|
Robert C. Clarke and David W Pate are both cannabis biologists at the International Hemp Association in Amsterdam, The Netherlands.
Introduction
Cannabis has been cultivated throughout human agricultural history for its strong fiber and edible seed as well as for its drug properties. It has clothed our ancestors, sustained them in times of hunger, sailed them to the farthest reaches of the globe, provided books to record their history, soothed their ills, and strengthened communion with their deities. Today cannabis provides many valuable products that can supplement or potentially replace many of their marketplace equivalents. It possesses the unique ability to produce textiles, paper products, building materials, nutritious food (including a valuable oil), and effective natural medicines.
This extremely versatile plant also serves as a crop that fits into a healthy and balanced ecosystem model, slowing or even reversing the degradation of our environment through its potential for bioremediation and as a source of non-petrochemical raw materials (e.g., chemical feedstock) and biomass energy. Popularization of ecologically sound products and the establishment of appropriate global management strategies are important to our planet's future and cannabis can play a significant role.
Cannabis as a Plant
Almost all of the cannabis found worldwide is classified as Cannabis sativa. Many taxonomists argue that C. indica, C. afghanica, and C. ruderalis are also valid species names for three different small subgroups of the genus Cannabis. However, even accounting for these additional putative species, 95 percent of the cultivated cannabis in the world would still be classified as Cannabis sativa.
A rapidly maturing annual crop like cannabis is well adapted for temperate climates. Ancient northern Asian and European cultures used cannabis mostly for its fiber and seed. Cannabis is also an aggressive weed at higher latitudes worldwide. South Asian and African cultures used cannabis mostly for its drug content as the more tropical climates allow maturation of the potent marijuana resin. More intense levels of ambient ultraviolet radiation and of insect predation in the tropics may also have contributed to a natural selection for these drug types (Pate 1994). In any case, cannabis has evolved into two basic races. Plants grown for their fiber, seed, and pulp are universally called hemp, while those grown for their drug content are commonly called drug cannabis or marijuana. This is really the only important taxonomic distinction most people need to make.
Most of the psychoactive properties of marijuana can be attributed to its content of a compound called delta-9-tetrahydrocannabinol (THc). In some literature, it is designated as delta-l-tetrahydrocannabinol due merely to a conflict between two methods of naming chemicals, but it is the very same molecule. Modern hemp varieties are nearly devoid of THC, and it is virtually impossible to divert hemp crops into the drug trade. Hemp has been heavily selected for high fiber content, high stalk yield, high seed yield, and low THC content (<0.3 percent). Drug-type cannabis varies widely in THC content from approximately 1 percent in unselected strains to over 10 percent in the most potent modern varieties. It is not feasible to "get high" on hemp (Karus et al. 1995), and marijuana produces very little low-quality fiber. Hemp should never be confused with marijuana as they are not interchangeable.
In temperate climates, cannabis is an annual crop sown in the spring or early summer and harvested in the summer or autumn. It is also sown during these seasons in more tropical climates to provide proper timing for seasonal rainfall for sufficient moisture to sustain the plants at least until flowering. A cannabis "seed" is actually a small hard-shelled nut (achene) with a single true seed inside. The seeds germinate within two or three days after they are moistened by rain and a pair of rounded green cotyledons (seed leaves) emerges from the soil. Cannabis grows quite rapidly when it receives plenty of water, nutrients, and sunlight. Alternating pairs of palmate leaves with an odd number of long leaflets form along the main stalk as it grows. The first pair of leaves has only a single leaflet, the second pair has three leaflets, the third five, and so on, up to a possible nine or eleven leaflets per leaf.
Hemp grown for fiber is sown densely, the plants only one or two inches apart, so each plant must grow rapidly, tall, and straight to compete with the neighboring plants for sunlight. This results in single smooth stalks without any branches. Seed and marijuana crops are sown sparsely so that the plants have sufficient space and sunlight to grow long branches with many flowers. Widely spaced seed and marijuana crops begin to branch as soon as the primary leaves are fully formed. A small bud appears at the base of each leaf where it joins the main stalk and a branch begins to form. Seed and marijuana plants usually take on a conical or candelabra shape resulting from their extensive branching.
Short day-length triggers and promotes a usuallr-clioecious flowering pattern (separate male and female plants) in cannabis. At this time, the number of leaflets on each leaf decreases from eleven or nine to seven, five, three, and then finally one as the flowers develop and ripen. Most types of cannabis in the Northern Hemisphere begin to flower in July and continue through August. Typical crops develop approximately half of each gender. Fiber hemp is usually harvested at the time when the male plants begin to shed pollen, and as a result few if any seeds are produced. This is done so that the stalks are uniform in fiber content and quality among both male and female plants. The male plants in seed crops are allowed to shed large amounts of pollen, and many seeds begin to form in the female plants a few days later. The male plants die soon after dispersing pollen, but the female plants continue to live up to two months longer as their seeds ripen. Seed crops are harvested when ripe, but before the seeds begin to fall from the flowers. If the crop is harvested too late, most of the seeds will be lost when the plants are handled during harvesting.
Male plants are often removed from marijuana crops before they shed any pollen so that no seeds will form in the female flowers, since female plants die when their seeds mature. This marijuana product is called sinsemilla, which is a slight corruption of the Spanish phrase sin semilla (without seed).
