Methane And Carbon What Should UK Farmers Do?

The standout pledge at COP26 for farmers was the target to reduce methane emissions by 30% by 2030. Eyes, as usual, turned to ruminant production. We know that agriculture is responsible for around 40% of total UK methane emissions, with most of those associated with ruminant livestock and livestock manures.

But the picture is more complicated than simply eradicating ruminant production – and I believe we need to bring arable farmers into the picture when we look at reducing emissions from livestock farming. We need to look at the level of meat and dairy consumption that is appropriate for our health, what production systems we should transition to, and make sure that we consider the potential benefits of some productions systems for nature restoration.

At the Soil Association we call for a less but better approach – we should eat less meat overall, and what we do eat should be of a higher quality. For this, we need more mixed farming, bringing more livestock into arable rotations. This leads us to the “Ten Years for Agroecology in the UK” agricultural model, which defines a clear pathway towards an agroecological farming system for the UK. It recognises that the UK has a production advantage in ruminant product production, in terms of weather and appropriate agricultural land. Adoption of such a farming system across the UK would see us able to reduce overall emissions by around 40% (before any additional sequestration activity through for instance tree planting). This model includes key assumptions around future diets, future use of artificial inputs, and that much more mixed model of farming.

Manures from animals would help us to reduce nitrogen fertiliser, which we must do if we are to reach net zero. At the moment some 43% of total emissions from every loaf of bread we eat comes from the artificial fertilisers used to grow wheat, so we can’t ignore this problem. We also need to find ways to bring legumes into crop rotations in a way which makes them profitable to grow – including peas and beans more in livestock concentrate feeds as well as eating more of them ourselves. If this were possible then farmers could routinely adopt legumes as break crops and fertility building crops.

Alongside such changes, it will be essential to revisit how we select crop varieties in future, and this begs the question about the place of yield as a key trait for selection in future. Increasingly we might wish to move to maximum sustainable output for any given land area under any given crop. This would identify the optimum output possible without reducing the area’s natural capital (over a rotation length). Such a change would greatly change the traits required and internalise those externalities of production which are currently picked up by society, or by consumers who choose to purchase products from farmers who have internalised those costs, such as organic farmers.

Alongside these changing imperatives for farm businesses to reduce greenhouse gas (GHG) emissions there is also the new voluntary market for soil carbon to consider.

The new voluntary market for carbon

Although the voluntary carbon market has been around for more than 20 years, there is currently huge interest in the sale and purchase of landbased carbon credits as offsets. This interest is because the net zero policy agenda has ramped up significantly over the last 18 months, with many organisations and companies making net zero emission commitments and needing to deliver on them. Almost all these net-zero strategies plan for continued carbon emissions, that need to be offset by compensatory carbon credits (offsets), to achieve the stated net zero target. There is increasing debate around this, as it is becoming clear that emissions reduction is the key requirement rather than paying a third party to sequester carbon whilst continuing to emit at the same level. As a consequence of this, the focus on supply chain emissions is coming to the fore, with retailers committing to support reductions in emissions from their supply chains. The latest of these being one multiple retailer supporting chicken farmers to produce insect protein from food waste to replace imported soya in poultry diets, thus reducing the potential for deforestation, one of the largest sources of worldwide GHG emissions.

At the moment in the UK, the majority of voluntary carbon offset projects are provided by afforestation via the Woodland Carbon Code, followed by peatland restoration via the Peatland Code. These voluntary standards were established to provide guidance to project developers to deliver high integrity carbon benefits and assurances to voluntary carbon buyers that the climate benefits they purchase are real, quantifiable, additional and permanent. Standards are now being developed in the UK, funded by the Environment Agency’s Natural Environment Investment Readiness Fund, including the creation of a proposed UK Farm Soil Carbon Code to reward farmers for the carbon sequestration benefits of more regenerative practices. At the moment there is no common UK agreed code, leaving scheme developers to develop their own, resulting in a range of different opportunities for farmers. Most, if not all, schemes are focussing on arable farmers with opportunities to sequester carbon through increasing below ground productivity and reducing removals of above ground biomass; adding external sources of carbon (soil amendments); reducing soil disturbance; maintaining high water tables and minimising soil erosion. Schemes for grassland farmers are less common, mainly due to the need for additionality over current farming practice.

