Anaerobic digestion: the unsung hero of sustainability in agriculture

Anaerobic digestion is a ‘natural ally’ for UK farmers under pressure to adopt sustainable farming practices, says the Anaerobic Digestion and Bioresources Association (ADBA), as it asks if Defra will ‘take note’ on how it can help with the UK government’s ‘levelling up agenda’.

By transforming methane-emitting agricultural wastes into, on the one hand, green energy to power both machinery and premises and, on the other, digestate to restore our soils, anaerobic digestion (AD) is a natural ally for UK farmers under pressure to adopt sustainable farming practices.

Selling the biogas produced into the grid also helps diversify their income in the transition away from the EU’s Common Agricultural Policy (CAP).

At national level, AD helps reduce the sector’s greenhouse gas emissions at a time when decarbonisation of agriculture is high on the agenda of both the government and the National Farmers’ Union (NFU).

In 2018, agriculture was responsible for 10% (45Mt CO2E) of the UK’s total emissions, with manure management and agricultural soils1 contributing 1.6% (7Mt) and (2.5%) 11.39Mt CO2e respectively.

In 2019, the NFU launched a strategy to achieve Net Zero in agriculture by 2040, in which AD was recognised as a significant enabler towards reaching that goal. Meanwhile, in recent months, Defra has been developing the Environmental Land Management Scheme (ELMS) as part of the Agricultural Bill to reward farmers for delivering public benefits (“public money for public goods”), as well as carry out work that enhances the environment and tackles climate change.

Putting AD on the government’s radar

The Anaerobic Digestion and Bioresources Association (ADBA) has been lobbying the government to ensure that AD is recognised and rewarded within ELMS for its ability to improve sustainability in farming.

Financial support through the ELMS could encourage the on-farm digestion of manures, slurries and crop residues to produce renewable energy and biofertilisers as alternatives to fossil-based materials, whilst also helping replace the CAP subsidies.

There are 380 AD plants in the UK with capacity to take on agricultural wastes, most of them being on-farm facilities. Yet, it seems there is still some work to do for AD to get integrated into Defra’s plans.

On 9th March, ADBA chaired the AD and Biogas session at the Low Carbon Agriculture Show, during which ELMS was examined in a keynote speech by NFU’s Jonathan Scurlock.  A large part of the scheme, divided into three tiers, focusses on carbon reduction – one of the key benefits of AD.

There are 380 AD plants in the UK with capacity to take on agricultural wastes, most of them being on-farm facilities. Yet, it seems there is still some work to do for AD to get integrated into Defra’s plans

Tier 1 rewards encouraging environmentally sustainable farming and forestry that all farmers can engage with. Tier 2 acknowledges localised targeted environmental outcomes and collaboration between farmers, and Tier 3 covers landscape scale land-use change projects that are critical in commitments such as Net Zero.

Under Tier 1 of ELMS’ strategic objectives – nutrient management- in addition to helping abate fugitive methane from manure by recycling it rather than it being spread on the land (where it emits harmful methane gas), AD generates digestate, an easy-to-apply biofertiliser with readily available nutrients that displaces the use of chemical- or fossil-based fertilisers.

In other words, AD offers a double whammy of carbon reductions whilst providing the soil with appropriate nourishment.

Disappointingly, despite their obvious environmental and sustainable farming benefits, AD and digestate are not mentioned – yet – within ELMS even though they deliver on many of its specific requirements2. A first look at the scheme indicates that it has indirect relevance to the AD industry by offering financial rewards to farmers for a range of activities including:

  • Improving the soil structure and biology by inputting organic matter over some (or more) of their arable and horticultural land
  • Limiting application rates of inorganic fertiliser and manures on grassland (under the low and no input grassland standard)
  • Using slurry more efficiently by testing content, managing application rates and using low emission technologies (on grasslands)

Sequential cropping: the way forward for sustainable farming and net zero

Covering all three Tiers of ELMS, sequential cropping, which consists of growing food and bioenergy crops alternately, is a process that helps restore soil health and maximises the use of land for both food and energy production.

ADBA actively promotes sequential cropping over monocropping, as not only does it allow food and fuel to be generated from the same piece of land, it also draws down carbon – thus replenishing soil organic matter, sequestering carbon, and improving yields for farmers.

Bioenergy crops are necessary to achieve Net Zero targets, as recommended by the UK’s Climate Change Committee (CCC) in their 6th Carbon Budget, and sequential cropping ensures that they complement rather than compete with food crops.

Bioenergy crops are necessary to achieve Net Zero targets, as recommended by the UK’s Climate Change Committee (CCC) in their 6th Carbon Budget

The CCC recognises the importance of energy crops, indicating that they could sequester up to 2MtCO2e by 2035 and 6MtCO2e by 2050 – and even more so when accompanied by Carbon Capture and Storage technologies.

The principle of sequential cropping for bioenergy is long-established, especially in Italy with the Biogasdoneright model. Many UK farms with AD plants have pursued the practice, but in Italy it has been done at scale.

“Farmers are part of the solution”, commented Stefano Bozzetto, executive member of the Italian Biogas Consortium, a 600-strong group of farmers who came together in 2010 to exploit the opportunities presented by on-farm AD. “Biogasdoneright led to a systematic change in the way we farm, a wholly different land use, recycling all the resources to soil, using precision farming techniques and a lot of renewable energy.  We quickly realised that AD was infrastructure for agro-ecological farming.”

More than just environmental and Net Zero benefits

This should be music to Defra’s ears as they finalise the ELMS criteria.  Under ELMS, farmers using on-farm AD could be rewarded for soil and biodiversity restoration and for meeting society’s food and energy needs whilst reducing agriculture’s carbon footprint.

By encouraging the take-up of on-farm AD, the use of digestate fertiliser, and sustainable energy crop production practices such as the Italian model of sequential cropping as part of the strategy, the ELMS would not only deliver on the government’s and NFU’s environmental agenda, but also boost rural economies through the creation of jobs.

This would help meet the broader UK government’s levelling up agenda. Will Defra take note?

  1. Agricultural soil emissions arise from: the use of fertilisers (synthetic and animal manures); biological fixation of nitrogen by crops; ploughing in of crop residues; cultivation of organic soils; indirect emissions from atmospheric deposition of NOxand NH3; and leaching and runoff of nitrate

  2. The three-year national pilot of ELMS, to be launched in October 2021, will consist of three schemes: The Sustainable Farming Incentive (SFI), the Local Nature Recovery and Landscape Recovery schemes. The SFI, first to be launched, is designed to pay farmers for completing “sustainable land management actions” and allows farmers to build up bespoke agreements on at least eight different standards built up around assets such as grasslands, woodlands, hedgerows, waterbodies and woodland. Two other schemes are expected to begin in 2022, with Defra due to release more information over the coming years on these remaining schemes..
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