Hemp as Field Crop.
Edited by Ivor Hughes.
HEMP : Economic Importance.
Hemp is grown chiefly for the bast fiber in the stalks that is used for
making rope and twine. The average acre yields in the United States have
been about 900 pounds of fiber or 400 pounds of seed. It formerly was grown
rather extensively in the United States, chiefly in Kentucky, but the
acreage declined to less than 200 acres in 1933. This was increased to 7,400
acres in 1941. Then the Japanese invaded the Philippine Islands, the chief
source of abaca or Manila hemp, which is used for marine ropes. Thereafter,
production of hemp in tie United States expanded until about 146,000 acres
were harvested for fiber and 40,000 acres for seed in 1943.
Most of the fiber was produced in Minnesota, Iowa, Illinois, Wisconsin,
Indiana, and Kentucky. The seed was grown chiefly in Kentucky. Production
declined to 4,600 acres for fiber in Wisconsin and 400 acres for seed in
Kentucky in 1946. Production in the United States practically ceased shortly
thereafter. The fiber is now being imported. Most of the crop is grown in
the Soviet Union, and in southern and eastern Europe. It is grown in Chile
Hemp probably is native to central Asia. It has been grown in
China for many centuries. It was grown by the ancient Greeks and is still
grown in central Europe. Hemp has been grown in the United States since
early Colonial days.
Hemp escaped from cultivation in the United States many years ago. It now
occupies large areas of uncultivated land, chiefly in the bottomlands along
the lower Missouri River and its lower tributaries. Harvesting of the wild
growth has not been feasible because of scattered and irregular stands and
growth and because of mixtures with other types of vegetation.
Hemp like Plants:
In addition to the true hemp (Cannabis sativa), grown in the
United States as well as in various parts of both hemispheres, several fiber
plants sometimes called hemp are grown in other countries. These include
abaca or Manila hemp (Musa textilis), a relative of the banana plant grown
in the Philippines and other Pacific islands; Sunn hemp (Crotalaria juncea),
a legume cover crop also harvested for fiber in India and other parts of
Asia; Mauritius hemp, the green aloe, or piteira (Furcraea gigantea) of
Africa; New Zealand hemp (Phormium tenax); (Jute or India hemp (Corchorus
capsularis); and sisal hemp. The latter type includes sisal (Agave sisalana)
grown in Africa and the West Indies, and henequen or Mexican or Cuban sisal
(Agave fourcroydes). Henequen, sisal, and abaca are the chief fibers used in
binder twine. Jute is used in making burlap. All the above fibers are used
to make rope or twine. Sansevieria or bow-string hemp has been tested in
Florida as a possible substitute for Manila hemp.
Hemp is adapted to sections that produce a good crop of corn. It
requires a frost-free season of about four months for fiber production, or
five months for seed production. It will withstand light frosts. For good
uniform growth of hemp, the rainfall or soil moisture should be ample
throughout the season. A higher quality of fiber usually is obtained in the
more humid climate east of longitude 95" because of better conditions
for dew retting than commonly occur west of the meridian. Well-drained,
deep, fertile, medium-heavy loams have produced the best hemp. Barnyard
manure, commercial fertilizers, or lime should be applied to soils where
other crops respond to these supplements.
Hemp (Cannabis sativa) belongs to the family Urticaceae, tribe
Cannabinaceae. It is a stout, erect annual that grows to a height of 5 to 15
feet. It is dioecious; the male plants, which comprise one-half the Hemp is
of considerable historical interest because it first revealed sex in plants
to Camerarius in 1694. It has continued to serve as the subject for
determining the nature of sex in plants. Under normal field conditions, hemp
is strictly dimorphic (has two forms) as to flowers and vegetation parts.
The carpellate and staminate plants show almost no sex reversal. However,
individual bisexual plants occur under unfavorable conditions such as
reaction to old pollen, mutilation, and reduced light.
The main stem of hemp is hollow and produces a few branches near the top.
The bast fibers are not so fine as those of flax, even when the plants are
grown close together. The staminate inflorescences are in axillary, narrow,
loose panicles. The pistillate flowers are in erect leafy spikes. The hemp
ovary matures into a hard ovoid achene. The seeds mature on the lower part
of the spikes first and on the upper part last.
Types of Varieties:
The common fiber hemp has larger stalks than the drug-plant type,
which is grown in the hot climates of India, Syria, and elsewhere, often
being classified as a separate species, Cannabis indica. The variety grown
in the United States, known as Kentucky or domestic hemp, is of Chinese
Hemp should be planted on fall-plowed land just before the time
foe planting corn. Hemp responds to fertilizers on some of the less fertile
soils of the Com Belt States, hut heavy nitrogen fertilization reduces the
strength of the fibers.
For seed production in Kentucky, the hemp usually is planted in hills 5
feet by 5 feet, with six to ten seeds per hill or about 1.5 pounds of seed
per acre. Later the hills are thinned to two or five plants per hill.
Harvesting for seed occurs when the seeds in the middle branches are ripe.
Harvesting and shocking when the plants are damp save much seed that
otherwise would he shattered.
For fiber production, hemp should be sown with a grain drill � to
1 inch deep at the rate of 5 pecks (55 pounds) of seed per acre to produce
fine uniform stems suitable for machine processing. Hemp is harvested for
fiber when the male plants are in full flower and shedding pollen. Earlier
harvesting yields weak fiber. Harvesting is done with a modified 8-foot rice
hinder or a self-rake reaper that delivers the stalks in an even swath on
the ground. The stalks are left in this position for dew retting. After
retting is complete, the stalks are gathered up and bound by a pick-up
binder. The bundles are shocked and later hauled to the processing plant any
time after drying.
Preparation of Hemp for Market:
In dew retting, the stalks lying on the ground are exposed to
cool moist weather or, sometimes, to alternate freezing and thawing. The
process is complete when the bark separates easily from the woody portion of
the stem. The stalks are turned once or twice to provide uniform exposure.
Water retting is practiced in Europe.
In the breaking process, the inner cylinder of brittle woody tissue is
broken into short pieces called hurd, while the long flexible fibers are
left largely intact. This permits the wood to he separated from the fibers.
Scutching is the beating or scraping off of the broken pieces of wood.
The rough fiber is combed out by drawing it over coarse hackles. Hemp tow
consists of short, more or less tangled strands. A ton of dry retted hemp
stalks processed by modern machine methods yields about 340 to 360 pounds of
fiber, of which slightly more than half is line (long) fiber and the
remainder is tow.
Hemp is used in commercial twine, small cordage, thread, hemp carpet
twines, oakum, and marline.30 It ranks next to Manila hemp for marine ropes.
Hemp Seed and Leaves:
Hemp seed is often fed to caged birds after the germination of
the seed has been killed in accordance with federal regulations (in order to
prevent its use for planting). The seed contains 20 to 25 per cent of an oil
that sometimes is extracted for use in making soft soaps or is used as a
substitute for linseed or other oils. A drug is derived from the stems and
leaves of common hemp. The glandular hairs secrete both a volatile oil and
the strong narcotic resin (cannabin). The drug, called marijuana in North
America and hashish or bhang in Asia, is obtained from the flowers and
leaves of both Cannabis sativa and C. indica. Hemp is the source of the
so-called "reefer" cigarettes that are sold illegally. Hemp can be
grown only under a license issued by the Commissioner of Narcotics.