A mixed-methods evaluation of circular agricultural practices for greenhouse gas reduction: integrating modelling and stakeholder insights

Abstract

Adopting more circular farming systems that prioritise renewable and recycled resources could enhance nutrient cycling, reduce farm costs and lower greenhouse gas (GHG) emissions by decreasing reliance on external inputs. This thesis investigates the potential of circular strategies to deliver these benefits, while also exploring the factors influencing farmers’ decision-making, to support wider adoption.

A lack of consensus on how to measure circularity in agriculture presents a key challenge. To address this, we assessed five nitrogen (N)-focused circularity indicators across eight circular management practices and five representative UK farm types (mixed, arable (with livestock), dairy, dairy-beef and beef-sheep), using mass flow models. Indicator results varied widely, from a 49% increase in the secondary input use ratio through the application of recycled biosolids on the arable farm to a 12% improvement in N use efficiency achieved via anaerobic digestion on the beef-sheep farm. The findings demonstrate the practical value of circularity indicators within decision-support tools, helping farmers and policymakers optimise N use, enhance waste valorisation, and assess self-sufficiency and land use.

GHG mitigation potential, N efficiency and cost-effectiveness of the same practices were evaluated using the Agrecalc carbon calculator. Mass flow models informed changes in N balances and emissions, while N–GHG abatement cost comparisons assessed cost-effectiveness and N efficiency. The results highlight that modest GHG reductions—for example, a 4.8% decrease from implementing solid-liquid slurry separation on the dairy farm—can be achieved alongside broader co-benefits, such as cost savings (£129 Mg CO2e-1 yr-1) and improved nutrient management (a reduction in N balance of 17 kg N Mg CO2e-1 yr-1). These benefits align with diverse farmer priorities and may encourage adoption.

To better understand farmer adoption, semi-structure interviews and focus groups were conducted with farmers, industry experts and policymakers in the UK. Guided by the COM-B (Capability/Opportunity/Motivation-Behaviour) model, findings revealed that farmers viewed circular agriculture as a ‘win-win’ solution, aligning economic, social and environmental priorities. They recognised its principles as ‘common sense’ and aligned with their identity as ‘good farmers’. Policy and industry actors could support wider adoption by facilitating collaboration, providing knowledge exchange platforms, and offering financial support to mitigate risk.

A comparative analysis with stakeholders in Italy, Norway and the UK extended these insights. Using a mixed-methods approach that combined sentiment analysis and thematic analysis, the study explored how farming systems, policies and cultural norms shape decision-making across national contexts. The findings underscore the value of culturally sensitive strategies, targeted policies and effective communication to support circularity across Europe.

In summary, this thesis demonstrates how increasing circularity within and between farms can deliver not only GHG reductions but also broader environmental, economic and social benefits. It highlights how circular practices affect N use efficiency and cycling, emission reductions, and cost-effectiveness across UK farm types and identifies key drivers and barriers influencing stakeholder engagement. These insights could inform the design of practical tools, policies and incentives to support the wider uptake of circular practices and help meet sustainable agriculture and climate goals.

Date of Award	12 Feb 2026
Original language	English
Sponsors	Department for Environment, Food and Rural Affairs (Defra), UK
Supervisor	James Gibbons (Supervisor), Sophie Wynne-Jones (Supervisor), Prysor Williams (Supervisor) & Dave Chadwick (Supervisor)