Bi-weekly Bulletin
Vol. 7 No. 23
December 16, 1994
Hemp
(Cannabis Sativa)
Prior to the end of World War II, hemp made a significant
contribution to the economic and social fabric of society. In competition
with cotton, jute and other fibre crops, it was used extensively for ropes,
twines, tough thread, textiles, paper, building materials, cellulose plastics
and resins as well as food and oil from the seeds. However, since it belongs
to the species Cannabis sativa, its production was made illegal in some
of the developed countries in the mid-1930s. Growing interest in adaptation
and diversification has created new opportunities for hemp. Several European
countries have passed legislation allowing its commercial cultivation under
license. In Canada, cannabis sativa (hemp) can only be grown for research
purposes under the license granted by the Minister of Health. This issue
of the Bi-weekly Bulletin examines the agronomics and economics of hemp
production.
History of hemp
World production of vegetable fibre was 22.7 million
tonnes in 1992 with hemp accounting for slightly more than one half of
one per cent. Production of hemp originated in Central Asia over 8500 years
ago. From the 16th to the 18th century, hemp and flax were the major fibre
crops in Russia, Europe and North America. During the late 19th and early
20th centuries, increasing labour costs encouraged a shift away from hemp
to cotton, jute and tropical fibres which were less labour intensive. Technological
advances, such as the cotton gin, encouraged production of competitive
crops . This decline has continued, due to the advent of synthetic fibres
and because the cultivation of hemp has been made illegal in many countries.
In 1937, the United States government imposed a heavy tax on producers
under the Marijuana Tax Act. Canada prohibited production in 1938 under
the Opium and Narcotics Control Act. During World War II, the Canadian
and U.S. governments lifted the restrictions on hemp production to provide
materials for the war effort.
World production peaked in 1940 at about
832,000 tonnes of fibre. After the war, the restrictions were reapplied.
In the early 1960's, the U.S. deemed it unconstitutional to tax production
and therefore removed the tax but retained the requirement for a growers
permit. In 1961, the Canadian Narcotics Control Act (CNCA) allowed Cannabis
to be grown, at the discretion of the Health Minister, for research purposes
only. In 1992, world production of hemp fibre was 124,000 tonnes with India,
China, Russia, Korea and Romania as the major producers. In 1994, under
the CNCA, one license was granted to a Canadian company, Hempline Inc.,
to grow hemp in Canada under the strict supervision of the authorities.
Hemp is distinct from marijuana
Although hemp and marijuana are from the same plant
species, they have different uses and physical characteristics. Hemp generally
refers to the fibre-producing strain of Cannabis. Marijuana usually refers
to a mixture of leaves and flowers that is used for the drug, delta-9 tetrahydrocannabinol
(THC). A THC level of 0.3 per cent is specified in some studies as delimiting
narcotic and non-narcotic strains of Cannabis, although narcotic strains
generally average three to five per cent THC, about 10 to 15 times the
delimiting value.
New strains of low THC hemp have been
developed by the French. However, many of the traditional cultivars formerly
grown in Canada and the U.S. contained very low amounts of THC. Increased
worldwide demand for products developed from the hemp fibre, hurds and
seed has resulted in a renewed cultivation of hemp in Europe and the crop
is being considered by other countries.
Bill C-7, the Controlled Drugs and Substances
Act, was introduced Feb. 2, 1994 by the Ministers of Health and Justice
to bring Canadian law in line with international accords to which the country
is party. The Bill is in the committee stage being considered for possible
amendments. If passed it would replace the CNCA and parts III and IV of
the Food and Drugs Act. The cultivation of hemp would still be illegal
without a license issued by the Minister of Health.
Agronomic characteristics
Hemp is a herbaceous annual that can reach up to
nine metres in height, but under cultivation it averages between two to
four metres. In four months it can produce seven to 15 tonnes per hectare
(t/ha) of dry stalk. It is dioecious (having male and female flowers borne
on separate plants), but monoecious cultivars have been bred. Modern plant
breeding in Europe has produced several dozen hemp strains with the emphasis
on the creation and perfection of monoecious varieties. Selecting monoecious
strains overcomes the problem of different maturation times between male
and female plants, and results in consistent height and weight of the stalk
for more uniform quality and higher productivity. Hemp is a short-day plant,
and since production has historically bee n concentrated in north-temperate
areas, fibre selections are generally photoperiodically adapted to mature
in early fall.
Hemp stalk
The stalk is harvested for the fibre and hurds.
The centre of the stalk is hollow except at the nodes (where the leaves
are attached) and in the best fibre producing types the hollow space occupies
at least one-half the diameter. Next is the innermost layer or pith surrounded
by thick, short woody cells which support the plant during its growth.
