Comparison of two methods for the estimation of greenhouse gas flux from rice ecosystems in India

In India the greenhouse gas emissions from agricultural field are mainly measured by conventional closed chamber (CCC) method. An experiment was conducted to compare the methane (CH4) and nitrous oxide (N2O) flux from rice fields using the CCC method and the modified closed chamber (MCC) method. The air-circulatory pump and Tedler® sampling bag in the CCC method were replaced with a power supply (18 V) and three-way valve attached glass syringe, respectively, to reduce the operational cost and ensure safe transportation of samples to the laboratory for analysis. The experiment was conducted under irrigated, upland and deepwater rice growing ecosystems in Odisha, India. The study demonstrates that there was no significant difference in the CH4 and N2O flux measured with the CCC and MCC methods throughout the rice growing season under irrigated condition. However, in the upland rice ecosystem, significantly higher CH4 flux was recorded with the MCC method during maximum tillering stage of rice. N2O flux was recorded higher in deepwater rice ecosystem during the maximum tillering stage with the MCC method. These maybe attributed to high spatial variability of CH4 flux from upland area and higher dissolve rate of N2O in water. As the study has recorded no significant differences in CH4 and N2O emissions measurement using the two methods from different rice growing environments during most of the crop growth stages, the cost-effective MCC method maybe used for large-scale field sampling.