Phytochemical Changes and Product Potential of NM Grown Hemp Varieties as Influenced by Production Location and Cultural Practices

There are two main objectives to this research: 1) evaluate how the phytochemistry of common hemp varieties differs from their expected profiles when grown at multiple sites throughout New Mexico as influenced by environmental conditions and production practices; and 2) determine how phytochemical profiles in resulting hemp crops impact choices for post-harvest processing to ensure a profitable feedstock is maintained for downstream product manufacturing.

Licensing was obtained from the NMDA per the hemp plan approved by the USDA according to the final rule for Establishing A Domestic Hemp Program (2021). Licenses for each trial site were obtained prior to procuring propagative materials and planting. The production trials are being conducted at three NMSU facilities representing the different geographical regions of the state: the Leyendecker Plant Science Center in Las Cruces (south), the Agricultural Science Center at Los Lunas (mid), and the Sustainable Agriculture Science Center at Alcalde (north). Each location is currently operating under annual production licenses that were issued on March 18, 2022 and are valid until November 13, 2022.

Four hemp varieties are being grown at three trial locations with duplicate plots. The varieties include CBD-type (varieties: Sweetened and The Wife) and dual purpose grain/fiber-type (varieties: Orion 33 and Future 32) hemp. The CBD varieties were chosen due to their use in trials the previous year and popularity among NM producers. The dual purpose varieties were chosen in order to screen new genotypes for low-latitude suitability, since these had not been grown in NM previously. One of the two plots at each site is being managed by a standard set of best production practices. The other plot is being subject to a treatment or management practice specific to the local growing regions. The standard practices were based on extension publications and guidelines from states with successful hemp programs (Southwest Hemp Extension Council, 2020; University of Vermont, 2019). All sites are equipped with drip irrigation. The cultural/sustainability treatment at each site is specific to challenges facing that area or the research speciality of the particular location (Table 1).

Table 1. Summary of planting dates and cultural/sustainability treatments applied at each trial location

^* Transplanting and direct seeding were performed approximately 2 weeks after the historic last frost dates (± 5 days) at each location (Old Farmer’s Almanac, 2021; Southwest Hemp Extension Council, 2020)

^† Companion planting crop failed due to miscommunication; seedlings were mistakenly removed during general field maintenance as weeds

All CBD-type seedlings were transplanted by-hand. Seedlings were planted 3 feet (0.9144 m) apart, in six rows of five plants each, per each plot. The grain-type varieties were direct seeded at a rate of 30 lb/acre, in alternating rows (3 per plot) 30 ft in length. A diagram depicting the design of a single plot is provided below.

Figure 1. Plot design for trial locations

Because clonal propagative material was not available, all CBD-type transplants were grown as seedlings for four weeks by the supplier. Plants were notably stressed and root-bound upon pick up from the supplier at the time of the first planting. As a result, the transplants at Leyendecker were all stressed upon planting on April 18. However, the seedlings for the other sites were transplanted from 1-inch cells to 4-inch pots and kept in an outdoor shade house until the other plantings on May 3 and May 13 and showed improved growth/mortality compared to the initially placed transplants at Leyendecker.

There are not defined conditions for management of pest, diseases, weeds, or nutrient deficiencies (including pesticide/herbicide applications and micronutrient supplementation). The purpose of this is to allow for observations about these issues to be documented such as prevalent weed species, present diseases, symptoms of nutrient deficiency. Taking note of all the potential issues under the conditions at each trial location will allow for development of the most realistic recommendations for producers to consider.

Although there is a dominant view among CBD-hemp producers that the presence of male hemp plants in a field will dramatically decrease CBD content, this has been disputed by fiber/grain producers. In this study, therefore, any male plants of the dioecious fiber and grain varieties will not be removed. This will allow observation of the percentage of males appearing and how that presence of males impacts CBD content of the female floral structures. This will also allow for observation of the yields of fiber and grain materials, in addition to CBD content, indicating the potential of the tested varieties to be grown as dual-purpose crops.

Monitoring for legal compliance will be conducted regularly throughout the production season. Sampling methods will be performed as per the USDA final rule for Establishing A Domestic Hemp Program (2021). The first test will be conducted at the initiation of flowering, after which plants will be tested every two weeks. Once monitoring results indicate plants are nearing their legal limit (total THC > 0.3%), a harvest notice will be filed with NMDA. After the NMDA harvest inspection and final potency analysis has been completed by Scepter Labs in Santa Fe, NM, the plants will be hand harvested. 

Plants are predicted to be harvested toward the end of September 2022. Upon harvest, plants will be dried in a space with both temperature and humidity control. The drying conditions are to maintained at 60-70 °F and 45-55% humidity (University of Vermont Extension, 2019) until moisture content reaches approximately 8-10% (Żuk-Gołaszewska & Gołaszewski, 2020). After drying, the major components (stalks, seeds, flowers, and leaves) will be separated and the yields recorded for each plant by weight. The average weights of each component per variety per management technique at each location will be determined from the plant replicates. Floral material will be analyzed for cannabinoid content and essential oil profiles. American Society of Brewing Chemists (ASBC) methodology will be used for characterization of biomass (primarily floral material) due to the limited number of accepted standardized analysis methods for hemp, and because of the similarity between hops and hemp inflorescence from their shared family phylogenetic categorization. Each analysis will be performed in triplicate to obtain data for statistical analysis. Approximately 500 g of biomass per experimental variety/treatment will be used to perform the following analyses (adapted from):

• Moisture content by oven drying (ASBC Hops Method 4, 2008)
• Essential oil extraction by steam distillation (ASBC Hops Method 13, 2008)
• Essential oil characterization by gas chromatography with flame ionization detection (ASBC Hops Method 17, 2004)
• Cannabinoid solvent extraction and characterization by high performance liquid chromatography (Mandrioli et al. 2019)

Materials required for hemp production and analysis described above include:

• Hemp seedlings: 90 per variety (180 total)
• Hemp seeds: approx. 1/4 pound per variety (less than 1 pound per variety)
• Irrigation equipment and supplies
• Fertilizer
• Drying space (climate-controlled space)
• Solvents/analysis gases
• Standards (cannabinoids, essential oils)
• Sample storage containers

To accomplish the second research objective, a subset of floral biomass will be processed into oil using supercritical fluid extraction (SFE). SFE using carbon dioxide is one of the most common methods for obtaining cannabinoid-rich oil from hemp biomass (Ramirez et al., 2019). The same processing method will be applied to hemp from each trial location and the extracts analyzed for cannabinoid content and essential oil profile using the following methods:

• Lab-scale supercritical CO₂ extraction (Rochfort et al., 2020)
• Cannabinoid content – final product (Sexton et al., 2018)
• Essential oil profile – final product (Sexton et al., 2018)

Materials required for objective two are the same as those needed for objective one (solvents, gases, standards, containers).

Production and analysis of hemp from the production trials will provide the following results for each variety for each management style: yields, average plant cannabinoid content, average plant essential oil profile, average extract cannabinoid content, and average extract essential oil profile. Statistical analysis will be performed to determine which relationships are significant. This will allow comparison of product quality from similar management practices at different geographic locations and from different management practices at the same locations, thus enabling recommendations for producers regarding cultivar selection and best management practices to yield the highest quality product.