Effects of Rice Husk Charcoal Application on Rice Yield, Methane Emission, and Soil Carbon Sequestration in Andosol Paddy Soil

Biochar application is an effective option for promoting soil carbon sequestration. Rice husk charcoal (RC) produced from pyrolysis of rice husk (RH) is characterized by a higher silicon content as compared to wood-derived biochar. A study was conducted using pots to evaluate the short-term effects of RC application at 0, 0.4, 2.0, 4.0, 20.0, and 40.0 g pot(-1) (CONT, RC0.4, RC2, RC4, RC20, and RC40, respectively), or RH application at 4.0 g pot(-1) (RH4) on rice yield, methane (CH4) emission, and soil carbon sequestration in an Andosol paddy soil. The results showed that the significant increase in brown rice yield with RC40 was attributed to increases in the grain number and percentage of ripened grains. Plants treated with RC20 or RC40 absorbed greater amounts of silicon than those treated with lower RC rates. RC application did not significantly increase CH4 emission. The soil carbon content after rice cultivation increased in proportion to the RC application rate. The balance between cumulative CH4 emission and soil carbon sequestration, based on the 100-year global warming potential, suggested that RC40 served as CO2-equivalent sink. No differences were observed in the measured parameters between RH4 and RC4. These findings suggest that the higher rates of RC application in the RC20 and RC40 treatments function as a silicon fertilizer while promoting soil carbon sequestration.