This paper summarizes current knowledge on the impacts of changes of nitrogen (Nr) use in agriculture on the global warming potential (GWP) by its impact on carbon dioxide (CO2), nitrous oxide (N2O) and methane (CH4) emissions from agricultural and terrestrial nonagricultural systems and from aquatic and marine ecosystems. Ranges in ‘N induced exchange factors’, giving responses of CO2–C, N2O–N and CH4–C exchange per kg N input, are presented for all ecosystems. Using these factors, a quantification is made of CO2, N2O and CH4 exchange (emissions or uptake) induced by the use of Nr in agriculture at European scale for the year 2000. This includes: (i) direct impacts in the agricultural systems due to Nr inputs by fertilizer and manure and NH3 deposition and (ii) indirect impacts due to Nr leaching and NH3 deposition caused by agriculture on terrestrial, aquatic and marine ecosystems. Results show that the increase in GWP caused by elevated N2O emission due to Nr use in agriculture is completely counteracted by elevated carbon sequestration in nonagricultural systems. Nr effects on biodiversity, eutrophication and human health, however, need to be considered when considering the overall impacts of Nr use in agriculture.
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