Chamber-based fluxes measurements

Chamber-based flux measurements were conducted to quantify greenhouse gas (GHG) emissions from rice paddies. A closed static chamber system was employed, consisting of permanently installed bases (50 × 50 cm) inserted 5 cm into the soil and detachable chambers of different heights to accommodate crop growth stages. During each sampling event, the chamber was placed on the base and sealed with a water-filled groove to prevent leakage. Headspace air samples were collected at fixed intervals (0, 15, and 30 minutes after chamber closure) using pre-evacuated gas sampling bags connected to a portable pump. Collected gas samples were analyzed with a Picarro G2508 cavity ring-down spectrometer, which simultaneously measures CO₂, CH₄, and N₂O concentrations with high precision. Fluxes were calculated from the linear change in concentration over time, normalized by chamber volume, chamber area, air temperature, and pressure. Measurements were conducted regularly throughout the cropping season to capture temporal variations in flux dynamics under different irrigation regimes.