This article's lead sectionmay be too short to adequately summarize the key points. Please consider expanding the lead to provide an accessible overview of all important aspects of the article.(April 2021)
Figure 1: The nitrogen cycle in a soil-plant system. One potential pathway: N is fixed by microbes into organic compounds, which are mineralized (i.e. ammonification) and then oxidized to inorganic forms (i.e. nitrification) that are assimilated by plants (NO3−). NO3− may also be denitrified by bacteria, producing N2, NOx, and N2O.Estimated nitrogen surplus (the difference between inorganic and organic fertilizer application, atmospheric deposition, fixation and uptake by crops) for the year 2005 across Europe.
Human impact on the nitrogen cycle is diverse. Agricultural and industrial nitrogen (N) inputs to the environment currently exceed inputs from natural N fixation.[1] As a consequence of anthropogenic inputs, the global nitrogen cycle (Fig. 1) has been significantly altered over the past century. Global atmospheric nitrous oxide (N2O) mole fractions have increased from a pre-industrial value of ~270 nmol/mol to ~319 nmol/mol in 2005.[2] Human activities account for over one-third of N2O emissions, most of which are due to the agricultural sector.[2] This article is intended to give a brief review of the history of anthropogenic N inputs, and reported impacts of nitrogen inputs on selected terrestrial and aquatic ecosystems.
