Thanks to Wikepedia for this article:
"Hemp" is also a name for the Cannabis plant. Some use it to mean only the low tetrahydrocannabinol (THC) strains of the plant, although this is a neologism. In modern times, hemp has been used for industrial purposes including paper, textiles, biodegradable plastics, construction, health food and fuel with modest commercial success. Since 2007, commercial success of hemp food products has grown considerably.
Hemp is one of the faster growing biomasses known, producing up to 25 tonnes of dry matter per hectare per year. A normal average yield in large scale modern agriculture is about 2.5–3.5 t/ac (air dry stem yields of dry, retted stalks per acre at 12% moisture). Approximately, one tonne of bast fiber and 2–3 tonnes of core material can be decorticated from 3–4 tonnes of good quality, dry retted straw.
For a crop, hemp is very environmentally friendly (with the exception of chemical fertilizers used in industrial agriculture) as it requires few pesticides and no herbicides. Results indicate that high yield of hemp may require total nutrient levels (field plus fertilizer nutrients) similar to a high yielding wheat crop.
Hemp is one of the earliest domesticated plants known.
Cannabis sativa L. subsp. sativa var. sativa is the variety grown for industrial use, while C. sativa subsp. indica generally has poor fiber quality and is primarily used for production of recreational and medicinal drugs. The major difference between the two types of plants is the appearance and the amount of Δ9-tetrahydrocannabinol (THC) secreted in a resinous mixture by epidermal hairs called glandular trichomes, although they can also be distinguished genetically. Oilseed and fiber varieties of Cannabis approved for industrial hemp production produce only minute amounts of this psychoactive drug, not enough for any physical or psychological effects. Typically, hemp contains below 0.3% THC, while cultivars of Cannabis grown for marijuana can contain anywhere from 6 to over 20%.
The world leading producer of hemp is China with smaller production in Europe, Chile and the Democratic People's Republic of Korea. While more hemp is exported to the United States than to any other country, the United States Government does not consistently distinguish between marijuana and the non-psychoactive Cannabis used for industrial and commercial purposes.
Hemp is used for a wide variety of purposes, an estimated 50,000 products can be produced from hemp in the United States, including the manufacture of cordage of varying tensile strength, everlasting clothing and nutritional products. The bast fibers can be used in 100% hemp products, but are commonly blended with other organic fibers such as flax, cotton or silk, for apparel and furnishings, most commonly at a 55%/45% hemp/cotton blend. The inner two fibers of hemp are more woody, and are more often used in non-woven items and other industrial applications, such as mulch, animal bedding and litter. The oil from the fruits ("seeds") oxidizes (commonly, though inaccurately, called "drying") to become solid on exposure to air, similar to linseed oil, and is sometimes used in the manufacture of oil-based paints, in creams as a moisturizing agent, for cooking, and in plastics. Hemp seeds have been used in bird seed mix as well. Hempseed is also used as a fishing bait. 
Hemp seeds can be eaten raw, ground into a meal, sprouted, made into hemp milk (akin to soy milk), prepared as tea, and used in baking. The fresh leaves can also be eaten in salads. Products include cereals, frozen waffles, hemp tofu, and nut butters, to name a few. A few companies produce value added hemp seed items that include the seed oils, whole hemp grain (which is sterilized by law in the United States, where they import it from China and Canada), dehulled hemp seed (the whole seed without the mineral rich outer shell), hemp flour, hemp cake (a by-product of pressing the seed for oil) and hemp protein powder. Hemp is also used in some organic cereals, for non-dairy milk somewhat similar to soy and nut milks, and for non-dairy hemp "ice cream."
Within the UK, the Department for Environment, Food and Rural Affairs (Defra) has treated hemp as purely a non-food crop. Seed appears on the UK market as a legal food product, and cultivation licenses are available for this purpose. In North America, hemp seed food products are sold, typically in health food stores or through mail order. The United States Department of Agriculture estimates that "the market potential for hemp seed as a food ingredient is unknown. However, it probably will remain a small market, like those for sesame and poppy seeds."
