Evaluation of variation in background nitrous oxide emissions: A new global synthesis integrating the impacts of climate, soil and management conditions.

Robust global simulation of soil background N2 O emissions (BNE) is a challenge due to the lack of a comprehensive system for quantification of the variations in their magnitude and location. We mapped global BNE based on 1,353 field observations from globally distributed sites and high-resolution climate and soil data. We then calculated global and national total BNE budgets and compared them to the IPCC estimated values. The average BNE was 1.10, 0.92, and 0.84 kg N ha-1 yr-1 with variations from 0.18 to 3.47 (5-95th percentile, hereafter), 0.20 to 3.44, and -1.16 to 3.70 kg N ha-1 yr-1 for cropland, forestland, and grassland, respectively. Soil pH, soil N mineralization, atmospheric N deposition, soil volumetric water content, and soil temperature were the principle significant drivers of BNE. The total BNE of three land use types was lower than IPCC estimated total BNE by 0.83 Tg (10^12g) N yr-1 , ranging from -47% to 94% across countries. The estimated BNE with cropland values were slightly higher than the IPCC estimates by 0.11 Tg N yr-1 , and forestland and grassland lower than the IPCC estimates by 0.4 and 0.54 Tg N yr-1 , respectively. Our study underlined the necessity for detailed estimation of the spatial distribution of BNE to improve estimates of global N2 O emissions and enable the establishment of more realistic and effective mitigation measures.