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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

The change in mean headspace N2O (injected N2O)−1 for mean soil water contents of, (a) 12% WFPS; (b) 39% WFPS; (c) 54% WFPS; and also, (d) 100% biochar and acid-washed sand (error bars represent ± s.e.m., n = 3). At tmax for 12% WFPS the significance of difference in mean nett headspace N2O (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.10, 0.0058 and 0.018 respectively. For 39% WFPS the corresponding values were p = 0.31, 0.0054 and 0.016, and for 54% WFPS were p = 0.020, 0.00022 and 0.00079. Accounting for N2O in WFPS and AFPS, at tmax for 12% WFPS the significance of difference in mean nett (column) total N2O content (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.12, 0.0069 and 0.021 respectively. For 39% WFPS the corresponding values were p = 0.34, 0.00076 and 0.018, and for 54% WFPS were p = 0.022, 0.00024 and 0.00092.
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f1: The change in mean headspace N2O (injected N2O)−1 for mean soil water contents of, (a) 12% WFPS; (b) 39% WFPS; (c) 54% WFPS; and also, (d) 100% biochar and acid-washed sand (error bars represent ± s.e.m., n = 3). At tmax for 12% WFPS the significance of difference in mean nett headspace N2O (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.10, 0.0058 and 0.018 respectively. For 39% WFPS the corresponding values were p = 0.31, 0.0054 and 0.016, and for 54% WFPS were p = 0.020, 0.00022 and 0.00079. Accounting for N2O in WFPS and AFPS, at tmax for 12% WFPS the significance of difference in mean nett (column) total N2O content (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.12, 0.0069 and 0.021 respectively. For 39% WFPS the corresponding values were p = 0.34, 0.00076 and 0.018, and for 54% WFPS were p = 0.022, 0.00024 and 0.00092.

Mentions: For each of the 0, 1 and 5% biochar additions to soil, water-filled pore space (WFPS) values of 12 (0.48), 39 (0.47) and 54 (0.50) % were established, hereafter termed low (L), medium (M) and high (H) WFPS (standard error of the mean (s.e.m.) in parentheses, n = 3). Moisture contents of the 100% biochar (BC100%) and sand were estimated to be 6 and 3% WFPS respectively. At the end of the sampling periods (tmax) the change in estimated total quantity of N2O in air-filled pore space (AFPS) and headspace and dissolved N2O in WFPS, divided by the estimated quantity of N2O injected (∆N2O/inj.N2O) for all 0% biochar and acid-washed sand treatments was close to unity (Table 1). Treatments of 1 and 5% biochar had mean values (across all WFPS) of ∆N2O/inj.N2O at tmax of 0.91 and 0.67 respectively. This suggested that some injected N2O was intercepted by these treatments. Treatments were injected with a mean of 22.2 nmol N2O (s.e.m. = 1.23 nmol, n = 6). When compared with the mean N2O intercepted by 0% biochar treatments (−25 pmol), the 1 and 5% biochar treatments significantly lowered N2O emitted, by 2.14 and 7.97 nmol respectively (p = 0.0094 and p = 5.6 × 10−8). Although there were differences in ∆N2O/inj.N2O at tmax between treatments of differing mean WFPS at the same biochar content (Table 1), only that between the 39 and 54% WFPS treatments with 5% biochar was significant (p = 0.018). For the BC100% treatments, ∆N2O/inj.N2O at tmax was only 0.16 (Table 1). The apparent loss of N2O within the sampling periods for any treatments containing biochar suggests that some of this gas might have been adsorbed, at least temporarily, or decomposed. Figure 1 shows the mean change in headspace N2O (injected mol N2O)−1 for each treatment. For soil/biochar columns the associated (Fig. 1) caption includes the significance of differences at tmax between treatments of 0, 1 and 5% biochar, based on both headspace N2O (injected mol N2O)−1 and estimated ∆N2O/inj.N2O. Estimated from headspace N2O concentration ([N2O]) at tmax, the mean unaccounted N2O from headspace and AFPS (injected N2O)−1 (i.e. N2O injected that was ‘missing’ from the combined volume of headspace and estimated AFPS) for 1% and 5% biochar composites was significantly greater than for BC100% treatments per unit weight of biochar (p = 0.044 and 0.015 respectively). For treatments of 1% biochar this measure of unaccounted N2O was 8.7 (s.e.m. = 1.7, n = 3) times greater than the mean for BC100% treatments, and the comparable ratio for treatments of 5% biochar was 4.0 (s.e.m. = 0.37, n = 3).


