Quantifying Nitrous Oxide Emissions from Agricultural Soils and Management Impacts

Nitrous oxide (N 2 O) is the primary greenhouse gas associated with most non-flooded cropping systems. N 2 O emissions have been measured from numerous experimental plots around the world; most often using ground based chambers but recently estimates based on top down approaches have become available. Data resulting from these measurements led to the development of N 2 O emission models of varying complexity. Comparing N 2 O fluxes estimated by different methods shows that as scale increases, estimates based on different modeling and measuring approaches tend to converge. As scale decreases, complex models that simulate the plant-soil system usually agree more closely with measurements than simple models that are based on regression equations. Because about 25-50% of the N fertilizer added to soils is typically lost from the plant-soil system, there is potential to reduce N 2 O emissions with improved management. Promising technologies include N fertilizers with urease and nitrification inhibitors and time released fertilizers. At the farm level, complex models appear to be the best method to quantify the management impacts on emissions because extensive measuring is too expensive and simple models are not reliable at this scale. But the ability of the models to represent how available land management options interact with environmental conditions to control soil greenhouse gas emissions is incomplete and further model development and testing are required. In particular, model outputs need to be compared with observations of N 2 O emissions and other nitrogen and carbon fluxes at various spatial and temporal scales.