The energy and resource needs
of cultivation, especially on an industrial agricultural scale, are important to
understanding. How will hemp fit into a
world with diminishing, easily available fossil fuels? How will hemp fit into a world where basic
resources are becoming less concentrated and more energy demanding?
Often, in the heat of
enthusiam, the energy and resource requirements of a product are
overlooked. It is also important that
the equipment in the field and in the manufacturing of the various products not
become invisible.
I have divided this essay
into two parts, two entries. The first
part is extracts from multiple sources on cultivation mainly in the field. The second essay is primarily videos of
cultivation and the making of products.
I have found videos to be a productive way to reveal the machines,
buildings and equipment required.
A lot of effort was put into
looking for the energy requirements for both field work and for the manufacturing
of products. I have contacted
researchers studying/working with hemp.
I have had very little success finding explicit energy information. The charts included from the one source I
found do not give clear information on the energy used in various
operations. If anyone knows of other energy
assessments, please comment. Perhaps,
this will be the next phase in the study of hemp.
CULTIVATION
Soil: One common
myth is that hemp can be grown anywhere. Hemp grows best on a loose,
well-aerated loam soil with high fertility and abundant organic matter, with a
pH of 6.0-7.5. Well-drained or tiled clay soils can be used, but poorly-drained
clay or poorly structured soil often results in establishment failures, as
seedling and young plants are prone to damping-off. Sandy soils can grow good
hemp with adequate irrigation and fertilization, but these additional costs
often make production uneconomical.
Industrial hemp can be grown on a wide variety of soil types.
Hemp prefers a sufficiently deep, well-aerated soil with a pH of 6 or greater,
along with good moisture and nutrient holding capacity. Poorly drained soils,
however, are not recommended as excess surface water after heavy rains can
result in damage to the hemp crop. Hemp is extremely sensitive to flooding and
soil compaction.
Fertility:
Another myth regarding hemp production is that it doesn’t
require additional nitrogen or potash inputs. Hemp production requires inputs
of up to 100-130 lb of nitrogen/ acre, 45-70 lb/acre phosphorus, and 35-80
lb/acre of potash (to keep potassium levels in a medium to high range of
>250 ppm). Hemp particularly requires good nitrogen fertilization, more so
for seed production than fiber. . . . .
In addition to well-aerated, loamy soils, hemp does best when
organic matter is greater than 3.5%. To provide perspective, hemp requires
about the same fertility inputs as a high-yielding crop of wheat, or corn.
Approximately
42% of the plant’s biomass returns to the soil in the form of leaves, roots and
tops. These contain over half of the nutrients applied to the crop in the first
place and many of these nutrients will be available to help feed the following
crop.
Nutrition:
To achieve an optimum hemp yield, twice as much nutrient must be
available to the crop as will finally be removed from the soil at harvest. A
hemp field produces a very large bulk of plant material in a short vegetative
period. The nitrogen uptake is most intensive the first 6 to 8 weeks, while
potassium and in particular phosphorous are needed more during flowering and
seed formation. Industrial hemp requires 80 to 100 lbs/ac (90 to 112 kg/ha)
nitrogen, 35 to 50 lbs/ac (39 to 56 kg/ha) phosphate and 52 to 70 lbs/ac (60 to
80 kg/ha) potash.Growing Conditions:Hemp
prefers a mild climate, humid atmosphere, and a rainfall of at least 25-30
inches per year. Good soil moisture is required for seed germination and until
the young plants are well established.
Hemp Rotations: Hemp can be successfully grown in continuous rotation for
several years on the same land. However, the risk of pest buildup, particularly
root worms, borers, and rots, makes this a risky proposition. Hemp could be
used to diversify current rotations of bean, wheat, or alfalfa. Based upon
reports from Ontario, Canada, it has been recommended that hemp not follow
canola, edible beans, soybeans or sunflowers due to the risk of white mold and
other pests and diseases.
Weed Control:
Industrial hemp is an extremely efficient weed suppressor. No
chemicals are needed for growing this crop. Industrial hemp is a low
maintenance crop. There are no registered chemicals for weed control in hemp. A
normal stand of 200 to 300 plants per square meter shades out the weeds,
leaving the fields weed-free at harvest.
Pest Management. Like most plants, hemp is prone to insects and pathogens. As the
acreage of industrial hemp increases, the number of insect pests and pathogens
will tend to increase, as well.
Disease. Historically,
the fungal pathogens gray mold (Botrytis cinerea) and white mold (Sclerotinia
sclerotiorum) have been reported to infect and impact industrial hemp
production. In Indiana, white mold in particular, is expected to be a major
pest north of highway 70, particularly when soybeans are grown in adjacent
locales, or in rotation with hemp. Hemp is also prone to numerous fungal and
bacterial leaf spots, viruses, and Pythium root rot and blight during
establishment.
Insects. European
corn borer, armyworm and grasshoppers have done some damage to hemp crops in
North America.