The adherent woody core, after it is freed by retting, is referred to as
hurds. Outside of the hard woody portion is the soft cambium, or growing
tissue which develop into the hurds on the inside, or into the bast and
bark on the outsides. It is in this layer that the fibre bearing bast splits
away from the hurds during retting and breaking. Outside of the cambium
is the phloem parenchyma, comprised of short, thin-walled cells, filled
with chlorophyll giving it a green colour, and long thick walled cells,
making the bast fibres. Between 15 to 35 fibre bundles are found in this
layer. Outside of the primary bast fibre is the cortex, which is a continuation
of the thin-walled chlorophyll-bearing cells free from fibre. The outside
of the stalk is covered by a thin epidermis.
There are three types of fibre: primary
bast fibres which are long and low in lignin, secondary bast fibres which
are of intermediate length and high in lignin content and libriform fibres
which are short and high in lignin. Fibre length and the contents of cellulose
and lignin are important quality parameters for raw materials used in the
cordage, textile, paper and fibreboard industries.
Frost tolerant
Hemp grows best in a humid environment when the
ambient temperature ranges between 14C and 27C, although it can endure
greater temperature variations. Hemp grows best with plenty of rainfall
during the growing season, especially during the first six weeks. Once
well rooted, hemp can endure dry conditions although it hastens maturity,
dwarfs growth and reduces yields. Depending upon the area and rainfall
conditions, hemp is usually planted between early March and late May in
the northern latitudes when the ambient temperature is around 10 =C. Seedlings
can survive a short frost of -8 to -10 = C while older plants tolerate
frosts of -5 to -6 = C. Since hemp is sensitive to photoperiod, the earlier
plantings produce better crops.
Seeding
The optimum seeding depth is two to four centimetres
(cm). Row spacing is usually 6 to 15 cm when using a narrow-width seed
drill. The proportion of stem biomass and the content of the more valuable
bast fibres in the stem increases with plant density, therefore dense crops
are usually desired. Recommended seeding rates for fibre hemp vary between
40 and 150 kilograms per hectare (kg/ha), corresponding to plant densities
shortly after emergence of about 200 to 750 plants par square metre. If
the hemp is grown as a seed source then the seeding density ranges from
1 to 24 kg/ha (5 to 120 plants par square meter). Unless plant densities
are very low (10 to 30 plants par square meter) the hemp crop will suppress
weeds, and herbicides are not required. When planted on fertile soils,
hemp is the best smother crop for all kinds of weeds. If the hemp makes
a short, weak growth, owing to unsuitable soil, drought or other causes,
it will have little effect in checking the growth of weeds, but a good
dense crop will leave the ground practically free from weeds at harvest
time.
Low net nutrient requirement
Hemp grows best on rich and fertile, neutral or
slightly alkaline, well-drained clay-loam or silt-loam soils in which the
subsoil is fairly retentive of moisture. Although hemp makes heavy nutrient
demands on the soil, research conducted at Canadian experimental farms
during the 1930s showed that hemp takes less from the soil than wheat or
corn when taking into account that up to 70 per cent of the nutrients absorbed
by the plants are returned to the soil, in particular with the large numbers
of failing l eaves and through the retting process. Cleaning or mechanical
stripping of the leaves and flowers in the field also allows for maximum
nutrient recycling. However, prior to the nutrient recycling, hemp extracts
more nutrients per hectare than grain crops, removing about two to three
times as much nitrogen, three to six times as much phosphorus, and 10 to
22 times as much potassium per hectare, owing to fast biomass production.
Therefore, to achieve an optimum hemp
yield, at least twice as much nutrient must be available in an easily assimilable
form as will finally be removed from the soil by the leaf-free harvest.
Fertilizer rates vary depending on soil type, end use of the plant and
crop rotation. A three-year, but preferably a four-year rotation, such
as cereals, clover for green manure, corn, hemp and then back to cereals
is recommended to help maintain soil fertility.
Harvesting
Harvesting of hemp for high quality fibre occurs
as soon as the crop is in flower. Harvesting for seed production and fibre
occurs four to six weeks after flowering, however the fibre will be of
poorer quality because of lignification of the bast fibre ma king it stiff
and course. If the goal is maximum stem yield, the implication for fibre
hemp breeders is clearly to breed late- or non-flowering cultivars.
