Denitrification and Agriculture

This chapter focuses on denitrification, which is an important source of N loss from agricultural soils. It deals with the most important factors controlling denitrification: the presence of an electron donor or energy source for the denitrifying bacteria, mostly available organic carbon, anoxic conditions, and the nitrate content in the soil. This loss of plant-available N can lead to yield depression and a decline of quality (e.g., the protein content) of the harvested products. From an environmental point of view, denitrification has both positive and negative effects. The positive effect of denitrification is that it decreases the leaching of nitrate to ground and surface waters. The negative effect is that denitrification is a major source of the greenhouse gas N2O and a loss of N otherwise available for the growth of plants. There are three approaches to quantify denitrification losses from agricultural soils, namely, measurement, N budget calculations, and modeling. Several computer models with a wide range of complexity have been developed to calculate denitrification rates. The mitigation of denitrification and N2O emissions from agricultural and horticultural soils is possible within limits; its total elimination is, however, impossible. Mitigation may also further be possible by the adaptation of soil management. Denitrification losses and N2O emission may also be decreased by avoiding the application of fertilizers and manure during wet conditions, especially nitrate-containing fertilizers.