title: A chronology of human understanding of the nitrogen cycle.
abstract: Nitrogen over the ages! It was discovered in the eighteenth century. The following century, its importance in agriculture was documented and the basic components of its cycle were elucidated. In the twentieth century, a process to provide an inexhaustible supply of reactive N (Nr; all N species except N2) for agricultural, industrial and military uses was invented. This discovery and the extensive burning of fossil fuels meant that by the beginning of the twenty-first century, anthropogenic sources of newly created Nr were two to three times that of natural terrestrial sources. This caused a fundamental change in the nitrogen cycle; for the first time, there was the potential for enough food to sustain growing populations and changing dietary patterns. However, most Nr created by humans is lost to the environment, resulting in a cascade of negative earth systems impacts-including enhanced acid rain, smog, eutrophication, greenhouse effect and stratospheric ozone depletion, with associated impacts on human and ecosystem health. The impacts continue and will be magnified, as Nr is lost to the environment at an even greater rate. Thus, the challenge for the current century is how to optimize the uses of N while minimizing the negative impacts.
authors.affiliation: Environmental Sciences, University of Virginia, Charlottesville, VA 22904-4123, USA. jng@virginia.edu
authors.forename: James N
authors.initials: JN
authors.lastname: Galloway
authors.forename: Allison M
authors.initials: AM
authors.lastname: Leach
authors.forename: Albert
authors.initials: A
authors.lastname: Bleeker
authors.forename: Jan Willem
authors.initials: JW
authors.lastname: Erisman
mesh_terms: D015258:Acid Rain / Q000032:analysis; D000383:Agriculture / Q000266:history / Q000379:methods*; D002627:Chemistry, Physical / Q000266:history*; D004787:Environmental Pollution / Q000032:analysis* / Q000266:history; D005068:Eutrophication; D005308:Fertilizers / Q000032:analysis / Q000266:history; D017752:Greenhouse Effect; D049672:History, 19th Century; D049673:History, 20th Century; D049674:History, 21st Century; D006801:Humans; D058458:Nitrogen Cycle; D010126:Ozone / Q000737:chemistry
chemical_list: D015258:Acid Rain; D005308:Fertilizers; D010126:Ozone
keywords: Haber–Bosch; cascade; history; nitrogen