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Abstract Urease and nitrification inhibitors are designed to mitigate ammonia (NH 3) volatilization and nitrous oxide (N 2 O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N -(n -butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH 3 volatilization and N 2 O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22–36% and 23–32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture. Graphical abstract Unlabelled Image Highlights • Effects of urease and nitrification inhibitors on N dynamics of a subtropical pasture were examined. • NBPT and DMPP decreased NH 3 volatilization by 44% and N 2 O emission by 15%, respectively. • The use of these inhibitors increased pasture biomass and N uptake by ~20–30%. • These inhibitors can provide environmental, agronomic and economic benefits. [ABSTRACT FROM AUTHOR]

A recently developed slant-path flux gradient (FG) technique, combined with open-path Fourier transform infrared (OP-FTIR) spectroscopy, was deployed to concurrently measure gas emissions of ammonia (NH 3 ), nitrous oxide (N 2 O), carbon dioxide (CO 2 ), and methane (CH 4 ) from an intensive vegetable farm in Australia. Gas fluxes were continuously measured for three weeks following chicken manure application to a celery crop, followed by intermittent measurements for three days a week for another three weeks. The average flux measured over the 41 day measurement period for NH 3 and N 2 O, was 5.2 and 2.9 mg N m −2  h −1 , respectively, CH 4 was 1.1 mg C m −2  h −1 , and CO 2 was 0.7 C g m −2  h −1 . Manure and fertilizer application substantially increased the emissions of these gases, by providing carbon (C) and nitrogen (N) substrates to the soil. The cumulative N losses as NH 3 and N 2 O following fertilizer application were 6.7% and 3.7% of total N applied, respectively. Using this FG/OP-FTIR technique, we demonstrated that the N 2 O emission factor for this vegetable farm is much higher than the IPCC default emission factor for manure applied to managed lands. These results highlight the need for large-scale measurements to quantify multiple gas losses from intensive agricultural systems. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors are effective in decreasing direct nitrous oxide (N 2 O) emission from agricultural soils but may stimulate ammonia (NH 3 ) volatilization. Part of the NH 3 deposited to land is converted to N 2 O and emitted to the atmosphere, termed indirect N 2 O emission. While vegetable production systems entail a considerable risk of NH 3 and N 2 O loss from high nitrogen (N) input to the soil, the simultaneous effects of nitrification inhibitors on these N loss pathways have rarely been examined. We conducted paddock-scale (ca. four hectares) measurements using micrometeorological techniques to simultaneously quantify the effects of a nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on NH 3 and N 2 O emissions from two intensive vegetable farms. We found that DMPP decreased direct N 2 O emission by 37–38% (2.2–7.3 kg N ha −1 ) across the farms during the most intensive period of N input (18 days), but could increase NH 3 volatilization by 3–39% (1.6–4.8 kg N ha −1 ). The results highlight the importance of considering multiple N loss pathways when developing a strategy for mitigating agricultural greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

The emission and mitigation of nitrous oxide (N2O) from high nitrogen (N) vegetable systems is not well understood. Nitrification inhibitors are widely used to decrease N2O emissions in many cropping systems. However, most N2O flux measurements and inhibitor impacts have been made with small chambers and have not been investigated at a paddock-scale using micrometeorological techniques. We quantified N2O fluxes over a four ha celery paddock using open-path Fourier Transform Infrared spectroscopy in conjunction with a backward Lagrangian stochastic model, in addition to using a closed chamber technique. The celery crop was grown on a sandy soil in southern Victoria, Australia. The emission of N2O was measured following the application of chicken manure and N fertilizer with and without the application of a nitrification inhibitor 3, 4-dimethyl pyrazole phosphate (DMPP). The two techniques consistently demonstrated that DMPP application reduced N2O emission by 37-44%, even though the N2O fluxes measured by a micrometeorological technique were more than 10 times higher than the small chamber measurements. The results suggest that nitrification inhibitors have the potential to mitigate N2O emission from intensive vegetable production systems, and that the national soil N2O emission inventory assessments and modelling predictions may vary with gas measurement techniques. [ABSTRACT FROM AUTHOR]