No pesticides
(insecticides, herbicides or fungicides) are registered for use on hemp in the
United States. For now, crop rotation is the only management option available
to avoid disease build-up until more is known about hemp’s susceptibility to
disease organisms. A 4-year rotation is recommended. Do not grow hemp on the
same fields following canola, edible beans, soybeans or sunflowers.
HARVESTING
The first
thing to consider is: what will be the end use of this hemp? If you
are looking to harvest seeds, you will need different equipment and hemp
varieties than if you are looking to harvest stalks for fiber. It turns
out that the optimum time to harvest hemp for fiber is well before the optimum
time to harvest hemp for seeds. So it is probably best to decide on one
goal or the other before you plant a field. It is possible to harvest
both seeds and stalks, however.
If harvesting
hemp for fiber on a smaller plot, a well-maintained sickle-bar mower or hay swather
may be used to cut the stalks. The stalks are cut and left in the field
and allowed to rot slightly to begin separating the fibers from the
stalk. This process is called “retting”. After retting, a baler may
be used to bale the hemp stalks, at which point the stalks are ready for
storage, drying, and sale.
If harvesting
hemp for seed, a combine may be used, although this can be a challenge.
It is recommended to raise the blade a meter or higher, but even then the long
fibers of the hemp plant can cause wear and tear on the machine by winding
through moving parts.
Harvesting Fibre
Hemp
Air dry stem
yields in Ontario have ranged from 2.6-14.0 tonnes of dry, retted stalks per
hectare (1-5.5 t/ac) at 12% moisture. Yields in Kent County have averaged 8.75
t/ha (3.5 t/ac). Northern Ontario crops averaged 6.1 t/ha (2.5 t/ac) in 1998.
Researchers feel earlier planting, optimum production management and more
suitably adapted varieties can result in higher yields.
Approximately
one tonne of bast fibre and 2-3 tonnes of core material can be decorticated
from 3-4 tonnes of good quality, dry retted straw.
Fiber hemp is ready to harvest about the time the plant is
finished producing pollen and the first seeds start to develop. However, this
does vary with the variety and maturity of the fiber desired. If left beyond
this stage, the fiber becomes too coarse. Fiber from the male plant dies soon
after pollination. It is coarse and good for fiberboard and other products
since it is stronger than younger fiber.
Because hemp is sensitive to light, early planting will produce
taller crops and thus more fiber. Stems must not be chopped or broken too much
in the harvesting process since long fibers are more desirable.
http://innvista.com/health/foods/hemp/harvesting-hemp/
Chemical Defoliation
Removing the leaves from hemp by hand is virtually out of the
question. . . . .
. Therefore, many farmers resort
to chemical defoliation. . .
. . .
Chemical Defoliants
Roundup is one chemical defoliant. . .
. . . .
Purivel is a supposedly gentler chemical that contains the active substance
Metoxuron (by Sandoz). . .
. . .
Basta . . . . is
toxic to fish and may be used only on fields from which the flow-time is at
least 50 days to the next water treatment facility.
Alternatives to Chemical Defoliation
Ecologically-minded textile manufactures in western Europe are
no longer accepting goods that have been subjected to chemical defoliation.
. .
. . Alternatives include labor-intensive manual
removal of the leaves, mechanical removal (but new machines need to be
invented), or water-retting without defoliation. All have disadvantages. Newer
methods developed in the west do not require chemical defoliation since they no
longer employ water retting.
http://innvista.com/health/foods/hemp/harvesting-hemp/
Retting
Once the hemp is harvested, it must go through a process called
retting in order to separate the fiber from the rest of the plant. This is not an
easy process and can be accomplished through several methods where moisture,
microorganisms, or chemistry break down the bark tissue that binds the fiber
and non-fiber portions, making them easier to separate.
• Dew
retting occurs when the stalks are left in the field so that rain, dew, or
irrigation is used to keep the stems moist. This may take up to 5 weeks and
produces a coarse fiber with a light brown color.
• Water
retting occurs when stems are bundled and then submerged in water so that
bacteria break down the pectin. This takes 7-10 days and produces a better
quality fiber.
• Warm
water retting occurs when bundles are soaked for 24 hours after which the water
is replaced. Heat is then applied to warm the batch for the next two or three
days. This gives a very uniform, clean fiber.
• Green
retting is an all mechanical process that separates the components and used
when the fiber is needed for textiles, paper, or fiberboard products.
Green Retting
Machines
Energy balance
Energy input
The four base scenarios differed substantially in their
relative amount of energy
input (Figure 18). The energy input in cultivation was found
to be 10.8 and
10.4 GJ ha-1 for baled and briquetted solid biofuel
production from spring
harvested hemp, respectively, and 7.4 GJ ha-1 for
autumn-harvested, ensiled
hemp biomass for biogas production (Figure 18; Paper
IV).
