Methane emission from the plant can be measured by closed chamber technique using a transparent chamber of 60 cm x 60 cm base and 122.5 cm height (Figure 1 and Figure 2). The chamber is placed on a metal frame which is inserted into the paddy soil and remained in this position throughout the vegetation period. After completion of the measurements, the chamber is then removed. The metal frame on this set-up prevents the soil from being disturbed and its further release of CH4 from the soil air spaces. The gas chambers are also furnished with a fan inside them to enhance the homogenization of the air at the headspace (Figure 1 inset and Figure 3). Figure 2 also shows the direction of the irrigation.
Figure 1. The flux chamber for gas sampling (inlet picture: electric fan, above and sampling port, below).
Figure 2. The field set up of the four chambers showing the direction of the irrigation.
Gas Sampling
The gas samples are drawn out from the chamber headspace using a 60-mL PVC syringe with a 26 G x 1” stainless steel needle. Sixty milliliters of gas sample are obtained from each of the 4 chambers right after the lid of the chamber was closed. The syringes are equipped with stopcock to ensure that the gas will not escape from the syringes. The sample obtained is then labeled as t = 0 mins. The headspace gas samples are transferred to Vacutainers® (Figure 4) having the same labels. Another set of 60 mL samples are taken after 10, 20 and 30 minutes and were then labeled as t = 10 mins, t = 20 mins and t = 30 mins, respectively.
Emissions are monitored starting from transplanting of the rice plant until before its harvest.
Figure 3. Diagram of the gas chambers and sampling set up showing the embedded metal frames.
Figure 4. Vacutainers and 60-mL syringe with Luer lock used for sampling.
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