Nitrous oxide emission from agricultural soils

A review of the salient features of N 2 O emissions from agricultural soils was done to assess our current understanding and associated problems. Nitrous oxide is an important globe warming gas and a destructive agent of ozone in the stratosphere. A major concern is the increasing contribution of chemical fertilizers to atmospheric N 2 O buildup. There is only a limited understanding of the contributions from manures, biological N 2 fixation and crop residues. A recent estimate suggests that agriculture's share of N 2 O emissions is 80% although such estimates are highly uncertain because of imprecise data and the physical and biological complexities of the production process. As a product of the nitrification and denitrification process in soils, a major problem is our understanding of the proportion of N 2 O produced, i.e. the product ratios, although there is a good general understanding of the processes involved. Measurements of N 2 O emissions from the soil surface fail to take into account N 2 O flux from the bottom of the root zone into the subsoil and aquifers although they are generally considered to be significant. There is a need to apply newly available methodology and for combining this methodology and modelling together to predict N 2 O emissions on the landscape (or field) scale taking climate, soil and cropping variables into account. There is enough information available now to exercise some control of N 2 O emissions from cultivated soils. It is suggested that this be done focusing on factors that directly affect the soil microbes involved with the nitrification (NH 4 + , O 2 ) and denitrification (NO 3 − , C, O 2 ) processes. Cropping practices and some soil characteristic amendments are suggested herein for this purpose. Key words: Denitrification, nitrification, emission control, gas ratios