N2O emissions from agricultural lands: a synthesis of simulation approaches

Nitrous oxide (N₂O) is primarily produced by the microbially-mediated nitrification and denitrification processes in soils. It is influenced by a suite of climate (i.e. temperature and rainfall) and soil (physical and chemical) variables, interacting soil and plant nitrogen (N) transformations (either competing or supplying substrates) as well as land management practices. It is not surprising that N₂O emissions are highly variable both spatially and temporally. Computer simulation models, which can integrate all of these variables, are required for the complex task of providing quantitative determinations of N₂O emissions. Numerous simulation models have been developed to predict N₂O production. Each model has its own philosophy in constructing simulation components as well as performance strengths. The models range from those that attempt to comprehensively simulate all soil processes to more empirical approaches requiring minimal input data. These N₂O simulation models can be classified into three categories: laboratory, field and regional/global levels. Process-based field-scale N₂O simulation models, which simulate whole agroecosystems and can be used to develop N₂O mitigation measures, are the most widely used. The current challenge is how to scale up the relatively more robust field-scale model to catchment, regional and national scales. This paper reviews the development history, main construction components, strengths, limitations and applications of N₂O emissions models, which have been published in the literature. The three scale levels are considered and the current knowledge gaps and challenges in modelling N₂O emissions from soils are discussed.