Industrial hemp has been scientifically proven to absorb more CO2 per hectare than any forest or commercial crop and is therefore an ideal carbon sink (1). The CO2 is permanently bonded within the fibre that is used for anything from textiles to building materials. Hemp fibres are currently used by BMW in Germany to replace plastics in car construction.
Industrial Hemp can be constantly replanted and, as such, meets crop permanence criteria as defined by the Kyoto Protocol.
Industrial hemp is not marijuana. Industrial hemp is a variety of Cannabis Sativa with levels of the chemical Tetrahydrocannabinol (THC), the psychoactive component of cannabis, below 0.2% by weight. Hemp has been developed to grow long fibres and can be planted in high density, maximising the biomass produced per unit area of cultivation. Jersey Hemp is a low-level biomass producer currently concentrating on the food and nutritional uses of the plant.
Jersey Hemp and The Carbon Farm believe that regeneratively farmed industrial hemp could contribute significantly to Jersey’s ambition to be carbon neutral by 2030.
A brief history of hemp
Historically, cultivation of hemp has been in Jersey since the 15th century most notably to produce ropes for naval vessels. In the mid 1930’s, the invention of nylon and the spread of plastics saw a general trend away from all things natural. At the same time, use of marijuana as a recreational drug increased and hemp was included in the ban on cultivation of any plant of the cannabis family. With political pressure from the US, the stigma attached to hemp cultivation became global.
Governments around the world have slowly realized that this valuable crop is not a threat and have encouraged the planting of hemp as a means of CO2 sequestration (2).
Major global hemp producers include Canada, France, and China. In several countries, farmers have been rewarded with carbon credits for growing the crop. (3)
Hemp can be grown on existing agricultural land (unlike most forestry projects) and can be included as part of a farm’s crop rotation with positive effects on yields, pest and disease resistance for follow on crops.
The Channel Islands have been leading the UK hemp market by encouraging the growth of industrial hemp and issuing licenses to companies that meet stringent criteria. Jersey Hemp was awarded a license for the cultivation of hemp in 2017.
The science behind hemp as a carbon sink
One hectare of industrial hemp can absorb 22 tonnes of CO2 (4). If soil conditions have sufficient soil organic matter (SOM), between 5-10%, and the correct fungal: bacterial ratio for hemp is present, “Under appropriate conditions, 30-40% of the carbon fixed in green leaves can be transferred to soil and rapidly humified, resulting in rates of soil carbon sequestration in the order of 5-20 tonnes of CO2 per hectare per year”. (5)
It is possible to grow 2 crops per year in the right soil conditions and hemp’s ability to grow rapidly, up to 4 meters in 100 days, makes it a great candidate crop for CO2 sequestration and soil carbon retention – more efficient than agro-forestry.
Plant biomass is produced by the photosynthetic conversion of atmospheric carbon to form carbohydrates which are transported to plant regions requiring growth. The carbon uptake of hemp can be validated by calculations derived from dry weight yield (6). The total biomass fresh weight is recorded at the weighbridge for commercial and licensing reasons prior to processing and the dry weight is recorded after processing for compliance. Accurate figures for total biomass yield and carbon uptake can be obtained, giving a level of certainty not available through any other natural carbon absorption process such as carbon offsets for tree planting.
Carbon uptake estimates are calculated by examining the carbon content of the molecules that make up the fibres of the hemp stem. Industrial hemp stems consist primarily of cellulose, hemicellulose, and lignin in the following proportions:
- Cellulose is 70% of stem dry weight. Cellulose is a homogeneous linear polymer constructed of repeating glucose units. The carbon content of cellulose accounts for 45% of its molecular mass (7).
- Hemicellulose is 22% of stem dry weight. Hemicellulose provides a linkage between cellulose and lignin. It has a branched structure consisting of various pentose sugars with a carbon content of 48% (7).
- Lignin is 6% of stem dry weight. Lignin is a strengthening material usually located between the cellulose microfibrils. The lignin molecule has a complex structure that is variable with carbon constituting 40% of the molecular mass (8).
It follows that every tonne (T) of industrial hemp biomass contains 0.445 tonnes of carbon absorbed from the atmosphere (44.46% of stem dry weight). (9)
According to the IPCC (10) 12 tonnes of carbon equates to 44 tonnes of CO2, equating to 1.63 tonnes of CO2 absorption per tonne of hemp biomass harvested. On a land use basis, using Jersey Hemp’s and UK hemp yield averages of 5.5 to 8 T/ha, this represents 8.9 to 13.4 tonnes of CO2 absorbed per hectare (ha) of hemp cultivation.
For estimation purposes, we use an average figure of 10 T/ha of CO2 absorption in the above ground canopy, a figure we hold to be a reasonably conservative estimate. This is used to predict carbon yields, but CO2 offsets will be based on dry weight yields as measured after drying the biomass.
