Impacts of irrigation system, irrigation rate, and cultivar on hemp production in the semiarid Intermountain West

Abstract

The industrial hemp (Cannabis sativa L.) industry rapidly emerged in Utah in 2019 with nearly 480 ha of production. Production declined rapidly due to flooded floral hemp markets, but the industry is still viable in the state. Two of the most pressing questions about hemp management among growers in this region include cultivar selection and irrigation management. An outdoor hemp research trial was established in 2020 near Logan, UT (41.66 N, −111.91 W), to investigate fundamental irrigation strategies and cultivar performance. This trial (2020–2021) examined combinations of three hemp cultivars, four irrigation technologies, and three irrigation rates (100%, 75%, 50% of estimated evapotranspiration of corn [Zea mays L.] given lack of data for hemp) nested within each irrigation technology. Female hemp clones were transplanted in late May and harvested in September and October based on flower maturity. The irrigation technology (mid-, low-elevation spray, low-elevation precision application, and mobile drip) had no significant impacts on hemp yield or cannabinoid concentrations. Hemp biomass yield and cannabidiol concentrations often increased with less applied irrigation in all irrigation technologies. The three hemp cultivars responded similarly to irrigation management, although there was high plant-to-plant variability in delta 9 tetrahydrocannabinol (THC) concentrations. This research suggested that floral hemp could be irrigated less than other crops in the region, and irrigation requirements among some hemp cultivars may be similar. Further, robust and representative sampling protocols for THC monitoring are needed to ensure variability is accounted for.