Impacts of alternate wetting and drying floodwater management on rice water use and methane emissions in a humid climate

Authors: Anapalli, Saseendran; PINNAMANENI, SRINIVASA - Oak Ridge Institute For Science And Education (ORISE)

Submitted to: American Geophysical Union
Publication Type: Abstract Only
Publication Acceptance Date: 8/12/2023
Publication Date: N/A
Citation: N/A

Interpretive Summary: Reducing the amount of water pumped out of the Mississippi Valley Alluvial Aquifer to support flooded rice production is critical for sustainable irrigated agriculture in the Mississippi Delta region. Equally critical is reducing methane, a potent greenhouse gas with about thirtyfold global warming potential than carbon dioxide, emissions from flooded rice fields. We investigated possible reductions in irrigation water use and methane emissions from practicing intermittent flooding (also known as alternate wetting and drying) method of floodwater management over conventional continuous flooded rice cultivation system in farmer’s fields in the Mississippi Delta. State-of-the-science instruments and methods were used for monitoring methane and water vapor emitted from rice cropping systems. The study revealed that water pumped out of the aquifers for floodwater management could be reduced by about 24% and methane emissions by about 54% without compromising grain production by practicing the intermittent flooding systems over continuous flooding systems in rice cultivation in the Delta region. The investigation carried out in large-scale farm fields gives better confidence in recommending the intermittent flooding practice to farmers for adaptation in rice production systems for saving water and reducing greenhouse gas emissions.

Technical Abstract: Reducing methane emissions and water use in agriculture is critical for combating the impacts of global warming and declining aquifers on food production. Reductions in irrigation water use and methane emissions are known benefits of practicing alternate wetting and drying (AWD) over continuous flooding (CF) water management in lowland rice (Oryza Sativa L.) production systems. In a two-year (2020 and 2021) study, methane emissions from large farm-scale (above 50 ha) rice fields managed under CF and AWD in soils dominated by clay were monitored. An open-path laser gas analyzer was used to monitor methane densities in the air over the rice-crop canopies. Canopy microclimate was also monitored for filling gaps in the flux data caused by rains and sensor errors. Total water pumped into the field for floodwater management was higher in CF compared to AWD by 32 and 16 %, respectively, in 2020 and 2021. Considerable variations between seasons in the amount of methane emitted from the CF and AWD treatments were observed: CF emitted 29 and 75 kg ha-1 methane, respectively, in 2020 and 2021, and AWD emitted 14 and 34 kg ha-1. Notwithstanding, the extent of reduction in methane emissions due to AWD over CF was dramatically close across the two crop seasons (52% in 2020 and 55% in 2021). Rice grain yield harvested differed between AWD and CF by only ± 2%. This investigation in large-scale farm fields further confirmed that by practicing AWD floodwater management in rice, water pumped from aquifers and methane emissions from rice fields could be cut down by about half.