Carbon Farming: Sequestering Carbon in Plants and Soil
Our current agricultural systems are broken, and are a major contributor to the climate crisis. As well as using vast quantities of fossil fuels, contemporary farming practices release millions of tons of carbon dioxide and other greenhouse gases each year. The ability to feed a growing population is crucial to human survival, yet food security is under threat.
Carbon farming offers major solutions, which we’ll investigate in this article, by delving into the sequestration of carbon in plants and soil. And we’ll discuss how carbon farming has utilised natural cycles to capture carbon more effectively, with positive impacts on both food production and tackling the climate crisis.
What is Carbon Farming?
Carbon farming implements agricultural practices known to improve the rate at which CO₂ is sequestered. These practices increase the rate at which carbon is taken from the atmosphere and locked away into plant material and/or soil organic matter.
Implementation of carbon farming generally involves two key strategies:
- Planting for carbon sequestration by making the most effective choices and combinations of plants.
- Maintaining soil to boost carbon capture through the addition of organic material and the avoidance of practices that deplete soil carbon, resulting in overall carbon losses from the land.
👉 The goal of carbon farming is to turn agricultural production from a net emitter of carbon dioxide to a net absorber, by adopting a series of measures that can significantly reduce the carbon footprint of conventional farming.
Simple steps taken by farmers and growers can turn their land into part of the solution for climate change, rather than part of the problem. A wholesale adoption of carbon farming practices – a form of regenerative agriculture – could go a long way towards tackling our climate crisis and creating a sustainable future for global food production and security.
Why Is It Important to Sequester Carbon in Plants and Soil?
Carbon is present in the atmosphere, the ground, oceans, and in living organic materials. It is exchanged between these different reservoirs through a wide range of natural processes. Without human interference, the natural flow of carbon would keep levels fairly stable, meaning that the carbon cycle would remain in harmonious balance.
As you are no doubt aware, human activity has dramatically increased the amount of carbon released into the atmosphere each year, creating an imbalance in the world’s carbon cycle. But what you may not be aware of is that in addition to its carbon emission, human activity has also reduced the amount of carbon sequestered by plants and in the soil, in a number of ways.
👉 According to the Salk Institute, every year plants and other photosynthetic life capture 746 gigatons of CO₂ and then release 727 gigatons of CO₂ back – locking away 19 gigatons.
Plants absorb carbon dioxide during photosynthesis: the use of sunlight to derive nutrients from carbon dioxide and water. With cells known as chloroplasts, plants absorb light energy and use it to split water into oxygen and hydrogen. The oxygen is released as a waste product, but the plant absorbs the carbon dioxide – which, combined with hydrogen to create sugars, becomes the food on which they survive. The carbon from the air is stored within plants’ tissues, where it can remain until the plants decay, or is absorbed into the soil. Naturally-decaying plant matter releases CO₂ back into the atmosphere. ☘️
Increasing the capacity of vegetative life to draw carbon from the atmosphere is crucial for climate change mitigation. However, it is also important to consider how the world’s soil sequesters carbon, and how carbon farming can increase its capacity to do so.
Cutting carbon emissions is not enough; we also have to look to the full variety of planetary environments and ecosystems. The oceans are by far the largest carbon sink on Earth, storing carbon in vegetation, coral, and algae, which currently absorb about a quarter of the carbon dioxide humans put into the air1. Nevertheless, the land is also important; deforestation and soil degradation have reduced our planet’s ability to self-regulate, but effective land management can make a big difference.
We need to increase the amount of carbon that agricultural land can hold, and the length of time for which it can do so. Currently, the agriculture and forestry industry offsets approximately 20% of its emissions through carbon sequestration 2, but carbon farming practices can allow us to improve this statistic. The agriculture sector accounts for approximately 10% of the UK’s greenhouse gas emissions (GHG) emissions; carbon farming can therefore play a crucial role in reducing greenhouse gas emissions here.
