Estimating global terrestrial denitrification from measured N2O:(N2O + N2) product ratios

The use of nitrogen (N) fertilizers and cultivation of N-fixing crops has grown exponentially over the last century, with severe environmental consequences. Most of the anthropogenic reactive nitrogen will ultimately be returned by denitrification to the atmosphere as inert N2, but the magnitude of denitrification and the ratio of N2O to (N2O + N2) emitted (RN2O) is unknown for the vast majority of terrestrial ecosystems. This paper provides estimates of terrestrial denitrification and RN2O by reviewing existing literature and compiling a N budget for the global land surface. We estimate that terrestrial denitrification has doubled from 80 Tg-N year−1 in pre-industrial times to 160 Tg-N year−1 in 2005 with a mean RN2O of approximately 0.08. We conclude that upscaling of RN2O can provide spatial estimates of terrestrial denitrification when data from acetylene inhibition methods are excluded. Recent advances in methodologies to measure N2 emissions and RN2O under field conditions could open the way for more effective management of terrestrial N flows.