AbstractThere has been much debate about the uncertainties associated with the estimation of direct and indirect agricultural nitrous oxide (N₂O) emissions in developing countries and in particular from tropical regions. In this study, we report an up-to-date review of the information published in peer-review journals on direct N₂O emissions from agricultural systems in tropical and sub-tropical regions. We statistically analyze net-N₂O-N emissions to estimate tropic-specific annual N₂O emission factors (N₂O-EFs) using a Generalized Additive Mixed Model (GAMM) which allowed the effects of multiple covariates to be modelled as linear or smooth non-linear continuous functions. Overall the mean N₂O-EF was 1.2% for the tropics and sub-tropics, thus within the uncertainty range of IPCC-EF. On a regional basis, mean N₂O-EFs were 1.4% for Africa, 1.1%, for Asia, 0.9% for Australia and 1.3% for Central & South America. Our annual N₂O-EFs, estimated for a range of fertiliser rates using the available data, do not support recent studies hypothesising non-linear increase N₂O-EFs as a function of applied N. Our findings highlight that in reporting annual N₂O emissions and estimating N₂O-EFs, particular attention should be paid in modelling the effect of study length on response of N₂O.