The volumetric water content was also measured at depths of
15 cm, 20 cm, 25 cm, and 30 cm from the soil surface for every water
table treatment using a soil water meter (TDR; Campbell Scientific
Ltd., USA). The O2 concentration in the soil was measured at depths
of 10 cm and 20 cm from the soil surface for every water table treatment
using an O2 meter (OXY-4; Pre Sens Co., Germany). The CO2
concentration in the soil was measured by inserting tubes to depths
of 10 cm and 20 cm from the soil surface and using a syringe to sample
soil gas for every water table treatment. These samples were
then analyzed using gas chromatography.