Late-season Irrigation Lapses Impact the Physiology, Yield, and Metabolite Production of Yakima Valley Hops

This study investigates the effects of irrigation water loss late in the season on hop physiology, cone yield, quality, and essential oil composition in the Yakima Valley, a critical hop-growing region in the United States. The study examines the impact of withholding irrigation 15 days and 30 days before harvest, comparing these treatments with an untreated control during a 2-year period. A lapse in irrigation late in the season caused significant plant physiological changes, including reduced stomatal conductance, transpiration, and photosynthetic efficiency despite soil water levels remaining above critical levels. Withholding irrigation water 15 days before harvest reduced yield moderately (9.5%), while at 30 days, the lapse caused more severe declines (28.8%), emphasizing the vulnerability of hops to a lapse in irrigation earlier in the lupulin gland formation stage. Despite these challenges, bittering compounds like α-acids and β-acids showed exceptional stability across all irrigation regimes, suggesting that stress from a lapse in irrigation or drought conditions do not significantly compromise brewing quality. In contrast, essential oil composition showed notable variability. Monoterpenes, such as geraniol, linalool, and ocimene, decreased following a lapse in irrigation, likely due to disrupted photosynthesis. On the other hand, sesquiterpenes like humulene and caryophyllene generally increased under water shortage conditions, particularly with earlier water stress, suggesting an upregulation of sesquiterpene biosynthesis. Our findings suggest that the impact of late-season water shortages may be mitigated by maintaining soil water content at or near full capacity in anticipation of irrigation disruptions. This research provides valuable insights to inform adaptive irrigation practices and support the sustainability of hop production under changing climatic conditions.