The cultivation of crops like maize has rapidly increased for the purpose of producing biomethane as a more environmentally friendly substitute for fossil fuels, helping the goal of achieving Net Zero. However, a new study suggests that this rise in maize farming on drained peatlands is resulting in three times more carbon dioxide emissions than it prevents by reducing the reliance on natural gas. This research was conducted by the UK Centre for Ecology & Hydrology (UKCEH).
The study indicates that the area of UK peatland dedicated to maize cultivation, which is processed in anaerobic digesters to generate biomethane, has tripled since 2015. Yet, the researchers stress that the emissions from draining these carbon-rich wetlands for farming have been largely overlooked.
This analysis, supported by the Department for Environment, Food and Rural Affairs (Defra), centers on maize in the UK, but the study team emphasizes that any farming on deeply drained peatlands can lead to significant greenhouse gas emissions. The results of this study underline the necessity of accounting for soil carbon losses associated with all bioenergy crops cultivated on drained peatlands globally to enhance decision-making regarding renewable energy.
“While biomethane is a vital renewable energy source, it may not be wise to utilize drained peatlands mainly for bioenergy production if it results in higher CO2 emissions compared to the fossil fuels it replaces,” warns Professor Chris Evans from UKCEH, who led the study published in Nature Climate Change.
Draining our carbon reservoirs
Although all gas combustion emits greenhouse gases, the concept behind biomethane production is that the carbon released during its combustion comes from recent atmospheric carbon absorbed through photosynthesis, thus not contributing additional CO2 to the atmosphere.
However, drained peatlands emit much more carbon than is offset by not burning natural gas. This occurs because draining these wetlands for crop growth releases carbon that has been sequestered in their soils for centuries. Once exposed to atmospheric oxygen, this carbon converts into CO2, contributing to significant additional greenhouse gas emissions.
For reference, burning every cubic metre of natural gas emits about 2kg of CO2. In contrast, UKCEH’s field measurements show that the soil carbon loss from maize farming on drained peatlands equates to emissions of up to 6kg per cubic metre of biomethane produced. This figure does not account for additional greenhouse gas emissions from fertilizer application, crop harvesting, transport, or biomethane production itself.
Significant growth in production
The study estimates that the area of drained peat soils used for maize cultivation in the UK grew from approximately 6,000 hectares in 2015 to over 11,000 hectares in 2021. Additionally, the percentage of maize grown for bioenergy, rather than for food, increased from 20% to 34%, marking an overall three-fold rise.
The researchers clarify that their findings do not suggest that all bioenergy production on drained peat will necessarily lead to increased emissions. For instance, cultivating dedicated biomass crops on agricultural peatlands that maintain higher water levels—known as paludiculture—could effectively mitigate climate change.
Professor Evans suggests that using maize as a ‘break crop’—in crop rotation systems to minimize weeds, pests, and diseases—could be less damaging than completely removing land from food production for biomethane, while still having commercial value and helping to reduce some CO2 emissions linked to food farming on peat.
The researchers also point out that maize grown on mineral soils affects the long-term soil carbon balance less severely. Therefore, the overall process in these non-peat areas might contribute more effectively to emission reductions.
Enhancing decision-making
Biomethane production in the UK has quadrupled since 2000, primarily due to government incentives supporting biogas generation to aid in decarbonizing the energy sector, including the Green Gas Support Scheme and, previously, the Renewable Heat Incentive.
Dr. Rebecca Rowe from UKCEH, a co-author of the study, states: “The transition towards net zero will not be perfectly linear. Alongside successes, we will witness failures and unintended outcomes.”
“As scientists, our mission is to assist the Government, land managers, and industries by providing the most relevant knowledge regarding the impacts of their choices, enabling them to make better-informed decisions about energy crop production and land use.
“Our aim is to collaborate to secure a sustainable future.”