A lapse of nearly 60 years in the development
of hemp harvesting equipment in North America requires some innovative
ideas. Equipment developed for other fibre crops, such as Kenaf, may be
used for hemp with minor modifications. Attempts at using sickle m owers,
haybines and round balers have been used with some success depending on
the end use of the hemp stalk. Requirements for chopped stalk by the pulp
and paper and fibreboard industry would allow the use of these types of
equipment.
Harvesting hemp for the long bast fibre
for the cordage and textile industries requires the fibre to be undamaged
negating the use of haybines and balers. To ensure the long bast fibres
are undamaged a retting process is required.
Retting
This is the process of decomposition by bacteria
and moulds by which the pectin that binds the fibre and the non-fibrous
portion of the stalk is broken down. Once the binding agent is broken down,
the fibre and the stalk are easily separated. There are se veral different
retting procedures that can be used.
Dew retting is the traditional method
induced by frequent rains and dews. After the hemp stalk is cut, it is
spread evenly on the ground to allow decomposition of the pectin. There
is a fine line between retting and rotting. If continued wet weather prevents
the straw in the field from being lifted at the proper time, it becomes
over-retted and is of little value. Without the proper equipment dew retting
is labour intensive. It may take one to two weeks if the weather is warm
and humid, b ut usually four to five weeks are required. The retting process
is followed by a period of drying and the bunches are then stored for further
processing. The fibre from dew retted hemp is light brown in colour and
rather coarse. It is used primarily for t wine, cordage and fine paper.
Water retting: Bundles of hemp are submerged
in clear water low in calcium and chlorides allowing bacterial activity
to break down the pectin. The average retting period is seven to 10 days
after which retted bundles are then rinsed, wash ed, sun-dried and stored
for fibre extraction. Although water retting is more costly than dew retting,
the fibre is of a higher quality. It can be combed one or more times, refined,
dyed, spun and woven into whatever extent is required for cable, rope,
st ring, thread, cloth, clothing, linen, etc.
Warm water retting is similar to water
retting but the hemp is soaked for 24 hours then new water is added and
brought to an elevated temperature for about two to three days. A very
uniform, clean fibre is produced.
Green retting: As the name implies, green
stalks are mechanically processed to separate the fibre from the stalk.
The high quality fibre can be refined for the textile industry while the
remaining stalk can be used in the paper and fibre board industries.
Chemical retting: Hemp stalks are placed
in a processing tank where chemical agents are used to dissolve the pectin.
By maintaining a constant processing temperature the retting time can be
reduced to 48 hours while producing a very hig h quality fibre.
After the retting process the hemp fibre
and the stalk are loosely held together and must be decorticated, scutched,
hackled and combed to remove the remaining pieces of stalk, broken fibres
and extraneous material. Mechanical decortication equipment can be used
in conjunction with turbine scutchers to separate the fibre and the nonfibrous
portion of the stalk. Inventors and implement companies are working together
developing machinery to harvest and process hemp for the textile, paper,
fibreboard and see d industries.
Hemp hurds
In 1916, USDA predicted a papermaking future for
nonfibrous portions of the hemp stalk. Extraction of the fibre from the
hemp stalks results in a second highly useful by-product called "hurds".
The lignin content of the hurds is lower than in wood, offeri ng better
opportunities for non-chlorine bleaching or the production of unbleached
pulp. The hurds, about 45 per cent cellulose, 35 per cent hemicellulose
and 20 per cent lignin, can be used to produce a variety of products -
rayon, fuel, cellophane, food additives, industrial fabrication materials,
and paper products. Before 1883, about 75 to 90 per cent of the world's
paper was manufactured from hemp bast fibre. In 1989, 92 per cent of the
virgin fibre used to manufacture paper came from wood, the remai ning eight
per cent was from annual crops or other residues. As world paper consumption
increases by about four per cent annually, interest in hemp as a potential
raw material for paper production has been revived since hemp can produce
more paper per hec tare than 20-year-old trees. Another prominent end-use
for hemp is industrial fabrication. Hemp fibres and hurds are an excellent
natural material used in the manufacturing of lumber, plywood, particleboard
or composite construction material.
Hemp seed and oil
The seed is light brown to dark grey, in some cases
mottled, containing between 25 to 35 per cent oil and 25 per cent protein.
Hempseed contains eight essential proteins and three essential fatty acids.
It can be ground up and used in soups, cereals, cakes and other foods.
Raw hempseed has commonly been used as feed for domesticated animals. The
oil pressed from hempseed contains 55 per cent (flax has 58 per cent) linoleic
acid and 25 per cent linolenic acid. Hemp oil is among the lowest in saturated
fats at eight per cent of total oil volume; canola contains six per cent.