Sinsemilla is more potent than seeded marijuana because the female plants devote all of their energy to producing flowers and resin as they wait in vain for pollination. All drug cannabis crops are matured as long as climatic and other conditions allow in order to increase their potency.
Cannabis as a Resource
NATURAL MEDICINE
Most people in need of medicinal cannabis must obtain it illegally from friends. Improved varieties of cannabis are constantly being developed by amateur marijuana growers and used for personal small-scale cultivation of crude cannabis medicines. Criteria for medical use are imposed upon existing varieties in an effort to select promising candidates. The ultimate goal of breeders of medicinal cannabis is to create varieties that express specific reproducible cannabinoid chemotypes appropriate to the patient's individual medical requirements and personal preferences. Many of these amateur cannabis cultivators are in direct contact with patients who use the drug and are often provided with comments as to which varieties are more effective for various medical problems. Patients who are physically able will sometimes grow their own plants. This is especially true in regions of the United States where the movement for allowing the cultivation of cannabis for medical purposes is gaining popularity. Actively participating in such a nurturing hobby as gardening is good for a patient's attitude and helps foster a positive mental outlook for the fulfillment of life and expectations about death. Outdoor gardening is often included in recuperative therapy programs for ambulatory patients.
Cannabis is a very attractive and responsive plant that is well suited for indoor growth. Hospital wards for terminally ill cancer and AIDS patients could conceivably provide access to rooftop atriums or indoor grow rooms so that patients might enjoy participating in the growing and harvesting of their own herbal medicines without having to venture outdoors. However, there is some cause for concern as to whether these patients would have the ability to produce a consistent and contaminant-free cannabis product. In addition, there remains the unfortunate fact that many of these people do not have the time or strength to tend to such a project. Undoubtedly, these people would prefer to simply purchase this medicine at their local pharmacy. Until these scenarios are legally possible, however, patients will continue to patronize the various Cannabis Buyers' Clubs that have been established to provide access to this medicine.
Domestic cultivation of drug cannabis has increased steadily since the early 1970s and advanced glasshouse and grow room technologies have spread into American homes. It is now possible to set up nearly sterile grow rooms. This is a prophylactic measure designed to minimize contaminants (e.g., fungi) that might prove harmful to patients with suppressed immune systems (Randall 1991). The few extant persistent cannabis pests can be effectively controlled, if not eliminated, by using safe, nontoxic, biological controls. No chemical pesticides are required to grow high-quality, medicinal cannabis, and no chemical pesticides should be used because of the potential harm related to ingestion or inhalation of such chemicals. Many varieties are currently available that contain enough THC (5-10 percent) to be medically effective when only a small amount of the crude drug is smoked. Seeds and cuttings of improved strains are sold openly and legally in a number of seed shops in the Netherlands. In the near future, cannabis varieties with a high THC content and very low amounts of the other cannabinoids may be developed. This could serve as raw material for the extraction of natural THC useful in pharmaceutical preparations (Clarke and Pate 1994). When more of the naturally occurring cannabinoids are approved as therapeutic agents, additional single-cannabinoid varieties will likely be developed for this use.
Vaporizing purified cannabis resin is a much more efficient method for delivering concentrated doses of natural THC to the patient, simultaneously providing more immediate relief than orally ingested synthetic THC capsules and offering a healthier alternative to smoked whole marijuana or crude hashish. Resins from different varieties can be blended to provide differing effects.
The mechanical isolation of cannabis resin by filtration is a totally natural, solvent-free method of concentrating the medically active ingredients of cannabis and can be performed at home. First, the very dry female flowers and small leaflets are thoroughly crushed by hand or put through a coarse metal sieve, such as window mesh, above a tautly framed 135-150 micron
pore silk-screen. This debris is then lightly brushed over the surface of the silk-screen, taking care not to press much of the green leafy material through the pores. The resin powder found underneath is then collected with a stiff card and can be further cleaned by rubbing it firmly over a 50 micron pore silk-screen, discarding any of the inert materials that have fallen through. The
material remaining on top consists mostly of resin glands that are between approximately 50 and 130 microns in diameter and can contain more than 30 percent THC.
NUTRITIOUS FOOD
Hemp seed can be consumed whole, used to produce processed food, or employed as a feed for birds and fishes (Deferne and Pate 1996). Although nominally free of THC, it can contain traces of cannabinoids, probably as a residue of adherent resin originating from its flower bract (Matsunaga et al. 1990). Whole hemp seed contains approximately 20-25 percent protein, 20-30 percent carbohydrates, and 10-15 percent insoluble fiber, as well as a rich array of minerals, particularly phosphorous, potassium, magnesium, sulfur, and calcium along with modest amounts of iron and zinc. It is also a fair source of carotene, a vitamin A precursor. Most hemp seed also contains approximately 25-35 percent oil, although some strains have been claimed to exceed this range.
The crushed seed by-product of oil production is suitable for animal feed and as a human staple due to its spectrum of amino acids, including all eight of those essential to the human diet, as well as to its carbohydrates, fiber, and a small amount of residual oil. Its protein is primarily edestin, a highly assimilable globular protein of a type similar to the albumin found in egg whites and blood. This ease of digestibility is particularly important in the nutritional maintenance of patients with diseases such as tuberculosis and
AIDS.
