Use of Nitrification Inhibitors to Reduce N2O Emissions From Southern Pastures.

Agriculture contributes 75% of national nitrous oxide (N₂O) emissions in Australia, with the majority coming from agricultural soils. Nitrous oxide is produced in soils by both nitrification and denitrification. By inhibiting the activity of nitrifying bacteria, nitrification inhibitors reduce N₂O emission, but the performance of the inhibitors is highly variable, both spatially and temporally. A field experiment to determine N₂O emission, soil mineral N transformations, and biomass production was conducted over an eight month period on ryegrass (Lolium perenne L) in southern Australia. Fertilizer at the rate of 40 kg N/ha was applied as 1) granular urea and 2) ENTEC® urea (urea treated with the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP)). A third treatment, granular urea with the nitrification inhibitor dicyandiamide (DCD) was applied during spring only. Nitrous oxide emission was determined at weekly intervals, or more intensively following fertiliser application and rainfall events, using manual chambers. Soil mineral N was measured at two weekly intervals, and pasture biomass and N content were measured monthly.

Nitrous oxide emissions were greatest in spring after a wet winter. Nitrous oxide emission from the ENTEC urea and DCD treated urea in spring was ~36% less than that from granulated urea. Using ENTEC urea instead of granular urea resulted in a net reduction in N₂O emission over the eight month period of 64%. Biomass and soil mineral N responses to the use of the inhibitors were variable.