Are nitrification inhibitors effective in reducing N2O from farm-scale emission hotspots?

Abstract

Livestock congregation areas are nitrous oxide (N 2 O) hot-spots and could be key areas to focus mitigation action. We tested whether combined cattle urine and fertiliser N 2 O-N emission factors (EFs) would be higher from a farm gateway area compared to a standard pasture under sub-tropical conditions, and whether the nitrification inhibitor, dimethyl pyrazole phosphate (DMPP), would lower N 2 O EFs from the gateway area. Treatments ( n = 3) included: (i) fertiliser applied to a standard pasture (50 kg urea-N ha −1 ), (ii) fertiliser (50 kg urea-N ha −1 ) + urine (350 kg N ha −1 ) applied to a standard pasture, (iii) fertiliser (50 kg urea-N ha −1 ) + urine (350 kg N ha −1 ) applied to the gateway area, and (iv) fertiliser (50 kg urea-N ha −1 ) + urine (350 kg N ha −1 ) + DMPP (1.5 kg ha −1 ) applied to the gateway area. Emissions were monitored via an automated static chamber-based system and 15 N-labelled urine treatments ( n = 4) used to assess N 2 O + N 2 emissions, N 2 O:N 2 and 15 N recovery from the pasture. No significant differences ( p > 0.05) were observed for EFs between the fertiliser + urine treatment for the standard pasture (1.10 ± 0.17%) or the gateway area (1.46 ± 0.40%). DMPP did not lower the N 2 O-N EF from the gateway area (1.50 ± 0.22%), where wet and warm conditions may have accelerated DMPP degradation. In the 15 N-labelled urine treatments, significantly ( p < 0.05) greater N 2 O + N 2 emissions occurred in the gateway compared to the standard pasture, but disaggregating EFs between the contrasting areas was not warranted.

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