The effect of sustainable agricultural land managements (agroecology & permaculture) on soil nitrogen and carbon cycling, microbial diversity and greenhouse gas emissions

Degrading topsoil, declining habitat and biodiversity, climate change and social and political unrest alongside a growing population and demand for food are calling for a sustainable alternative to the current industrialised agricultural systems. Permaculture and agroecology are two potential alternative sustainable food systems that are currently lacking scientific evidence base. This study compared the two alternative management approaches against a conventionally practiced control in terms of their soil fertility, microbial abundance and diversity (via PLFA analysis) and greenhouse gas mitigation potential. The permaculture site comprised of a no-dig, organically amended market garden for vegetable production, while the agroecology site was minimally tilled and organically amended, whereas the control was tilled & fertilised with a legacy of herbicide and pesticide use. Monthly soil sampling and greenhouse gas emission monitoring via closed chambers over a 12-month period assessed the soils biogeochemistry, microbial abundance and greenhouse gas fluxes. Permaculture soils supported the most abundant microbial community, with an annual mean total microbial biomass of 89.92 ± 20.84 µg g^-1 (23.23 ± 30.7 µg g^-1 and 28.69 ± 30.7 µg g^-1, more than the minimally tilled and conventionally managed soil, respectively). The same soils also exhibited more than double soil organic matter content (annual mean 16.87%) relative to the conventional management, alongside a significantly lower proportion of soil organic carbon (SOC) loss as CO₂ (1.98%, compared to 7% under conventional management). Surprisingly, nitrous oxide (N₂O) fluxes at the conventional site were limited, despite the build-up of the soil nitrate pool during summer, which was attributed to the exceptionally dry soil conditions that prevailed during the year of study, suppressing microbial N₂O production. However, the denitrification product ratio (N₂O/N₂+N₂O) was consistently lower under permaculture soils compared with agroecology and conventional soils, an indication of a strong potential for N₂O emission mitigation. Seasonal warming during spring further stimulated microbial activity, accelerating nutrient acquisition and carbon turnover, with permaculture no-dig soils maintaining three times greater total soil carbon (0.67 ± 0.02 %, annual mean), suggesting a more stable carbon pool. Overall, this study demonstrates permaculture and agroecology practices, particularly no dig management combined with organic amendments, enhances soil fertility, microbial activity, and carbon retention, indicative of a more balanced food system. Multi-year assessments across contrasting climatic conditions are warranted to reduce the uncertainty of temporal variability in GHG flux dynamics and assess long-term carbon stability under these managements.