Analytical data reported for the fatty acid composition of hemp seed oil reveals that it is unusually high in polyunsaturated fatty acids (70-80 percent), while its content in saturated fatty acids (below 10 percent) compares favorably with the least saturated commonly consumed vegetable oils. This high degree of unsaturation explains its extreme sensitivity to oxidative rancidity, as the chemical double bonds that provide such unsaturation are vulnerable to attack by atmospheric oxygen. This degradation is accelerated by heat or light. For this reason, the oil is unsatisfactory for frying or baking, although moderate heat for short periods is probably tolerable. It is best consumed as a table oil in salads or as a butter or margarine substitute for dipping bread, similar in use to olive oil. Proper steam sterilization of the seed probably does not do significant damage to the oil, but it does destroy the integrity of the seed, allowing penetration by air and molds. By the same reasoning, one should avoid eating whole hemp seed that has been subjected to any cooking process, unless it is reasonably fresh.
The two polyunsaturated essential fatty acids, linoleic acid (C„H3202) or LA and linolenic acid (C181-13002) or LNA, account for approximately 50-70 percent and 15-25 percent respectively, of the total fatty acid content of the seed. Such a 3:1 balance has been claimed optimal for human nutrition and is apparently unique among the common plant oils, although black currant seed oil approaches this figure (Erasmus 1993). Preliminary studies indicate that cannabis seeds from tropical environments apparently lack significant quantities of LNA. Oils from temperate varieties are more unsaturated, perhaps due to a natural selection in northern latitudes for a seed energy storage medium that remains liquid at lower temperatures.
Hemp seed oil has also been reported (from sterilized seed in the United States) to contain 1.7 percent gamma-linoleic acid (C18H3006) or GLA (Wirtschafter 1995), and considerably higher levels (3-6 percent) in other specimens have been measured by German investigators (Theimer and Molleken, 1995, Theimer 1996), although it is apparently rare in most tropical varieties of cannabis. The metabolic conversion of LA to GLA is slow in mammals. Moreover, it has been suggested that due to stress, aging, or pathology (e.g., hypertension, diabetes, etc.), formation of a sufficient amount may be impaired. This problem may be relieved by direct GLA supplementation, although caution is warranted since overconsumption could be harmful. Its alleviating action on psoriasis, atopic eczema, and mastalgia are already well documented, and GLA preparations are now frequently prescribed for the treatment of the latter two maladies. The GLA has also been under investigation for its beneficial effects in cardiovascular, psychiatric, and immunological disorders.
TEXTILES
The stalks of some varieties of cannabis contain up to 35 percent usable textile fiber. These long, thin fibers can be extracted from the stalks by simple, albeit labor-intensive, methods. Thus hemp is an appropriate crop for rural peasant agriculture and the cottage industry manufacture of fiber products. The dried stalks are first retted (moistened and fermented) to free the fibers from the wood of the stalks by microbial decomposition, dried again, and then run through a brake that crushes their woody center. These broken pieces of pith or "hurds" are removed from the fibers by pulling them through the teeth of a hackle, an apparatus resembling an inverted turf rake. Afterward, the strands of fiber are combed to remove any remaining small debris and to lay the fibers parallel. They are then bundled and stored. Further processing and the spinning of yarn and weaving of cloth are traditionally performed within the hemp farmer's own home or village. In industrialized hemp agriculture, factories buy either dried stalks (Eastern Europe) or stripped fiber ribbons (China) from the farmers.
Although cannabis was traditionally seldom used for fine textile production, it has long served as the peasant's mainstay for cordage and cloth across Europe and Asia and was used extensively in the former colonies in the New World. A wide range of textile products can be made from hemp. New technology has made possible the manufacture of cloth with outstanding texture and versatility. Compared to cotton, hemp fibers are longer, more lustrous, more absorbent, have a higher tensile strength, and are more resistant to sunlight and mildew damage. These qualities of the basic fiber allow the manufacture of soft, warm (or cool), absorbent, and durable textile materials of all types and weights useful for clothing, mattresses, blankets, linens, carpets, draperies, wall coverings, upholstery, artist's canvas, sails, tarpaulins, sack cloth, etc. Rot-resistant maritime ropes and netting as well as cords, twine, thread, and carpet or linoleum-backing can also be manufactured from hemp.
Natural fiber textiles have steadily gained popularity since the early 1970s and the international textile market is eager for a new natural fiber. Pure hemp textiles possess a natural luster and resilient body that offers interesting and attractive opportunities for clothing designers. Hemp yarn can be woven along with yarns from other fibers to make blended textiles that incorporate much of the appearance and character of the other fiber and can be marketed at lower prices. Further, hemp fibers can be readily spun in combination with cotton, silk, wool, or other bast fibers to produce a wide variety of blended yarns.
If hemp is to replace or supplement other fibers, then the finished fibers must be made softer, and this effort can be initiated through genetic plant improvement. Chinese, Japanese, and Korean varieties produce a moderate content of long, thin, and supple primary fibers. Oriental hemp farmers have traditionally grown hemp that is harvested when it is very young, before flowering. Modern European varieties have traditionally been bred for high primary fiber content as well as higher coarse and stiff secondary fiber content. European hemp farmers usually allow their crop to mature longer, until flowering begins. The total fiber yields of the best Hungarian and Russian varieties are much higher than those of the East Asian varieties from China, Korea, and Japan, but the fiber quality is not as fine.
