The alternate wetting and drying (AWD) irrigation technique can reduce methane emissions from rice fields by 32.5 percent, while saving 21 percent of irrigation water, the Tainan District Agricultural Research and Extension Station said yesterday.
Flooding irrigation has been widely applied in Taiwan’s rice cultivation, but it can easily cause oxygen deficiency in soil and root suffocation, leading to akagare — or “suffocating disease” — that reduces both yield and quality, the station said.
By keeping farmland moist without constant flooding, AWD promotes stronger root development and lowers the risk of suffocation, it said.
Photo courtesy of the Tainan District Agricultural Research and Extension Station
Simulation results using the Denitrification-Decomposition model showed that the method can cut methane emissions by 32.5 percent and reduce water consumption by about 2,500 tonnes, or 21 percent, it added.
AWD assistant researcher Hsu Lung-hsin (許龍欣) yesterday said the AWD technique was initially introduced as a water-saving measure, but has since been found effective in reducing methane.
Microorganisms in oxygen-deprived conditions, such as flooded rice paddies, decompose organic matter and release large amounts of methane, she said, adding that AWD interrupts this process.
To apply the technique, farmers install a perforated tube with internal gradations to monitor water levels in the field, she said.
By digging into the tube with their fingers, they can check the underground water depth and determine when irrigation is needed, she added.
Although the original technique was developed by the International Rice Research Institute, which recommends irrigating when water levels fall to minus-15cm, the approach has proved unsuitable for Taiwan, as it reduces rice yields, Hsu said.
Most rice paddies in Taiwan have clayey soils that dry and crack if irrigation is delayed until minus-15cm, she said, adding that subsequent research found that irrigating at about minus-5cm is optimal for clayey soils in Taiwan.
Agricultural workers can easily make field water tubes themselves by purchasing polyvinyl chloride pipes from hardware stores, she said.
The tubes must be perforated so that the water levels inside and outside remain consistent, and farmland should be leveled in advance to ensure accurate measurements, she added.
Regarding irrigation frequency, fields with clayey soil typically require watering about once a week under the AWD system, while sandy soils might need irrigation as frequently as once a day, she said.
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