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HEMP
PHYSIOLOGY & FACTS
Physiological and Environmental Aspects of
Hemp
HEMP PHYSIOLOGY
Hemp is an excellent source of fibre for the
production of many goods, such as fabric, but in particular, for paper-making
because of its physiological characteristics. Fibre
length, cellulose and lignin contents are important quality parameters of raw
materials for paper (van der Werf,
van Geel, & Wijlhuizen
1995, p2). "Fibre hemp stems consist of
high-cellulose low-lignin bark containing long fibres
and low-cellulose high-lignin core containing short fibres.
The bark, which contains a variable proportion of less valuable secondary bast fibre, is more valuable as
a raw material for paper than the core" (van der
Werf 1994, p30). For more information on any
aspects of hemp physiology, consult Hayo van der Werf's doctoral thesis, Crop
physiology of fibre hemp. He was closely
involved with the Netherlands Hemp Research Programme
(see Part 5.2).
Lignin
Lignin, as defined in the Resource Assessment Commission (RAC) Forest and Timber Inquiry Final Report 1992, is one of
the major constituents of wood, the other being cellulose. Lignin is
the extractive component of wood that binds the cellulose fibres
together and is removed during the pulping process (p519). In
paper-making, lignin is removed by environmentally unfriendly pulping
procedures, (typically bleaching) (van der Werf 1994, p3 1).
Excluding bark and leaves, a tree is comprised of 50% water and 50% solids;
in hardwood trees, like eucalyptus, 28% of the solids is
lignin (Milburn-Clarke, K., pers. comm., 6 June 1995). (As Part 2.1.4
shows, the lignin in hemp bast fibre
is only 4%). When there is a high lignin content, like most trees used
for pulp in Australia,
such as eucalyptus trees, there is consequently a need for more
bleaching. Rance, quoted by van der Werf, found a low lignin
content is desirable because it means less polluting bleaching techniques are
required to remove lignin (1994, p31). Appendix
C is a table showing the cellulose and lignin percentages in
different cultivars studied by the Dutch.
Cellulose
Cellulose, as defined in the RAC Report, is the chief constituent of the cell
walls of plants and forming an essential part of wood and paper (p514).
"Cellulose content is an important parameter, because in chemical
pulping the pulp yield corresponds to the cellulose content of the raw
material" (van der Werf
1994, p3 1).
Length
"The
strength of paper increases with fibre length"
(as cited from Nelson et al. 1961 in van der Werf, 1994 p31) "The anatomy of the stem of hemp is
crucial to its quality as a raw material for paper. The bark contains
primary bast fibres
(about 20 mm long), and may contain secondary bast fibres (about 2 mm long). The core contains fibres 0.5 to 0.6 mm long" (as cited from Bosia 1976 in van der Werf 1994, p30). In comparison, the average fibre length for softwood (pine) ranges between 2.8 to 3
mm. The average fibre length for hardwood
(eucalypt) ranges between 0.8 to 1 mm (Milburn-Clarke, K., pers. comm., 6
June 1995). Because of the extraordinary length of the bast fibres, as compared to the
length of tree fibres used in Australia, bast fibres produce higher
quality goods, such as paper and fabric.
The outer 'bast' fibre
of a hemp stem
The outside portion of a hemp stem is referred to as the. bark or bast fibre.
Bast fibres produce very
high quality paper and they are used to make fabric. This is primarily
due to the long length of the bast fibres. "In the bark, fibres
are longer, cellulose content is higher, and lignin content is lower than in
the core" (van der Werf,
van Geel, & Wijlhuizen
1995, p2).
Bark and core differ in their chemical composition: Bedetti
& Ciaralli (1976) reported 67% cellulose, 13% hemicellulose and 4% lignin in the bark of an Italian
hemp cultivar... Its core contained 38% cellulose and 18% lignin.
Bosia (1976) presented similar results. In
stems from a number of experiments conducted in the Netherlands,
the mean cellulose content of bark was 64.8%, of core it was 34.5%. The
mean Lignin contents were 4.3% in bark and 20.8% in core (as cited from van der Werf et al. 1994a).
As a result, bark is more valuable as a raw material for paper than core and
the value of hemp stems therefore depends primarily on its bark content Van der Werf, van Geel, and Wijlhuizen, 1995,
p2).
