Hemp

Cannabis sativa ssp.

General info

Hemp is one of the most ancient ‘domesticated’ crops in the world, it originated in temperate Asia but migrated worldwide. It is a naturally herbaceous dioecious plant that can grow between 1 – 6 meters tall and produces woody stalks. Though hybrid varieties have been developed that are monoecious to improve reproduction and uniformity of plants for agricultural plantation purposes. It is among the fastest growing plants on earth alongside bamboo.

Whilst certain strains were bred for their high THC content (1 – 20%) and hallucinogenic properties, other varieties were bred for their excellent fibre potential for utilisation as canvas and cordage (which inherently had lower THC values, max 0.2% in Europe for example). Alongside its well-known and -studied medicinal benefits, Hemp has numerous applications from pulp/papermaking to textiles and bio composites.

Cultivation and agronomy

Yields range from 2 – 18 tonnes ha^-1 yr^-1 depending on cultivars, environment and cultivation techniques. Optimal temperature growth is between 13 – 22 °C making it feasible for growth outdoors in some temperate environments. It has a variety of self-protective properties, making it resistant to diseases and insect damage, reducing biocide requirements. It also requires far less water than crops such as maize and other bioenergy crops. For liquid fuel biodiesel considerations, hemp was demonstrated to outperform canola, soybean, and corn and was only marginally outperformed by oil palm produced biodiesel, with regards to L/ha (hemp – 784 L/ha) it notably had lower sulphur content and a higher flash point temperature than most of these making it a desirable biodiesel. Since the production of biodiesel from hemp doesn’t utilise the straw or seeds, this can act as a desirable production strategy for increased economic benefits.

Despite this, solid fuel considerations of hemp, including briquettes and pellets, are far better with a significantly high value of around 100 GJ ha^-1 yr^-1 which, whilst lower than some competing energy crops, is mitigated by the low growth requirements of hemp and possible co-production benefits. It possesses a higher heating value of 19.24 MJ Kg^-1 comparable to, and exceeding, species such as poplar and willow. The strong fibres are a challenge to cultivation requiring adapted machinery. Post-harvest separation and processing are also required to achieve the highest economic gain from the crop.