Comparative Effects of Straw and Biochar on N₂O Emissions from Acidic Soils

Biochar amendment is widely considered as a potential strategy to mitigate soil acidification and N₂O emissions. However, the effect of biochar on N₂O emissions from acidic soils remains unclear. This study aims to compare the effects of straw and biochar on N₂O emissions from acidic soils in tea fields with different cultivation years in South Central China.

A 48-day microcosm experiment was conducted with soils from two fields after 5 years (pH = 5.8, slightly acidic) and 15 years (pH = 4.5, acidic) of tea cultivation to examine the N₂O emissions in response to straw and biochar amendment.

Biochar addition alone significantly increased the soil pH by 1.14 and 0.54 units and further reduced N₂O emissions by 28.46% and 68.34%, but straw addition alone increased the cumulative N₂O emissions by 141.97% and 127.45% in 5-year and 15-year tea field soils, respectively. Combined application of straw and biochar significantly (p < 0.01) reduced N₂O emissions relative to single straw application in both field soils. Furthermore, N₂O emissions from the acidic soil (15-year tea cultivation) were 7.12-fold those from slightly acidic soil (5-year tea cultivation) of the control treatment. Correlation analysis indicated that N₂O emissions are positively correlated with dissolved organic carbon (DOC), microbial biomass carbon (MBC), and NH₄⁺-N, but negatively correlated with pH.

The results suggested that compared with straw, biochar could increase soil pH and further mitigate N₂O emissions from acidic soils, which may be an optimal strategy to reduce soil N₂O emissions and alleviate soil acidification.