Biochar Effects on Soil Microbial Biomass and Activity
Environmental benefits of production of biochar and use as a soil amendment include increased soil carbon (C) sequestration, enhanced microbial activity, and altered soil nitrogen (N) transformations. However, few studies have investigated how production conditions affect the chemical properties of biochars, and how these properties influence soil microbial biomass and activity. This study investigated effects of biochars produced through pyrolysis at 200, 400, 600ºC, and gasification at 700ºC and that of biochars activated with steam and carbon dioxide (CO2) at 800ºC. Pyrolysis temperatures had significant effect on biochar chemical properties. The 13C nuclear magnetic resonance (NMR) spectra of biochars showed that conversion of labile C consitutents of biomass feedstocks to aromatic C structures increased with increasing pyrolysis temperature. Cation exchange capacity (CEC), basic cations, ammonium (NH4+) adsorption capacity and pH of the biochars increased with increasing pyrolysis temperature, but decreased CEC and NH4+ adsorption with activation. Amendments with biomass feedstocks significantly increased soil microbial biomass (C and N) and activity whereas biochars produced by pyrolysis at 400 and 600ºC and by gasification at 700ºC had no significant effect. Amendments with activated biochars significantly decreased soil microbial activity. Biochars produced at 400 and 600ºC and activated biochars significantly decreased soil inorganic N accumulation. This study indicates that production temperature is a key factor affecting biochar properties. While there is a benefit to increased soil C storage for biochars produced at temperatures >200ºC, they have no effect on soil microbial biomass and activity. Further studies are needed to investigate the effects of biochar production method and temperature on the chemical properties and their biological effects on soil C and N dynamics.