The advance of hemp fiber will also depend on the development and application of modern processing techniques. The Germans invented a hemp "cottonizing" process that was used from the 1930s through World War II, allowing the less expensive hemp fiber to be spun in combination with cotton and rayon. Later, the Hungarians also developed their own techniques. These processes rely on alkaline chemical digestion of the naturally occurring hardening and stiffening compounds (i.e., lignins) remaining on the fiber following the preliminary mechanical processes that isolate them from the plant. The Chinese have recently developed a patented hemp "degumming" process that softens the fibers so that they can be spun into supple, fine-count yarns. The feasibility of their techniques for the European hemp varieties possessing a higher secondary fiber content has not been established. It also remains to be seen if modern fiber processing steps can be performed on an increasing scale with a minimum of environmental stress. Forethought will be required to develop environmentally sound practices from the onset, since their implementation is more difficult in an already established industry.
Relatively coarse hemp textiles of a canvas grade and a somewhat lighter (but still heavy) clothing grade in several weights and weaves from China and Eastern Europe appeared in the United States around 1990. In the mid-1990s, hemp blends with cotton and silk became very popular. North America and northern Europe are realizing a hemp textile boom resulting from the resurgence of hemp in the news media. Many new hemp textile products are expected to be developed in the near future. Because of its resistance to wear and to the damaging effects of light and moisture, hemp textiles are well suited for upholstery, draperies, carpets, and other furnishings. Since hemp textiles are not restricted by the laws against cannabis drugs, this trade is expected to grow rapidly over the next few years. Currently, the problem is that hemp is in short supply. Hungary, Romania, and China are the only nations producing any commercial quantities of high quality hemp cloth, and they are not producing enough to satisfy current market demand in both the East and the West. As Western capitalization of the Hungarian and Chinese hemp industries continues, supplies of quality hemp products will rise to meet increasing consumer demand, and prices will become more competitive with cotton. However, this will require several years, and such developments must occur in many other regions before total world hemp textile production even approaches the current trade levels of the major natural fibers. Canada must import cotton and flax fiber and is eager to participate in this global expansion. During hemp's time of renewed industrialization, the demand for these textiles will exceed supply, so hemp will continue to command a high price in comparison with similar natural products. Traditional hand-made hemp cloth will always attract a premium price because of its beauty, rarity, and cultural significance. It remains to be seen to what degree hemp's presence in the marketplace will increase and whether it will eventually rival other sources of textile fiber.
PAPER PRODUCTS
Hemp provides a renewable resource for the production of the cellulose used in paper manufacture. This "tree-free paper" results in a low environmental cost because over a comparable period of time, the cellulose yield of hemp per hectare is many times greater than that of a forest. Further, if a forest burns down, it represents the loss of many years of biomass accumulation, but if a hemp field burns down or fails due to drought or other climatic conditions, only one year's growth is lost, and the crop can be replanted the following year. In addition, since hemp contains less than 25 percent of the natural lignin "glue" that binds wood fibers together, pulp processing can be milder and the environmentally safer peroxide bleaching process can be used. Hydrogen peroxide breaks down into oxygen and water, causing no environmental damage. The wood pulp industry almost universally uses a sulfite and chlorine process that produces large amounts of toxic waste (e.g., acids, chlorine, sulfur, and dioxin), which often enter the environment.
Hemp paper resists decomposition and does not exhibit the usual age-related sulfur-yellowing of wood-derived papers. Paper containing hemp cellulose is currently used for such high quality products as archival records, museum mounts, currency and other monetary instruments, artwork, fine books, and postage stamps. Paper produced from a mixture of the hurds and short fibers can be used for textbooks, computer paper, photocopy paper, bags, carton stock, and corrugated cardboard. Low-acid hemp fiber papers are also highly recyclable. In recent years, several hemp related books and journals have been printed on paper with hemp content.
Hemp fiber and hemp hurd pulp also blend well with pulp from other sources that may serve as a less expensive filler in specific paper formulations. One of the most economically viable uses for hemp fiber is to strengthen post-consumer pulp by adding a long, strong fiber to the short and weak fibers from recycled wood pulp paper, extending the number of recyclings possible with used paper pulp. Hemp crops have been grown for this purpose in the Netherlands.
Currently, 100 percent hemp paper is produced only in limited amounts for fine art use and limited printings. Pure hemp papers are not competitively priced with wood pulp papers unless purchased in very large amounts. However, several German, English and East European smooth-surfaced papers are currently available that incorporate 30-60 percent cannabis pulp blended with post-consumer waste. These papers are generally suited for office work and photocopying and many are of a sufficiently high quality to be suitable for printing paper or stationery. Many existing paper mills would be able to handle cannabis pulp, were sufficient amounts produced to make it practical. It is estimated that hemp stalks can be produced in Europe for ECU 50-70 (approximately U.S. $50-70) per ton (EC-MR 1993). This is comparable to the price of softwood pulp. Cannabis-based cellulose pulp is also produced in France and Spain and is usually used in formulations for the high quality, low acid, blended-pulp specialty papers used in tea bags and cigarettes. Spanish pulp is used in the British and German hemp papers. Because hemp fiber is resistant to sun and moisture damage, it is also ideal for garden mulching paper, greenhouse weed mats, and the nonwoven geo-textiles used for landscaping and erosion control.
ADDITIONAL PRODUCTS
Hemp hurds make an excellent, naturally absorbent material for cat litter and for covering the floor of animal pens. The English, French, and Dutch produce a horse stable bedding by crushing dried cannabis stalks in a brake and packaging them in lightly compressed sacks. These hurds are readily composted, especially after they are saturated with nitrogenous animal wastes. This is a fine example of the direct use of a hemp product without complex processing.
