School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemDecreasing ammonia loss from an Australian pasture with the use of enhanced efficiency fertilizers(Elsevier BV, 2019-11)Mitigating ammonia (NH3) volatilization from intensive pasture systems is critical for environmental sustainability. However, field-scale evaluation on the potential of enhanced efficiency fertilizers (e.g. urease inhibitors and controlled-release fertilizers) in mitigating NH3 volatilization is limited. Using a micrometeorological technique, we conducted two field trials to investigate the effects of Green UreaNV® (urea coated with the urease inhibitor N-(n-butyl)thiophosphoric triamide, NBPT) and polymer-coated urea (a controlled-release fertilizer) on NH3 volatilization from an intensive rainfed pasture in southern Australia. We found that NH3 volatilization from urea was 5.8 and 5.6 kg N ha–1, respectively, in the autumn and spring trials, equivalent to 11–12% of the applied urea in each season. The use of Green UreaNV® and polymer-coated urea decreased the cumulative NH3 volatilization by 45–55% and 80%, respectively. Taking into consideration the high environmental damage cost of NH3 as found in the European Union, we hypothesize that both Green UreaNV® and polymer-coated urea can be cost-effective in mitigating NH3 loss from this pasture. Our findings suggest that the extra cost of using these enhanced efficiency fertilizers for farmers is not compensated by the fertilizer N value of decreased NH3 loss. However, from a societal perspective the extra cost for Green UreaNV® is likely outweighed by reduced environmental cost of NH3. New fertilizer technology should be developed to improve the cost-effectiveness of polymer-coated urea to the farmers.
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ItemNitrifier-induced denitrification is an important source of soil nitrous oxide and can be inhibited by a nitrification inhibitor 3,4-dimethylpyrazole phosphate(WILEY, 2017-12)Soil ecosystem represents the largest contributor to global nitrous oxide (N2 O) production, which is regulated by a wide variety of microbial communities in multiple biological pathways. A mechanistic understanding of these N2 O production biological pathways in complex soil environment is essential for improving model performance and developing innovative mitigation strategies. Here, combined approaches of the 15 N-18 O labelling technique, transcriptome analysis, and Illumina MiSeq sequencing were used to identify the relative contributions of four N2 O pathways including nitrification, nitrifier-induced denitrification (nitrifier denitrification and nitrification-coupled denitrification) and heterotrophic denitrification in six soils (alkaline vs. acid soils). In alkaline soils, nitrification and nitrifier-induced denitrification were the dominant pathways of N2 O production, and application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) significantly reduced the N2 O production from these pathways; this is probably due to the observed reduction in the expression of the amoA gene in ammonia-oxidizing bacteria (AOB) in the DMPP-amended treatments. In acid soils, however, heterotrophic denitrification was the main source for N2 O production, and was not impacted by the application of DMPP. Our results provide robust evidence that the nitrification inhibitor DMPP can inhibit the N2 O production from nitrifier-induced denitrification, a potential significant source of N2 O production in agricultural soils.
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ItemUsing nitrification inhibitors to mitigate agricultural N2O emission: a double-edged sword?(WILEY, 2017-02)Nitrification inhibitors show promise in decreasing nitrous oxide (N2 O) emission from agricultural systems worldwide, but they may be much less effective than previously thought when both direct and indirect emissions are taken into account. Whilst nitrification inhibitors are effective at decreasing direct N2 O emission and nitrate (NO3- ) leaching, limited studies suggest that they may increase ammonia (NH3 ) volatilization and, subsequently, indirect N2 O emission. These dual effects are typically not considered when evaluating the inhibitors as a climate change mitigation tool. Here, we collate results from the literature that simultaneously examined the effects of nitrification inhibitors on N2 O and NH3 emissions. We found that nitrification inhibitors decreased direct N2 O emission by 0.2-4.5 kg N2 O-N ha-1 (8-57%), but generally increased NH3 emission by 0.2-18.7 kg NH3 -N ha-1 (3-65%). Taking into account the estimated indirect N2 O emission from deposited NH3 , the overall impact of nitrification inhibitors ranged from -4.5 (reduction) to +0.5 (increase) kg N2 O-N ha-1 . Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N2 O emission can be undermined or even outweighed by an increase in NH3 volatilization.
