Ian Porter1 and David Riches1
1 School of Life Sciences, La Trobe University, Bundoora, Vic 3086, Australia, [email protected]
Vegetable producers in some temperate regions of Australia use up to 1 tonne of nitrogen (N) as inorganic (fertilizers) and organic N (chicken manure) to produce 3 to 4 crops from the same land each year. Trials in Victoria showed great potential to reduce N inputs and to mitigate N2O losses from soil by use of nitrification inhibitors on manures and fertilizers compared to the standard grower practice (SGP) used at the sites without reducing yield. Annual N2O emissions ranged from 9.1 to 12.5 kg-N/ha for the unfertilized soil, and the combined fertiliser and manure program, respectively. Higher daily emission rates occurred when manures were applied to the soil and these were up to 20-fold greater for a single event than those from fertilizers. The inhibitors, DMPP and to a lesser extent 3MP/TZ, reduced N2O emissions from the fertilizer and manure program, with a maximum reduction of 64% occurring over the three crops, compared to the SGP. Pre-plant application of chicken manure resulted in short periods where daily N2O fluxes ranged from 70-213 g N2O-N/day and DMPP reduced the net N2O cumulative emission by 53% over this period. Annual cumulative N2O emissions were up to 40-fold higher at the Victorian site than reported in similar trials in Queensland and Tasmania. The Emission Factor of 0.45% from the SGP was considerably lower than the IPCC default value (1% of N applied). Nitrogen measurements indicate that up to 60% of the applied N may be lost to the atmosphere or leached in high N use vegetable systems in Victoria.