5:15 PM - 7:15 PM
[AGE34-P01] Effects of Artificial Macropore and Drainage on Reducing GHG Emissions from Paddy Soils within Mesoscale Columns
Keywords:artificial macropore, drainage, greenhouse gas, paddy soil, mesoscale column experiment
Reducing CH4 emissions from rice paddies is an important climate change mitigation measure in the agricultural sector. Since CH4 is produced in an anaerobic environment, our study group has attempted to improve soil drainage and downward infiltration by artificial macropores, which artificially mimic the structure of soil macropore, so that it could effectively deliver oxygen to the lower layers of paddy soil and reduce CH4 emissions. Previous results from simple column experiments suggested that artificial macropore and drainage application were effective in reducing CH4 emissions. However, these results did not fully take into account realistic conditions, such as emissions through the aerenchyma of rice plants, which is a well-known CH4 emission mechanism in rice paddies. The purpose of this study is to reduce CH4 emissions from rice paddy soil using artificial macropore technology. In particular, we focused on verifying the effectiveness of this technology in a mesoscale experiment.
The column design was made to bring the experimental scale closer to the field scale by introducing rice plants and changing the drainage application method (from automatic continuous drainage to manual gravity drainage). Based on a design in which rice plants are planted in flooded paddy soil, a total of six column conditions were designed: 1) with/without drainage and 2) macropore with soil layer/macropore without soil layer/without macropore. These columns were kept in a growth chamber under constant temperature, relative humidity, and sunlight conditions (10 hours light and 14 hours dark) for 60 days, and CH4 gas flux and other parameters were measured every two days. At the end of the 60-day measurement period, surface water and soil samples were collected from all columns.
The average CH4 flux over 60 days was significantly lower in the columns with drainage, but did not differ by macropore type. The CH4 emissions in this experiment were generally lower than in the previous experiment. CO2 gas was no longer detected in all columns after the first few days of the experiment. It is possible that most of the CO2 in the columns was used for photosynthesis by the rice plants. No clear trend in soil ORP was observed between conditions with and without drainage, nor was there a difference in surface water pH. However, the EC and some cation concentrations of the drained water seemed to be related to the soil water permeability, indicating that the worse the drainage, the higher the solute concentrations in the water. The same trend was observed for the surface water, most cation concentrations in the water were higher under the condition of no drainage application. In cases with drainage, there were some differences in the temporal fluctuation of the volumetric water content, which represents the generation and transfer of CH4 bubbles, among different types of macropore. Therefore, it was suggested that the type of macropore causes the difference in soil water transfer characteristics when drained. In this experiment, it may be necessary to consider that the strong flow generated by gravity drainage allowed CH4 bubbles and solutes in the water to escape from the column through the drainage.
In this study, CH4 emissions from all columns with drainage were significantly reduced. Rice plants and gravity drainage, introduced into the columns for the first time for mesoscale experiments, may have had different effects on the mass transfer mechanisms in the columns than previous conditions in this series of studies.
The column design was made to bring the experimental scale closer to the field scale by introducing rice plants and changing the drainage application method (from automatic continuous drainage to manual gravity drainage). Based on a design in which rice plants are planted in flooded paddy soil, a total of six column conditions were designed: 1) with/without drainage and 2) macropore with soil layer/macropore without soil layer/without macropore. These columns were kept in a growth chamber under constant temperature, relative humidity, and sunlight conditions (10 hours light and 14 hours dark) for 60 days, and CH4 gas flux and other parameters were measured every two days. At the end of the 60-day measurement period, surface water and soil samples were collected from all columns.
The average CH4 flux over 60 days was significantly lower in the columns with drainage, but did not differ by macropore type. The CH4 emissions in this experiment were generally lower than in the previous experiment. CO2 gas was no longer detected in all columns after the first few days of the experiment. It is possible that most of the CO2 in the columns was used for photosynthesis by the rice plants. No clear trend in soil ORP was observed between conditions with and without drainage, nor was there a difference in surface water pH. However, the EC and some cation concentrations of the drained water seemed to be related to the soil water permeability, indicating that the worse the drainage, the higher the solute concentrations in the water. The same trend was observed for the surface water, most cation concentrations in the water were higher under the condition of no drainage application. In cases with drainage, there were some differences in the temporal fluctuation of the volumetric water content, which represents the generation and transfer of CH4 bubbles, among different types of macropore. Therefore, it was suggested that the type of macropore causes the difference in soil water transfer characteristics when drained. In this experiment, it may be necessary to consider that the strong flow generated by gravity drainage allowed CH4 bubbles and solutes in the water to escape from the column through the drainage.
In this study, CH4 emissions from all columns with drainage were significantly reduced. Rice plants and gravity drainage, introduced into the columns for the first time for mesoscale experiments, may have had different effects on the mass transfer mechanisms in the columns than previous conditions in this series of studies.