After intermediate storage, processing of the stored biomass
requires energy
inputs for conversion and additional transport. Conversion
energy requirements
differed substantially between the scenarios: inputs were
low for solid biofuel
combustion in the form of briquetted biomass (0.8 GJ ha-1)
and for CHP
production from bales (1.5 GJ ha-1) (Figure 18). CHP
production from biogas
was more energy-intensive (2.8 GJ ha-1). The most
energy-demanding
conversion was the production of vehicle fuel (14.1 GJ
ha-1), where upgrading
of the biogas to 97% methane content represented 45% of the
total energy
input. This reflects in the high amount of electricity
required for scrubbing and
compression of the biogas (Figure 18).
One gigajoule equals almost 7
gallons of diesel fuel
One gigajoule equals almost 7.5
gallons of gasoline.
One hectare equals 2.47 acres
Energy output
For CHP production from solid biofuel, approx. 23 and 41% of the energy contained in the biomass in the field was made available as useful power and heat, respectively (Scenario I, Figure 19). Heat production from hemp briquettes resulted in approx. 55% of the energy being made available as useful heat (Scenario II, Figure 19).
The production of 1 ha of hemp .
. . an energy use of 11.4 GJ, and a land use of
1.02 ha.year.
One gigajoule equals almost 7
gallons of diesel fuel
One gigajoule equals almost 7.5
gallons of gasoline.
One hectare equals 2.47 acres
Net
energy yield
The
net energy yield (NEY) per hectare was highest for CHP production from
bales
and heat from briquettes with 81 and 65 GJ ha-1, respectively (Figure 21; Paper
IV). Overall, conversion efficiencies for these pathways were high (86 and 80%,
respectively) as were the output-to-input ratios (RO/I of 6.8 and 5.1, respectively).
The NEY of biogas CHP and vehicle fuel production was
substantially
lower, 24 and 42 GJ ha-1, respectively. Conversion efficiency was
38%
for upgraded biogas (vehicle fuel) and 21% for biogas CHP. Both scenarios had
RO/I = 2.6.
ENVIRONMENTAL
Hemp has been described as a carbon sink. It takes up vast
amounts of carbon during its rapid growth and this can be locked up in durable
products. Hemp’s bio-remedial qualities enable it to improve soil structure and
mop up toxic wastes including heavy metals and excess nutrient. Planted densely
it achieves weed suppression and doesn’t require pesticides or fungicides. It
is also exceptionally good in the farm nutrient cycle as a rotation crop.
A supporting but stricter
view:
Although
the environmental and biodiversity benefits of growing hemp have been greatly
exaggerated in the popular press, C. sativa is nevertheless exceptionally
suitable for organic agriculture, and is remarkably less “ecotoxic” in
comparison to most other crops (Montford and Small 1999b).
Cannabis
sativa is also relatively resistant to weeds, and so usually requires
relatively little herbicide. Fields intended for hemp use are still frequently
normally cleared of weeds using herbicides, but so long as hemp is thickly
seeded (as is always done when hemp is grown for fiber), the rapidly developing
young plants normally shade out competing weeds.
Most
insects cause only limited damage to hemp, and substantial insect damage is uncommon,
so the use of insecticides is very rarely required.
The
most valid claims to environmental friendliness of hemp are with respect to
agricultural biocides (pesticides, fungicides, herbicides). Cannabis sativa
is known to be exceptionally resistant to pests (Fig. 51), although, the degree
of immunity to attacking organisms has been greatly exaggerated, with several
insects and fungi specializing on hemp. Despite this, use of pesticides and
fungicides on hemp is usually unnecessary, although introduction of hemp to
regions should be expected to generate local problems. Cannabis sativa
is also relatively resistant to weeds, and so usually requires relatively
little herbicide. Fields intended for hemp use are still frequently normally
cleared of weeds using herbicides, but so long as hemp is thickly seeded (as is
always done when hemp is grown for fiber), the rapidly developing young plants
normally shade out competing weeds.
BIBLIOGRAPHY
Small, E. and D. Marcus. 2002.
Hemp: A new crop with new uses for North America. p. 284–326. In: J. Janick and
A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria,
VA.
This covers much of the issues and questions as well as a
huge bibliography
How Hemp Textiles Are Produced
http://eiha.org/media/2014/10/Ecological-benefits-of-hemp-and-flax-cultivation-and-products-2011.pdf
Baxter, J. 2000. Growing
Industrial Hemp in Ontario. Agdex#
153/20. Available at http://www.omafra.gov.on.ca/english/crops/facts/00-067.htm#fertility
Small, E. and D. Marcus. 2002.
Hemp: A new crop with new uses for North America. p. 284–326. In: J. Janick and
A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria,
VA.
Small, E. 2016. Cannabis,
A Complete Guide. CRC Press. FL.
Van der Werf, H.M.G. and W. Van den Berg. 1995. Nitrogen
fertilization and sex expression affect size variability of fibre hemp
(Cannabis sativa L.) Oecologia, 103: 462–470
Small, E. and D. Marcus. 2002.
Hemp: A new crop with new uses for North America. p. 284–326. In: J. Janick and
A. Whipkey (eds.), Trends in new crops and new uses. ASHS Press, Alexandria,
VA.
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