An independent report has shown that Scotland’s agriculture sector could comfortably reduce its GHGs by 38% by 2045, and could even go further. Agriculture is at risk from a changing climate but can be part of the climate solution; we must produce food in a way that reduces emissions and locks up more carbon. By adapting current farming methods, Scotland could be at the forefront of the global transition to climate-friendly farming; it’s already leading the way in carbon farming, and the rest of the UK could follow suit. The National Farm Union (NFU) says the industry could reduce GHGs to almost nothing by 2040 – a decade ahead of the government’s overall zero-emissions target.
Carbon farming, both in the UK and globally, is crucial to achieving net-zero goals and transitioning to a sustainable, ethical, and fair future for all.
The Role of Trees in Carbon Farming
In order to understand carbon farming a little better, let’s take a look at the role that plant choices play in this practice. Firstly, the most important of all carbon farming plants: trees.
👉 Trees play an important role in carbon farming because their size (including large root structures) allow high carbon sequestration, and being perennial means this can happen year-round.
Generally speaking, trees have an astonishing capacity to store carbon while growing. Research has shown that all tree species absorb CO₂ from planting to old age (200 years plus). However, they reach their peak in terms of carbon sequestration in their ‘teenage’ years (from 10 to 45 years after planting). 🌳
Despite trees’ carbon-retention, forests increase or decrease in efficacy depending on location, time of year, and the use made of them.
Meanwhile, determining how much carbon an individual tree can sequester each year, and over its lifetime, is a complex business, since these rates are influenced by species, size and age, and many other environmental factors including temperature. Even the best figures are only estimates, and accurate figures are difficult to obtain, because of their variability, and relevance to only the very specific area where they were taken.
While deforestation has played its part in global warming, reforestation is not a panacea for undoing these effects. Planting in temperate zones could actually reduce the amount of sunlight reflected from the planet’s surface3 – demonstrating just some of the complexity involved in solving the problems caused by greenhouse gas emissions.
It is also important to remember that these benefits will be lost if trees are chopped down and burnt, since the CO₂ would be released and return to the atmosphere. Forests’ permanence is therefore key.
Which Trees to Choose
Carbon-capture schemes often favour younger trees, which grow more quickly – but slower-growing trees can sequester much more carbon over their considerably longer lives. Therefore, the best strategy, from an environmental standpoint, is generally to plant a number of different tree species, maximising shorter- and longer-term sequestration.
The best trees to plant will often be those which provide additional benefits to humanity, limiting their likelihood of being chopped down; fruit and nut trees are therefore often good choices.
Other options include trees which can be coppiced (repeatedly cut back to ground level, allowing successive new growth) – meaning that material can be harvested without stopping the trees’ ability to sequester in future. In a coppicing system, less land can be given over to trees while providing the same overall carbon benefit.
How Trees Are Used in Carbon Farming
Careful management of forest or woodland can result in far more than just plantations of trees. As well as increasing biodiversity, a true forest or woodland system can incorporate layers of planting, promoting complex systems which increase carbon sequestration.
Traditional orchards are often laid out with grass sward beneath the trees, this ground cover protecting the soil while trees absorb carbon. However, while this cover can be beneficial, a mixed ground-cover including nitrogen-fixing plants, and guilds of beneficial planting in layers around the trees, would greater increase carbon sequestration, creating a more dynamic and stable ecosystem.
Orchard or woodland management incorporating carbon-trapping trees with layers of other beneficial plants is usually referred to as forest gardening, or, on the larger scale, agroforestry. This is a key strategy in carbon farming, and can also involve integrating trees into other types of agricultural production, such as traditional field-crop growth or livestock-rearing. These integrations might take the form of:
Forest farming utilises forested/wooded land for the cultivation of high-value speciality crops, including non-timber-forest products such as mushrooms and fungi, fruits, nuts, shade-tolerant vegetables, herbs, etc, as well as items for decoration and handicrafts, for example.
Silvoarable systems involve alley-cropping arable crops between rows of productive/useful trees. The trees can provide an additional yield – such as fruit or nuts, or be coppiced for fuel or timber – while continuing to provide carbon-capture benefits. The trees in such a system may also be chosen to add fertility to the site – nitrogen-fixing species, for example.
