Jordon, M.W. (2022) Regenerative Agriculture practices and their influence on soil organic carbon and farm productivity in temperate regions. Ph.D. thesis. University of Oxford.
Abstract
Global food production is currently contributing to numerous environmental challenges including anthropogenic climate change, biodiversity loss and widespread declines in soil health. Regenerative Agriculture (RA) is an emerging paradigm which proposes that restoring soil health, by adopting a suite of management practices that align with so-called ‘regenerative’ principles, will not only improve agricultural productivity but also contribute to climate change mitigation through increased soil organic carbon (SOC). Despite a plethora of policies and suggested practices emerging over the past decade to support the introduction of RA across the world, there is still remarkably little scientific evidence to quantify potential improvements in soil organic carbon or agricultural productivity as a result of adopting ‘holistic’ RA systems. This represents a large knowledge gap that I set out to address in my DPhil thesis using currently available evidence for individual management practices.
Research for my thesis was divided into four parts. First, I used gold-standard systematic review methods to collate the state of current knowledge and assemble datasets from published studies of management practices forming part of a RA approach. My study area was temperate oceanic regions and I examined papers that considered the following RA approaches: reduced tillage intensity, cover cropping and ley-arable rotations in arable systems, and rotational grazing, multi-species or herbal leys, and agroforestry in pasture systems. Second, using the datasets obtained from these published studies, I conducted Bayesian meta-analyses of the impact of these practices on SOC and agricultural productivity (crop yields, herbage production, livestock growth). I found that adoption of rotational grazing and herbal leys can increase herbage dry matter production and livestock growth rates in pasture systems, but there is currently insufficient evidence to determine their impact on SOC. Conversely, my results identified clear potential for RA practices in arable systems to increase SOC but no evidence of a SOC-yield win-win. Third, using this finding I simulated adoption of these arable RA practices across Great Britain using the soil carbon model RothC, and found that in the UK there is the potential to mitigate 16-27% of current agricultural emissions through soil carbon sequestration. Finally, I conducted semi-structured interviews with industry representatives and livestock farmers in England to further understand advantages and disadvantages of implementing rotational grazing, herbal leys, ley-arable rotations and trees on farms. This final part of my research highlighted potential constraints on the ability to realise the theoretical advantages demonstrated from my earlier analyses.
