Effects of biochar aging in the soil on its mechanical property and performance for soil CO2 and N2O emissions

Biochar application into the soils has been reported to have huge carbon sequestration potential, although it remains unclear that how the biochar aging in the soil affects its mechanical properties and soil CO2 and N2O emissions. This work assessed the impact of soil biochar aging on its physicochemical properties, microbiota community in the biochar, and soil CO2 and N2O emissions. Various characterizations (e.g., SEM-EDS, XRD, and FTIR) of fresh and aged biochar indicated that soil minerals accumulated on the biochar during the field aging process, forming organo-mineral complexes and blocking the cracks and channels on the biochar. The measured hardness and compressive strength of aged biochar were significantly higher than those of fresh biochar, consistent with the presence of soil minerals on the aged biochar. The soil CO2 and N2O emissions were significantly decreased after the addition of aged biochar particles, as compared to fresh biochar particles. This was probably because that the improved mechanical properties could inhibit the fragmentation of biochar particles, reducing the release of labile fractions from the biochar and the subsequent CO2 and N2O emissions. Moreover, the presence of CO2-fixing bacteria (e.g., Chloroflexi) and inhibited nitrification and ammonia oxidation in aged biochar particles might also reduce CO2 and N2O emissions. These findings suggest aged biochar particles with improved physical stability to the soil could enhance soil carbon sequestration and greenhouse gas emission reduction. [Display omitted] •Soil minerals would accumulate on the surface of biochar after aging in the soil.•Mechanical strength of biochar particles was improved after the field aging.•The aged biochar could significantly inhibit CO2 and N2O emissions from the soil.•Field aging could affect the microbial community structure in the biochar.