Cannabis can also be used to make building materials. Suitably fireproofed hemp hurds are used as wall-fill insulation and are also being marketed by several companies in France as a constituent of construction blocks. Hemp hurd houses may be an answer to housing shortages in countries with few remaining forest resources, such as China and India. In Hungary, Poland, and the Netherlands particle board is manufactured from chipped hemp stalks. The dried hemp stalks are chopped into short pieces and pressed together with a binder to form the coarse interior matrix of a surfaced particle board. In 1991 Hungarian researchers were granted a patent for a more advanced and stronger laminated board made from crossed layers of whole hemp stalks also held together with a binder. So far, this type of product has not been marketed. An Austrian process that uses extreme pressure to compress hemp pulp into plasticlike molded products also shows great potential.
As a chemical feed stock, hurds can be treated in a manner similar to wood pulp and converted to the same wide range of products: plastics, propellants, explosives, etc. Cannabis seed oil makes a suitable ingredient in soap and other body care products, detergents, nontoxic paints, varnishes, and printer's ink. This oil can also be polymerized (the molecules linked) into plastics and other industrial materials that are currently derived from petrochemical sources, or it can serve as an alternative starting material for the production of these industrial chemicals (e.g., alcohols, ketones, aldehydes, etc.).
ENERGY APPLICATIONS
Cannabis is one of the plant kingdom's most efficient photosynthetic converters of atmospheric CO, into usable biomass and could serve as an inexpensive feed stock for fuel and energy production. Hemp seed oil is,somewhat flammable and of limited use in lamps and diesel-type engines. The oil might also be "cracked" (a standard petroleum processing procedure) to break up its long chain molecules, providing a more easily combustible fuel. Perhaps microbial conversion of plant biomass to ethanol will also prove feasible. However, the real energy contribution of this plant might be best realized through the controlled pyrolytic conversion (i.e., at high temperatures in an oxygen-deprived atmosphere) of its whole biomass to methane, methanol, fuel oil, and charcoal. Unlike coal, these fuels contain little, if any, sulfur, a major contributor to the production of acid rain from industrial stack emissions. Certainly, the most direct energy utilization technique involves simply rolling the raw cannabis biomass into large bales and burning them in an electrical power generating facility. Growing a clean-burning, low-sulfur coal substitute at a rate of several tons per hectare (1 ha = 2.5 acres) could present an attractive alternative to fossil fuels. Much of the world's forest resources are burned for cooking and heating. Environmental pressure is particularly acute across much of Africa, Asia, and South America. Hemp and other renewable fuel sources can substitute for petrochemicals and save forests.
It will be necessary to perform a careful overall economic analysis of the potential of hemp for biomass production in comparison to other valuable crop candidates. Several sources of biomass are currently available and yet are not utilized for energy production. Many annual crops in the temperate zone have been shown to have a biomass limit of 20 tons of dry matter per hectare per crop cycle. Tropical sugarcane has been recorded as yielding up to 64 tons per hectare in a year, which is approximately comparable to temperate crops on a per month basis (Simmonds 1979). One would expect cannabis biomass production to approach the same approximate limits. In frost-free regions cannabis can be cultivated all year long. Late and slow-maturing varieties with indeterminate flowering could be adapted to tropical biomass production and be harvested without regard to floral maturity. In northern temperate regions, tropical cannabis varieties grow rapidly under the long photoperiod of summer, becoming very large but never maturing. Therefore, they do not produce either viable pollen and seed or much potent resin, but they do produce large amounts of biomass. In a single summer season, temperate hemp produces up to 12 tons of dry stalks per hectare per crop cycle, and foliage could add 50 percent to this total (EC-AIR 1993). Research must be carried out to determine just how efficient cannabis might be as a biomass producer under different cropping systems.
Multi- Use Strategies
Cannabis is the only plant that is used for fiber and pulp from its stalks, food and oil from its seed, and medicines from its resin. With the possible exception of certain members of the Cruciferae (i.e., turnip, kale, mustard, and canola are used for vegetables, fodder, and oil) no other crop plant is used for so many purposes (Simmonds 1976). Certainly no other single plant can be put to such a wide range of uses as cannabis.
As with other multiuse plants, specific cannabis varieties have been developed for differing purposes, selected from their widely diversified gene pool. Hemp fiber varieties have been selected for high yield of stalks, uniform maturation, low THC content, high fiber content, and, to some degree, high fiber quality. Seed varieties have been selected for factors contributing to high seed yield. Drug varieties have been selected for high THC content or high resin production and high flower/leaf ratios. The enforcement of these different sets of selection criteria has resulted in three groups of cannabis varieties suited for the manufacture of differing products. However, cannabis has never been intentionally bred for several other potentially valuable characteristics (e.g., bulk cellulose or seed protein or fatty acids). Varieties are also needed that are resistant to fungal pests encountered in the humid maritime climates of England, the Netherlands, and other parts of Northern Europe and Scandinavia. Tropical and semitropical hemp varieties low in THC are entirely lacking. It is expected that cannabis breeders will respond as do breeders of other crop plants: developing varieties that the agricultural industries find appropriate for making marketable products. It is unfortunate that hemp breeders must first overcome political obstacles, especially the lowering of plant THC content to very low limits, before they can begin to develop the other beneficial characteristics of cannabis.
