Biochar addition under straw return reduces carbon dioxide and nitrous oxide emissions in acidic tea field soil

Straw return and biochar application are prevalent agricultural practices that bolster soil health, enhancing crop yields. However, their synergistic effects on carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions in the acidic tea field soil at different age stages have not been fully elucidated. Herein, tea field soil with 5 and 15 years planting (5a and 15a, respectively) were individually incubated in five distinct indoor experiments: control, soil with urea (N), soil with urea and biochar (N + C), soil with urea and straw (N + S), and soil with urea, biochar, and straw (N + C + S). The results demonstrated that the pH values under 15a (4.1-5.6) were significantly lower than those under 5a (5.8-7.3), and both straw and biochar addition effectively improved soil acidification. Straw or biochar addition alone acted as carbon sources, leading to heightened N₂O and CO₂ emissions. N + S increased N₂O emissions (3.17 and 5.85-fold) and CO₂ cumulative emissions (6.43 and 2.33-fold) under 5a and 15a compared with the control. Relative to N treatment, biochar addition alone increased CO₂ emission (1.22 and 1.35-fold) under 5a and 15a, and increased N₂O emissions by 14.73% under 5a, decreased N₂O emissions by 74.65% under 15a. However, the combined application of straw and biochar reduced N₂O (49.4%,17.58%) and CO₂ emissions (57.83% and 33.60%) due to stimulating biochar adsorption, respectively, compared with N + S treatment under 5a and 15a. Therefore, biochar and straw addition together can effectively increase soil fertilizer and inhibit greenhouse gas emissions, this study provides an insightful way and effective option for improving acid soil and protecting high soil health with a low greenhouse gas emission intensity.