Hemp cultivation - the potential

Most people probably associate ‘cannabis’ with the narcotic known variously in its many forms as ganja, hashish, marijuana, or by a assortment of slang terms of which dope, grass, hash, pot and weed are probably the least offensive.

Cannabis has a bad reputation. For example, it is from ‘hashish’ that the English word ‘assassin’ is derived - social-justice-seeking Shia Ismaili Islamic militants, based at Alamut mountain in Iran, were described by their establishment opponents as hashish-drugged terrorists.

‘Ganja’ is derived from the Sanskrit ‘ganjika’, and it was considered a sacred narcotic in ancient India. It has been used for millennia in ayurvedic medicine, to treat neuralgia, gout, rheumatism, delirium tremens, insanity, infantile convulsions and insomnia; and generally for easing pain. The oil is used in healing inflammations and nervous ailments, for example de Quervain’s tenosinovitis.

However, the plant has many other uses, neither recreational nor medicinal. There are 41 European-licensed varieties of cannabis, with low levels of tetrahydrocannabinol (THC) which is what provides the narcotic effect.

Medicinal purposes

The narcotic-producing, high-THC variety of cannabis probably originated in South-central Asia. The ancient Greek historian Herodotus reported, circa 480 BC, that the Scythian people of the Eurasian steppes smoked the plant. However, varieties of cannabis have been grown in China for 10,000 years, the fibre being used to make cloth, shoes, ropes and even paper.

Cannabis plantation

American presidents George Washington and Thomas Jefferson both grew cannabis and its cultivation was practically obligatory in the colonies of the British Empire. The reason was that the Royal navy needed hemp (another name for cannabis): canvas (the term derives from the Latin cannabis) sails as well as hemp rigging were required in profusion by sailing ships.

A typical naval vessel required about 80 tonnes of hemp rope and sails, which had to be replaced every 3-4 years. Hence, each ship required about 40 hectares of cannabis to be kept in continuous cultivation.

The use of hemp rope was phased out after ‘Manila hemp’ (obtained from the Abacá plant, Musa textilis), which is less vulnerable to water rot, was introduced. Other uses of the fibre declined after the introduction of petroleum-based synthetic fibres. Recently, however, hemp fibres have made something of a comeback.

Cannabis, for industrial hemp, is cultivated legally in a variety of countries, notably China, France, Chile, North Korea and Russia. The varieties (generally cultivars of Cannabis sativa) grown for industrial purposes are generally low in THC (0.3 percent or less), although varieties with high levels of the substance are raised commercially for medicinal purposes.

Cannabis is an ideally ‘green’ crop. It requires no herbicides, few pesticides or fertilisers and has one of the fastest biomass growth rates (upto 25 tonnes per hectare) known. Unlike cotton, it does not require copious amounts of water.

It can be used for weed control, its thick and high foliage and high planting density minimising weed seed content of the soil without the use of herbicides. It can also be used to clear out toxic matter from the soil, animal litter and from wastewater and sewage. It is being used to remove radioactive and other contaminants from the Chernobyl nuclear disaster site.

Each tonne of hemp straw yields about 400 kg of bast fibre (strong fibres from the outside of the stem) and 600 kg of hurd (the fibrous, decorticated core material). The yield of straw from one hectare can be as high as nine tonnes, that of seed over one tonne. It is grown at very high density for straw and moderate density for seed (and low density for medicinal purposes).

Hemp seed can be used can be used as a nutritious food item, as animal fodder or to obtain hemp oil which, in turn can be used as food or as biodiesel - known as ‘hempoline’. The waste hurd is now used for producing ‘hempcrete’ building blocks or to make viscose, the fluid from which rayon and cellophane is made.

However, it is the bast fibre which is the really valuable part of the plant. It is used for rope and for hemp cloth, which is becoming increasingly important. Hemp fibre has greater heat resistance and moisture absorption than cotton. Its high rate of absorption of toxic gases makes it an excellent household textile material.

The problem with the bast fibre is the high content of lignin, which makes it stiff and binds it together. Hence for clothing it must be spun with cotton or other, softer fibre materials. Chinese scientists have recently developed techniques for reducing the lignin content from 10 percent to 0.2 percent, making hemp fibre far more viable as a textile material.

Textile industries

The use of hemp in plastics and in paper making has also increased. Hemp fibres are used in composites, for example with glass and other fibres in automotive body panels. Mercedes Benz C-class cars contain up to 20 kg of hemp. Hemp fibre paper is much less damaging to the environment than tree-paper: it does not cause deforestation, and is bleached with hydrogen peroxide rather than toxic chlorine bleach.

Sri Lanka spends a lot of time and money eradicating illicitly grown narcotic cannabis plants. However, it could learn from countries which grant licences to farmers to grow low-THC hemp for seed and fibre, particularly from China.

China is actively pursuing a pro-hemp policy. It currently cultivates industrial hemp on about 20, 000 ha, compared to 5.6 million acres in cotton. A hemp processing mill with an annual throughput of 50,000 tonnes of hemp fibre has been set up at Xishuangbana, in China’s Yunnan Province, mainly for use in cotton-hemp blends.

Sri Lanka could use the labour of the farmers in backward areas to produce licensed, low-THC hemp to supply our textile industries as well as the paper mills. They could also concurrently be growing our diesel fuel.