The cannabinoid profile and growth of hemp (Cannabis sativa L.) is influenced by tropical daylengths and temperatures, genotype and nitrogen nutrition

Hemp (Cannabis sativa L.) has regained worldwide interest as a crop across temperate and subtropical regions. However, there is a paucity of information about the responses of hemp to environmental conditions and interactions between genotype and environment. This study compared the growth responses of a temperate hemp variety (Morphet Late) and three tropical/subtropical varieties (ECO-GH15, ECO-MC16 and ECO-YP16) to tropical daylengths (11.5 h and 12.5 h), temperatures and varying nitrogen (0, 50, 100, 150 kg ha-1 of N) rates. Three experiments under controlled environmental conditions were conducted to test the growth, and cannabinoid production responses to N. Analysis of phenological data revealed significantly different responses between varieties in terms of days to emergence, time to flowering, growth patterns and final biomass showing predominant responses to daylength or temperature depending on the variety. Two tropical/subtropical varieties (ECO-GH15, ECO-MC16) responded similarly under all conditions; the other (ECO-YP16) showed a marked response to temperature rather than daylength, although all varieties had a strong biomass response to N increase. For all varieties, except the temperate variety, the concentration of Δ9-tetrahydrocannabinol (THC), cannabidiol (CBD), and some minor cannabinoids were significantly increased by a one-hour daylength increase. This study highlights the importance of temperature, daylength, and nitrogen for growth, time to flowering, and cannabinoid concentrations of different hemp varieties grown under tropical conditions and shows the importance of selecting low THC varieties for production in tropical/subtropical environments.