The Farming Forum – Carbon Audits Q&A

A recent thread on The Farming Forum discussing carbon audits attracted significant attention. We pulled out the most common questions and have answered them here.

Are crops grown for immediate consumption included in a carbon sequestration calculation?

Partly. The carbon sequestered in the part of crops that are harvested is not included in a carbon sequestration calculation because that carbon will be released back into the atmosphere when it is consumed (humans/animals consume the carbon in the food and then respire CO2 out) or decomposed (the carbon is respired by microorganisms). Because the carbon is stored in crops short-term, it is not considered sequestration.

However, the carbon in the roots of the crops and the crop residues are included in sequestration calculations, but whether long-term sequestration actually occurs depends on crop residue management and tillage method.

How much carbon is sequestered through photosynthesis?

As you might expect, different crops photosynthesise at different rates. This is influenced by a range of factors, for example, a plant’s biomass. Despite this, some first-generation carbon calculators don’t make this distinction; they see an apple tree as comparable to a wheat plant. To generate the most accurate sequestration figures you should use a second-generation carbon calculator that makes this distinction, such as Sandy by Trinity Agtech.

How locked away is soil carbon?

Unsurprisingly, there isn’t a simple answer to this question.

Soil organic matter is divided into ‘fractions’, depending on density. Short term fractions are easily decomposed by microorganisms, which result in the carbon being lost as C02. Long term fractions are less accessible to microorganisms, so carbon is locked away for longer.

Many of us will already be familiar with the impact of tillage on soil carbon. Disturbing the soil makes the carbon more accessible to microorganisms, which increases the rate of loss of CO2 from the soil.

The most effective way to gain an accurate measure of soil carbon over time is to use a solution that combines soil sampling and soil modelling. Combining approaches reduces the limitations associated with using just one.

When selecting a carbon calculator, it’s also worth ensuring that its methodology is based on the most recent IPCC Soil Carbon Guidelines, which were published in 2019. (Many solutions are still based on the 2006 Guidelines.)

Does permanent pasture (grazed) sequester more carbon than trees?

Our understanding of the positive role of grasslands in carbon sequestration is growing, though most research still points to tree planting as being the more effective of the two.

However, blanket comparisons like this are rarely helpful. Some eco-systems will be better suited to grasslands than others, and vice versa. The age, species, and management of woodlands and grasslands will influence carbon footprints too.

Carbon sequestration must also be considered alongside other land uses, such as food production, health & wellbeing, and habitat restoration. 

This highlights an issue with the current approach to carbon, i.e. its focus on carbon. 

Carbon calculators and trading platforms do not enable land managers to easily assess the comparative benefits of different strategies - e.g. permanent pasture vs. silvopasture vs. agroforestry – on profitability and production.

For this, holistic natural capital and farm management software is needed.

Do hedges capture more carbon than grasslands?

Like above, it isn’t helpful to blanket compare these two land uses. Actual sequestration figures will depend heavily on species and management.

Sandy, by Trinity Agtech, contains pasture and hedgerow management modules that support farmers to answer this question with regard to their scenario.

Beyond carbon, hedgerows are likely to have additional benefits, e.g. for biodiversity. If farmers are intended to trade carbon, then hedgerows can add valuable biodiversity co-benefits to carbon credits; these can more than triple their value.

What timeframe does the carbon sequestration of trees work over and what happens to the CO2 when the trees are felled? 

Trees sequester at different rates throughout their lifetime. They start slowly, increasing from years 5 to 10 and plateauing as they become mature. When trees are felled, the carbon is either released if the wood is burnt or locked if used as timber (until it degrades).

However, it should be noted that productive tree enterprises – such as timber plantations - are financially viable and therefore would not be eligible for carbon credits; this is because carbon credits must satisfy ‘additionality’. 

What is additionality? Additionality refers to carbon sequestration that would not have occurred in the absence of a market for offset credits. For example, woodland creation can only generate carbon credits if it would be financially unviable without trading those credits, e.g. profitable commercial woodland is excluded.

How much sequestered carbon is held back when trading and is it utilised by Trinity Natural Capital Markets (NCM)?

Trinity NCM sets aside 20% of removal credits (credits generated from sequestering carbon) into a buffer pool. This is a non-marketable pool of credits only used if there is a ‘reversal event’, i.e. when carbon that was traded as removal credits is released back into the atmosphere unintentionally. This buffer pool is an important tool in protecting farmers who trade their carbon.

Who owns the carbon in the land is it the landlord or the tenant and therefore who can trade the credits?

This will need to be negotiated between landlord and tenant; however, Trinity does put in place a risk management framework to protect the signatories of these agreements.

Does Trinty Natural Capital Markets set the price of the credits?

No. Trinity NCM operates an ethical marketplace that connects sellers with high quality, sustainable investors.

This means that farmers choose the sale price of their credits and to who they sell those credits. We believe this represents the fairest deal for farmers vs. a broker model that takes away their control and typically charges higher commissions.

Furthermore, the value of these credits can be amplified with the addition of biodiversity and water co-benefits, which most farms can generate. A recent sale of carbon + biodiversity attracted more than £100 per credit. Trinity takes a 5% commission on the price of these trades.

Why do different calculators give such varying figures?

First generation carbon calculators such as Cool Farm Tool, Agrecalc, and Farm Carbon Toolkit are now a decade old. The science has moved on significantly during this time. For example, the IPCC’s recently updated guidelines on soil carbon and peatland, which are not present in these tools.

The first-generation calculators prioritised certain enterprises in their development, with the tools retrofitted to account for others. This can clearly be seen in the treatment of perennial crops (they see no difference between apple trees, vineyards, and wheat) and peatland (no difference between lowland Fens and upland Wales).

Trinity Agtech’s team includes former experts from Cool Farm Tool and Agrecalc alongside a team of 37 leading scientists.

Our goal was to create the most scientifically rigorous carbon calculator available. One that was suitable for all farms of all sizes, soils, systems, and Enterprise types – one that distinguishes between wheat, hops, pears, vines, and olives.

This enhanced scientific credibility is one reason why the credits we generate are traded for a premium – more than 3 times the value advertised by our competitors.