The inner 'core' fibre of a hemp
stem
The inner portion of a hemp stem is referred to as the core or hurds. As noted above, the core contains
lower-cellulose, higher-lignin in, and shorter fibre
lengths than the bast fibres.
Paper can be made from the hurds, but it is of a
lesser quality than the paper made from bast fibre. The hurds can be
used to make packaging and cardboard materials. Also, the hurds are used to make animal (horse) bedding and
building materials (see Parts 4.2 & 4.3).
Quality of hemp stem
Since the bark of hemp has properties which make it more suitable for higher
quality paper, it is important to know the proportion of bark in the stem, as
mentioned in Part 2.1.4. "The proportion of
bark in the stem of hemp has been found to vary between 14% and 48% (Bredemann 1952, Arnoux et al.
1969), depending on genotype and plant height"(van der
Werf 1994, p3 1). Appendix
C contains a table illustrating these findings.
Yield
In 1916, when the US Department of Agriculture published Bulletin No. 404,
the researchers found that hemp yielded four times more than trees did per
hectare. Van der Werf
looks at many different factors which influence yield such as: daylength, plant density and self-thinning, nitrogen fertilisation and row width. In his research, he
also looks at the effect sowing and harvesting dates have on yield. He
concludes that sowing and harvesting dates do have a large effect on
yield. They experimented with moving the dates, and eventually found
dates that gave them optimal yield, sowing on April 15 and harvesting on
September l5 [it is important to draw attention to the fact that their
experiments were conducted in the Northern Hemisphere]. Van der Werf also mentions that the
biggest factor influencing yield was the type of cultivar used (Van der Werf 1994).
Hemp's high yield (Van der Werf
found the largest yield to be 17 tonnes of dry stem
matter per hectare) makes it a very attractive crop. Obviously, a high
yield per hectare is very desirable. It is important to continue the
research of breeding cultivars that will produce high yields.
THC CONTENT
Difference between drug-type and fibre-type
hemp
"Delta-9-tetrahydrocannabinol (THC) is the cannabinoid
responsible for the main psychoactive effects of most Cannabis drug
preparations" (Pate n d., n.p.).
Typically, the percentage of THC in hemp that produces a hallucinogenic
effect is between 3.0% and 10%. Fibre or
industrial hemp, of which this report is focusing on, has THC levels of 0.3%
or below. THC levels at 0.3% or below are incapable of producing any
hallucinogenic effects.
There are many different species of cannabis plants, but their
psychoactive properties mainly depend on the concentration of tetrahydrocannabinol (THC), which may vary according to
genetic factors and environmental influences. On the basis of the THC
content all cannabis plants are divided into fibre-type
and drug-type plants. The concentration of cannabinoids
in a cannabis plant depends on genetic factors and on environmental
influences such as light, temperature, moisture and oxygen (Avico, Pacifici & Zuccaro 1985, p61).
There is some concern that after time and exposure to environmental
influences, a low-THC cultivar could develop a higher concentration of
THC. When South Australia bought their
seeds from a French seed company, they were assured the low-THC levels would
remain so, as they have in France
(see Appendix B). "Results from another recent study also suggest
that low-THC varieties cannot be misused as a drug and that the [EC] limit of
0.3% is sufficient" (Karus & Leson 1994, 54).
During the next few years, efforts will be made to breed hemp cultivars that
contain no THC. At the Krasnodar Research Institute of Agriculture, in Russia,
scientists have accomplished a series of experiments breeding southern hemp
with an absence of active cannabinoids.
Southern hemp with no THC content has proven to produce high yields and high
fiber content (Rumyantseva & Lemeshev 1994, p49). This would be an ideal
cultivar: one that produces a lot of fibre per
hectare, has a high percentage of bast fibre, and has no THC.
United Nations Single Convention on Drug Use 1961
Under the United Nations Single Convention on Drug Use, there is a specific
exemption for the industrial cultivation and horticultural use of the
cannabis plant. Article 28, section 2, reads: "This convention
shall not apply to the cultivation of the cannabis plant exclusively for
industrial purposes (fibre and seed) or
horticultural purposes".
Commission of the European Communities (Union)
In 1984, the Commission of the European Communities established a set of
guidelines that allowed for the industrial cultivation of cannabis which
contained a THC level of 0.3% or below (Avico, Pacifici & Zuccaro 1985, p64).
