Publication Date:
2012-05-05
Description:
In earlier work, we compared the amount of newly fixed nitrogen (N, as synthetic fertilizer and biologically fixed N) entering agricultural systems globally to the total emission of nitrous oxide (N 2 O). We obtained an N 2 O emission factor (EF) of 3–5%, and applied it to biofuel production. For ‘first-generation’ biofuels, e.g. biodiesel from rapeseed and bioethanol from corn (maize), that require N fertilizer, N 2 O from biofuel production could cause (depending on N uptake efficiency) as much or more global warming as that avoided by replacement of fossil fuel by the biofuel. Our subsequent calculations in a follow-up paper, using published life cycle analysis (LCA) models, led to broadly similar conclusions. The N 2 O EF applies to agricultural crops in general, not just to biofuel crops, and has made possible a top-down estimate of global emissions from agriculture. Independent modelling by another group using bottom-up IPCC inventory methodology has shown good agreement at the global scale with our top-down estimate. Work by Davidson showed that the rate of accumulation of N 2 O in the atmosphere in the late nineteenth and twentieth centuries was greater than that predicted from agricultural inputs limited to fertilizer N and biologically fixed N (Davidson, E. A. 2009 Nat. Geosci . 2 , 659–662.). However, by also including soil organic N mineralized following land-use change and NO x deposited from the atmosphere in our estimates of the reactive N entering the agricultural cycle, we have now obtained a good fit between the observed atmospheric N 2 O concentrations from 1860 to 2000 and those calculated on the basis of a 4 per cent EF for the reactive N.
Print ISSN:
0962-8436
Electronic ISSN:
1471-2970
Topics:
Biology
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