The roots and leaf mulch (not including the hard to measure fibrous root material) left in situ represents approximately 20% of the mass of the harvested material in initial field trials. The resulting carbon content absorbed and remaining in the soil, is estimated to be 0.084 tonnes per tonne of harvested material. (42% w/w) (11).
Yield estimates of 5.5 – 8 tonnes of biomass per hectare representing 0.46 to 0.67 tonnes of absorbed carbon per hectare or 1.67 to 2.46 t/ha of CO2 (1) which remains in situ after hemp cultivation. Allowing for 16% atmospheric moisture content by dry weight, final estimates of CO2 absorption are as follows:-
CO2 Absorbed per tonne of hemp stem 1.37t
CO2 Absorbed per hectare (stem) (Jersey) 7.47 to 11.25t
CO2 Absorbed per hectare (root and leaf) Jersey) 1.40 to 2.06t
Industrial hemp is a self-offsetting crop.
According to Aether, Jersey farming emitted a total CO2 equivalent of 14,814 tonnes in GHGs in 2017 (12). Jersey’s agricultural land covers 6,000 hectares. This amounts to an average of around 2.5 tonnes of CO2 per hectare – total embodied emissions. The use of regenerative farming practices means there is no requirement to add synthetic fertilisers and the need to use herbicides and pesticides is minimal, making hemp a great CO2 drawdown crop and an attractive crop for carbon offset options.
Soil and Soil Carbon Sequestration
Hemp can be grown on sandy soils with minimal watering. It can be cultivated on existing agricultural land, unlike most forestry projects, and can be included as part of a farms crop rotation, with positive effects on yields as well as pest and disease resistance of follow on crops. It therefore aligns with the Jersey Governments’ plan to diversify agriculture.
Agriculture in Jersey mainly consists of potato growing and dairy herds. Neither potato or dairy farming practices return significant crop biomass to the soil and the traditional practice of applying vrack (local seaweed) is rarely practiced today. As a result, Jerseys’ agricultural soils are lacking soil organic matter (SOM) in the topsoil. Ideally, SOM should comprise around 5-10% of the topsoil mass, however, in highly depleted potato and dairy fields SOM averages between 2.5-3.25% according to government estimates. Conventional chemical and nutrient depleting farming methods remove SOM and contribute to GHG emissions. Conversely, soil regeneration practices increase soil carbon content and assist in the sequestration of CO2.
Jersey Hemp follow a rule of soil health management known as “the law of returns”. The law states that whatever you remove from the land, you must return in some form or another. As hemp cultivation removes nitrogen, phosphorous, potassium and organic matter, The Carbon Farm returns these and other nutrient cycling benefits, by producing and applying Biocomplete™ compost – a practice encouraged by the Soil Food Web (13). Soil is a bank account – you cannot withdraw more than you put in and that is why Jersey Hemp have invested in their own on farm composting facility.
Has Covid-19 presented an opportunity for farming?
“Covid-19 has shown that nature can recover in a very short time if we stop polluting it and farmers reduce harmful inputs by transitioning to regenerative farming practices” (14).
While Jerseys’ communal composting site was shut down during the height of the covid crisis, garden waste, alongside other organic waste, including food waste, was incinerated. During this period, the parish of St. Saviour delivered 34.5 tonnes of green waste to Warwick Farm (Jersey Hemp) for composting. We estimate that this prevented 9,000 tonnes of CO2 in one month from entering the atmosphere as CO2.
The Biocomplete™ compost produced at Warwick Farm contains high levels of colloidal humates of which 60% is carbon. The compost is spread on organic fields cultivated using a no till approach with a minimum 8-way cover crop. The addition of high organic matter compost to soils increases the soil carbon content providing a source of nutrition for soil microorganisms, while at the same time fixing nitrogen, mobilising potassium, phosphorus, and other nutrients. Under appropriate conditions 30-40% of the carbon fixed in green leaves can be transferred to soil and rapidly humified, resulting in rates of soil carbon sequestration in the order of 5-20 tonnes of CO2 per hectare per year. (5)
According to Lehmann and Marcus Kleber of Oregon State University “Soil organic matter makes up and absorbs more carbon than the world’s vegetation and the atmosphere combined. So small changes in the soil carbon content have huge impacts on the climate.” (15). Similar findings have been endorsed at COP21 where the majority of countries supported the French 4 per 1000 initiative (16).
The above figures do not account for the additional carbon dioxide that is negated by substituting unsustainable raw materials to end products derived from harvested hemp, which further lock in CO2. The absence of equipment such as a decorticator in Jersey limits our options in this respect. According to American Lime Technology, Hemcrete locks up around 110kg of CO2 per m3 of wall compared to the 200kg of CO2 emitted by standard concrete. It also excludes the carbon savings from replacing tree-derived products and leaving trees to continue to absorb CO2.
In the past, Jersey Hemp’s biomass has been utilized as a carbon rich ingredient for the biologically complete compost which is used to increase the humic acid of soil in the fields at Warwick farm.
