For the second year in a row, Cultivators organized, with the support of GreenTech Americas in Mexico to help lead the conversation around hydroponic leafy greens in Latin America. Together with partners and speakers from across the value…
Published on 27/08/2021
Introduction
With experience in the recreational and medicinal cannabis industry, Cultivators observe a shift towards compound production instead of production for kilograms. Thus, ensuring safe and sound ingredients is critical for cannabis growers.
A multidisciplinary team of students from Wageningen University and Research (WUR) have been commissioned to conduct interviews with stakeholders within the supply chain and to perform a literature review based on these observations. Their report investigates which cropping methods and crop strategies exist. It can be used to steer the production of specific secondary metabolites, responding to the needs of cannabis buyers and consumers.
They address this through the following questions:
Cultivation Methods
Cannabis sativa L. is mainly cultivated for its flowers. As it is believed that in cannabis cultivation, the composition and concentration of these secondary metabolites (e.g. cannabinoids and terpenes) are more important than the overall yield. Leading to, cultivation methods that alter the growing environment have the potential to influence the composition and concentration of secondary metabolites. However, these correlations are not yet fully understood.
Since, the concept of crop steering has become a popular topic in cannabis cultivation. Due to traditional crops where yield is of great interest and the focus in cannabis cultivation may shift to cultivation for compounds. Unfortunately, there is little information on cultivation steering in cannabis, leaving growers to rely on anecdotal information. This presents a challenge for both experienced and inexperienced growers to improve their knowledge of crop steering.
Specifically, crop steering is the manipulation of the growing environment to influence, for example, hormonal levels within the plant, which result in a desired plant structure and/or chemical profile. Basically crop steering utilises cues that promote vegetative or generative growth through three main factors: Climate, root zone and crop architecture management. Steering vegetatively tends to be done through low electrical conductivity (EC), higher water content, lower VPD, lower temperatures, and lower light intensities. Steering generatively is obtained in more stressful environments through higher EC, lower water content, higher VPD, drought stress, higher temperatures, and higher light intensities.
Furthermore, the breeding and selection of phenotypes mainly control the dry floral yield and cannabinoid concentration within C. sativa (Muntendam et al., 2012). Although genetics largely determine the phenotype, environmental factors can alter it depending on the degree of plasticity, allowing different phenotypes to express (Fig. 1). When targeting specific compounds, the phenotypic traits of interest include cannabinoid profile, terpene profile, trichome size and density, and effects (medicinal or recreational).
Control over phenotypic expression drives revenue, as the previously mentioned characteristics determine variables such as active-compounds kW-1, extract-yield batch-1, operating-cost pound-1, and trim-to-flower-ratio. The expression of phenotypic traits is mainly influenced by ten parameters: light, temperature, airflow, nutrients, microbes, oxygen, water, carbon dioxide, and humidity.
Moreover, different cultivation methods effectively steer the cannabinoid concentration in cannabis. Researchers have demonstrated the effectiveness of lighting (Magagnini et al., 2018), fertilisation (Bócsa et al., 1997; Caplan et al., 2017), substrate (Caplan et al., 2017), air temperature (Chandra et al., 2011; Latta & Eaton, 1975), and photoperiod (Potter, 2009).
Figure 1: The degrees of plasticity affect how environmental parameters influence the phenotype
Drought Stress
Controlled drought stress (dry-backs) overnight or between irrigation cycles (Fig. 2) can be a useful tool to enhance the production of secondary metabolites in oil-producing crops (Caplan et al., 2019). The effect of dry-backs on secondary metabolites depends on the choice of an appropriate growing substrate. These, substrates can differ in their physical properties. Such as, substrates with a lower water-holding capacity require more frequent irrigations to maintain stable water content compared to substrates with higher water-holding capacity (Raviv and Lieth, 2008; Zheng, 2016).
Most greenhouse or indoor facilities where C. sativa is cultivated employ soilless cultivation systems, which utilise peat-based substrates or inert substrates, such as stone wool (Farag and Kayser, 2015). Full control over water content within the substrate enables controlled exposure to stress, which may lead to an increased production of secondary metabolites in C. sativa (Caplan et al., 2018).
Several studies have demonstrated that drought stress strongly stimulates the production of secondary metabolites in various herbaceous species (Baher et al., 2002; Bettaieb et al., 2009; Kleinwächter and Selmar, 2015). Researchers have shown that drought stress not only increases the concentration of secondary metabolites but also boosts oil yield (Bettaieb et al., 2009; Nowak et al., 2010).
Nonetheless, drought stress can also reduce yields, as it limits carbon assimilation through stomatal closure and metabolic constraints (Chaves, 1991; Flexas et al., 2002). Therefore, growers must apply drought stress at the right time and intensity to minimise yield loss while maximising secondary metabolite production (Nakawuka et al., 2014).
