Perspective Nitrogen fertilizer: Retrospect and prospect

The rising fertilizer use accompanying more people eating more has been called exponential (1) and prompted fears of polluted water and consequent methemoglobinemia (2) and hypoxia (3). It also has raised alarm about greenhouse warming (4) and an altered global N cycle and thus primary production (5) and diversity (1) of vegetation. In this plethora of issues we concentrate on a few, beginning with the fundamental one of how fast N fertilizer use has risen in the world and in an industrial nation, the United States, where early, rapid adoption may foretell the course in the world. We also shall explore how much deposition of N from the atmosphere has increased. After examining the changing ratio of fertilizer N application to its intended incorporation in crop yield, we shall discuss prospects for more or less N fertilizer by 2070 when the earth’s farmers may be feeding 10 billion people and sparing more or less habitat for nature.