N2O emission factors across a gradient of pasture intensification in Highlands of Southern Brazil: Towards regionalizing greenhouse gas inventories

Abstract

Abstract Accurate greenhouse gas inventories require region-specific emission factors (EFs). Current nitrous oxide (N 2 O) inventories often rely on IPCC Tier 1 defaults, which may not accurately represent subtropical grazing systems where field-based data remain scarce. This study aimed to evaluate how pasture intensification gradients interact with different nitrogen sources (urea fertilizer, cattle urine, and dung) to regulate N 2 O emission factors in the Southern Brazilian Highlands, providing regionally calibrated data to assess their alignment with IPCC default values. Nitrous oxide emissions were measured over 100 days using static chambers in four systems: natural grassland (NG), improved natural grassland (ING), perennial pasture (PP), and annual pasture with soil disturbance (AP). Measured EFs suggested a trend toward lower values than IPCC defaults for most sources. Urea in AP was the only treatment exceeding the 1.6% default (EF = 1.7%), while urea-EFs in PP and ING averaged 0.77%. Urine-EFs averaged 0.71% in AP/ING and 0.23% in NG/PP, while dung consistently showed the lowest values (mean = 0.28%). These findings suggest that N 2 O emissions are governed by two interacting hierarchies: management intensity (NG < ING ≈ PP < AP) and nitrogen source (urea > urine ≈ dung). Overall, these findings suggest that the monitored subtropical grazing systems with stable soil structures tended to exhibit lower N 2 O emission factors than current IPCC Tier 1 default values. Disaggregating EFs by source and management intensity improves national inventories and informs mitigation strategies, such as reducing soil disturbance to preserve the naturally low N 2 O emission potential of subtropical pastures.