Approximately 44% of the weight of hempseed is healthy edible oils, containing about 80% essential fatty acids (EFAs); i.e., linoleic acid, omega-6 (LA, 55%), alpha-linolenic acid, omega-3 (ALA, 22%), in addition to gamma-linolenic acid, omega-6 (GLA, 1–4%) and stearidonic acid, omega-3 (SDA, 0–2%). Protein is the other major component (33%), second only to soy (35%), but more easily digestible because it's primarily globular proteins, 33% albumin and 65% edestin (a Greek word meaning edible). Its amino acid profile is close to "complete" when compared to more common sources of proteins such as meat, milk, eggs and soy. The proportions of linoleic acid and alpha-linolenic acid in one tablespoon (15 ml) per day of hemp oil easily provides human daily requirements for EFAs. Unlike flaxseed oil, hemp oil can be used continuously without developing a deficiency or other imbalance of EFAs. This has been demonstrated in a clinical study, where the daily ingestion of flaxseed oil decreased the endogenous production of GLA.
Hempseed is an adequate source of dietary fiber, calcium and iron, and contains antioxidants and chlorophyll. Whole hempseeds are also a good source of phosphorus, magnesium, zinc, copper and manganese.
Hempseed is usually very safe for those unable to tolerate nuts, gluten, lactose, and sugar. In fact, there are no known allergies to hemp foods. Hempseed contains no gluten and therefore would not trigger symptoms of celiac disease.
Hemp oil can spontaneously oxidize and turn rancid within a short period of time if not stored properly; it is best stored in a dark glass bottle, in a refrigerator or freezer (its freezing point is –20 °C). Preservatives (antioxidants) are not necessary for high quality oils that are stored properly.
Hemp oil has anti-inflammatory properties.
The fiber is the most valuable parts of the hemp plant. It is commonly called bast, which refers to the fibers that grow on the outside of the woody interior of the plant's stalk, and under the outer most part (the bark). Bast fibers give the plants strength. Hemp fibers can be between approximately 0.91 m (3 ft) and 4.6 m (15 ft) long, running the length of the plant. Depending on the processing used to remove the fiber from the stem, the hemp may naturally be creamy white, brown, gray, black or green.
The use of hemp for fiber production has declined sharply over the last two centuries, but before the industrial revolution, hemp was a popular fiber because it is strong and grows quickly; it produces roughly 10% more fiber than cotton or flax when grown on the same land. Hemp has been used to make paper. It was often used to make sail canvas, and the word canvas derives from cannabis. Abaca, or "Manila hemp", a relative of the banana plant, replaced its use for rope. Burlap, made from jute, took over the sacking market. The paper industry began using wood pulp. The carpet industry switched over to wool, sisal, and jute, then nylon. Netting and webbing applications were taken over by cotton and synthetics.
Concrete-like blocks made with hemp and lime have been used as an insulating material for construction. Such blocks are not strong enough to be used for structural elements; they must be supported by a brick, wood, or steel frame.
The Renewable House was the UK's first home made from hemp-based materials. Construction was completed in 2009. The first US home made of hemp-based materials was completed in August 2010 in Asheville, North Carolina.
A mixture of fibreglass, hemp fiber, kenaf, and flax has been used since 2002 to make composite panels for automobiles. The choice of which bast fiber to use is primarily based on cost and availability.
The first identified coarse paper, made from hemp, dates to the early Western Han Dynasty, two hundred years before the nominal invention of papermaking by Cai Lun, who improved and standardized paper production using a range of inexpensive materials, including hemp ends, approximately 2000 years ago.
In 1916, U.S. Department of Agriculture chief scientists Lyster H. Dewe and Jason L. Merrill created paper made from hemp pulp, they concluded that paper from hemp hurds was "favorable in comparison with those used with pulp wood." Modern research has not confirmed the positive finding about hemp hurds. The content of cellulose is only between 32% and 38%. The actual production of hemp fiber in the U.S continued to decline until 1933 to around 500 tons/year. Between 1934-35, the cultivation of hemp began to increase but still at a very low level and with no significant increase of paper from hemp.
