Gaseous Nitrogen Losses from Coastal Acid Sulfate Soils: A Short-Term Study

NO(x) and N(2)O emissions from coastal acid sulfate soils (CASS) cultivated for sugarcane production were investigated on the coastal lowlands of northern New South Wales, Australia. Two series of short-term measurements were made using chambers and micrometeorological techniques. Series 1 occurred during the wet season, the water-filled pore space (WFPS) was between 60%-80% and the site flooded during the measurements. Measurements were made directly after the harvest of soybean crop, which fixed an estimated 100 kg N ha(-1), and the emission amounted to 3.2 kg NO(x)-N ha(-1) (12 d) and 1.8 kg N(2)O-N ha(-1) (5 d). Series 2 was made towards the end of the dry season when the WFPS was less than 60%. In Series 2, after an application of 50 kg N ha-1, emissions were markedly less, amounting to 0.9 kg N ha(-1) over 10 d. During both series when the soil was moist, emissions of NO(x) were larger than those of N(2)O. The emission of NO(x) appeared to be haphazard, with little time dependence, but there was a clear diurnal cycle for N(2)O, emphasising the need for continuous measurement procedures for both gases. These results suggest that agricultural production on CASS could be important sources of greenhouse gases and nitrogen practices will need to be optimised to reduce the offsite effects of atmospheric warming, acidification or nitrification. Many questions still remain unanswered such as the emissions during the soybean bean filling stage and crop residue decomposition, the longer-term losses following the fertiliser application and emissions from CASS under different land uses.