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
‘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
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.
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
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
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
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
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
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