Summary
This methodological study evaluated three isotope correction models for determining N₂O source partitioning in soil denitrification processes. Using 431 N₂O measurements from six soil incubation studies, the authors demonstrated that fixed-isotope-effect closed-system models substantially overestimate N₂O reduction bias, particularly at high reduction rates, leading to systematic underestimation of nitrification contributions. A dynamic apparent NIE function accounting for variable reduction rates across soil micropores provides improved accuracy and is recommended for future SP-based source apportionment studies.
UK applicability
The methodological improvements are directly applicable to UK soil studies measuring N₂O emissions from agricultural soils, particularly under UK climate and soil conditions where denitrification is prevalent. Adoption of the dynamic NIE approach would refine national greenhouse gas inventory calculations and N₂O source attribution in UK farming systems.
Key measures
N₂O site preference (SP) values (δ15N and δ18O); N₂O and N₂ concentrations; net isotope effects (NIE) during N₂O reduction; source contribution percentages from nitrification/fungal denitrification versus bacterial denitrification
Outcomes reported
The study quantified the impact of N₂O reduction on site preference (SP) isotope values and compared three correction approaches (closed-system, open-system, and dynamic apparent NIE models) for accurately partitioning N₂O sources in soil incubations. Results showed that the closed-system model significantly underestimated nitrification/fungal denitrification contribution (18.7%) compared to dynamic (28.3%) and open-system (31.0%) models.
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