INTERACTION OF IRON AND NITROGEN CYCLES: IMPLICATIONS FOR FERTILISER MANAGEMENT AND GREENHOUSE GAS EMISSIONS

NITROUS OXIDE (N2O) is a powerful greenhouse gas, 298 times more potent than carbon dioxide (CO2). Coastal lowland acid sulfate soils (ASS) occupy ~18 000 ha and constitute only about 5% of Australia’s sugarcane soils but they could contribute about a quarter of the national N2O emissions from sugarcane. It has been proposed by a number of authors that the large differences between the N-gas emissions from ASS and non-ASS are due to the fact that, in ASS, nitrate oxidises reduced iron in the soil producing N2O and other N-gases. In this paper, we report on laboratory studies that investigated the geochemical pathways that cause these gas emissions. The presence of pyrite enhanced gaseous nitrogen (N) and sulfur dioxide (SO2) emissions and the flux was also dependent on sample moisture content. This chemical denitrification pathway needs to be considered in fertiliser management and other crop nutrient models. Most of the gas evolution reactions are favoured by acid conditions and it is suggested that increasing surface soil pH and controlling water logging may decrease N-gas emissions.