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 also.

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.

Botanical Description:
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 origin.

Cultural Methods:
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.