The C 2 H 2 ‐block method was used to measure denitrification in a maize ( Zea mays L.) field over the 85‐d period between sidedressing with N fertilizer and harvest. Measurement locations were changed weekly in order to avoid problems associated with microbial utilization of C 2 H 2 and inhibition of nitrification. Nitrous oxide (N 2 O) fluxes were measured both with and without C 2 H 2 addition to soil. Without C 2 H 2 addition to soil, 0.3 kg N ha −1 was evolved from both unfertilized and Ca(NO 3 ) 2 treated soil, whereas 2.5 kg N ha −1 was evolved from urea treated soil. This difference was attributed to formation of N 2 O during nitrification of NH + 4 liberated from urea. With C 2 H 2 addition to soil, 1.6, 2.0, and 2.4 kg N ha −1 were evolved as the result of denitrification in the zero N, Ca(NO 3 ) 2 , and urea treated sites, respectively. Total gaseous N loss from a particular N treatment was approximated by adding together the N 2 O‐N loss with and without C 2 H 2 addition to soil. The gaseous N loss associated with fertilizer addition was <3% of that applied. The ratio of N 2 /N 2 O evolved without C 2 H 2 addition to soil was estimated to be in the range of 4:1 to 7:1 for the zero N and Ca(NO 3 ) 2 treatments and about 1:1 for the urea treatment. Denitrification was responsible for at least 80% of the measured gaseous N loss from the zero N and Ca(NO 3 ) 2 treatments. About equal amounts of gaseous N loss from the urea treatment occurred via denitrification and during nitrification of liberated NH + 4 .
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Duxbury et al. (1986) studied this question.