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Field studies of emissions of nitrous oxide (N 2 O) from a fallow soil treated with different forms and amounts of fertilizer N showed that N 2 O emissions from plots treated with N in the form of ammonium sulfate or urea markedly exceeded those from plots treated with the same amount of N in the form of calcium nitrate. This supports evidence from laboratory research that most of the N 2 O evolved from soils treated with ammonium and ammonium‐producing fertilizers is generated by nitrifying microorganisms during oxidation of ammonium to nitrate and not, as previously assumed, through reduction of fertilizer‐derived nitrate by denitrifying microorganisms. Emissions of N 2 O from plots treated with fertilizer N as ammonium sulfate or urea increased with the amount of N applied. Emissions of N 2 O in 25 days were increased 329‐524% by application of 125 kg N ha −1 as ammonium sulfate or urea and increased 1024‐1319% by the application of 250 kg N ha −1 in these forms, but these applications did not markedly increase N 2 O emissions after 25 days, and the fertilizer‐induced emissions of N 2 O‐N observed in 96 days from plots treated with ammonium sulfate or urea represented only 0.11‐0.18% of the fertilizer N applied. Emissions of N 2 O from plots treated with different amounts of N as calcium nitrate did not increase with the amount of N applied and were not appreciably greater than the emissions observed when no fertilizer N was added.
Breitenbeck et al. (Tue,) studied this question.