Effects of biochar content on gas diffusion coefficient of soil with different compactness and air contents

Biochar has been found to be a potentially suitable amendment for landfill cover material and agricultural soil. The addition of biochar can improve the physical (e.g., adsorption capacity) and hydrological properties (e.g., water/gas permeability) of soil. However, no experimental study is available about the effect of biochar content (BC) on the gas diffusion coefficient (D_P) of soil. The present study investigated the effect of BC on D_P under different degree of compaction (DOC; 85%, 90%, and 95%) and soil air contents (SAC; 5%, 10%, and 15%). It was found that DOC and BC had negligible effects on D_P when SAC was low (~ 5%). In contrast, when the SAC was relatively high (~ 15%), soil with DOC of 85% had the largest D_P for BC ranging from 0 to 15% (w/w). Only when the SAC was large (~ 15%), the addition of biochar generally increased D_P.