Nitrous Oxide-Novel Mitigation Methodologies: Objective 1 - Hippuric Acid effects on N2O emissions
Authors: Dr T J Clough, Dr J L Ray, Associate Professor R R Sherlock, Professor L M Condron, Dr M O'Callaghan, Ms L E Buckthought
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Executive summary
- Increasing the concentration of hippuric acid in the applied urine did NOT reduce the emissions of N2O from the urine patches with emissions accounting for 1.28 to 1.65% of the N applied. This was despite 3 previous studies demonstrating significant reductions.
- Hippuric acid treatments appeared to influence soil NO2--N concentrations (the gateway for N2O production) but no definitive conclusions could be drawn.
- The application of a nitrification inhibitor, dicyandiamide, did suppress N2O emissions with an N2O emission factor equal to 0.6% of N applied. This was due to the prolonged occurrence of higher soil ammonium and lower soil nitrate levels.
- Microbial analyses identified changes in community composition in terms of nitrite oxidisers (nitrifiers; nxrA genes) particularly under the DCD treatment and the benzoic acid treatment. While nitrite reducers (denitrifiers; nirS gene) showed no differences over time or treatment.
- This work has highlighted gaps in our knowledge with regard to the movement, fate and longevity of hippuric acid and its break down products when applied in a pasture situation.
- Further work must be performed to examine the movement and fate of isotopically labelled hippuric acid over time. This will clarify if hippuric acid has any further potential as a novel N2O mitigation methodology.
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