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ItemEffects of nitrification inhibitors on gross N nitrification rate, ammonia oxidizers, and N2O production under different temperatures in two pasture soils(SPRINGER HEIDELBERG, 2018-10)Australian pasture soil for cattle and sheep industries constitutes the principal land use with considerable N fertilizer consumption, which is one of the causes of local environmental problems. Nitrification plays a key role in regulating soil inorganic N concentration and its environmental diffusion. The effects of different nitrification inhibitors (NIs) on gross N nitrification (ngross) rate and N2O production under different temperatures in pasture soils remain unclear. A laboratory incubation experiment was conducted to determine the effect of NIs (dicyandiamide [DCD], 3,4-dimethylpyrazole phosphate [DMPP], and 3-methylpyrazol and 1H-1,2,4-triazol [3MP + TZ]) on N2O emissions, ngross and net N nitrification (nnet) rates, and the abundance of ammonia oxidizers, namely, ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB), in two Australian pasture soils incubated at temperatures of 15, 25, and 35 °C. All NIs reduced both ngross and nnet rates and N2O production rate from the two pasture soils but to different extents. The inhibitory rates of NIs on ngross and nnet reached 6.80-63.8 and 5.91-62.3%, respectively, whereas that on N2O production rate totaled 4.5-41.4% in the tested soils. NIs reduced nitrification and N2O production by inhibiting the growth of AOB rather than AOA. The inhibitory effects of NIs were temperature-dependent, that is, decreasing with increasing temperature from 15 to 35 °C. In general, DMPP performed better than DCD and 3MP + TZ at 15 and 35 °C, whereas DCD performed more effectively than the other two NIs at 25 °C. Our results suggest that the utilization of NIs will depend on the conditions present, especially soil temperature. Additionally, AOB is the target of inhibition when mitigating nitrification and N2O emission by applying NIs in pasture soils.
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ItemNitrogen transformation rates and N2O producing pathways in two pasture soils(SPRINGER HEIDELBERG, 2018-09)Purpose: Better understanding of N transformations and the regulation of N2O-related N transformation processes in pasture soil contributes significantly to N fertilizer management and development of targeted mitigation strategies. Materials and methods: 15N tracer technique combined with acetylene (C2H2) method was used to measure gross N transformation rates and to distinguish pathways of N2O production in two Australian pasture soils. The soils were collected from Glenormiston (GN) and Terang (TR), Victoria, Australia, and incubated at a soil moisture content of 60% water-filled pore space (WFPS) and at temperature of 20 °C. Results and discussion: Two tested pasture soils were characterized by high mineralization and immobilization turnover. The average gross N nitrification rate (ntot) was 7.28 mg N kg−1 day−1 in TR soil () and 5.79 mg N kg−1 day−1 in GN soil. Heterotrophic nitrification rates (nh), which accounting for 50.8 and 41.9% of ntot, and 23.4 and 30.1% of N2O emissions in GN and TR soils, respectively, played a role similar with autotrophic nitrification in total nitrification and N2O emission. Denitrification rates in two pasture soils were as low as 0.003–0.004 mg N kg−1 day−1 under selected conditions but contributed more than 30% of N2O emissions. Conclusions: Results demonstrated that two tested pasture soils were characterized by fast N transformation rates of mineralization, immobilization, and nitrification. Heterotrophic nitrification could be an important NO3−–N production transformation process in studied pasture soils. Except for autotrophic nitrification, roles of heterotrophic nitrification and denitrification in N2O emission in two pasture soils should be considered when developing mitigation strategies.
