Nitrous oxide and nitric oxide fluxes from an upland field in Japan: effect of urea type, placement, and crop residues

Fertilizer type and application mode may influence nitrous oxide (N2O) and nitric oxide (NO) emissions as well as crop yield. Using a static chamber method, fluxes of both gases from a Chinese cabbage field in Japan were measured in situ following the application of easily decomposable urea by broadcasting (U-BC) and banding (U-B) and coated urea by banding (CU-B), respectively, at an application rate of 250 kg N ha(-1). The measurements were made throughout the growing season and continued 3 more months after harvest to determine the effect of crop residues on the emissions. Large NO fluxes from U-BC occurred within about 2 weeks after the application of the N fertilizer, while that from both U-B and CU-B was prolonged by about 2 weeks, and significant emissions lasted a longer time but with a smaller emission size. Substantial N2O fluxes derived from crop residues were observed in the late growing season (especially following rainfall) as well as after harvest, at all treatments including the control plots (CK). Large NO fluxes occurred only at U-BC within the first 2 weeks through the measurements. Total emissions were estimated to be 38.1, 78.3, 77.8, and 100.4 mg N2O-N m(-2) and 0.7, 194.9, 8.5, and 11.4 mg NO-N m(-2) at CK, U-BC, U-B, and CU-B, respectively. Statistical analyses indicate that neither the band mode nor the coated urea was able to significantly reduce the total N2O emission through the season, but the band mode substantially reduced the NO emission. However, the application of urea by the band mode presented a 22.8% increase in crop yield as compared with urea applied by broadcasting. Therefore, by improving fertilizer use efficiency to decrease the amount of N needed to better meet the crop growing demand, the band mode may be a good agricultural practice to also reduce N2O emission. In addition, the experiment demonstrated that crop residue is a large source of N2O emission.