Nitrogen (N) availability is a key factor in food, feed and fiber production. Providing plant available N through synthetic fertilizer in the 20th and 21st century has contributed greatly to the increased production needed to feed and clothe the increasing human population. Because of increased accessibility to N fertilizer, human activity has greatly altered nitrogen cycling globally and at the scale of large regions.

Information on components of the N cycle has accumulated at a rapid pace in the last few decades especially with regard to processes of transfer in different terrestrial, aquatic and atmospheric environments. Much of this information was synthesized in a recent Scientific Committee on Problems of the Environment assessment of the efficiency and consequences of fertilizer N in the context of overall N inputs to agricultural systems. Improvements need to be made to the currently low efficiency with which N is usually utilized within production systems if we are to continue to meet the global demands for food, animal feed and fiber and minimize environmental problems. However, there are still major uncertainties regarding the fate of fertilizer N added to agricultural soils and the potential for reducing emissions to the environment. Enhancing the technical and economic efficiency of all nitrogen sources is essential for both agricultural production and protection of the environment.