The molar H:Corg ratio of biochar is a key factor in mitigating N2O emissions from soil
- •An updated meta-analysis including 56 studies finds that biochar reduces soil N2O emissions by 49 ± 5%.
- •Field studies show lower reductions in N2O emissions (28 ± 16%) compared to laboratory studies (54 ± 5%).
- •The lower the biochar molar H:Corg ratio the higher the N2O mitigation.
“A previously published meta-analysis of biochar impacts on soil N2O emissions by Cayuela et al. (2014) found a “grand mean” reduction in N2O emissions of 54 ± 6% following biochar application to soil. Here we update this analysis to include 26 additional manuscripts bringing the total to 56 articles. The updated meta-analysis confirms that biochar reduces soil N2O emissions by 49 ± 5% (mean ± 95% confidence interval). Importantly, this meta-analysis has sufficient data to investigate the impact of biochar under field conditions, showing a statistically significant lower average reduction in the field (28 ± 16%) compared to controlled laboratory studies (54 ± 3%). A key finding is the importance of the molar H:Corg ratio of biochar in determining mitigation of N2O. Biochars with a molar H:Corg ratio <0.3, indicative of a high degree of aromatic condensation, lowered N2O emissions by 73 ± 7% while biochars with a molar H:Corg ratio >0.5 were less effective at 40 ± 16%. Together with previously published information, our new results suggest that a key mitigation mechanism is linked to the degree of polymerization and aromaticity of biochar.”
It would be great to see some comment from the NZ Agriculture Greenhouse Gas Research Centre on this meta-analysis in the context of their plans for future work with nitrous oxide and soil carbon.