HEMP: Devil Weed or Valuable Crop Plant

In the age of sustainability, MIKE NICHOLS explores the agricultural value of hemp crops for medicines, oil seed, fibre and phytoremediation. Despite opposition to research and use put forward by most governments, hemp does have many well-documented benefits.

Some varieties of hemp can grow very tall.

Some varieties of hemp can grow very tall.

To the majority of people, cannabis is the illegal recreational drug marijuana. In fact, marijuana is the common name for certain varieties of cannabis, which can contain high (up to 25%) of the psychoactive drug D9-tetrahydrocannabinol (THC), but the species Cannabis sativa and Cannabis indica include a wide range of plant types not only selected for drug production but also selected for fibre and for oil seed production.

My involvement with cannabis began in 2002 when the New Zealand Hemp Industries Association (NZHIA) contacted the University for assistance, and as a result I was appointed ‘Research Team Leader’ for the Association. I knew absolutely nothing about cannabis at that time so it resulted in a very fast learning curve, which took me overseas to Kuopio in Finland to talk with Dr Jace Calloway, the developer of a dwarf cannabis variety for oil seed, and to London to talk with Justin Gover, the Managing Director of G.W. Pharmaceuticals (and his colleagues) to discuss the medical use of cannabis, and more recently to The Netherlands for discussions with the Dutch medicinal cannabis producers Bedrocan.

Historically, cannabis has played an important role as a crop plant. In the 19th Century, when Britannia ruled the waves, each warship required many tonnes of hemp fibre every year to replace the rigging as hemp is renowned as the strongest naturally occurring fibre. Of course, this importance disappeared with the move from sail to steam. Cannabis-based medicines were also an important part of the pharmacist’s armoury for pain relief until the early 1930s when they became a prohibited drug.

The international prohibition of hemp dates from the mid-1930s, when it became a prohibited plant in the United States. Cynically, one should note that in the USA the growing of cannabis was heavily promoted during the 1939-45 war for hemp fibre production (for mooring ropes and for parachute webbing), but immediately after the war all the advisory information on the crop was destroyed!

Following this war, strenuous efforts were made to prohibit cannabis production world-wide through the United Nations and this resulted in a ban in the majority of countries except for the former Eastern Block countries, particularly Russia and Hungary.

It is only over the past 20 years that interest in the plant has developed in the western World, particularly in Western Europe (Italy, France, Germany and The Netherlands) and in Canada. It is still virtually a prohibited plant in the USA!

There would appear to be little doubt that high THC cannabis (marijuana) used regularly as a recreational drug is a health hazard. The link between alcohol, marijuana and psychiatric problems and the potential to cause chromosome damage appears to be well substantiated, and a link from marijuana to the harder (more addictive drugs) has recently been suggested. Nevertheless, cannabis does appear to have considerable potential for medical uses, and the low THC varieties seem to have excellent potential for a wide range of other uses. Of course, the most serious addictive (and harm-causing) drug is alcohol, followed by tobacco, but these are legal (in most societies) and are big business!

Agricultural value of cannabis
Cannabis has a wide range of possibilities in agriculture:

• as an oil seed
• as a fibre crop
• for phytoremediation.

Hemp being grown in Finland for the oil from the seed.

Hemp being grown in Finland for the oil from the seed.

As an oil seed
The initial thrust of development of cannabis in New Zealand was directed primarily as an oil seed crop, and secondly for fibre. In the early years (2001-2002) growers were enthusiastic about the tremendous vigour of their crops. However, if one is producing seed from which to press the oil, then there is no point in growing a 2-metre high crop if similar yields of seed can be achieved with a crop 60 cm tall. In fact, tall crops may prove extremely difficult to harvest.

Midland Seeds in Ashburton have shown that commercial yields of 800-1000 kg/ha of seed can be obtained, while research yields at both Massey University (by MacMcIntosh) and Lincoln University (by Steve Cutler) have suggested that potential yields could exceed 1,500 kg/ha.

