ABSTRACT
Nitrogen is essential to all life. It is the nutrient that most often limits biological activity. In agricultural and natural ecosystems, nitrogen occurs in many forms. The use of nitrogen fertilizers has become essential to increase the productivity of agriculture, and has resulted in an almost doubling of the global food production in the past 50 years. However, this also implies that the natural nitrogen cycle has substantially been disturbed. This entry provides an overview of the different nitrogen transformation processes in the soil.
