Hemp

Hemp (from Old English hænep) is a term reserved mainly for low tetrahydrocannabinol (THC) varieties of the plant Cannabis sativa. Of the approximately 2000 cannabis plants varieties known, about 90% contain only low-grade THC and are most useful for their fiber, seeds and medicinal or psychoactive oils. Hemp is one of the earliest domesticated plants known.

In modern times hemp is used for industrial purposes including paper, textiles, clothing, biodegradable plastics, construction (as with Hemcrete and insulation), body products, health food and bio-fuel. Hemp is thus legally grown in many countries across the world including Spain, China, Japan, Korea, France, North Africa and Ireland. Although hemp is commonly associated with marijuana (hemp's THC-rich cousin), since 2007 the 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 typical 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.

Hemp is considered by a 1998 study in Environmental Economics to be environmentally friendly due to a decrease of land use and other environmental impacts, indicating a possible decrease of ecological footprint in a US context compared to typical benchmarks. However, a 2010 study which compared the production of paper specifically from hemp and eucalyptus concluded that "industrial hemp presents higher environmental impacts than eucalyptus paper"; however, the article also highlights that "there is scope for improving industrial hemp paper production". Hemp is also claimed to require few pesticides and no herbicides, and it has been called a carbon negative raw material. Results indicate that high yield of hemp may require high total nutrient levels (field plus fertilizer nutrients) similar to a high yielding wheat crop.

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 recreational and medicinal purposes. 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 recreational use can contain anywhere from 2% to over 20%.

The world leading producer of hemp is China with smaller production in Europe, Chile and North 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.