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)

The change in mean headspace N2O (injected N2O)−1 for mean soil water contents of, (a) 12% WFPS; (b) 39% WFPS; (c) 54% WFPS; and also, (d) 100% biochar and acid-washed sand (error bars represent ± s.e.m., n = 3). At tmax for 12% WFPS the significance of difference in mean nett headspace N2O (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.10, 0.0058 and 0.018 respectively. For 39% WFPS the corresponding values were p = 0.31, 0.0054 and 0.016, and for 54% WFPS were p = 0.020, 0.00022 and 0.00079. Accounting for N2O in WFPS and AFPS, at tmax for 12% WFPS the significance of difference in mean nett (column) total N2O content (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.12, 0.0069 and 0.021 respectively. For 39% WFPS the corresponding values were p = 0.34, 0.00076 and 0.018, and for 54% WFPS were p = 0.022, 0.00024 and 0.00092.
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f1: The change in mean headspace N2O (injected N2O)−1 for mean soil water contents of, (a) 12% WFPS; (b) 39% WFPS; (c) 54% WFPS; and also, (d) 100% biochar and acid-washed sand (error bars represent ± s.e.m., n = 3). At tmax for 12% WFPS the significance of difference in mean nett headspace N2O (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.10, 0.0058 and 0.018 respectively. For 39% WFPS the corresponding values were p = 0.31, 0.0054 and 0.016, and for 54% WFPS were p = 0.020, 0.00022 and 0.00079. Accounting for N2O in WFPS and AFPS, at tmax for 12% WFPS the significance of difference in mean nett (column) total N2O content (injected N2O)−1 between 0 and 1%, 0 and 5% and 1 and 5% biochar was p = 0.12, 0.0069 and 0.021 respectively. For 39% WFPS the corresponding values were p = 0.34, 0.00076 and 0.018, and for 54% WFPS were p = 0.022, 0.00024 and 0.00092.
Mentions: For each of the 0, 1 and 5% biochar additions to soil, water-filled pore space (WFPS) values of 12 (0.48), 39 (0.47) and 54 (0.50) % were established, hereafter termed low (L), medium (M) and high (H) WFPS (standard error of the mean (s.e.m.) in parentheses, n = 3). Moisture contents of the 100% biochar (BC100%) and sand were estimated to be 6 and 3% WFPS respectively. At the end of the sampling periods (tmax) the change in estimated total quantity of N2O in air-filled pore space (AFPS) and headspace and dissolved N2O in WFPS, divided by the estimated quantity of N2O injected (∆N2O/inj.N2O) for all 0% biochar and acid-washed sand treatments was close to unity (Table 1). Treatments of 1 and 5% biochar had mean values (across all WFPS) of ∆N2O/inj.N2O at tmax of 0.91 and 0.67 respectively. This suggested that some injected N2O was intercepted by these treatments. Treatments were injected with a mean of 22.2 nmol N2O (s.e.m. = 1.23 nmol, n = 6). When compared with the mean N2O intercepted by 0% biochar treatments (−25 pmol), the 1 and 5% biochar treatments significantly lowered N2O emitted, by 2.14 and 7.97 nmol respectively (p = 0.0094 and p = 5.6 × 10−8). Although there were differences in ∆N2O/inj.N2O at tmax between treatments of differing mean WFPS at the same biochar content (Table 1), only that between the 39 and 54% WFPS treatments with 5% biochar was significant (p = 0.018). For the BC100% treatments, ∆N2O/inj.N2O at tmax was only 0.16 (Table 1). The apparent loss of N2O within the sampling periods for any treatments containing biochar suggests that some of this gas might have been adsorbed, at least temporarily, or decomposed. Figure 1 shows the mean change in headspace N2O (injected mol N2O)−1 for each treatment. For soil/biochar columns the associated (Fig. 1) caption includes the significance of differences at tmax between treatments of 0, 1 and 5% biochar, based on both headspace N2O (injected mol N2O)−1 and estimated ∆N2O/inj.N2O. Estimated from headspace N2O concentration ([N2O]) at tmax, the mean unaccounted N2O from headspace and AFPS (injected N2O)−1 (i.e. N2O injected that was ‘missing’ from the combined volume of headspace and estimated AFPS) for 1% and 5% biochar composites was significantly greater than for BC100% treatments per unit weight of biochar (p = 0.044 and 0.015 respectively). For treatments of 1% biochar this measure of unaccounted N2O was 8.7 (s.e.m. = 1.7, n = 3) times greater than the mean for BC100% treatments, and the comparable ratio for treatments of 5% biochar was 4.0 (s.e.m. = 0.37, n = 3).

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