It is unlikely that the primary use of cannabis will be for the production of industrial raw materials alone, since biomass is the low value by-product of all cannabis industries and is usually plowed back into the land. Hemp hurds and mill scraps are often wasted by the hemp textile industry because it is not cost-effective to transport them to a paper factory off-site. Produc-
tion for these and other end uses may not prove economically feasible unless incorporated within the framework of an integrated plan to process hemp for multiple purposes simultaneously. The ultimate solution may be the development of a multiuse variety yielding an optimized combination of products from one plant. This would be especially advantageous in areas such as Western Europe, where arable land and manual labor are at a premium. Separate machinery would still be required for each of the differing product processing steps (as with single-use varieties), but total utilization of a uniform feed stock strain and decentralized processing on-site would make more efficient use of fuel and raw materials.
Plant breeders must overcome the effects of "resource partitioning" in order to develop a valuable multiuse variety with sufficient economic yield in each trait superior to that of existing single-use varieties. These partitioning effects tend to increase one economically valuable trait at the expense of another. Fortunately, because of the ancient cultural and geographical isola-
tion of the early unimproved cannabis "land-races" (naturally established varietal types) and the selective breeding of these separate varieties for fiber, seed, and drug use, the gene pool is diverse, and overcoming partitioning effects may not be as much of a problem in cannabis as it has been with other crop plants.
Although the cultivation and processing of cannabis are perfectly adapted to manual peasant labor, the trend in modern agriculture toward automation continues. All modern industrial varieties must be selected for uniformity and acceptability for machine harvesting and processing. This could lead to a compromise between the quality of fiber, seed, or resin and the preferences of engineers who develop agricultural machinery. The modern tomato provides us with a typical example of a machine-harvestable and processable fruit that suffers from a lack of flavor and lowered vitamin content.
Conservation of the genetic diversity of cannabis is of the greatest importance to the future of breeding improved cannabis varieties. Many of the original, relatively unmodified land-races that formed the basic building blocks of modern drug and fiber hemp cannabis varieties have been lost. The remaining variability expressed in cannabis is crucial to the success of future breeding programs. Variability cannot be created in crop plants but can only be reshuffled into different combinations. Seed collections must be grown out in genetic isolation from other types periodically and on a large scale to keep each varietal line viable and genetically diverse. Every effort must be made to preserve all available varieties of cannabis before many more become extinct. We may already have lost unique varieties containing compounds of medical value or exhibiting other beneficial traits. Once a variety is lost, it is very difficult to recreate it through the recombination of other varieties and once its genes become extinct, it is essentially lost forever.
The successful industrialization of all newly introduced crops requires a period of "protected" introduction (often supported by government research grants and production subsidies to the farmer) before sufficient demand for the products of the new crop builds in the marketplace. This is being provided in the European Community, and similar incentives will be required if hemp is to enter quickly into mainstream agriculture in the United States. Eventually, demand alone will drive the market, where hemp proves to be superior as well as competitively priced. Unfortunately, it is likely that due to a lingering confusion between the value of cannabis as a crop plant and its misperceived threat as a drug problem, the United States will miss its opportunity to become a leading hemp-producing nation. Despite American agricultural prowess in other endeavors, the foreseeable future promises that this crop will come primarily from the new producers in Canada and Western Europe and from traditional producers in the semi-industrialized nations of Asia and Eastern Europe.
Environmentally Friendly Crop
Cannabis crops grow rapidly and tend to overgrow and shade out competing weeds. Herbicide use is usually not necessary in densely planted hemp fields provided with sufficient autumn and spring plowing. In the rare cases where herbicides may be required, they are usually applied only once as a pre-emergent before the seed is sown. Few insect pests attack field crops of cannabis, and pesticide applications are also rarely necessary. Hemp presents a stark contrast to cotton cultivation, which disastrously depletes the soil and consumes far more agricultural chemicals than any other crop. In glasshouses and grow rooms, insect pests and fungal diseases are a much more serious problem, but they can be controlled preventively through environmental manipulation and correctively through the use of natural biocontrols. The few chemical pesticides that may be required can be of low toxicity and can be incorporated into an "Integrated Pest Management" (iPm) approach to control.
Contrary to the often quoted report of Dewey (1913) stating that hemp requires little fertilizer and does not lower soil fertility, cannabis is actually a quite heavy feeder. It withdraws two to three times as much nitrogen, phosphorous, and potassium from the soil as cereals (Dempsey 1975), although farmers consider this crop beneficial to the soil structure. While high application rates of chemical fertilizers are not required for adequate yields, good harvests require sufficient soil fertility. Cannabis is particularly responsive to manuring (as marijuana growers are well aware). Hemp does not deplete the soil as much if the harvested plants are dried and processed (and their stalks retted) in the field, where they are repeatedly moistened by dew and acted upon by fungi. A significant amount of the nutrients contained in the foliage, plant debris, and roots is thereby returned to the soil when plowed under each autumn. This "dew-retting" is simple, easily automated, and causes little, if any, environmental damage. Unfortunately, it also produces an inferior grade of hemp suitable only for the coarsest applications such as the production of ropes and sacking.
Dutch researchers have developed an ensilaging system whereby hemp stalks can be stored in a partially anaerobic fermenting state without field drying and can be used later for pulp and fiber extraction as the need arises. This technique will allow hemp to be profitably cultivated in regions with humid summer and autumn climates where the field drying of hemp stalks is not possible (EC-AIR 1993).
