GHG Measurement Guidelines
Field measurements on GHG emissions from rice fields can be conducted through different approaches, but the closed chamber techniques with manual sampling has clearly evolved as a kind of standard used by many research groups around the world. This approach is relatively easy to implement, but the sampling frequency and the number of field sites are limited by extensive labor requirements.
In Vietnam, the Ministry of Agriculture and Rural Affairs, has issued a standardized guidelines for measuring GHG emissions as reference for determination, calculation of GHG emissions in paddy rice production. The Guidelines were published in a Handbook developed by Vietnam’s Institute of Agricultural Environment with support from IRRI, Winrock international, and SNV in 2016. The Handbook provides specific instructions as to preparation for sampling (equipment, selection of location, planning, and observation), sampling procedure, sample transportation and storage, and GHG analysis (environment and capacity requirements, methods, and quality assurance). It gives step-by-step guidance with demonstration photos for users to easily follow.
Users are also given a template to document and report analysis results in a scientific, concise and informative manner.
How does it work?
Chambers are arranged in pairs that close and open simultaneously with pressurized air applied to the lids, and gas samples are taken sequentially from all chambers. Within each measurement cycle, this procedure is repeated once per chamber block of the system. Monitoring takes place quasi-continuously with several measurements recorded daily. Gas chromatographs (equipped with FID and ECD detectors) are used to investigate CH4 and N2O, respectively. In addition, a set of probes measures continuously environmental parameters–for instance, soil temperature, soil moisture at different soil depths and precipitation. Data are stored by data logging modules. Chambers closing period and gas sampling temporal sequence–as well as the size and shape of the chambers–depend on the investigated ecosystem and the trace gasses of interest.