Quantification of NO_x and NH₃ emissions from two sugarcane fields

This paper reports emissions of NO_x 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 150kg N ha-1 into slits 100-150mm deep. Previous work at the site found that N₂O emissions accounted for ∼5kg N ha-1, or 3% of the applied N in the 2006-07 season. In the present study, NO_x and NH₃ were emitted in both the 2006-07 and 2007-08 seasons and accounted for ∼1.5kg N ha-1, or ∼1% of applied N. The main driver of NO_x emissions appeared to be the availability of a soil mineral N source. However, the maximum N₂O and NO_x fluxes were offset by nearly 20 days, which indicated different emission pathways. After the soil mineral N was exhausted, the emissions of NO_x 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 NO_x or NH₃.