"Water-retting" is used to produce hemp fiber of fine quality. It has traditionally been the preferred retting technique in China, Japan, and Eastern Europe and is often done in ponds, waterways, and ditches. The stems are submerged for up to a week and while they decompose, butyric acid, pectins, and other by-products are released into the water. Water-retting requires large amounts of fresh water, and this retting water must be changed often. Dumping this nutrient-rich retting water into streams and lakes can cause eutrophication. This is a process initiated by a rapid algal bloom caused by these added nutrients. However, when this sudden growth exhausts the nutrients, the abrupt death of these organisms results in deoxygenation of the aquatic environment due to the consequent decomposition process. This soon suffocates the other species living in that water. If the retting compounds are sufficiently diluted before release into the environment, they do not cause such an effect or may even prove useful if utilized as an organically enriched irrigation water for crops. Research is also being carried on to determine which microbial organisms are most appropriate for environmentally friendly water-retting.
OXYGEN PRODUCTION AND CARBON FIXATION
Burning several million years of stored fossil fuels in just a few decades has increased atmospheric carbon dioxide (CO2) levels, causing the greenhouse effect (a trapping of planetary heat normally lost to outer space), resulting in global warming (the gradual increase of average temperatures worldwide). This, in turn, can result in climatic changes (i.e., extremes of temperature and moisture) and affect sea levels, potentially threatening established coastlines. Green plants are the primary organisms capable of using the energy of sunlight to "fix" (convert to a usable form) the carbon atoms contained in carbon dioxide, and the hydrogen and oxygen atoms contained in water into simple sugars (the building blocks of more complex molecules) through the biochemical process of photosynthesis. As plants perform this process, they also release vital life-supporting oxygen into the atmosphere. The increased cultivation of cannabis, like that of any other plant, would increase this oxygen production and carbon fixation, helping to replace at least this one function of our rapidly vanishing forests and other habitats not in plants, thus playing a critical role in the maintenance of planetary balance.
However, until comprehensive programs are in place to maintain and eventually increase our total photosynthetic capacity (rather than just tree-farming a limited percentage of the natural forests cut annually), cannabis or any other fast-growing and efficient plant will not be needed. What is really lacking is a coordinated international policy and a concerted, government-initiated effort to "green" our depleted planet. If cannabis merely replaces other crops because of the superior products that can be made from it, then there would be little or no net increase in global plant biomass and consequent photosynthesis and therefore, no increased direct benefit to the environment. One carbon-fixing and oxygen-producing crop would simply be replaced by another. Hemp, as a substitute for fossil fuels and forest resources, could utilize marginal or presently unused agricultural land to meet the growing demand for this new crop. Farmers would not need to cut down forests to grow hemp, so there could be a net increase in carbon fixation and oxygen production. Unlike fossil fuels, burning hemp would add no more CO, to the atmosphere than it had extracted during its growth. Certainly, forests could be better used for their unique wood products and appreciated for their intrinsic value rather than exploited as a source of pulp products better made from cannabis.
EROSION CONTROL
Cannabis is cultivated in a wide range of environments on every temperate continent and naturalizes readily as a weed throughout Eurasia and North America, especially in regions with a warm, moist summer growing season. One of the greatest adaptive tools of weeds is their heterozygosity (variation of genetic characteristics), allowing a broad range of inherited traits to be harbored within the population. This trait allows increased adaptation of a species to a wider variety of environmental conditions. Dioecious wind-pollinated plants, such as cannabis, are characteristically highly heterozygous, and this accounts in large part for their great adaptability. This heterozygosity is also the genetic basis for rapid progress in cannabis varietal improvement. Special varieties adapted for erosion control, possessing enhanced weed characteristics, such as rapid maturation and tolerance to environmental extremes, could be bred for their improved ability to colonize an area and establish reproductive populations. These varieties could incorporate traits such as increased root growth, low nutrient requirements, drought tolerance, and frost hardiness. However, caution should balance this initiative, lest an enhanced potential "pest plant" escape into the general environment.
LAND RECLAMATION
One method for absorbing and concentrating toxic compounds contained in contaminated soil is to cultivate plants that will selectively bioaccumulate them and then to properly dispose of the resulting crop. Cannabis is an active feeder and takes up large amounts of soil solutes. Its rapid biomass accumulation, weedy colonizing tendencies, and suitability for mechanized harvesting may make cannabis suitable for use in the reclamation of polluted land fills and dump sites. Preliminary experiments in Poland indicate that it may be useful for absorbing the heavy metal contamination of such soils (Kozlowski et al. 1995).
Future of Cannabis
Cannabis has largely been neglected by the formal agricultural community and has not received many of the benefits of modern research that have been applied to other more developed crops, although considering the legal and economic restrictions extant, it has progressed quite far. One can imagine that cannabis will become an even more productive crop plant as modern genetic techniques are brought to bear on its improvement.
Many members of the Fabaceae (bean family) contain the genes to provide a proper host environment in their roots for specially adapted Rhizobium bacteria. These nitrogen-fixing organisms fix atmospheric nitrogen gas (N2) into the water-soluble ions of nitrate (NO3) used by the host plant as a primary nutrient and ensure that the ecosystem as a whole receives a steady supply of usable nitrogen. This symbiotic (mutually beneficial) relationship with nitrogen-fixers reduces the amount of nitrogen fertilizer a crop requires and can potentially provide net gains of nitrogen to the soil through decomposition of the harvest remains. Through gene transfer techniques, cannabis could be genetically engineered to serve as a host to nitrogen-fixing organisms. This idea has been approached with limited success in other crops, such as corn. Lowered soil nitrogen requirements would enhance the potential for cannabis to be grown in marginal areas.
