Summary
This field study clarifies the mechanisms controlling N₂O emissions from sheep grazing on organic soils, demonstrating that nitrification—rather than the commonly assumed denitrification pathway—represents the rate-limiting step under the acidic and frequently anaerobic conditions typical of upland organic soils. The findings suggest that current emission factors used in UK and IPCC greenhouse gas inventories, which are largely derived from lowland agricultural systems, may significantly overestimate or mischaracterise N₂O release from extensive upland grazing and moorland systems, with implications for national climate accounting.
UK applicability
Directly applicable to UK upland and moorland grazing systems, particularly in Scotland and Wales where extensive sheep farming on organic soils is widespread. The results challenge the validity of default emission factors currently used in UK national greenhouse gas inventory reporting and suggest that upland grazing may warrant distinct methodologies in climate accounting frameworks.
Key measures
N₂O flux measurements, nitrification rates, denitrification rates, soil pH, soil oxygen status, and nitrogen transformations in urine-affected patches on organic soils
Outcomes reported
The study measured nitrous oxide (N₂O) emissions from sheep urine patches deposited on extensively grazed organic soils in upland UK moorland, and identified the biochemical pathways (nitrification vs. denitrification) controlling these emissions under acidic, oxygen-limited soil conditions.
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