As a crop, hemp is environmentally friendly and is naturally insect resistant requiring no herbicides, pesticide or fungicides. Hemp grows rapidly in comparison to trees and therefore starts absorbing CO2 from a very early stage.
Industrial hemp needs limited maintenance and increases soil carbon when farmed regeneratively because of its deep rooting characteristics.
Hemp grows in diverse soil types and conditions without the need for chemical support. It improves soil structure while also protecting and binding soil when farmers replace fertilisers with quality aerobic compost. The long roots of the hemp plant assist the binding process and combat erosion. Hemp is a natural weed suppressant due to the rapid growth of its canopy blocking light out so weeds cannot grow underneath. In addition, hemp adds nutrients to the soil by tapping into sub-soil nutrients other plants cannot access.
The cannabinoids present in hemp biomass are known to be anti-insecticidal and destroy root knot nematodes and other soil pests when returned to the soil, resulting in improved potato yields the following season (17)
Hemp cleans toxins from the ground by a process called phytoremediation. It was used in Russia to remove radioactive elements following the Chernobyl nuclear disaster. Work undertaken in Germany (18) suggested that hemp could be grown on soils contaminated with heavy metals, while the fibre remained virtually free of the metals. Hemp is currently being trialed as a ‘’mop up crop’’ to rehabilitate soils that have been contaminated by agricultural chemicals and where soils have become acidic due to acid rain. Planting a hemp crop restores the PH balance.
Industrial hemp has the potential to replace unsustainable raw materials. The vast quantities of hemp derived products and raw materials created by large scale cultivation could replace many oil-based unsustainable products and materials, particularly in construction, locking in captured CO2 and creating secondary benefits to the global environment. In particular, hemp has the potential to replace significant quantities of tree derived products, reducing the demand on existing tree populations, thus maintaining their CO2 uptake.
Hemp produces stronger and more versatile fibre than cotton, flax or jute, which often have high chemical input and water requirements. The extra processing required by hemp is partially offset by its recycling potential. Industrial hemp has thousands of uses with virtually no waste.
The cultivation of industrial hemp in Jersey plays an important role in reducing pollution, conserving precious water resources and improving soil quality.
Industrial hemp is unmatched as a means of sequestering carbon and binding it permanently in the materials it is manufactured into. The accreditation of industrial hemp as a generator of carbon credits along with regenerative farming practices will make its cultivation more attractive in the future.
Each additional percentile of carbon in the soil is considered equivalent to £240.00 – £480.00 of fertilizer stored beneath ground (19). Regenerative farms are seeing soil carbon levels rise from a baseline of 1-2% up to 5-8% over ten years. The Carbon Farm aims to increase SOM by 3% per annum through the implementation of biological soil analysis and embracing soil remediation programmes.
Adopting regenerative farming practices can help contribute to Jerseys’ Net Zero ambition, improve Jerseys’ water security and enhance biosecurity and ecosystems.
- James Vosper, BSCHons, FRGS GoodEarth Resources Pty Ltd
- Grießhammer, R. and C. Hochfeld. 2009
- Christine Jones 2009 https://www.amazingcarbon.com/
- Anne Belinda Thomsen, Soren Rasmussen, Vibeke Bohn, Kristina Vad Nielsen and Anders Thygese (2005) Hemp raw materials: The effect of cultivar, growth conditions and pretreatment on the chemical composition of the fibers. Riso National Laboratory Roskilde Denmark March 2005. ISBN 87-550-3419-5.
- Puls,J., J. Schuseil (1993). Chemistry of hemicelluloses: Relationship between hemicellulose structure and enzymes required for hydrolysis. In: Coughlan M.P., Hazlewood G.P. editors. Hemicellulose and Hemicellulases. Portland Press Research Monograph, 1993.
- Hon, D.N.S. (1996) A new dimensional creativity in lignocellulosic chemistry. Chemical modification of lignocellulosic materials. Marcel Dekker. Inc. New York
- Roger M Gifford (2000) Carbon Content of Woody Roots, Technical Report N.7, Australian Greenhouse Office.
- IPCC (2007) Fourth assessment report, climate change synthesis report. Cambridge University Press. UK.
- Bjerre, A.B., A.S. Schmidt (1997). Development of chemical and biological processes for production of bioethanol: Optimization of the wet oxidation process and characterization of products, Riso-R-967(EN), Riso National Laboratory, Roskilde, Denmark.
- CI Inventory Guide_FinalDeliverable.docx available on Gov.je
- Rattan Lal “Soil a living being, can boost farm output, mitigate climate change”
- Lehmann and Markus Kleber, of Oregon State University, have published “The Contentious Nature Of Soil Organic Matter” in Nature, Nov 23
- Jersey Hemp trials, 2018/2019 observed by Cranfield University
- Karus and Leson 1994
- Drawdown 2017 – P.Hawken