Linking biochars properties to their capacity to modify aerobic CH4 oxidation in an upland agricultural soil

Abstract

Aerobic soils are the largest biotic sink for atmospheric methane (CH4). Although agricultural intensification is known to adversely impact soil CH4 uptake, the application of organic amendments (e.g. composts, green residues) in agricultural soils has been found to stimulate the activity of CH4 oxidizers. However, little is known about the influence of biochar (a carbonaceous by-product of biomass pyrolysis) on the soil CH4 sink function. This study analyzes, through a series of laboratory incubation assays, how ten well-characterized biochars with contrasting properties influence CH4 oxidation rate constants (k) in an aerobic high-pH agricultural soil. Through the use of 13C-CH4, we demonstrated that both CH4 soil oxidation and CH4 assimilation were responsible for the decrease in CH4 concentration. A principal component regression (PCR) of the results suggested that the physico chemical properties of biochars were directly linked to their ability to enhance or inhibit the oxidation of CH4. Biochars from wood feedstocks and pyrolysed at 600 °C, characterized by a high pore area, led to the highest CH4 oxidation rates whereas biochars with high ash concentrations and electrical conductivity significantly diminished CH4 oxidation rates. Biochar redox properties were not found to be relevant for CH4 oxidation in soil.