Cannabis can be readily manipulated to be reproduced asexually, yielding many identical individuals (clones). Vegetative cuttings are made from a mother plant, transplanted and grown to desired size, then induced to flower by photoperiod (day-length) reduction. This has become the normal method of drug-cannabis production in the modern glasshouse or grow room. Tiny sterile meristem (shoot tip) cuttings that are easily rooted and stored in sterile glass vessels represent the current state of the art. Cultures of undifferentiated cannabis cells have also been maintained for many years. This callus tissue is potentially useful for cleaning up varieties infected with viral or fungal pathogens, screening for stress resistance, and early selection or creation of mutants. Probably the most exciting potential use for callus is as a genetic archive for thousands of individually cloned potential plants stored in a frozen state. However, though lumps of cannabis callus grow well and develop roots in response to growth hormone applications, it has proven very difficult to initiate shoot formation. Unless these undifferentiated cells can be thawed and regenerated (without mutations) into whole plantlets and then grown to form healthy mature plants suitable for seed production, they will be useless (e.g., undifferentiated cannabis cells have never been shown to produce THC in vitro).
In the distant future, other organisms might be genetically engineered to produce THC or other cannabinoids. Perhaps a plant family that already produces terpenoid essential oils, such as the Labiatae (mints), could be genetically engineered to produce cannabinoids. Plants of this family also produce appropriate glandular trichomes (hairlike resin-producing structures) on the surface of their leaves. It does not seem economically feasible to attempt the genetic engineering of bacteria or other simple life forms to produce THC, since the natural plant source of cannabinoids is so inexpensive to grow.
Despite these present technical challenges, further "biotech" discoveries will undoubtedly create exciting new cannabis-based products. We must then take care to avoid narrowing the cannabis gene base through narrow breeding selection for specific applications or even abandoning the cannabis plant altogether in favor of artificially bioengineered substitutes. With care, one might expect that our 12,000-year-old relationship with this useful plant will last well through the next several millennia!
Conclusion
There is no need to overglamorize the potentials of cannabis, as its value as a beneficial crop plant is self-evident. Cannabis alone will not "save our planet," as hemp activists have often claimed, but it can certainly provide a variety of effective medicines and environmentally friendly products in the near future. Cannabis may also prove itself as a valuable land management tool and provider of biomass for raw materials and energy production. Until restrictions on the cultivation and use of cannabis are lifted and new policies enacted to actively pursue a better understanding of this plant's potential for improving our quality of life, it will remain a crop of secondary importance, clouded in misunderstanding. Progress in cannabis research is accelerating despite the legal obstacles associated with this plant, and once the legal flood-gates are opened, significant discoveries can be expected. That a single plant can produce so many different valuable commodities is a natural wonder. It is a great oversight on the part of many governments that we are not now receiving more benefits from a strong alliance with such a venerable ally.
References
Clarke, R.C., and D.W. Pate. 1994. Medical marijuana. Journal of the International Hemp Association 1 (1): 9-12.
Deferne, J.L., and D.W. Pate. 1996. Hemp seed oil: A source of valuable essential fatty acids. Journal of the International Hemp Association 3 (1): 1,4-7.
Dempsey, J. M. 1975. Fiber crops. In Hemp, 46-87. Gainesville, FL: University of Florida Press. Dewey, L.H. 1913. Hemp. USDA Yearbook, 283-246.
EC-AIR Meeting. (August 24, 1993). Wageningen, Netherlands.
Erasmus, U. 1993. Fats That Heal, Fats That Kill. Burnaby, B.C., Canada: Alive Books. Karus, M., F. Grotenhermen, and H. Schaaf. 1995. Migbrauchpotential THC-armer Faserhan-
fsorten als Rauschdroge. Bioresource Hemp Symposium Proceedings, 589-605. (2d ed.).
Cologne, Germany: Nova-Institute.
Kozlowski, R., P. Baraniecki, L. Grabowska, and J. Mankowski. 1995. Recultivation of degraded areas through cultivation of hemp. Bioresource Hemp Symposium Proceedings. (2d ed.) 259267.
Matsunaga, T., H. Nagatomo, I Yamamoto, and H. Yoshimura. 1990. Identification and determination of cannabinoids in commercially available cannabis seeds. Eisei Kagaku 36 (6): 545-547.
Pate, D.W. 1994. Chemical ecology of cannabis. Journal of the International Hemp Association 1 (2): 29,32-37.
Randall, R.C. 1991. Marijuana and AIDS: Pot, Politics, and PWAs in America. Washington, DC: Galen Press.
Simmonds, N.W., ed. 1976. Evolution of Crop Plants (pp. 203-204). London and New York: Longman.
Simmonds, N.W. 1979. Principles of Crop Improvement (p. 42). London: Longman Scientific and Technical.
Theimer, R. 1996. Personal communication.
Theimer, R.R., and H. Molleken. 1995. Analysis of the oils from different hemp (Cannabis sativa L.) cultivars: Perspectives for economic utilization. Bioresource Hemp Symposium Proceedings. (2d ed.) 536-545a.
Wirtshafter, D. 1995. Nutrition of hemp seeds and hemp seed oil? In Bioresource Hemp Symposium Proceedings. (2d ed.) 546-555.
|
