Subsoiling reduces N₂O emissions by altering the relative gas diffusivity, O₂ status and microbial communities in grazed pasture soil

Abstract

Nitrous oxide (N₂O) is a potent greenhouse gas predominantly emitted from grazed pasture through denitrification, driven by soil oxygen (O₂) availability and urine-derived nitrogen (N). Pasture soils are vulnerable to compaction from animal treading, restricting gas diffusion and enhancing N₂O emissions. Although subsoiling alleviates compaction, its impact on soil O₂ status and N₂O emissions, particularly under high urine N load, remain poorly understood and rarely investigated. This in-situ field study (March-August 2023) evaluated the effect of subsoiling on soil moisture, O₂ content, relative gas diffusivity (Dp/Do), functional gene abundance, N₂O emissions, and pasture production. Treatments included non-subsoiling or subsoiling, each with or without synthetic ruminant urine (713 kg N ha‾¹). Subsoiling improved macroporosity, enhanced O₂ availability, increased Dp/Do at 5, 10 and 20 cm depth (P < 0.001), and reduced moisture at 10 cm depth (P < 0.001). Subsoiling significantly reduced N₂O emissions by 52% and 81% of non-subsoiled plots for non-urine and urine treatments, respectively (P < 0.05). Dp/Do was strongly correlated with N₂O fluxes during the first 15 days following urine application (R² = 0.59–0.87), suggesting its utility as a predictive indicator under high substrate availability. Molecular analysis showed reduced nirK gene abundance under subsoiling, with limited response for other denitrification genes. Subsoiling had no significant effect on pasture yield or N uptake. Overall, subsoiling mitigates N₂O emissions by improving soil aeration and Dp/Do while maintaining productivity, offering a promising strategy for sustainable N management in grazed pasture soils.