A high-level scoping review Farming, greenhouse gas emissions and carbon storage: cereals and oilseeds

AHDB Research Review No 94. 2020.  By Elizabeth Stockdale and Vera Eory

This high-level scoping project aimed to inform the design and development of the Evidence forAbstract
Farming Initiative (EFI). It provided information focused on the ‘net zero’ agenda that will allow prototype products and services to assist decision-makers seeking to reduce greenhouse gas (GHG) emissions in arable farming systems. A reduction in net GHG emissions within combinable cropping systems (whether assessed per unit of output, per unit of land area used, or at a national level) will be achieved most effectively by the implementation of on-farm interventions that increase productive efficiency and carbon storage, and produce materials/energy for the green economy. The UK research landscape underpinning the measurement or mitigation of GHG emissions in UK cropping systems was found to be widespread and diverse, with research teams often working in collaboration (in a range of configurations, depending on the research question under investigation). The links between bio-economy research and practical agronomic application appeared to be the least well developed; in addition, much of the underpinning work on renewable energy and fossil fuel replacement is not directly targeted at the agriculture sector (which is likely to benefit from ongoing research for construction and road haulage). However, there are relevant international collaborations in place, including informal knowledge sharing, via academic societies, as well as through formal research collaborations. There is a significant body of published research evidence that considers the impact of many of the potential interventions proposed to reduce net GHG of direct relevance to UK arable farming. For several interventions, there were a number of specific systematic reviews. Bringing together evidence, systematic evidence synthesis is a relatively new process and tends to have been applied where the interventions are new or where there has been some dispute/uncertainty about their impact. For other interventions, the underlying principles were well established – such as carbon storage in trees, and change in GHG balance in drained vs undrained wetlands – but detailed synthesis of evidence directly relevant to the application of the intervention in UK cropping systems was either not available or covered only part of the GHG balance. As part of the pilot development of EFI, this scoping review has confirmed that there is a body of high quality reviews linking the following interventions to net GHG in combinable cropping systems: • Optimising nitrogen (N) addition and avoiding N excess • Growing ground cover in leaching-risk periods, and the use of catch and cover crops (considered together) • Reducing intensity of cultivation • Use of manures and composts • Use of biosolids and industrial wastes • Use of controlled-release fertiliser/inhibitors • Use of biochar 2 However, there is lack of direct evidence for cropping systems for interventions relating to the generation of renewable energy, replacement of fossil fuel energy and producing materials/energy for the green economy. A range of indicators are currently used by Defra (and the other devolved governments) to measure progress towards net zero in the farming sector. Several GHG benchmarking tools are also available to estimate net GHG at farm/enterprise level. Such data are increasingly being required within supply chains. A key challenge for farm benchmarking will be the provision of sufficient and appropriate background data against which participating farms can robustly benchmark their performance. However, it is also important to consider GHG mitigation measures within a wider sustainability framework, particularly because of the trade-offs that may result, For example, the impact of use of crops supplying alternative biomaterials on ecological interactions (e.g. pollinators), herbicide and pesticide use. The review has confirmed that EFI needs to be underpinned by a clear and transparent theory of change that will allow EFI to identify where, how and when to intervene to impact change in agricultural systems to deliver mitigation of net GHG. Science and the evidence-base available for synthesis and systematic review is designed to answer “why does it work” questions and draw out common principles – hence the value of meta-analysis. However, for farmers the most important question is “will it work for me” and EFI will need an underpinning model that allows it to bring together evidence from science and practice effectively.