5:15 PM - 6:45 PM
[AGE29-P01] Effect of biochar application on methane emissions from paddy soil
Keywords:Biochar, Methane, Dissolved Organic Carbon, Adsorption, Paddy soil
As greenhouse warming becomes more serious, greenhouse gas control methods should be considered. Methane (CH4) has a 28-34 times greater global warming potential than CO2 over a 100-year scale. CH4 emissions from paddy fields account for 5-19% of global CH4 emissions. Therefore, it is essential to study the CH4 emissions from paddy soil.
Some researchers are supposed to use biochar to reduce CH4 emissions. However, papers have reported that biochar could not only reduce CH4 emissions but also increase CH4 emissions. This might relate to the release of the dissolved organic carbon (DOC) from biochar and the adsorption property of the biochar. Therefore, this study employed two biochar pyrolysis temperatures to explore DOC adsorption by biochar and CH4 emissions from the paddy soil.
Incubation experiments were conducted in this study. 480g of soil mixed with straw and 4.8g of biochar were filled into a 900 mL glass bottle, and pure water was ponded at 3 cm in depth. The incubation period is 32 days. Two biochars pyrolysis temperatures of 400℃ and 600℃ were used. The straw was added 1% and 1.5% of the mass of the soil. All the treatments were incubated in a 25℃ laboratory environment with a 12/12h (light/dark) cycle. During the incubation, soil Eh, DOC, CH4 flux, and dissolved CH4 concentration were measured weekly.
A stock DOC solution was prepared by incubating dry straw with water and diluted into 15, 40, 100, 150, 200, and 250 mg L-1 concentrations for the adsorption experiment. In brief, 0.4g biochar was put into the 40 mL DOC solution and shaken for 24 hours. The supernatant was taken and filtered through a 0.45 μm screen for DOC measurement.
The result of incubation demonstrated that biochar adsorbed soil DOC and thus reduced the CH4 emissions. During the incubation, soil DOC concentration continued to increase while the soil Eh kept decreasing, eventually reaching around -150 mV. CH4 emissions began to increase significantly after day 11 when Eh reached -105 mV. Thus, CH4 emissions show a negative correlation with Eh and a positive correlation with DOC content.
Control treatments with neither biochar nor straw demonstrated less CH4 emission and DOC concentration, while biochar application showed only tiny increases in DOC concentration and CH4 emission. However, the straw application led to higher DOC concentration and more CH4 emission. It is worth noting a significant reduction in DOC concentration and CH4 emissions in biochar with straw application treatments. After constructing the adsorption isotherm of DOC by biochar, we calculated the mass of carbon in each treatment. The result showed that carbon in the biochar treatments was clearly at the same level as the carbon mass in the straw-only treatments after estimating the amount of adsorption. Moreover, 600℃ biochar treatment exhibited less CH4 emission and less DOC concentration than 400℃ biochar. While the carbon mass balance remained conserved because 600℃ biochar shows greater adsorption capacity than 400℃ biochar. Thus, adsorption played a vital role in the carbon balance of the whole system.
It was also found that the amount of DOC adsorption and reduction in CH4 emissions exhibit a positive correlation. With the increase in the amount of DOC adsorption, the decrease in CH4 emissions also increased, regardless of what kind of biochar.
Acknowledge: We would appreciate NIAES and the Institute for Rural Engineering, NARO, for their help in the preparation of soil and biochar. This study is partly supported by KAKENHI 19H00958.
Some researchers are supposed to use biochar to reduce CH4 emissions. However, papers have reported that biochar could not only reduce CH4 emissions but also increase CH4 emissions. This might relate to the release of the dissolved organic carbon (DOC) from biochar and the adsorption property of the biochar. Therefore, this study employed two biochar pyrolysis temperatures to explore DOC adsorption by biochar and CH4 emissions from the paddy soil.
Incubation experiments were conducted in this study. 480g of soil mixed with straw and 4.8g of biochar were filled into a 900 mL glass bottle, and pure water was ponded at 3 cm in depth. The incubation period is 32 days. Two biochars pyrolysis temperatures of 400℃ and 600℃ were used. The straw was added 1% and 1.5% of the mass of the soil. All the treatments were incubated in a 25℃ laboratory environment with a 12/12h (light/dark) cycle. During the incubation, soil Eh, DOC, CH4 flux, and dissolved CH4 concentration were measured weekly.
A stock DOC solution was prepared by incubating dry straw with water and diluted into 15, 40, 100, 150, 200, and 250 mg L-1 concentrations for the adsorption experiment. In brief, 0.4g biochar was put into the 40 mL DOC solution and shaken for 24 hours. The supernatant was taken and filtered through a 0.45 μm screen for DOC measurement.
The result of incubation demonstrated that biochar adsorbed soil DOC and thus reduced the CH4 emissions. During the incubation, soil DOC concentration continued to increase while the soil Eh kept decreasing, eventually reaching around -150 mV. CH4 emissions began to increase significantly after day 11 when Eh reached -105 mV. Thus, CH4 emissions show a negative correlation with Eh and a positive correlation with DOC content.
Control treatments with neither biochar nor straw demonstrated less CH4 emission and DOC concentration, while biochar application showed only tiny increases in DOC concentration and CH4 emission. However, the straw application led to higher DOC concentration and more CH4 emission. It is worth noting a significant reduction in DOC concentration and CH4 emissions in biochar with straw application treatments. After constructing the adsorption isotherm of DOC by biochar, we calculated the mass of carbon in each treatment. The result showed that carbon in the biochar treatments was clearly at the same level as the carbon mass in the straw-only treatments after estimating the amount of adsorption. Moreover, 600℃ biochar treatment exhibited less CH4 emission and less DOC concentration than 400℃ biochar. While the carbon mass balance remained conserved because 600℃ biochar shows greater adsorption capacity than 400℃ biochar. Thus, adsorption played a vital role in the carbon balance of the whole system.
It was also found that the amount of DOC adsorption and reduction in CH4 emissions exhibit a positive correlation. With the increase in the amount of DOC adsorption, the decrease in CH4 emissions also increased, regardless of what kind of biochar.
Acknowledge: We would appreciate NIAES and the Institute for Rural Engineering, NARO, for their help in the preparation of soil and biochar. This study is partly supported by KAKENHI 19H00958.