The Effect of Water Management On Rice Yields and Greenhouse Gas Emissions.

Because rice paddy fields could be under either an aerobic or an anaerobic condition, they are one of the major sources of methane and nitrous oxide. This study was examined the effect of water management by measuring rice yields and greenhouse gas emissions during rice cultivation under different water management conditoins. The aim of this study was to advance water management in rice paddy fields to mitigate greenhouse gas emissions (CH₄, N₂O and CO₂) and maintain rice yields. Rice plants were cultivated in 1/2000-a Wagner pots and three water management practices, continuous flooding and two kinds of intermittent irrigations. The measurements of gas emissions, volume water content and soil temperatures were made using a closed chamber method, TDR sensors and thermocouples, respectively. Gas concentrations at 14 cm below the soil surface were measured using gas permeable tubes. Results showed that CH₄ flux was negative, but CH₄ concentrations in soil were much higher than that in the atmosphere under flooding conditions. CO₂ flux was negative by reflecting photosynthesis in rice plants, and positive in fallow. CO₂ concentrations in soil were higher under flooding conditions than under drainage conditions. N₂O flux was positive due to nitrification under drainage and denitrification under flooding conditions. N₂O concentrations in soil were higher under drainage conditions than under flooding conditions. Rice yields did not differ in water management practices. This study showed that CH₄ was produced in the soil under flooding conditions, but was not emitted to the atmosphere. Further research was needed to investigate CH₄ dynamics in soil.