Controlling water in rice fields cuts methane emissions

Filipino farmers, particularly those growing rice, can help reduce methane emissions into the atmosphere by adopting controlled irrigation or alternate wetting and drying (AWD) technology.

Developed by the Laguna-based International Rice Research Institute (IRRI), the world’s premier research organization dedicated to reducing poverty and hunger through rice science, AWD is a technology that allowed rice fields to dry for a certain period before applying irrigation water.

Also called controlled irrigation or intermittent irrigation, AWD technology can actually save farmers almost one-third of irrigation water without sacrificing yields. It also saves farm inputs like oil, fuel, and labor being utilized on the operation of water pumps.

Rice fields using this technology are alternately flooded and dried. The number of days of non-flooded soil can vary from one day to more than 10 days, according to IRRI. It uses an “observation well” that is made of bamboo, plastic pipes, or any hollow indigenous material. Perforations are made in the lower half of the tube.

The AWD technology can be started a few days after transplanting (or with a 10-centimeter tall crop in direct seeding). When many weeds are present, AWD can be postponed for two to three weeks until weeds have been suppressed by the ponded water. Local fertilizer recommendations as for flooded rice can be used. Nitrogen fertilizer maybe applied preferably on the dry soil just before irrigation.

“A practical way to implement AWD technology is by monitoring the depth of the water table in the field using a simple perforated field water tube,” IRRI explains. “When the water level is 15 centimeters below the surface of the soil, it is time to flood the soil to a depth of around five centimeters at the time of flowering, from one week before to one week after the maximum flowering.”

The water in the rice field is kept at five centimeters depth to avoid any water stress that would result in severe loss in rice grain yield. The threshold of water level at 15 centimeters is called “safe AWD,” as this will not cause any yield decline because the roots of the rice plants are still be able to take up water from the saturated soil and move it to root zone.

“The field water tube used in this technology will help to measure the water level in the field so that incipient water stress in the rice plants can be anticipated,” the rice research institute points out.

As such, the AWD technology does not only save water but can greatly reduce emissions of methane.

Studies conducted at the IRRI have shown that AWD technology reduces methane emissions by about 30% or even up to 70%, depending on water usage and management of rice stubble.

Rice, the staple food of Filipinos, consumes a lot of water to grow. It takes about 3,000 liters of water to produce one kilogram of rice, previous IRRI studies found out.

With the impending water crisis, it is not good for Filipino rice farmers.  Too much groundwater has been consumed for rice production instead of using it for drinking purposes.

“On a macro-level, it appears there is plenty of water, but we are now actually experiencing problems and, in some areas are even suffering from lack of water,” Elisea Gozon sounded the alarm when she was the secretary of the Department of Environment and Natural Resources.

In addition, rice production also contributes to global warming as it emits methane. H. Steven Dashefsky, author of “Environmental Literacy,” listed rice fields as the second top source of methane in the atmosphere, contributing 19.4%.  Wetlands top the list as they contribute 20.2%.

Rounding the top five were cud-chewing animals, particularly cattle (14%), biomass fires, such as burning forests (9.7%), and oil and natural gas pipeline leaks (7.9%).

After carbon dioxide, methane is the second most important greenhouse gas that is responsible for trapping the heat from the sun at it radiates back into space. Methane is created naturally as a waste product of anaerobic bacteria (living with little or no oxygen). These bacteria produce methane gas in waterlogged soil and wetland, but also in human-produced environment such as rice paddies.

Scientists explain that long-term flooding of the fields cuts the soil off from atmospheric oxygen and causes anaerobic fermentation of organic matter in the soil. During the wet season, rice cannot hold the carbon in anaerobic conditions. The microbes in the soil convert the carbon into methane which is then released through the respiration of the rice plant or through diffusion of water.

The United Nation’s Intergovernmental Panel on Climate Change (IPCC) described methane as “one of the most potent greenhouse gases on Earth,”

“Methane absorbs heat 21 times more than carbon dioxide and it has 9-15 year life time in the atmosphere over a 100-year period,” explained Dr. Constancio Asis, Jr., a recipient of the 2011 Norman E. Borlaug International Agricultural Science and Technology Fellowship Award.

Although atmospheric methane levels declined during 1983-99, they remained relatively constant during 1999-2006, according to a new report released by the Washington, D.C.-based Worldwatch Institute. “And they have been increasing since 2007,” it said.

Rice fields, as stated earlier, are one of the major contributors of methane in the atmosphere.  Rice crops emit methane starting from the transplanting to harvesting stage, peaking at two weeks after transplanting up to the tillering stage, Dr. Asis said.

The AWD technology is one of the farming systems that can help minimize methane emissions.  More importantly, it lessens the use of water.

“AWD technology can reduce the number of irrigations significantly compared to farmer’s practice, thereby lowering irrigation water consumption by 25%, reducing diesel fuel consumption for pumping water by 30 liters per hectare, and producing 500 kilograms more rice grain yield per hectare,” IRRI said in a statement.

However, the AWD technology has its shares of disadvantages. For one, rice productivity is reduced using AWD technology if moisture stress condition is induced. But studies have shown that the reduction of yield was less compared to the yield reduction due to the direct moisture stress effect.

Another disadvantage: emissions of nitrous oxide, also a greenhouse gas, are increased. –

But there are other ways of minimizing the release of methane into the atmosphere.  To do so, farmers release ducks after rice harvesting.  “Rice-duck culture can effectively decrease and control methane and nitrous oxide emissions, and it is an effective strategy to reduce greenhouse gas from rice paddy fields,” the UN Food and Agriculture said.

Some farmers in Zamboanga del Sur has been doing this.  “Under the system, ducklings are released to rice fields to graze and feed.  The paddling movement of the ducks in the rice fields increases the rice tillers, in effect raising annual yield by as much as 10% to 15%. Besides their paddling, ducks also eat the insects and unwanted weeds in the rice field,” Nonoy E. Lacson wrote in a report.

According to the Department of Agriculture, the integrated rice-duck farming system is one of the best strategies in increasing rice productivity as it reduces labor and inputs characterized by its devoid use of artificial fertilizers and chemicals.  Thus, shift from conventional way of planting using inorganic materials to this technology provides additional source of income and food to farmers.

The said technology is environmentally sound as it restores the relationship of people with nature.  This is a sustainable system as it helps in eliminating the contamination of soil, water and air brought by chemical substances which are harmful to both nature and human.

“The integrated rice-duck technology reduces the use of chemicals,” the agriculture department points out.  “Since ducks are grown alongside rice paddies, they eat harmful pests at the same time their dung fertilizes the soil.  Their paddling movement cultivates the soil and destroys the weeds. Its benefits to the farmers are immediately felt and tangible.”

Dr. Drew Shindell, a climatologist at NASA’s Goddard Institute for Space Studies, Columbia University in New York, once said: “If we control methane, which is viable, then we are likely to soften global warming more than one would have thought, so that’s a very positive outcome.”