Figure 2: Irrigation practices for applying controlled drought-stress during the dark period (source: Trym – Growers Guide to Crop Steering)
Flowering in C. sativa lasts between seven and twelve weeks, depending on the cultivar and growing conditions (Potter, 2014). C. sativa inflorescences have been shown to increase in mass most during the first four to six weeks of flowering. So for this reason, applying drought stress during the early stages of flowering would not be beneficial as yields could be negatively affected.
Conclusion
With many classic cultivation parameters such as, light quality and intensity have been researched for cannabis cultivation. These cultivation methods have been widely applied, but their effects have not been tested sufficiently. As cannabis is highly hybridised due to interspecific hybridisation between subspecies, different responses are seen between studies.
Particularly cultivar differences, studies dedicated to light quality and intensity reveal differences in parameters, which, in turn, make comparing results a challenge. Moreover, the effect of nutrient composition on secondary metabolism remains an under explored subject and currently appears to depend on the chosen cultivar, the substrate, and the plant’s developmental stage.
Cultivation methods that allow for controlled stress, such as drought stress, may have future applications in steering the production of compounds. Though the cannabis industry is still quite new, more research on cannabis, standardisation, and genomics is required. Cultivation specifically for compounds is an even newer field, and scientific literature on this in the context of cannabis is more limited.
The next section investigates cultivation methods used in other crops to identify possible ways to improve secondary metabolite concentration.
Opportunity for cultivation of compounds in different crops
Cultivation for high secondary metabolite concentration has been the focus long before the professionalisation of the cannabis market. However, in recent years, expertise entering the cannabis cultivation industry from different horticultural backgrounds has led to a more scientific approach in improving compound yields and overall quality.
Although researchers have studied secondary metabolite content in other crops, now the cannabis market has taken the lead in this area. Growers of crops cultivated for compounds have not yet begun altering or selecting for specific compounds. Such as vanilla for flavour, herbs for aroma, and medicinal crops. Instead, they currently focus on achieving high yields, without defining quality in terms of compound composition (Filip van Noort, Researcher, Wageningen University & Research, personal communication).
The most significant developments in research concerning cultivation methods in cannabis cultivation have focused on optimising growth conditions. Especially lighting (spectrum) has shown promising results in influencing the secondary metabolite profile in other crops (Manivannan et al., 2015; Ortega-Hernández et al., 2019; Shiga et al., 2009).
The connection between growers and processors
To provide insight into the needs of different industries regarding cannabis cultivation, specifically compound-based cultivation and we conducted interviews with various players in the industry. We approached companies across all sectors of the cannabis industry, including hemp, recreational, wellness, medicinal, and pharmaceutical, as well as other stakeholders such as growers, breeders, and field experts (Fig. 3). In this chapter, we summarise their views on key questions related to compound-based cannabis cultivation.
Figure 3: market overview of the cannabis industry
Conclusion
Requests for compound composition in cannabis (including hemp) differ across various industries.
In turn, the interviews offered valuable insights into different aspects of the cannabis industry. However, due to time constraints and the interview methodology, they reflect expert opinions rather than a universal truth about the industry. Therefore, future research should prioritise large-scale questionnaires to capture a more comprehensive perspective.
Firstly, the pharmaceutical and medical cannabis sectors, end-user effects determine the desired compounds. These industries require consistent compound composition, which demands a controlled and stable growing environment. If scientific studies fail to demonstrate the effects of individual cannabinoids or combinations beyond CBD and THC, these compounds hold no interest for this sector. However, the absence of intellectual property protection and the high investment needed to make clinical trials involving cannabinoids is unlikely.
Secondly, the recreational cannabis industry appears to allow more flexibility in developing cultivars with distinct cannabinoid and terpene profiles that cater to customer preferences. As most countries still prohibit recreational cannabis cultivation, consistent compound composition is not guaranteed. Furthermore, the industry lacks a standardised quality testing method to ensure uniform compound profiles. Addressing these issues is essential before pursuing individual compound specificity.
In the wellness sector, compound composition currently holds less importance. However, increased regulation of CBD use and the introduction of quality standards may shift this focus in the future.
Discussion & Advice
Based on our interviews, there is no self-awareness and clear product requirements of processors, which makes it difficult for cultivators to comply with the required quality standards. So, we recommend that you promote and maintain active communication between processors and growers by showing the mutual benefits in this relationship. This could happen by inviting both parties to a conference.
The interviewed experts agreed that genotype determines the secondary metabolite profile, so breeders play a more significant role than environmental conditions in shaping it. Once growers standardise cultivation, establish GACP and GMP protocols, and achieve consistent production, they can implement specific cultivation methods to influence compound profiles and enhance quality. Crop steering offers the potential to modify secondary metabolite composition.
The most promising techniques include adjusting the light spectrum (e.g., UV-B exposure, increased blue light) and applying controlled abiotic stress. These approaches could further enhance product quality and compound yield in the future.The industry has not yet reached a stage where growers actively steer and control compound profiles. In five to ten years, when cultivation is standardised, growers and processors engage in active collaboration, and steering methods gain scientific validation, these techniques may become applicable to high-quality production.
Until then, we advise the following:
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