Journal
SCIENCE OF THE TOTAL ENVIRONMENT
Volume 842, Issue -, Pages -Publisher
ELSEVIER
DOI: 10.1016/j.scitotenv.2022.156958
Keywords
Irrigation; Rice paddies; Greenhouse gas; Mekong Delta; Alternate wetting and drying; Triple rice cropping
Categories
Funding
- International Research Network Program on Global Issues of the Agriculture, Forestry and Fisheries Research Council, Ministry of Agriculture, Forestry and Fisheries of Japan
- JSPS KAKENHI [JP15H05267]
- JSPS [15J00001, 16J02509, 201960100]
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By altering the water regime of the cropping period, it is possible to reduce greenhouse gas emissions and increase rice yield in triple rice cropping systems. The potential of emission reduction may have been underestimated in previous studies.
For sustainable food production in the Mekong Delta, greenhouse gas (GHG) emissions from rice cropping activities need to be reduced without sacrificing rice productivity. Each year, a substantial amount of straw is incorporated into paddy soils through triple rice cropping, which is characterized by a short cropping period and nearly year-round flooding, such that a large amount of methane is emitted. Exposing these soils to oxidative conditions by altering the cropping-period water regime might have the potential to reduce GHG emissions with increased rice yield. To test this potential, a split-plot experiment was conducted in a typical triple-cropped alluvial farmer's paddy in a central delta area over five years and 15 consecutive cropping seasons. The emissions observed from the continuously inundated paddies were 1.1-2.7 times greater than the reported emission factors for Vietnamese continuously inundated paddies. A significantly higher emission peak was detected at the beginning of the rice cropping and flooding fallow periods in continuously flooded (CF) paddies than in alternate wetting and drying (AWD) paddies, although the differences in field water level and soil moisture among the paddies were negligible. AWD reduced annual methane emissions (-51 %) and increased rice yield (+9 %), presumably through enhanced translocation of carbohydrates from leaves to panicles. The amount of GHGs emitted from straw use also decreased (11 %) under AWD management because the straw production rate was significantly lowered (9 %) by enhanced nutrient translocation. These results indicate that GHG emission reduction potentials in the Mekong Delta have been underestimated by previous studies, corroborate the necessity of additional long-term observations of triple rice cropping systems and demonstrate the need for a robust methodology for monitoring the permanence of AWD effects after policies promoting its widespread dissemination take effect.
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