Hemp has never been used for commercial high-volume paper production due to its relatively high processing cost. Currently there is a small niche market for hemp pulp, for example as cigarette paper. Hemp fiber is mixed with fiber from other sources than hemp. In 1994 there was no significant production of 100% true hemp paper. World hemp pulp production was believed to be around 120,000 tons per year in 1991 which was about 0.05% of the world's annual pulp production volume. The total world production of hemp fiber had in 2003 declined to about 60 000 to 80 000 ton. This can be compared to a typical pulp mill for wood fiber, which is never smaller than 250,000 tons per annum. The cost of hemp pulp is approximately six times that of wood pulp, mostly because of the small size and outdated equipment of the few hemp processing plants in the Western world, and because hemp is harvested once a year (during August) and needs to be stored to feed the mill the whole year through. This storage requires a lot of (mostly manual) handling of the bulky stalk bundles. Another issue is that the entire hemp plant cannot be economically prepared for paper production. While the wood products industry uses nearly 100% of the fiber from harvested trees, only about 25% of the dried hemp stem — the bark, called bast — contains the long, strong fibers desirable for paper production. All this accounts for a high raw material cost. Hemp pulp is bleached with hydrogen peroxide, a process today also commonly used for wood pulp.
Hemp jewelry is the product of knotting hemp twine through the practice of macramé. Hemp jewelry includes bracelets, necklaces, anklets, rings, watches and other adornments. Some jewelry features beads made from glass, stone, wood and bones. The hemp twine varies in thickness and comes in a variety of colors. There are many different stitches used to create hemp jewelry, however, the half knot and full knot stitches are most common.
Hemp rope was used in the age of sailing ships, though the rope had to be protected by tarring, since hemp rope has a propensity for breaking from rot, as the capillary effect of the rope-woven fibers tended to hold liquid at the interior, while seeming dry from the outside. Tarring was a labor-intensive process, and earned sailors the nickname "Jack Tar". Hemp rope was phased out when Manila, which does not require tarring, became widely available. Manila is sometimes referred to as Manila hemp, but is not related to hemp; it is abacá, a species of banana.
Hemp shives are the core of the stem, hemp hurds are broken parts of the core. In the EU, they are used for animal bedding (horses, for instance), or for horticultural mulch. Industrial hemp is much more profitable if both fibers and shives (or even seeds) can be used.
Hemp can be used as a "mop crop" to clear impurities out of wastewater, such as sewage effluent, excessive phosphorus from chicken litter, or other unwanted substances or chemicals. Eco-technologist Dr. Keith Bolton from Southern Cross University in Lismore, New South Wales, Australia, is a leading researcher in this area. Hemp is being used to clean contaminants at Chernobyl nuclear disaster site.
Hemp, because of its height, dense foliage and its high planting density as a crop, is a very effective and long used method of killing tough weeds in farming by minimizing the pool of weed seeds of the soil. Using hemp this way can help farmers avoid the use of herbicides, to help gain organic certification and to gain the benefits of crop rotation per se. Due to its rapid, dense growth characteristics, in some jurisdictions hemp is considered a prohibited noxious weed, much like Scotch Broom.
Biofuels, such as biodiesel and alcohol fuel, can be made from the oils in hemp seeds and stalks, and the fermentation of the plant as a whole, respectively. Biodiesel produced from hemp is sometimes known as "hempoline". Hemp is clean burning and non-toxic.
Filtered hemp oil can be used directly to power diesel engines. In 1892, Rudolf Diesel invented the diesel engine, which he intended to fuel "by a variety of fuels, especially vegetable and seed oils, which earlier were used for oil lamps, i.e. the Argand lamp."
Millennia of selective breeding have resulted in varieties that look quite different. Also, breeding since circa 1930 has focused quite specifically on producing strains which would perform very poorly as sources of drug material. Hemp grown for fiber is planted closely, resulting in tall, slender plants with long fibers. Ideally, according to Britain's Department for Environment, Food and Rural Affairs, the herb should be harvested before it flowers. This early cropping is done because fiber quality declines if flowering is allowed and, incidentally, this cropping also pre-empts the herb's maturity as a potential source of drug material. However, in these strains of industrial hemp the tetrahydrocannabinol (THC) content would have been very low, regardless.
The name Cannabis is the genus and was the name favored by the 19th century medical practitioners who helped to introduce the herb's drug potential to modern English-speaking consciousness. Cannabis for non-drug purposes (especially ropes and textiles) was then already well known as hemp.
Hemp has been grown for millennia in Asia and the Middle East for its fibre. Commercial production of hemp in the West took off in the eighteenth century, but was grown in the sixteenth century in eastern England. Because of colonial and naval expansion of the era, economies needed large quantities of hemp for rope and oakum. Other important producing countries were China, North Korea, Hungary, the former Yugoslavia, Romania, Poland, France and Italy.
