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.