Hemp is considerably more efficient (high annual yields with low agrochemical/fertilizer input) than the traditional annual bioenergy crops (sugar beet and oilseed rape) and possesses similar greenhouse gas mitigation potential to the perennial bioenergy crops Miscanthus and willow (Finnan and Styles, 2013). Annual bioenergy crops like hemp can be appealing options for farmers to diversify and explore the bioenergy market without the demands of perennials, namely high establishment costs and long-term commitment (15–20 years) of their land to bioenergy (Finnan and Burke, 2013; Finnan and Styles, 2013).
Hemp biomass has good combustion properties and could be used to generate either heat or electricity (Finnan and Styles, 2013). There are multiple biofuel options: Biogas, solid fuel briquettes, bales, and bioethanol (Kraszkiewicz et al., 2019; Prade et al., 2012, 2011).
As hemp is an annual crop it can be readily integrated into crop rotation cycles, thus not competing with food supplies and can therefore contribute towards sustainable cropping systems (Finnan and Styles, 2013). Moreover, hemp has been reported to improve yields of crops subsequently grown thus complementing food production. Winter wheat planted after hemp had 10–20% yield increases (Bócsa and Karus, 1998), with similar observations recorded for soybean and alfalfa (Adesina et al., 2020). A low input crop, hemp can produce high yields similar to switchgrass and sorghum but with lower nutrient and pesticide requirements (Das et al., 2017). Hemp offers the combined potential of an effective break crop and an efficient energy crop, thus generating income while promoting productivity. Break crops like hemp can be used to disrupt pest cycles and the ability of hemp to tolerate high planting densities suppresses weed growth, thus pesticide and herbicide requirements of subsequently, cultivated crops are reduced (Bhattarai and Midmore, 2014). The hemp root system promotes soil health, as the large taproots penetrate deep into the soil facilitating aeration, but simultaneously forms soil aggregates to prevent soil erosion (Amaducci et al., 2008). Model analysis comparing the relationship between leaf nitrogen status and photosynthesis rate in hemp, cotton and kenaf revealed hemp to have a high photosynthetic capacity, even at low nitrogen levels (Tang et al., 2017). This provides an additional line of evidence that hemp may fulfil a future niche as a sustainable bioenergy crop that can be cultivated over a wide range of climatic and agronomic conditions.

11. Future prospects: Phytocannabinoids without Cannabis: In vitro synthesis using cell cultures

Phytocannabinoids have high potential for medical but also recreational use and therefore their production and extraction are of high commercial interest. However, plant breeding and cultivation come with their own challenges and phytocannabinoid yield and profiles can highly depend on environmental factors. Cell cultures methods are a powerful tool for the production of high-quality plant material in a manner that is time efficient, seasonally independent, and which can satisfy good manufacturing practice guidelines (Tekoah et al., 2015). This technology has attracted a lot of attention as it can allow the harvesting of high value products produced within cells in suspension or secreted into their surrounding medium (Weathers et al., 2010). Improvement of culture growth kinetics and product yield can be achieved via medium optimisation (Holland et al. , 2010; Ullischet al. , 2012; Vasilev et al. , 2013) and by selecting for high-producing cell populations using techniques such as fluorescent marker-based cell sorting (Kirchhoff et al. , 2012). Cell lines optimised in these ways can subsequently be cryopreserved to ensure consistent production going forward (Ogawa et al. , 2012).
Secondary metabolites, including pharmacologically valuable compounds such as paclitaxel and scopolamine or transgenic proteins to be used as vaccines, antibodies, immunomodulators and other therapeutics are already produced in cell suspension cultures on a commercial scale (Mountford, 2010; Paul et al., 2015). Hence, this might be a promising avenue to produce cannabinoids as well (Figure 10).