Quantifying patterns, sources and uncertainty of nitrous oxide emissions from global grazing lands: Nitrogen forms are the determinant factors for estimation and mitigation

Nitrous oxide (N2O) emissions from grazing lands (i.e., pasturelands and rangelands) are an important source of global warming while current estimations remain large uncertainties. This study has improved and applied the biogeochemical process-based model, TRIPLEX-GHG modelv2.0, to estimate the magnitude of the N2O emissions from global grazing lands. We used 60 independent site observations for model calibration and validation and the results suggested a high consistency between modeled and measured N2O emissions across the globe. Global simulations were conducted at 0.5° × 0.5° spatial resolution. After the significant increase between 1961—1990, modeled N2O emissions from global grazing lands exhibited a slightly decreasing trend from 2.34 ± 0.04 TgN yr−1 in the 1990s to 2.04 ± 0.02 TgN yr−1 in the 2010s. Spatially, Europe, North America, and southern Asia were major emission hotspots over study period. Using different scenario simulations, the deposited livestock excreta were identified as the predominant contributor, accounting for 30.76% of historical N2O emissions, while such contribution was probably overestimated by previous studies due to a lack of descriptions of the chemical properties of excreta and the effect of freeze-thaw cycles. The different forms of N inputs have a determinant role in spatial-temporal variations patterns of N2O emissions from grazing lands on a global scale. We suggest the different forms of N input to grazing lands should be addressed for model estimations and implies a possible mitigation method for mitigating N2O emissions.