Kevin Kelly1, Graeme Ward2
1 Agriculture Victoria, Department of Economic Development, Jobs, Transport and Resources, Tatura, Vic. 3616, Australia. [email protected],
2 Agriculture Victoria, Department of Economic Development, Jobs, Transport and Resources, Warrnambool, Vic. 3280, Australia.
The application of nitrogen (N) fertilisers to pasture is known to increase nitrous oxide (N2O) emissions. There is currently little information available on emissions from N fertilised dairy pastures in Australia. The objective of this work was to quantify the effect of inhibitor coatings on urea fertiliser on pasture DM production and N2O emissions.
Field experiments (five treatments by five replicates) were conducted at two sites in south-west Victoria with contrasting drainage characteristics. Treatments were nil, urea, urea coated with dicyandiamide (DCD), urea coated with 3,4-dimethyl pyrazole phosphate (DMPP) and urea coated with N-(n-butyl) thiophosphoric triamide (nBPT). The urea+DCD treatment was replaced with urea ammonium nitrate (UAN) in Years 2 and 3. The N treatments were applied at the start of the growing season and again after every second harvest. Pasture production was measured for three years and N2O emissions were measured for two years.
Pasture responded to the application of N fertiliser at both sites every year. There were no differences in pasture production between the urea, urea plus inhibitor coatings or the UAN treatments. Cumulative N2O emissions where no N was applied varied with year and site, ranging from 0.23 to 0.53 kg N2O-N/ha/year, while emission factors for urea use ranged from 0.09 to 0.31%. The use of a nitrification inhibitor reduced emissions by 30 to 75%, with the magnitude of the reduction influenced by soil water content around the time of N application. The urease inhibitor had no effect on N2O emissions.