The importance of hemp seed oil from a dietary point of view is the high levels (30% plus) of the two key polyunsaturated fatty acids omega 3 and omega 6, which it contains. These are critical fatty acids that the human body is unable to metabolise, and must be consumed from some source. Unfortunately, the fatty acids from hemp seed oil are not as nutritionally valuable as similar fatty acids derived from fish oils.

The value of hemp seed oil is not limited to its nutritional value, as it has industrial uses, which include cosmetics, paints and varnishes, and soap.
It must be emphasised that cannabis seed (and therefore oil) contains no THC.

As a fibre crop
When oil runs out in 20-30 years time the world will not only require a sustainable source of energy (presumably hydrogen derived from solar energy and wind power), but also a sustainable source of fibre. Nylon and similar oil-derived monofilament fibres have served us well over the past 50 years, but a sustainable source of fibre will be an essential component of living. It is likely that wool, cotton and silk will continue to provide much of our clothing, but no natural fibre is as strong as hemp. It is a versatile fibre, being suitable (after appropriate processing) for strong wearing textiles, speciality papers, press-moulded panels, thermal insulation of buildings, as well as ropes, etc.

The non-fibre content of hemp stalks is called ‘hurd’ and is 70-80% of the stalk weight. These are similar in structure to wood fibre, and could be used to produce newsprint, or even biodegradable disposable nappies! With a significant horse racing industry, the hurds could also find a role in animal bedding.

Cannabis mineral accumulation trial for gold.(NFT).

Cannabis mineral accumulation trial for gold.(NFT).

The removal of toxic chemicals from the soil is a major problem in many countries. One approach is to concrete over the affected area as has been done at a number of old gas work sites. Another is to use expensive treatments to break down the chemical. A third method is to use plants either to remove the toxic substance (so that it can be concentrated in a single land fill), or to use plants to stimulate bacteria in the soil to break down the toxic chemical. Obviously, using plants to break down chemicals in the soil is only effective (and worth-while) if the downstream products are no longer toxic.

Taking up toxic chemicals from the soil by plants is a rather different story. We have undertaken some preliminary research at Massey University to determine whether this has potential to absorb heavy metals such as copper, nickel and arsenic from the soil. Hemp has the advantage of producing a very large biomass in a very short time—probably 15 tonne/ha dry matter in three months from seeding. Italian research has showed that hemp was capable of absorbing some heavy metals, but that they were not transferred to the leaves and stems. This may in fact be a good thing, as it would mean that the hemp could be harvested for fibre, and then the roots dug for heavy metal removal.

New Zealand (like many countries) has a major problem in disposing of nutrient-rich solutions from dairy sheds and sewage works. Historically, these have been dumped in rivers, lakes and the sea. Such a strategy has resulted in the death or near death of many lakes and rivers, and alternative systems must be developed.

We have used hemp to successfully remove large quantities of nitrogen and phosphorous from the nutrient-rich water derived from a meat processing plant (PPCS at Ashburton), and from sewage (Feilding, near Palmerston North) – see Table 1. The only disadvantage was that hemp is not perennial and has to be re-established each season from seed, and that the bulk of the nitrogen and phosphorous is to be found in the leaves, and that the proportion of leaves on the plant decline with age.

Table 1. Effect of harvest date on the absorption of nitrogen and phosphorous by hemp plants on a soil irrigated by nutrient-rich waste sewage water.

Table 1. Effect of harvest date on the absorption of nitrogen and phosphorous by hemp plants on a soil irrigated by nutrient-rich waste sewage water.

Medical use of cannabis
Until the early 30s, cannabis was a common constituent in many medicines, and was a part of the normal pharmacist’s stock in trade.

It is considered that cannabis-based medicines have potential for a range of medical conditions. It must be emphasised, however, that cannabis-based medicines are not simply THC (D9-tetrahydrocannabinol), but also include a number of other cannabinoids of which CBD (cannabidiol) is the most common, and that in many cases it is the actual mixture of phytocannabinoids (plant-derived cannabinoids), which is important. In fact, in the USA they have developed a laboratory version of THC (called ‘Marinol’), which does not behave exactly the same as the plant sourced THC. This suggests that the other naturally occurring cannabinoids also make a valuable contribution!

Hydroponic cannabis trial using the nutrient film technique (NFT).

