A novel method for laboratory-scale estimation of methane flux from paddy soils using silicone tubes

Abstract

Methane (CH₄) is the second most impactful anthropogenic greenhouse gas (GHG) andis significantly emitted from rice paddies, contributing 6–11% of global CH₄ emissions. Accurate quantification of these emissions is critical for developing effective mitigation strategies. However, field-level measurements of GHGs are often challenging and costly. In paddy soils, approximately 90% of methane is emitted through rice plants, requiring large chambers to enclose the entire plant for accurate CH₄ emission measurements in the field. To address this, a laboratory experiment was conducted to develop a method for measuring CH₄ emissions from inundated paddy soil using gas-permeable silicone tubes (inner diameter: 1 mm; outer diameter: 1.5 mm) to simulate plant-mediated CH₄ transport. A closed chamber system with four chambers (each with a 500 ml headspace) was used to evaluate the feasibility of the using silicone tubes and to assess the effects of tube density and insertion depth on CH₄ flux. In the first experiment, five silicone tubes inserted to a depth of 5 cm were tested against a control condition without silicone tubes The second experiment assessed two insertion depths (5 and10 cm) and tube densities (5 and10 tubes), equally distributed over 68 cm². CH₄ emissions were measured every 2 minutes for 30 minutes, followed by a 10-minute ventilation period for gas collection and measuring system including the gas cell of the FTRI spectrometer. Results from the first experiment showed that CH₄ emissions increase significantly under the silicone tube treatment compared to the control. In the second experiment, CH₄ emissions were greater at the 10 cm insertion depth compared to at 5 cm, though the increase was not proportional to the depth, likely due to enhanced oxidation of CH₄ in the surface oxidized layer near the soil-water interface. These findings demonstrate that gas-permeable silicone tubes are a promising tool for simulate plant mediated CH₄ emissions in la