Silvopasture systems integrate trees and livestock, with trees commonly introduced into forage production systems. Sometimes, forage is introduced into an existing woodland or forest system, where pigs root around in an agroforestry environment, breaking up the soil, their trampling helping to integrate organic matter into the soil. Chickens and other poultry, and other livestock, can also be successfully allowed to forage between trees in such a system.
Using trees to improve environmental conditions for growing crops is another element of agroforestry/carbon farming. Permanent windbreaks/shelter-belts or on-contour rows of trees can also help increase an area’s overall carbon sequestration.
Riparian Buffer Strips
Protecting waterways from erosion and agricultural run-off with trees and other planting is another way in which trees are used in carbon farming. In addition to remaining in place to sequester carbon, this planting can provide a range of other benefits.
The Role of Shrubs and Hedgerows in Carbon Sequestration
Shrubs and hedgerows also play an important role in carbon farming. As permanent, perennial features of agricultural landscapes or gardens, shrubs and hedges are vital to carbon-conscious land management. The wider and higher a hedge, the more carbon it will generally sequester, but careful design and management of mixed hedgerow systems can also improve overall sequestration.
Windbreaks and shelter-hedges along the boundaries of fields can create permanence within a typical agricultural landscape, bringing a range of environmental benefits – including increased carbon sequestration.
The Role of Deep-Rooted Perennial Plants
All plants help with sequestering carbon to some degree, but those with deep tap roots will store that carbon more effectively within the soil. Other perennial plants, especially those with deep, thick roots, are therefore also effective in land management for carbon sequestration. By likely remaining in place for long periods, deep, woody roots are able to keep that carbon locked below the soil for years to come.
A perennial plant that is particularly interesting in terms of global carbon sequestration is bamboo. Giant, woody bamboos share characteristics with trees and have similarly impressive carbon-sequestering capabilities.
Again though, a range of factors can influence bamboo’s rates of sequestration, so notes of caution have been raised about putting too much trust into the results of individual studies. Nevertheless, living bamboo has been shown to store similar quantities of carbon to tree plantations: from around 100 to 400 tonnes of carbon per hectare. And like wood, it has the capacity to replace other carbon-costly products, and can keep carbon from the atmosphere for a significant length of time when managed and used effectively.
👉 While it may not play a vital role in carbon farming in the UK, bamboo is believed to have a globally significant potential in combatting climate change. It is predicted to have sequestered a total of 8.3 to 21.3 gigatons of carbon dioxide by 2050.
Carbon Sequestration and Annual Crops
Cropland soils are far lower in soil organic carbon (SOC) than natural ecosystems. When soil is converted from natural land or semi natural land such as forests, woodlands, grasslands, steppes, and savannahs to typical agriculture, the SOC content reduces by about 30 to 40%.
Annual crops typically have lower root biomass than perennials because they do not need to store energy in the same way. On average, plants allocate 76% of carbon stocks to shoots and only 24% to the roots. However, this can vary considerably due to differing climates and environmental conditions.
Interestingly, scientists are looking into how plants can be engineered for larger roots capable of storing more CO₂, which will only gradually break down and deposit carbon back into the soil. Getting these plants into the global agricultural food chain could potentially contribute a 20 to 46% reduction in excess CO₂ emissions annually.
Carbon Capture in the Soil
Soil holds four times the amount of carbon stored in the atmosphere, and more than is held in vegetation. This means that how we produce and care for soil is just as important as what we grow, and where; modifying agricultural and gardening practices with this in mind is a recognised method of increasing carbon sequestration. Soil can act as an effective carbon sink, offsetting a significant proportion of annual carbon dioxide emissions.
How well soil sequesters carbon depends on how land is used. Land used for annual cropping is depleted of its soil organic carbon, as the carbon-rich biomass of the crops is harvested and removed. Tilling and cultivation also reduce the carbon stored, releasing CO₂ into the atmosphere.
