The simultaneous determination of methane, carbon dioxide and nitrous oxide fluxes was calculated by using static black chamber method. We used closed box-gas chromatography (Zhang et al., 2015 (link)). Before transplanting rice to the plot, a PVC flux loop was permanently embedded in each plot to continuously monitor GHG emissions during the experiment period. A 5cm deep groove on the edge of each base was used to inject water and seal the gas chamber during gas production, in order to prevent gas exchange. The cross-sectional area of the gas tank was 0.25m2 (50cm* 50cm) and the height was 50cm. Once the rice grew taller, the height was increased to 1m.
Sponge and aluminum foil were wrapped around the exterior of the gas box to prevent drastic changes in temperature inside the chamber. The gas chamber was also equipped with a small fan to ensure that the gas in the box was fully mixed. Sampling was conducted 9:00 a.m. and 11:00 a.m. every time, using a 60ml medical syringe to collect gas from the top of the chamber, once every 5 minutes, for a total of four times (Hao et al., 2001 (link)).
Before gas chromatography analysis, the gas was transferred to a vacuum airbag for less than a day to ensure that the gas was not mixed with the outside environment. A gas chromatograph was equipped with an electron capture detector (ECD) and a flame ionization detector (Agilent 7890A network gas chromatograph, Gow Mac instruments, Bethlehem, PA, USA). It was used for the simultaneous analysis of methane, carbon dioxide, and nitrous oxide gas concentrations (Liu S. et al., 2016 (link)). The linear regression slope for the greenhouse gas concentration of the continuous samples was calculated, and the data with the linear regression value r2<0.9 was removed from the dataset for gas flux calculation (Liu et al., 2013 (link)). The gas flux calculation formula is as follows:
Where F is the gas emission flux (mg m-2 h-1), H is the height of the sampling chamber, ρ is the gas density in the standard state, and dC/dt is the slope of the concentration growth of the gas concentration fitted by a linear equation (mg m-3 h-1). T is the temperature in the sampling chamber at the time of sampling(°C). During the test, cumulative methane, carbon dioxide, and nitrous oxide emissions were sequentially accumulated from the flux of each two adjacent intervals. For N2O cumulative emission, the final value was multiplied by atomic mass of N2 divided by atomic mass of N2O (Liu et al., 2013 (link); Liu S. et al., 2016 (link); Iqbal et al., 2021 (link)). The gas flux calculation formula and the total cumulative GHG emission during one growing season was also calculated according to protocol given in (Iqbal et al., 2021 (link)).
Sponge and aluminum foil were wrapped around the exterior of the gas box to prevent drastic changes in temperature inside the chamber. The gas chamber was also equipped with a small fan to ensure that the gas in the box was fully mixed. Sampling was conducted 9:00 a.m. and 11:00 a.m. every time, using a 60ml medical syringe to collect gas from the top of the chamber, once every 5 minutes, for a total of four times (Hao et al., 2001 (link)).
Before gas chromatography analysis, the gas was transferred to a vacuum airbag for less than a day to ensure that the gas was not mixed with the outside environment. A gas chromatograph was equipped with an electron capture detector (ECD) and a flame ionization detector (Agilent 7890A network gas chromatograph, Gow Mac instruments, Bethlehem, PA, USA). It was used for the simultaneous analysis of methane, carbon dioxide, and nitrous oxide gas concentrations (Liu S. et al., 2016 (link)). The linear regression slope for the greenhouse gas concentration of the continuous samples was calculated, and the data with the linear regression value r2<0.9 was removed from the dataset for gas flux calculation (Liu et al., 2013 (link)). The gas flux calculation formula is as follows:
Where F is the gas emission flux (mg m-2 h-1), H is the height of the sampling chamber, ρ is the gas density in the standard state, and dC/dt is the slope of the concentration growth of the gas concentration fitted by a linear equation (mg m-3 h-1). T is the temperature in the sampling chamber at the time of sampling(°C). During the test, cumulative methane, carbon dioxide, and nitrous oxide emissions were sequentially accumulated from the flux of each two adjacent intervals. For N2O cumulative emission, the final value was multiplied by atomic mass of N2 divided by atomic mass of N2O (Liu et al., 2013 (link); Liu S. et al., 2016 (link); Iqbal et al., 2021 (link)). The gas flux calculation formula and the total cumulative GHG emission during one growing season was also calculated according to protocol given in (Iqbal et al., 2021 (link)).
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