Different Fertility Approaches in Organic Hemp (Cannabis sativa L.) Production Alter Floral Biomass Yield but Not CBD:THC Ratio

Abstract

Industrial hemp is once again legal in the United States but agronomic practices are not well characterized, especially for organic production systems. Many producers are concerned that while increased fertility may increase biomass yield it will also disproportionally increase that rate of total tetrahydrocannabinol (THC) accumulation, making their crop more likely to be noncompliant at harvest. We measured the effect of four organic fertility treatments: (1) no fertility (NA); (2) manure-based compost (CM); (3) an industry-standard organic fertilizer blend (ST); and (4) an intensive fertility treatment designed for cannabis production (BQ), on biomass yield and cannabinoid accumulation over multiple timepoints and two years. We found that higher fertility (ST and BQ) led to increased biomass but did not influence the ratio of cannabidiol (CBD) to THC over time. We also found the ST treatment yielded the most consistently across years, whereas CM and BQ were less predictable and more costly, respectively. Our results show that fertility recommendations can be made to increase biomass yield without increasing the chance of noncompliance. Additional research addressing specific fertility requirements in organic cropping systems for hemp will be needed to meet consumer demand while remaining profitable and sustainable for growers.