Hemp yield and cannabinoid concentrations under variable nitrogen and potassium fertilizer rates

With the passing of the 2014 US farm bill, there is more interest in industrial hemp (Cannabis sativa L. < 0.3% total tetrahydrocannabinol [THC]) grown for cannabinoid production. However, production recommendations that outline fertilizer requirements of cannabidiol (CBD) hemp do not exist. Our primary objective was to identify nitrogen (N) and potassium (K) fertilizer rates for maximizing biomass and CBD yield. A secondary objective was to identify the relationships between N and K rates and total THC and total CBD concentrations. Fertilizer rates from 0 to 224 kg N and 0 to 185 kg K ha(-1) were tested separately at four general locations in North Carolina. Two locations were used in 2019 and 2020, while the other two were used only in 2020. Dry weight yield was predicted to increase linearly from 1822 to 3384 kg biomass ha(-1) as N rate increased from 0 to 86.8 kg ha(-1). Nitrogen rates above 86.8 kg ha(-1) were not predicted to increase biomass. Likewise, as N rate increased from 0 to 84.2 kg N ha(-1), CBD yield was predicted to increase linearly from 204 to 389 kg CBD ha(-1). Additional N was not predicted to increase CBD yield. The CBD and THC concentrations showed a slight bell-shaped response curve over increasing N rates, ranging from 11.33% to 12.11% and 0.473% to 0.509%, respectively. Potassium application did not affect yield nor CBD and THC concentrations. Results from this work indicate that N is a more limiting factor than K for maximizing CBD hemp biomass production.