Quantification of NOx and NH3 emissions from two sugarcane fields

Abstract

This paper reports emissions of NOx and NH3 from a rain-fed, fertilised, residue-blanketed sugarcane field at Mackay, Queensland. Emissions were measured using a micrometeorological flux-gradient technique for the whole of the 2006–07 season and for the first 2 months of the 2007–08 season. Nitrogen (N) fertiliser was applied as urea at a rate of 150 kg N ha–1 into slits 100–150 mm deep. Previous work at the site found that N2O emissions accounted for ~5 kg N ha–1, or 3% of the applied N in the 2006–07 season. In the present study, NOx and NH3 were emitted in both the 2006–07 and 2007–08 seasons and accounted for ~1.5 kg N ha–1, or ~1% of applied N. The main driver of NOx emissions appeared to be the availability of a soil mineral N source. However, the maximum N2O and NOx fluxes were offset by nearly 20 days, which indicated different emission pathways. After the soil mineral N was exhausted, the emissions of NOx were reduced. Emissions of NH3 continued at around the same rate for the whole of the growing season. Water-filled pore space, which was a main driver of N2O emissions, did not seem to influence the measured emissions of NOx or NH3.