Oil extracted from the seeds can be used
in paints, varnishes, cooking, burning and precision lubrication, as well
as in cosmetics and medical uses. Seed yields ranging from 400 to 940 kg/ha
have been reported.
Is it profitable to grow?
YIELD
Market returns from hemp stalk, fibre, hurds
or seed depend on the quantity, quality, end use and the amount of value
added processing. Ongoing research in Eastern Europe and Asian countries
have improved hemp yield characteristics. For example, dry stem yields
of 15 t/ha, 2.6 t/ ha of total fibre and 0.94 t/ha of seed have been recorded.
PRICE
C&S Specialty Builder's Supply Inc. in
Harrisburg, Oregon will pay Cdn $60 to $75 a tonne landed basis for defoliated
chopped stalk. This is on par with the price of wood chips presently used
by fibreboard manufacturers. Others in the industry say hemp sh ould command
a premium because of its superior characteristics compared to wood fibre.
Harvesting chopped stalk is the lowest common denominator, generating a
gross revenue of about $750 per hectare, yield Gross Revenue comparable
to Ontario Corn. However , revenue for the raw fibre is not captured. Until
fibre extraction facilities are available, the raw stalk option remains
attractive until the infrastructure required is in place. Under optimum
conditions this would allow the raw fibre and the hurds to b e sold separately
generating larger returns per hectare.
Research and development is ongoing worldwide
to develop mobile processors to crush, hammer and sift the hemp for use
in the pulp and paper and fibreboard industries. It is estimated that value-added
processing would reduce transportation costs by allowin g 10 to 20 times
more material to be shipped per volume. Lower transportation costs would
increase net returns to the producers if end-users were closer to the source.
Canada Cordage, located in Kitchener, Ontario is the only cordage company
in North Amer ica that processes natural fibre crops. At $800 per tonne
for raw bast fibre, hemp would compete with imported jute which is processed
into yam, rope and electrical cable-filler.
Prices shown in the table are gross values,
therefore production and transportation costs need to be factored in to
determine farmgate prices. If hemp is approved for industrial or commercial
production the prices would reflect supply and demand. The cost of production
would also decline, for example, if certified seed were imported from the
Ukraine it would cost at least $2,700 a tonne landed basis. If certified
seed was propagated domestically the price would decline substantially.
Although foreign varieties of hemp do
well in their homeland it remains a question as to how well they would
do in Canada. Since hemp production was prohibited in Canada there has
been limited preservation of germplasm in gene banks. Coupled with the
exte nded lapse in North American breeding programs and declining interest
in maintaining cultivars, an impoverishment of germplasm resources has
resulted. Nevertheless, an enormous reservoir of natural variation is maintained
by wild, weedy forms, which may p rove invaluable in the future.
Future Prospects
Although alternative fibre crops have usually proven
to be more competitive in the past, a reawakening to hemp's industrial
potential is being observed worldwide. In an age increasingly interested
in sustainable agriculture and crop diversification, hemp offers some attractive
possibilities. It is exceptionally disease and herbivore-resistant, can
be easily grown in a wide range of agricultural systems and is an excellent
rotation crop which eliminates weeds. It is extraordinarily productive
of biomass, a nd has been shown to have excellent potential for textile
and cordage, paper, building materials, cellulose plastics and resins as
well as using the seed for food and oil.
For further information contact:: Gordon Reichert (204) 983-8473
Bi-weekly Bulletin is published in Winnipeg by the Policy Branch
of Agriculture and Agri-food Canada.
Information and articles in this newsletter may be reproduced with
credit.
Aussi disponible en francais.
Market Analysis Division
Adaptation and Grain Policy Directorate
Agriculture and Agri-Food Canada
P.O. Box 6200
Winnipeg MB R3C 4N1
Telephone : (204) 983-8473
Fax : (204) 983-5524
http:\\www.agr.ca\policy\winn\biweekly\index.htm
World production of Vegetable fibre - 1992
(,000 tonnes)
Cotton 18,064
Jute 3,530
Flax 610
Sisal 383
Hemp 124
Total 22,716
Source: FAQ 1993
Nitrogen Phosphorus Potassium
Crop ............(kg/ha).............
Hemp (Cannabis sativa L.) 102.0 66.0 117.0
Maize (Zea mays L.) 3,000 kg grain 48.0 18.5 5.2
Wheat (Triticum sp. L.) 2,000 kg grain 42.0 21.0 12.5
Rye (Secale cereale L.) 2,000 kg grain 43.0 10.7 10.7
Oats (Avena sativa L.) 1,500 kg grain 29.0 11.5 8.9
Source: Dempsey, J.M. 1975. Fiber Crops. University of Florida Press.
