Precision nitrogen management for optimal yield and cannabinoid profile in CBD hemp agronomy

Abstract

Industrial hemp (Cannabis sativa L.), displaying more than 25,000 products, has been grown in North America since the 16^th century. However, knowledge gaps persist in optimizing agronomic practices, including precision nitrogen (N) management, which is crucial for yield and phytochemical quality, for example, delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD). Addressing these gaps, a 2-year field trial (2022 and 2023) was conducted at the Rodale Institute-Pocono Organic Center in Blakeslee, PA, aiming to optimize CBD hemp production through precision N management. Forty experimental plots were established, with each assessing two main factors: (i) N rate: 0, 56, 112, 168, and 224 kg N ha⁻¹ using an OMRI-listed fertilizer, blood meal (12% N) and (ii) application method: banding and broadcasting. The 3-week-old hemp seedlings were transplanted into main plots, followed by fertilizer application and drip irrigation. Parameters including plant height, bud weight, biomass, and CBD yield were assessed, alongside CBD and THC concentrations in floral components and N concentration in leaves and flowers. There was a significant interaction of N rate and application method, impacting biomass yield, while the N rate also influenced CBD concentration. Blood meal supplied at 224 kg N ha⁻¹ yielded the highest biomass and elevated CBD and THC concentrations; however, this did not differ significantly from 168 kg N ha⁻¹ application. Therefore, the recommended optimal N fertilizer rate for Northeastern CBD hemp production is 168 kg N ha⁻¹, with an upper limit of 224 kg N ha⁻¹. Furthermore, the banding method of fertilizer application was more effective than broadcasting.