4.2. Period
The appropriate period of gas flux measurement depends on the research objectives.
Moreover, it may differ between CH4 and N2O, even if the objectives are the same, because of
differences in emission processes between the two gases. The IPCC (2006) recommended
that CH4 emission factors be applied only during the rice growing period (with notes for wet
fallow periods, see Chapter 4.4.3). In contrast, the IPCC recommends continuing N2O flux
measurements for an entire year (including dry and wet fallow periods) to derive the emission
factor with comparing N-applied with zero-N plots (IPCC, 2006). Therefore, researchers
should determine in advance the measurement period that is adequate for their specific
research objectives (Table 4.1).