How Growers Can Increase Soil’s Carbon-Capture Abilities
In the short term, there is much that farmers and gardeners can do to increase carbon sequestration when growing annual crops. Firstly: by incorporating perennial plants into annual food production, through forest gardening or agroforestry and polycultures (mixed planting schemes rather than mono-crop planting). Maintaining crop cover throughout the year by use of cover crops and successional planting is also important.
Conversion of agricultural land to pasture, and the use of permaculture techniques such as no-till farming, mulching, layered crops, and crop rotation – techniques used more commonly in organic farming systems – can also increase the carbon-sink capacity of farmland4.
Other measures to increase soil carbon include:
- Chopping and incorporating ‘green manures’ (plants ploughed into the soil).
📌 Green manures are cover crops grown on a site to protect the soil. They release nutrients (and carbon) to the topsoil and can improve soil structure when chopped down and incorporated.
- Adding compost/manures (brown organic matter).
- Incorporating biochar (black organic matter) into the soil.
- Boosting microbial/fungal life in the soil, protecting the fragile soil web.
- Effective crop management, crop rotation, and diverse planting schemes.
These can also minimise carbon loss from the soil, as will:
- Minimal cultivation, or cultivation at shallower depths (‘no till’ and ‘no dig’ practices).
- Careful use of farm machinery, and reduction of foot and vehicular traffic over soil.
- Avoidance of overstocking livestock, and careful livestock management.
- Management of soil, ensuring good soil health to avoid erosion and compaction at all times. Careful and appropriate planting.
All of these measures can bring a range of benefits, including increased sequestration of carbon and reduction of carbon losses from the soil. Farmers can use a carbon farm calculator to work out what measures they can take.
Evidence of the Benefits of Carbon Farming
Carbon farming has been researched by the Marin Carbon Project, a collaborative effort between landowners John Wick and Peggy Rathmann, and scientists at the University of California. Findings show that a single application of a half-inch layer of compost on grazed rangelands can increase grass and other forage-plant production by 40 to 70%, help soil hold up to 26,000 litres more water per hectare, and increase soil carbon sequestration by at least one ton per hectare per year for 30 years – all without re-application. Similar results have also been found by other carbon farming research projects around the world.
The James Hutton Institute undertakes important research into climate change and carbon farming, and sustainable agricultural/land management practices in the UK. They provide a range of invaluable resources for farmers and land managers who want to sequester carbon more effectively in plants and soil, including a soil carbon app to help landowners find out quickly and easily about the organic-matter content of their soil.
A range of case studies on the Farm Carbon Toolkit website show what can be done. Other useful information about these practices, and how they have been implemented, can be found through the international 4 per 1000 initiative . Launched in France in 2015 at the COP 21, the initiative encourages stakeholders to transition towards productive, highly resilient agriculture, based on appropriate management of lands and soils.
How We Can All Help Capture Carbon through Sustainable Farming
Those of us who are not farmers or landowners can still help develop a future for sustainable carbon farming. Remember, farms rely on consumers. Everyone should try to eat local, seasonal, organic produce whenever possible – ideally from farms that are already implementing integrated farm management systems and carbon farming solutions.
By heading to a local farmers’ market, visiting a local farm shop, or joining a veg box or local CSA scheme, we can support carbon farming initiatives, making it easier for farmers and landowners to make the necessary changes.
Carbon Farming Is about Ecosystems, Not Simply Plants and Soil
So far, we’ve focused on carbon sequestration by plants and soil in human-managed or cultivated systems. But carbon sequestration in wilder and more natural environments is also hugely important.
Reforestation, ecosystem restoration, and tree planting will undoubtedly play a role in tackling the climate crisis. Protecting existing forests and restoring degraded wooded ecosystems are both crucial to carbon sequestration. Though not a panacea, reforestation (planting on previously-wooded land) and afforestation (planting on non-previously-wooded land) will play an important role in combatting the climate crisis. And farmers can take the lead.