GROWING REQUIREMENTS
I am not going to discuss the many factors which must be considered when
growing hemp. Research in this area is still at an early stage and
there needs to be many more years of field and laboratory tests done to
answer questions. In van der Werf's book, Crop physiology of fibre
hemp, he talks about the crop physiology and agronomy of fibre hemp in the Netherlands. His thesis is
based on years of experiments. He talks about the effects plant
density, self-thinning, temperature, aging, row width, and daylength have on the yield and quality of fibre hemp.
In addition to the topics covered by van der Werf's research, there are other issues which still need
to be addressed; such as, what type of soil does hemp need to be grown
in? How much water does hemp need? I have not come across any
scientific research which fully address these
issues. However, it is important to remember that there is a lot of
research being done to develop cultivars which are capable of adapting to different
growing conditions.
ENVIRONMENTAL BENEFITS OF GROWING
HEMP
With many countries pushing toward more sustainable agricultural practices,
the idea of rotating crops is an appealing route to take. One of the
primary reasons the Netherlands
undertook a four year study, the Hemp Research Programme,
was to find a new crop to be introduced into the current rotations.
They were looking for a new crop that would be profitable, require little or
no biocide and help reduce the incidence of disease in the current crop
rotations. Fibre hemp was proposed as this
new crop. Its yield was reported to be high and it was claimed it could
suppress weeds and improve soil structure. The Dutch programme investigated the potential of fibre hemp as a raw material for the pulp and paper
industry (van der Werf
1994, p2).
Excellent rotation crop
A. Ability to suppress soil-borne diseases
"Even though hemp is an ancient crop, there are few reports on
soil-borne diseases in this crop and the general impression is that
cultivation of hemp poses few problems with plant diseases" (as cited
from (Termorshuizen 1991) in Kok,
Coenen & de Heij
1994, p6). Part of the Netherlands Hemp Research Programme
included a study of the effect a particular cultivar, Kompolti
Hybrid TC, had on selected soilborne
pathogens. "Kok et al. (1994)
investigated the effect of fibre hemp on three
major soil pathogens... all three pathogens were suppressed by hemp,
and the authors concluded that the introduction of hemp in a crop rotation
might improve soil health" (van der Werf, van Geel, & Wijlhuizen 1995, p5). This is
very important research because if it is found that fiber hemp can suppress
certain soil-borne pathogens, it could then be used as a rotation crop and
help eliminate or suppress these pathogens for other crops which are
more susceptible to them.
B. Herbicides, Pesticides
van der Werf concludes
his thesis by asking the question, is hemp a promising 'new' crop? He
says, "...on the whole there is no reason to use pesticides in hemp:
herbicides are superfluous, fungicides have not been found effective and
other biocides are not needed" (van der Werf 1994, pl39). Ian Low, the manager in charge of
the hemp trials in England, said in his report at the Bioresource
Hemp, "we have not found it necessary to use herbicides, insecticides,
or fungicides on the crop and have no reason to think this will change in the
future" (1994, p2).
C. Weed Smotherer
Hemp grows very quickly, approximately four meters in three months under
ideal conditions (Katelaris, Dr. A., pers. comm., 1
June 1995). Because it grows so fast and densely, it blocks out
sunlight to any other weeds trying to grow. Unless plant densities were
very low, the Netherlands'
experiments showed that hemp crops suppressed weeds. "This
confirms literature reports stating that fibre hemp
is an extremely effective weed suppressor... (Heuser
1927, Tarasov 1975, Lotz
et al. 1991)" (van der Werf,
van Geel, &: Wijlhuizen
1995, p5).
D. Improves soil structure
If sensitive farming methods of agriculture are practiced, hemp will improve
the soil structure due to its deep tap-route aerating the sub-soil.
Also, after the hemp is harvested, the remaining tops of the stalks (leaves
and seeds) will serve as a 'green' manure (Katelaris, Dr. A., pers. comm., 1 June 1995).
Consumption of carbon dioxide
Dr. Katelaris, who runs the Cannabis Clothing
Company in Sydney,
said hemp was very effective in eliminating carbon
dioxide from the environment. He said every tonne
of cellulose grown and used removes 1.5 tonnes of
carbon dioxide. For example, if 200,000 hectares of hemp were grown
(averaging a yield of 12 tonnes (dried stem matter)
per hectare) 3.6 million tonnes of carbon dioxide
would be removed (Katelaris, Dr. K., pers. comm., 4
May 1995). This would have obvious benefits for the greenhouse effect.
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