Wood vinegar and biochar co-application mitigates nitrous oxide and methane emissions from rice paddy soil: A...

Both biochar (BC) and wood vinegar (WV) influence the nitrous oxide (N₂O) and methane (CH₄) emissions from agricultural systems. However, the impacts of BC and WV co-application on rice production, N₂O and CH₄ emissions are not well documented. We here conducted a two-year soil columns experiment with four treatments: WV (5 t WV ha^-1), BC (7.5 t BC ha^-1), WV + BC (5 t WV ha^-1 +7.5 t BC ha^-1) and a control (no treatment). The results showed that BC and WV + BC produced higher rice grain yield than the control by 14.1-15.9% in 2016 and by 4.1-5.2% in 2017, respectively. While WV increased rice grain yield by 11.2% in 2016, it had no significant influence on yield in 2017. Both WV and BC significantly mitigated N₂O emissions by 22.4-41.8% in 2016 and 22.4-36.9% in 2017, respectively. Interestingly, WV + BC treatment showed the highest N₂O mitigation efficiency, with a 52.9-62.8% mitigations in 2016 and 2017. Furthermore, the co-application of WV and BC significantly mitigated CH₄ emissions by 42.6% in 2016 and 35.3% in 2017, respectively, while applying WV or BC alone had no annually-consistent mitigation effect on CH₄ emissions. Overall, GWPt of rice growth cycle was most significantly suppressed by WV + BC with a 48.7-56.1% reduction, followed by WV and BC with 20.4-28.0% and 19.7-35.7% reductions, respectively. Consequently, the WV + BC treatment had the highest GHGI mitigation effect, averaging with 56.7% over two consecutive rice growth cycles. In conclusion, co-application of WV and BC is recommended for rice cultivation, which can both improve rice yield and minimize GHG emissions.