In Western Europe, nobody banned the cultivation of hemp in the 1930s but the commercial cultivation ceased almost anyhow in the decades after the 1930s. Hemp was simply ousted by artificial fibres.
From the 1950s to the 1980s, the Soviet Union was the world's largest producer (3,000 km² in 1970). The main production areas were in Ukraine, the Kursk and Orel regions of Russia, and near the Polish border. Since its inception in 1931, the Hemp Breeding Department at the Institute of Bast Crops in Hlukhiv (Glukhov), Ukraine, has been one of the world's largest centers for developing new hemp varieties, focusing on improving fiber quality, per-hectare yields, and low THC content.
In Japan, hemp was historically used as paper and a fiber crop. There is archaeological evidence cannabis was used for clothing and the seeds were eaten in Japan back to the Jōmon period (10,000 to 300 BCE). Many Kimono designs portray hemp, or asa (Japanese: 麻), as a beautiful plant. In 1948, marijuana was restricted as a narcotic drug. The ban on marijuana imposed by the United States authorities was alien to Japanese culture, as the drug had never been widely used in Japan before. Though these laws against marijuana are some of the world's strictest, allowing five years imprisonment for possession of the drug, they exempt hemp growers, whose crop is used to make robes for Buddhist monks and loincloths for sumo wrestlers. Because marijuana use in Japan has doubled in the past decade, these "loopholes" have recently been called into question.
Air dry stem yields in Ontario have from 1998 and onward 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. Only a part of that is bast fiber. Approximately one tonne of bast fiber and 2-3 tonnes of core material can be decorticated from 3-4 tonnes of good quality, dry retted straw. For an annual yield of this level is it in Ontario recommended to add Nitrogen (N):70–110 kg/ha, Phosphate (P2O5): up to 80 kg/ha and Potash (K2O): 40–90 kg/ha. The average yield of dry hemp stalks in Europe was 6 ton/ha (2.4 ton/ac) in 2001 and 2002.
There are a lot of very uncertain, easily misleading and sometimes clearly incorrect numbers about the yield from hemp in ton/hectare or pounds/acre etc. on the Internet where it is not specified if the numbers is relevant for the total biomass or the total yield of biomass or the total yield of dried stalk or the total yield of fiber from the bark (and is the numbers for wet or dry material? Hemp can contain a lot of water)  In modern industrial agriculture is about 42% of the plants' biomass returned to the soil in the form of leaves, roots and tops.
Smallholder plots are usually harvested by hand. The plants are cut at 2 to 3 cm above the soil and left on the ground to dry. Mechanical harvesting is now common, using specially adapted cutter-binders or simpler cutters.
The cut hemp is laid in swathes to dry for up to four days. This was traditionally followed by retting, either water retting (the bundled hemp floats in water) or dew retting (the hemp remains on the ground and is affected by the moisture in dew, and by molds and bacterial action). Modern processes use steam and machinery to separate the fiber, a process known as Thermomechanical pulping.
There are broadly three groups of Cannabis varieties being cultivated today:
A nominal, if not legal distinction is often made between hemp, with concentrations of the psychoactive chemical THC far too low to be useful as a drug, and Cannabis used for medical, recreational, or spiritual purposes.
Hemp plants can be vulnerable to various pathogens, including bacteria, fungi, nematodes, viruses and other miscellaneous pathogens. Such diseases often lead to reduced fiber quality, stunted growth, and death of the plant. These diseases rarely affect the yield of a hemp field, so hemp production is not traditionally dependent on the use of pesticides.
Hemp use dates back to the Stone Age, with hemp fiber imprints found in pottery shards in China and Taiwan over 7,000 years old. They were also later used to make clothes, shoes, ropes, and an early form of paper. Contrary to the traditional view that Cai Lun invented paper in around 105 AD, specimens of hemp paper were found in the Great Wall of China dating back 200 years earlier.
The classical Greek historian Herodotus (ca. 480 BC) reported that the inhabitants of Scythia would often inhale the vapors of hemp-seed smoke, both as ritual and for their own pleasurable recreation.
