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Lowering N2O emissions from soils using eucalypt biochar: the importance of redox reactions.

Quin P, Joseph S, Husson O, Donne S, Mitchell D, Munroe P, Phelan D, Cowie A, Van Zwieten L - Sci Rep (2015)

Bottom Line: X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces.With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents.Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

View Article: PubMed Central - PubMed

Affiliation: University of New England, Armidale, NSW 2351, Australia.

ABSTRACT
Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N2O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N2O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C)--0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS)--in a soil column, following gamma irradiation. After N2O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N2O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N2O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH3, suggesting reactions between N2O and the carbon (C) matrix upon exposure to N2O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

No MeSH data available.


Related in: MedlinePlus

Pourbaix diagram of N representing its various forms in a 100 μM solution at 25 °C as a function of Eh (in V) and pH (diagram drawn using Medusa software60).
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f2: Pourbaix diagram of N representing its various forms in a 100 μM solution at 25 °C as a function of Eh (in V) and pH (diagram drawn using Medusa software60).

Mentions: The Pourbaix diagram (Fig. 2) shows that NH4+ would not be expected to be the dominant form of N in any of the treatments, and that NO3− would dominate, especially in the 5% biochar treatment at low WFPS. Yet this was clearly not the case, with NH4+-N dominant in all soil/biochar treatments. Nevertheless, as anticipated, NH4+-N increased substantially with increasing WFPS (Table 2). NH4+-N, relative to pre-packed soil (44 mg kg−1), had increased in all medium and high WFPS treatments but decreased at low WFPS. In all soils NO3−-N had decreased markedly (from 23 mg kg−1) to <2 mg kg−1 (Table 2). Increased NH4+-N would not be likely to result from dissimalatory NO3− reduction to NH4+, as this is catalysed by bacteria under anaerobic conditions26. Likewise, the abiotic reduction of NO3− to NH4+ involving green rust compounds [FeII4FeIII2(OH)12SO4 • yH2O], as proposed by Hansen, Koch27, is also only favoured in anoxic environments. The γ-irradiation of soil has been shown to produce an up to 30-fold increase of NH4-N228 and up to 100% decrease of NO3-N229. This would appear to be the most likely explanation for the changes observed, and the heightened effect of γ-irradiation on NH4-N with higher soil moisture30 very strongly supports this conclusion.


Lowering N2O emissions from soils using eucalypt biochar: the importance of redox reactions.

Quin P, Joseph S, Husson O, Donne S, Mitchell D, Munroe P, Phelan D, Cowie A, Van Zwieten L - Sci Rep (2015)

Pourbaix diagram of N representing its various forms in a 100 μM solution at 25 °C as a function of Eh (in V) and pH (diagram drawn using Medusa software60).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4663753&req=5

f2: Pourbaix diagram of N representing its various forms in a 100 μM solution at 25 °C as a function of Eh (in V) and pH (diagram drawn using Medusa software60).
Mentions: The Pourbaix diagram (Fig. 2) shows that NH4+ would not be expected to be the dominant form of N in any of the treatments, and that NO3− would dominate, especially in the 5% biochar treatment at low WFPS. Yet this was clearly not the case, with NH4+-N dominant in all soil/biochar treatments. Nevertheless, as anticipated, NH4+-N increased substantially with increasing WFPS (Table 2). NH4+-N, relative to pre-packed soil (44 mg kg−1), had increased in all medium and high WFPS treatments but decreased at low WFPS. In all soils NO3−-N had decreased markedly (from 23 mg kg−1) to <2 mg kg−1 (Table 2). Increased NH4+-N would not be likely to result from dissimalatory NO3− reduction to NH4+, as this is catalysed by bacteria under anaerobic conditions26. Likewise, the abiotic reduction of NO3− to NH4+ involving green rust compounds [FeII4FeIII2(OH)12SO4 • yH2O], as proposed by Hansen, Koch27, is also only favoured in anoxic environments. The γ-irradiation of soil has been shown to produce an up to 30-fold increase of NH4-N228 and up to 100% decrease of NO3-N229. This would appear to be the most likely explanation for the changes observed, and the heightened effect of γ-irradiation on NH4-N with higher soil moisture30 very strongly supports this conclusion.

Bottom Line: X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces.With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents.Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

View Article: PubMed Central - PubMed

Affiliation: University of New England, Armidale, NSW 2351, Australia.

ABSTRACT
Agricultural soils are the primary anthropogenic source of atmospheric nitrous oxide (N2O), contributing to global warming and depletion of stratospheric ozone. Biochar addition has shown potential to lower soil N2O emission, with the mechanisms remaining unclear. We incubated eucalypt biochar (550 °C)--0, 1 and 5% (w/w) in Ferralsol at 3 water regimes (12, 39 and 54% WFPS)--in a soil column, following gamma irradiation. After N2O was injected at the base of the soil column, in the 0% biochar control 100% of expected injected N2O was released into headspace, declining to 67% in the 5% amendment. In a 100% biochar column at 6% WFPS, only 16% of the expected N2O was observed. X-ray photoelectron spectroscopy identified changes in surface functional groups suggesting interactions between N2O and the biochar surfaces. We have shown increases in -O-C = N /pyridine pyrrole/NH3, suggesting reactions between N2O and the carbon (C) matrix upon exposure to N2O. With increasing rates of biochar application, higher pH adjusted redox potentials were observed at the lower water contents. Evidence suggests that biochar has taken part in redox reactions reducing N2O to dinitrogen (N2), in addition to adsorption of N2O.

No MeSH data available.


Related in: MedlinePlus