1 Emissions of Nitrous Oxide ( N 2 O ) and Di - Nitrogen ( N 2 ) from the Agricultural Landscapes , Sources , Sinks , and Factors Affecting N 2 O and N 2 Ratios

Nitrous oxide (N2O) is one of the key greenhouse and ozone (O3) depleting gas, constituting 7% of the anthropogenic greenhouse effect. On a molecular basis, N2O has 310 and 16 times higher global warming potential than that of CO2 and CH4 respectively over a 100-year period. To develop mitigation tools for N2O emissions, it is imperative to understand the processes of nitrogen (N) transformation and N2O and di-nitrogen (N2) production in soils as influenced by different land uses, management and environmental conditions. The aim of our chapter is to examine the current information and understanding of the sources of N2O and N2 production and the factors affecting N2O:N2 ratio from the agricultural landscapes. Nitrous oxide concentration has increased by 20% from 270 ppbv since 1750 to a current level of 322 ppbv and continues to increase currently by 0.3% per year. Intensification of agricultural and human activities, such as the increased use of synthetic fertilizer (103 M ton of N worldwide in 2010), increasing human population and changes in their diet, inefficient use of irrigation water, increased crop production, deposition of animal excreta (urine + dung) from grazing animals, excessive application rates of farm effluents and animal manures to croplands and pastures, and management practices that enhance soil organic N mineralization and C decomposition including cultivation, residues removal or burning, and following no crop rotation are to be blamed for the increased N2O emissions of 17.7 T g of N per year to the atmosphere. This book chapter focuses on the following sub-sections including nitrogen transformations, processes of N2O and N2 production across the agricultural landscape, challenges in N2O measurements and estimates across the agricultural landscape, factors affecting N2O and N2 emissions and possible mitigating options, conclusions and references.