Hemp in later Europe was mainly cultivated for its fibers, and was used for ropes on many ships, including those of Christopher Columbus. The use of hemp as a cloth was centered largely in the countryside, with higher quality textiles being available in the towns.
The Spaniards brought hemp to the Western Hemisphere and cultivated it in Chile starting about 1545. However, in May 1607, "hempe" was among the crops Gabriel Archer observed being cultivated by the natives at the main Powhatan village, where Richmond, Virginia is now situated; and in 1613, Samuell Argall reported wild hemp "better than that in England" growing along the shores of the upper Potomac. As early as 1619, the first Virginia House of Burgesses passed an Act requiring all planters in Virginia to sow "both English and Indian" hemp on their plantations. The Puritans are first known to have cultivated hemp in New England in 1645.
In 1937, the Marihuana Tax Act of 1937 was passed in the United States. It levied a tax on anyone who dealt commercially in cannabis, hemp, or marijuana. It was repealed by an overriding law in 1970.
Hemp was used extensively by the United States during World War II. Uniforms, canvas, and rope were among the main textiles created from the hemp plant at this time. Much of the hemp used was cultivated in Kentucky and the Midwest.
During World War II, the U.S. produced a short 1942 film, Hemp for Victory, promoting hemp as a necessary crop to win the war.
By the early twentieth century, the advent of the steam engine and the diesel engine ended the reign of the sailing ship. The production of iron and steel for cable and ships' hulls further eliminated natural fibres in marine use. Hemp had long since fallen out of favour in the sailing industry in preference to Manila hemp.
The world-leading producer of hemp is China, with smaller production in Europe, Chile and the Democratic People's Republic of Korea. Over 30 countries produce industrial hemp, including Australia, Austria, Canada, Great Britain, France, Russia and Spain.
France is Europe's biggest producer with 8,000 hectares cultivated. 70-80 % of the hemp fibre produced in Europe in 2003 was used for specialty pulp for cigarette papers and technical applications. About 15% is used in the automotive sector and 5-6% were used for insulation mats. Approximately 95% of hurds were used as animal bedding, while almost 5% were used in the building sector.
Canada Commercial production (including cultivation) of industrial hemp has been permitted in Canada since 1998 under licenses and authorization issued by Health Canada (9,725 ha in 2004, 5450 ha in 2009).
The United Kingdom, and Germany all resumed commercial production in the 1990s. British production is mostly used as bedding for horses; other uses are under development. The largest outlet for German fibre is composite automotive panels. Companies in Canada, the UK, the United States and Germany, among many others, process hemp seed into a growing range of food products and cosmetics; many traditional growing countries still continue to produce textile-grade fibre.
Hemp is not legal to grow in the U.S. under Federal law because of its relation to marijuana, and any imported hemp products must meet a zero tolerance level. It is considered a controlled substance under the Controlled Substances Act (P.L. 91-513; 21 U.S.C. 801 et seq.). Some states have defied Federal law and made the cultivation of industrial hemp legal. These states — North Dakota, Hawaii, Kentucky, Maine, Maryland ,Oregon ,California ,Montana, West Virginia and Vermont — have not yet begun to grow hemp because of resistance from the federal Drug Enforcement Administration.
Uruguay has also approved a project of hemp production as of the second half of 2010.
In the United Kingdom, these licences are issued by the Home Office under the Misuse of Drugs Act 1971. When grown for non-drug purposes, hemp is referred to as industrial hemp, and a common product is fibre for use in a wide variety of products, as well as the seed for nutritional aspects and for the oil. Feral hemp or ditch weed is usually a naturalized fibre or oilseed strain of Cannabis that has escaped from cultivation and is self-seeding.
Victoria, Queensland and, most recently, New South Wales issue licences to grow hemp for industrial use. Victoria was an early adopter in 1998, and has reissued the regulation in 2008. Queensland has allowed industrial production under licence since 2002, where the issuance is controlled under the Drugs Misuse Act 1986. Most recently, New South Wales now issues licences under a law, the Hemp Industry Regulations Act 2008 (No 58), that came into effect as of 6 November 2008.
Vermont and North Dakota have passed laws enabling hemp licensure. Both states are waiting for permission to grow hemp from the DEA. Currently[when?], North Dakota representatives are pursuing legal measures to force DEA approval. Oregon has licensed industrial hemp as of August 2009.