Effects of Straw Incorporation Time on Rice Yield and Methane Emissions from Sandy Loam Paddy Fields

Rice paddy fields are a significant source of anthropogenic methane emitted into the atmosphere with several studies reporting heightened emissions after rice straw incorporation into the paddy soils. These emissions may differ owing to the time of straw incorporation into the field, i.e. either during the fallow or growing seasons. In the current study, we evaluated the emissions from straw incorporated during both the rice growing and fallow seasons over a three-year period. Additionally, effects on soil chemical properties and rice yields were assessed. The treatments involved incorporating straw a few days before the main rice growing season (spring straw), incorporation of straw during the fallow season, i.e. immediately after the autumn harvest (autumn straw) and the control with no straw incorporated at all. The weekly emissions from both spring and autumn straw applications decreased with the progression of the experiment, i.e. the emissions went on reducing season after season until the end of the experiment. The emissions from the control remained mostly constant throughout the experiment. Of the two straw application times, autumn application resulted in the lowest methane emissions. The effects of all the treatments on soil chemical properties were mostly adverse while the total rice yields slightly increased over time in the straw amended soils. The adverse effects on soil chemical properties might have been caused by the incomplete decomposition of rice straw given that a single rice growing season may not be enough for its complete dissolution.