The practice which has the greatest capability for sequestering carbon s directly increasing the amount of biomass in the system through, for instance, adding hedgerows or trees. Again, the key tests are real, quantifiable, additional and permanent. These terms and their precise meaning are causing much debate. Take for example permanence: In the ideal offset project, reversals of carbon emissions are physically impossible or extremely unlikely. Standard convention in offset markets has been to guarantee that carbon is kept out of the atmosphere for 100 years. Yet, this is not practical for soil carbon, which is considered as “shortlived” storage carrying a higher risk of reversal. In the USA, Nori manages permanence by offering short-term credits that expire after 10 years. In Europe, Soil Capital has a 5-year crediting period, in which farmers can earn and generate credits, followed by a 10-year retention period. Carbon Farmers of Australia must choose between 25- and 100-year permanence guarantee. Without an agreed UK farmland soil carbon code, different definitions and offers are being developed in the UK and farmers should be aware of what they are signing up to before committing.

As retailers start to move to make good on their commitments to net zero, inevitably farmers will need to be able to demonstrate their credentials in terms of net zero. Farmers who have developed their own on farm mechanisms to reach net zero will need to be able to evidence these robustly, but it will potentially make them more attractive suppliers. However, if such a farm chose to sell carbon offsets, the carbon sold is removed from their balance sheet to appear on that of the purchaser. This could render the farmer a high emissions producer and hence less attractive to product customers. This needs to be considered when entering into any carbon offset agreements.

The quality of schemes also relies on the accuracy of soil data. Some schemes rely on regional data whilst others require field soil samples down to 50cm of more. The more granular the data the more accurate the picture on soil carbon levels should be. Taking soil samples requires attention to a number of features including timing, field selection, within field sampling, number of samples per field, depth of sampling and frequency of sampling. These features need to be standardised to provide consistency of results, which is necessary for entry to carbon markets.

The final question is to ask how best to test for carbon in soil. The three most common ways are loss on ignition (LOI), dry combustion (DUMAS) and potassium permanganate oxidation. LOI is the most common due to its traditional usage in evaluating the organic matter content. DUMAS is the most accurate and direct measure. Potassium permanganate oxidation (sometimes; permanganate oxidisable carbon (POXC)) is another way of characterising organic matter. It is less common and indicates “active carbon”. Although this is an informative quantity, if only one method is to be used, we want to measure all organic carbon that is built up and stable for the long-term. Each method has its own advantages and disadvantages for different soil types, budgets and uses.

The density change effect

The volume of soil carbon in any given area of soil depends on both the soil carbon content and the soil density. Changes in soil density can affect estimates of carbon storage, even without a change in the amount of carbon stored in the landscape. Shifts between conventional tillage and no-till are a classic example of this accounting problem.

Soil density leads to a depth-related effect on net carbon storage alongside the redistribution which occurs when tillage is practiced. This can lead to overestimation of carbon storage under no-till relative to conventional tillage. This potential source of bias is easy to correct for with the right sampling approach, though few soil carbon protocols currently account for it.

Tillage breaks up the soil structure, essentially “fluffing up” the soil and reducing its density. Conversion to no-till allows the soil particles to settle into a denser structure. As a result, the plough layer of no-till soils is on average roughly 2-3% denser than the plough layer of tilled soils. The difference in soil density under no-till versus conventional tillage can affect carbon stock estimates. The table below illustrates this. On the left, a field is sampled to a fixed depth of 30 cm and carbon stocks are calculated at that depth. After conversion to no-till, the density of the plough layer increases, shifting the soil surface downwards slightly. If soil is then collected to the same depth, soil particles that would have been left out before are now included, leading to a larger carbon stock estimate. This larger carbon stock estimate would be entirely due to changing the frame of reference for sampling.

This emphasises the need for a detailed protocol which all farmers can follow when taking soil samples. The Farm Carbon Toolkit Soil Monotiring Guide recommends it includes protocols for the following areas: 

• Timing: Spring or autumn are more suitable for field access and sampling ease; the most important factor is consistent sampling the same time each year

• Field selection: Choose fields which best represent current and historical land use and try and represent all soil textures across the farm

• Within field sampling: Make the sample as representative of the field as possible i.e. the main cropping area. Across this area sampling can be carried out in a straight line, W shape or grid pattern. If accuracy and precision are important and the sampling is to be repeated in future years, it is important to GPS log the sample points across the field

• Characteristics of the samples taken: A minimum of 5 sample points per field are recommended, but preferably 15 sample points will increase accuracy. Sampling is recommended to 30cm deep. This allows the assessment of the carbon that is held at depth and is therefore less likely to be released. It is recommended to carry out analysis every 3-5 years

The UK Farmland soil carbon code seeks to address the current lack of clarity for farmers in this new, evolving, voluntary carbon marketplace, including soil sampling testing and analysis protocols, and it cannot come soon enough. For now, though, the watchword for farmers has to be to look very carefully before entering into any agreements to sell carbon offsets.

Ask yourself – If I enter this agreement, what claims will I be able to make about my farm carbon footprint in the future? does the scheme have a transparent, robust methodology on permanence, additionality, measurement and verification? and am I happy to be doing business with the credit buyer?