(418b) Effects of Engineered Biochars on Greenhouse Gas Emissions from Dairy Manure-Applied Soil

Greenhouse gas (GHG) emissions from manure-amended soils represent a major environmental concern due to the enhanced microbial decomposition of organic matter. In this study, we evaluated the effects of wood biochar (BC), calcium-modified biochar (Ca-BC), and activated carbon (AC) at varying doses (1%, 5%, and 10%) on CO₂, CH₄, and N₂O emissions from dairy manure-amended sandy loam soil. Incubation experiments were conducted for 70 days at 22 °C in sealed jars, with GHG fluxes measured weekly. Results revealed that manure addition increased CO₂, CH₄, and N₂O emissions by approximately 95-, 120-, and 16-fold, respectively, compared to unamended soil, highlighting the stimulatory role of manure-derived organics and microbial activity. The addition of BC enhanced CO₂ emissions by 4–47%, but markedly suppressed CH₄ and N₂O emissions by 50–71% and 40–100%, respectively. Activated carbon treatments showed a similar trend, with 35–89% and 14–86% reductions in CH₄ and N₂O emissions, while CO₂ decreased by up to 61% at higher AC doses, likely due to microbial inhibition and mass transfer limitations. Interestingly, Ca-BC exhibited a divergent pattern. While low-dose Ca-BC (1%) increased CO₂ by 16%, higher doses (5% and 10%) decreased CO₂ by 13% and 48%, respectively. N₂O emissions were substantially reduced (73–100%) across all Ca-BC treatments. However, CH₄ emissions increased by 74% under 5% Ca-BC, indicating potential pH-mediated stimulation of methanogenic activity. Microbial community analysis revealed that Firmicutes were dominant in BC- and Ca-BC-treated soils, especially under high Ca-BC conditions (>94%), whereas Proteobacteria and Bacteroidota were suppressed. Methanosarcina emerged as the sole methanogen detected, particularly under manure and biochar treatments, with peak abundance in Ca-BC5, suggesting its role in CH₄ dynamics under alkaline conditions. This study demonstrates that engineered biochars can differentially modulate GHG emissions via shifts in microbial communities, offering insights into tailored soil amendments for sustainable manure management.