Direct Nitrous Oxide Emissions From Tropical And Sub-Tropical Agricultural Systems - A Review And Modelling Of Emission Factors

There has been much debate about the uncertainties associated with the estimation of direct and indirect agricultural nitrous oxide (N 2 O) 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 N 2 O emissions from agricultural systems in tropical and sub-tropical regions. We statistically analyze net-N 2 O-N emissions to estimate tropic-specific annual N 2 O emission factors (N 2 O- 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 N 2 O- EF was 1.2% for the tropics and sub-tropics, thus within the uncertainty range of IPCC- EF . On a regional basis, mean N 2 O- EFs were 1.4% for Africa, 1.1%, for Asia, 0.9% for Australia and 1.3% for Central & South America. Our annual N 2 O- EFs , estimated for a range of fertiliser rates using the available data, do not support recent studies hypothesising non-linear increase N 2 O- EFs as a function of applied N. Our findings highlight that in reporting annual N 2 O emissions and estimating N 2 O- EFs , particular attention should be paid in modelling the effect of study length on response of N 2 O.