Hydroponic cannabis trial using the nutrient film technique (NFT).

Work in the UK has shown that high THC cannabis-based medicines have the potential to reduce cancer and peri-operative pain. There is research being undertaken on the use of combinations of THC and CBD to provide relief from multiple sclerosis, phantom pain (from amputated limbs), spinal cord injury, inflammatory bowel diseases, rheumatoid arthritis and HIV/Aids, and CBD is currently being considered for strokes, head injuries and psychotic disorders.

One of the more interesting aspects of THC is its appetite-stimulating characteristic. It is common knowledge that marijuana users tend to raid the fridge, and this fact has the potential to be of medical importance in a number of areas.

HIV-AIDS is known as the wasting disease, because the victims lose appetite. Stimulating hunger is important because lower calorie intake and poor absorption of nutrients are associated with wasting. If you eat better, and therefore obtain more nutrients, minerals and vitamins, you are more likely to be resistant for a longer time to the infections, which inevitably kill people with this disease.

The author with a crop of medicinal cannabis in a plant factory in The Netherlands.

The author with a crop of medicinal cannabis in a plant factory in The Netherlands.

Anorexia and cachexia are diagnosed in more than two-thirds of all cancer patients with advanced disease, and are independent risk factors for morbidity and mortality. Anorexia, nausea and vomiting often are described as more significant inhibiting factors for quality of life of cancer patients than even intense pain.

As long ago as 1986, delta-9-tetrahydrocannabinol (THC), the main effective constituent of cannabis, was licensed as an anti-emetic drug in cancer patients receiving chemotherapy. In addition, in clinical studies THC has shown significant stimulation of appetite and increase of body weight in HIV-positive and cancer patients. The appetite-stimulating effect of cannabis itself has also been well documented in many anecdotal cases. There are strong indications that cannabis is better tolerated than THC alone, because cannabis contains several additional cannabinoids, like cannabidiol (CBD), which antagonise the psychotropic actions of THC, but do not inhibit the appetite-stimulating effect.

Ageing is associated with a reduction in appetite and food intake, which has been termed the ‘anorexia of ageing’. After age 70-75 years average body weight decreases, even in healthy people, due to the loss of lean tissue. Marked weight loss is common in the elderly and a major cause of morbidity and increased mortality. The cause(s) of the anorexia of ageing are largely unknown. Apparently, we tend to have smaller appetites when we reach 70-75 years. It is possible that low doses of THC might enhance longevity, while at the same time providing an improved quality of life.

Medicinal cannabis spray applicator developed by G.W. Pharmaceuticals in UK.

Medicinal cannabis spray applicator developed by G.W. Pharmaceuticals in UK.

Delivery systems
It is generally considered that smoking is not an acceptable means of delivery for cannabis-based medicines. There are difficulties in dispensing the correct quantity of drug, and the system is too similar to recreational cannabis use, even so this is the usual delivery method for most medicinal cannabis users. In addition, smoking anything has the potential to produce carcinogens in the smoke.

In fact, the medical side of cannabis use should be no different from that of any controlled prescription medicine. G.W. Pharmaceuticals (in the UK) have developed a system which allows the patient to dispense precisely the desired level of relief through an under the tongue applicator. Another method of delivering the drug is by vaporisation, which delivers the drug directly to the lungs without the danger of burning, and without the addition of a solvent (such as alcohol). In 2008, the New Zealand government approved the use of medicinal cannabis under very specific conditions.

Cannabis production for medicine
This is, of course a very delicate subject. It is being grown in the UK by G.W. Pharmaceuticals in greenhouses at a secret location, and I recently visited a plant factory in The Netherlands where Bedrocan produce their medicinal cannabis.

Medicinal cannabis production is a highly skilled occupation, as it is essential that the product is of high quality, standardised, and is free from any toxic chemicals (such as heavy metals or pesticides) if it is to be used medicinally. In some American states (e.g. California), it is now permitted to grow medicinal cannabis for personal use if you have a major health problem. A strange situation when it is a Federal offence to grow the crop! In fact, in California (population 35 million), in 2008, the value of medicinal cannabis sold legally in the State was US$2 billion, as measured by the sales tax paid.