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ItemThe effect of temperature and moisture on the source of N2O and contributions from ammonia oxidizers in an agricultural soil(SPRINGER, 2017-01)In recent years, identification of the microbial sources responsible for soil N₂O production has substantially advanced with the development of isotope enrichment techniques, selective inhibitors, mathematical models and the discoveries of specific N-cycling functional genes. However, little information is available to effectively quantify the N₂O produced from different microbial pathways (e.g. nitrification and denitrification). Here, a ¹⁵N-tracing incubation experiment was conducted under controlled laboratory conditions (50, 70 and 85% water-filled pore space (WFPS) at 25 and 35 °C). Nitrification was the main contributor to N₂O production. At 50, 70 and 85% WFPS, nitrification contributed 87, 80 and 53% of total N₂O production, respectively, at 25 °C, and 86, 74 and 33% at 35 °C. The proportion of nitrified N as N₂O (P N₂O) increased with temperature and moisture, except for 85% WFPS, when P N₂O was lower at 35 °C than at 25 °C. Ammonia-oxidizing archaea (AOA) were the dominant ammonia oxidizers, but both AOA and ammonia-oxidizing bacteria (AOB) were related to N₂O emitted from nitrification. AOA and AOB abundance was significantly influenced by soil moisture, more so than temperature, and decreased with increasing moisture content. These findings can be used to develop better models for simulating N₂O from nitrification to inform soil management practises for improving N use efficiency.
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ItemLignite Improved the Quality of Composted Manure and Mitigated Emissions of Ammonia and Greenhouse Gases during Forced Aeration Composting(MDPI, 2020-12)Lignite amendment of livestock manure is considered a viable ammonia (NH3) emission mitigation technique. However, its impact on the subsequent composting of the manure has not been well studied. This work compared changes in biochemical parameters (e.g., organic matter loss and nitrogen (N) transformation) and also the emissions of NH3 and greenhouse gases (GHGs) between lignite-amended and unamended cattle manure during forced aeration composting. Amending manure with lignite did not alter the time to compost stability despite delaying the onset of the thermophilic temperatures. Lignite treatments retained N in the manure by suppressing NH3 loss by 35–54%, resulting in lignite-amended manure composts having 10–19% more total N than the unamended compost. Relative to manure only, lignites reduced GHG emissions over the composting period: nitrous oxide (N2O) (58–72%), carbon dioxide (CO2) (12–23%) and methane (CH4) (52–59%). Low levels of CH4 and N2O emissions were observed and this was attributed to the continuous forced aeration system used in the composting. Lignite addition also improved the germination index of the final compost: 90–113% compared to 71% for manure only. These findings suggest that lignite amendment of manure has the potential to improve the quality of the final compost whilst mitigating the environmental release of NH3 and GHGs.
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ItemMeasurement and mitigation of nitrous oxide emissions from a high nitrogen input vegetable system(NATURE PORTFOLIO, 2015-02-03)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.
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ItemInfluence of urea fertiliser formulation, urease inhibitor and season on ammonia loss from ryegrass(Springer Nature, 2013-03)This paper reports the results of experiments to determine whether ammonia (NH) loss can be reduced and nitrogen (N) use efficiency improved by using two relatively new commercial urea formulations rather than granular urea and urea ammonium nitrate. Four nitrogen treatments were applied at a rate of 40 kg N ha: granular urea, 'Green Urea™ 14' [containing 45.8 % N as urea and 'Agrotain' (N-(n-butyl) thiophosphoric triamide) @ 5 L t of urea as a urease inhibitor], 'Nhance', a fine particle spray [containing 46 % N as urea, 'Agrotain' @ 1 L t of urea and gibberellic acid (applied at a rate of 10 g ha)] and urea ammonium nitrate in solution (UAN) surface applied. Ammonia loss was determined in autumn and spring using a micrometeorological method. In autumn, use of the Green Urea and Nhance reduced NH loss from the 30 % of applied N lost from the granular urea to 9 and 23 % respectively. Loss from all treatments in spring was very small (<2 % of applied N), because 4 mm of rain fell within 24 h of application onto an already wet site. The use of the Nhance and Green Urea instead of granular urea did not result in increased agronomic efficiency or recovery efficiency of the applied N, and this is most likely due to the presence of sufficient available N from both fertiliser application and the soil. A N study recovered 72.8 % of the applied N in the plants and soil, and showed that 30 % of the total N taken up by the plant was derived from the fertiliser, and 70 % from the soil.