Multiple inter-tillage weeding effect on methane and nitrous oxide emissions pathways from rice paddy fields in Hokkaido, Japan
Creators: name: Namie, Hiyori
name: Shimada, Kasane
name: Zhao, Shuangshuang
name: Toma, Yo
name: Ishiguro, Munehide
name: Hatano, Ryusuke
Publisher: name: Taylor & Francis
Year: 2025
Subjects: subject: Biophysics
subject: Microbiology
subject: FOS: Biological sciences
subject: Physiology
subject: Pharmacology
subject: Environmental Sciences not elsewhere classified
subject: Chemical Sciences not elsewhere classified
subject: Ecology
subject: Biological Sciences not elsewhere classified
subject: Plant Biology

description: Rice paddy fields are important sources of methane (CH<sub>4</sub>) and nitrous oxide (N<sub>2</sub>O). Generally, CH<sub>4</sub> is emitted predominantly via rice, with smaller contributions from ebullition and diffusion, while CH<sub>4</sub> oxidation varies by pathway. Research on N<sub>2</sub>O emissions remains ongoing. Multiple inter-tillage weeding (MIW), a traditional Japanese practice, is believed to enhance rice yield and improve anaerobic soil conditions. However, its effects on CH<sub>4</sub> and N<sub>2</sub>O emission pathways remain unclear. This study aimed to quantify MIW’s impact on CH<sub>4</sub> and N<sub>2</sub>O emissions through three pathways and MIW-mediated. Diffusive gas flux was determined by extracting net gas flux based on threshold values. Ebullitive gas flux was measured using a bubble-trapping method. Rice-mediated gas flux was calculated as the difference between total gas flux and the sum of diffusive and ebullitive gas fluxes. A chamber with disturbance functionality was developed to measure the MIW-mediated gas flux. Treatments of 0 (T0), 2 (T2), and 5 (T5) MIW practices were compared with conventional rice farming as a reference. Analysis of CH<sub>4</sub> and N<sub>2</sub>O emission pathways during the MIW period revealed that gaseous CH<sub>4</sub> influenced the ebullition and rice-mediated pathways, increasing the relative contribution of the diffusion pathway. High-frequency MIW (T5) enhanced the release of CH<sub>4</sub>-rich bubbles, temporarily reducing rice-mediated CH<sub>4</sub> emissions. However, the contributed rate of MIW-mediated CH<sub>4</sub> emission to the total CH<sub>4</sub> emission during cultivation period were low. High-frequency MIW (T5) promoted N<sub>2</sub>O production in soil and paddy field water, but the emission rate exceeded its formation and consumption rates, potentially increasing atmospheric-soil concentration gradients and enhancing N<sub>2</sub>O absorption via the rice pathway. At medium frequency (T2), N<sub>2</sub>O emissions during the MIW period were similar to those under no MIW (T0). MIW-mediated N<sub>2</sub>O emissions accounted for 4–5% of the total cultivation period emissions at T2 and about 30% at T5, highlighting MIW-mediated N<sub>2</sub>O emissions playing a secondary role under high-frequency MIW. During the cultivation period, CH<sub>4</sub> emissions were 72–86% via rice, 13–27% via diffusion, and 1–2% via ebullition. N<sub>2</sub>O was slightly emitted via diffusion and ebullition, whereas absorption was observed in rice.