Producing high THC cannabis (marijuana) is very different from the production of low THC cannabis (hemp). Plants are normally grown from cuttings (clones) rather than from seed, and only female plants are grown as the male plants do not produce a flower head. Also, if pollination occurs the value of the flower head is severely reduced due to the presence of seed. Selection of the ‘mother’ plants, which are used to produce the cuttings, is a critical part of the operation, because there can be large differences in productivity between different plants when grown from seed.

The growing of high THC cannabis in New Zealand and Australia is currently illegal and the level of technology used by illegal growers generally leaves very much to be desired. This is very apparent in the many cases I have been involved with as an expert witness. Developing a legal drug production facility would result in markedly enhanced yield by making use of our current knowledge on plant factories crop nutrition, and the potential to use LED lighting, and adjust the environment and the nutrient levels of the hydroponic solution to maximise the quantity of medicinal drug produced. A plant factory approach would also make security (an important consideration) much easier.

Hemp yields
Cannabis productivity will depend on the purpose for which the crop is being grown. It is true that low THC cultivars (such as Kompolti) can be grown for both hemp fibre and also for hemp seed (and therefore hemp oil) but in the main it is preferable to concentrate on a single product, and take anything else as a bonus.

In fact, hemp fibre is best if grown at a high density, so that the stems are relatively thin. This is unlikely to be the most satisfactory system for producing hemp seed oil, as at high density the proportion of seed/plant biomass tend to fall. Cannabis fibre is the strongest of the natural fibres.

There are two varieties, which come to mind for the production of hemp seed oil, and these are Finola (which originates in Finland, and does not appear to be particularly day length sensitive), and Anka. Finola is dioecious (with distinct male and female plants), but this does not appear to cause any yield reduction as immediately after flowering the male plants die, and the female plants expand into the extra space available. Anka is a monoecious plant (with male and female flowers on the same plant), and both appear to crop reasonable well under a range of different climates.

The yields of hemp seed are about 1t/ha, and about ⅓ of its weight is edible oil, which contains about 80% of the valuable essential fatty acids (omega 3 and omega 6). Birds can be a major problem with this crop, both when seeding, and also close to harvest.

The production of cannabis stems appears to be about 7t/ha of dry stems, of which comprises a mixture of bast fibre, and core material in a 1: 3 ratio. The core material is not waste, however, as it has considerable value for horse stable bedding, insulation etc.

Medicinal cannabis is produced either in greenhouses or in plant factories under artificial lights. Yields under lights appear to be linked very closely with the wattage of lights used, and the general ‘rule of thumb’ appears to be that 1 watt produced about 1g of dry cannabis head material. This is substantiated by the yield data provided by Bedrocan bv, the Dutch company that produces medicinal cannabis, who produce about 420g/m2 of dried cannabis head at a light intensity of 400 w/m2. VanHove (and his colleagues) at the University of Ghent (in Belgium) have shown a similar relationship with about 600 g/m2 of dried cannabis head being produced when using 600 w/m2 of High Pressure Sodium (HPS) lights.

Temperature can also play in role in determining productivity, and yield of medicinal cannabis can be shown to fall with temperatures higher than 22 C. Medicinal cannabis is not necessarily high THC cannabis, as there is currently considerable interest in the medicinal properties of some of the other cannabinoids present in cannabis.

Cannabis has been used in bioremediation – in this case to remove nitrogen and phosphorous from the nutrient rich water of town sewage. We have obtained figures which suggest that in spite of a later than optimum sowing date, hemp produced some 16,000 kg/ha of dry matter, and removed an estimated 160 kg/ha of N and 30kg/ha of P.

A similar study at at PPCS Meat Processing Works at Ashburton removed 160 kg/ha of N and 30 kg/ha of P ion, some 8000kg/ha of dry matter.

It must be noted that the majority of the nitrogen and phosphorous was found in the leaves, even though the bulk of the biomass was in the stems.

About the author
Dr Nichols is a retired University teacher from Massey University. He is frequently found in court as an expert witness in cannabis trials. Email: oxbridge@inspire.net.nz 


PH&G June 2013 / Issue 132