Fraction of nitrous oxide production in nitrification and its effect on total soil emission: A meta-analysis and global-scale sensitivity analysis using a process-based model

Nitrification in terrestrial soils is one of the major processes of emission of nitrous oxide (N(2)O), a potent greenhouse gas and stratospheric-ozone-depleting substance. We assessed the fraction of N(2)O emission associated with nitrification in soil through a meta-analysis and sensitivity analysis using a process-based model. We corrected observational values of gross nitrification and associated N(2)O emission rates from 71 records for various soils in the world spanning from 0.006% to 29.5%. We obtained a median value of 0.14%, and then assessed how the nitrification-associated N(2)O emission fraction has been considered in terrestrial nitrogen cycle models. Using a process-based biogeochemical model, we conducted a series of sensitivity analyses for the effects of different values of nitrification-associated N(2)O emission fraction on soil N(2)O emission. Using an empirical relationship between soil pH and nitrification-associated N(2)O emission fraction, the model well simulated global emission patterns (global total in the 2000s, 16.8 Tg N(2)O yr(–1)). Differences in the nitrification-associated N(2)O emission fraction caused differences in total N(2)O emission of as much as 2.5 Tg N(2)O yr(–1). Therefore, to obtain reliable estimation of soil N(2)O emission for nitrogen and climate management, it is important to constrain the parameterization in models by ensuring extensive and accurate observations.