Reduction of Greenhouse Gas Emission from Soil Mixed Biochar during Sterilization with Hot Water.

A large amount of Greenhouse Gases (GHGs) is emitted from soil during soil sterilization with hot water. We tried to reduce GHGs emission by mixing biochar into soil. We measured GHGs flux and heat movement in soil during sterilization with hot water. Experiments were conducted in a greenhouse at Meiji University, Japan in 2013. We used three soil columns, 0.20 m in dia. and 0.45 m high. We used air-dried Kanto loamy soil as a specimen. We prepared soil by mixing with 0, 5 and 10 (t ha^-1) rice husks biochar.  We measured soil temperature (^oC), water saturation degree (%), redox potential (mV), gas fluxes at the soil surface (mg m^-2 h^-1), gas concentration in soil (ppm) and pH. We applied hot water (=95 ^oC) for 200 L m^-2 on DOY=267. The biochar mixed didn’t hinder heat transfer in soil. Fluxes of CO₂ and N₂O from the 5 and 10 (t ha^-1) columns were less than those from the 0 (t ha^-1) column. The fluxes from the 5 (t ha^-1) column were less than those from the 10 (t ha^-1) column. Those phenomena were only occurred with water saturation degree < 80 (%) and redox potential > 0 (mV). The CO₂ and N₂O gas concentrations in 5 and 10 (t ha^-1) soil were higher than those in 0 (t ha^-1) column. We speculated that biochar trapped CO₂ and N₂O before they were released. Values of pH during the experiment changed little. During sterilization with hot water, reducing CO₂ and N₂O emission from soil may be feasible by adding biochar without hindering heat transfer. Long term effects of biochar and microbial activities are needed for future study.