However, ecosystem conservation does not only relate to forests and woodlands. Wetlands store 14.5% of the world’s soil carbon, and yet cover only 6% of its total land area. Effective protection and restoration of wetlands is therefore crucial to climate crisis mitigation and adaptation. Our oceans need protection too, with seaweed and seagrass restoration also being beneficial to carbon sequestration.
Carbon farming and sustainable food production must therefore always take wider ecosystems into account. Farmland creation must not result in the reduction or destruction of crucial carbon-sink ecosystems; sustainable agriculture should always seek to preserve and protect such ecosystems, as well as growing food and other resources for humanity.
Rewilding and Its Link to Carbon Farming
Rewilding – large-scale conservation and ecosystem restoration – is linked to carbon farming. It involves thinking holistically about entire ecosystems, and how wildlife and wider natural systems can be integrated into sustainable food production and land management.
Rewilding shows that farms cannot think only in terms of their own land when implementing carbon farming measures, but also look more broadly at wider environments. Ideally, the carbon farmers within a bioregion should work together to rehabilitate and improve carbon-capturing systems. For example, tree-planting schemes over a wide area can become part of wildlife corridors and conservation areas. By working with others in their region in this way, farmers and landowners can do even more to help sequester carbon.
Rewilding also shows that we should work with nature, rather than fighting against it. On individual farms and in larger ecosystems, the best approach to conservation is often to let nature take its course – so what we don’t do can be just as important for carbon farming and carbon sequestration as what we do.
Where apex predators are in short supply, or have been made extinct, re-introductions of key species can also be very important in enabling landscapes to sequester more carbon. Natural ecosystems and farms can become unbalanced when there are too many herbivores (such as deer or sheep), since excessive populations can deplete the vegetation of a given piece of land. So rewilding and reintroduction of natural predators can also play an important role in ensuring strong rates of carbon-sequestering vegetation in a particular area.
The Future of Carbon Farming
A recent study has shown that a quarter of natural climate solutions’ potential to sequester carbon involve measures to do with soil carbon. That 25% represents the total potential to sequester 23.8 gigatons of CO₂-equivalent per year, of which 40% involves protecting existing soil carbon. The other 60% involves increasing soil carbon and rebuilding depleted stocks. Clearly, sustainable carbon farming really can play a major role in combatting climate change in future.
The team on this study, led by researchers at the Nature Conservancy (TNC), estimated that if implemented globally, soil conservation and soil-building activities could provide nearly 10% of the carbon reduction needed to avoid breaching the two-degree climate change barrier.
Though research makes it clear that sequestering carbon in plants and soil will play a major role in climate change mitigation, carbon farming is certainly not without its challenges. It can be difficult for farmers to implement, and even when they do, there is a limit to the amount of carbon that can ultimately be sequestered.
It is unlikely that mitigation and carbon sequestration alone will be enough to tackle the climate crisis. So we should all do what we can to implement, promote, and enable carbon farming in our own jurisdictions, and around the world. But cutting carbon emissions in the first place, and adapting to our changing climate, are also vitally important.
Moving forwards, it will be vital for farmers and land managers, governments and individuals to work together. Farmers must implement more sustainable practices (such as those described above) on their land. Governments and authorities can help by passing a carbon farming bill or act, or by introducing other carbon farming legislation. They can aid farmers and growers by instigating carbon farming grants, or otherwise financially incentivising carbon farming. And we can all play our role by supporting farmers financially by buying their produce, and by voting for those who promote a sustainable agenda. We can also all use our voices, and speak up for a better future for all.
1. Reconstruction of the Anthropogenic CO₂ Concentrations in the Oceans, S. Khatiwali, F. Primeau, T. Hall, 2009
2. FAO (2014) Agriculture, Forestry and Other Land Use Emissions by Sources and Removal by Sinks
3. Climate Effects of Global Land Cover Change, Geophysical Research Letters 32, 2005
4. Environmental, Energetic and Economic Comparisons of Organic and Conventional Farming Systems, Bioscience 55, 2005