ENVIRONMENT: CONTROLLING METHANE EMISSIONS IN AGRICULTURAL PRODUCTION

“If we did not have rice, our deepest comfort food, we would probably feel less Filipino,” the late food columnist Doreen Fernandez once said.

Studies have shown that for every peso Filipinos spent on food, 20 centavos go to rice.  Statistics showed that from 1980s to 1990s, a Filipino consumed an average of 92 kilograms. The consumption went up to 111 kilograms from 2008 to 2009. From 2009 to 2010, it even increased to 119 kilograms.

Today, Filipinos consume about 31,450 metric tons of rice per day, according to Secretary Emmanuel F. Piñol of the Department of Agriculture.

The Philippines is one of the world’s top producers of rice.  Unknowingly, rice fields are one of the major contributors of methane in the atmosphere.  “An estimated 19 percent of world’s methane production comes from rice paddies,” admits Dr. Alan Teramura, a botany professor at the University of Maryland.  “As populations increase in rice-growing areas, more rice – and more methane – are produced.”

“Rice is a plant that grows best in wet soil, with its roots flooded,” explains L. Hartwell Allen, an American soil scientist at the Crops Genetics and Environmental Research Unit in Gainesville, Florida.  “But flooded rice crops emit substantial amounts of methane to the atmosphere.”

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.

On the other hand, decomposition of organic material in flooded rice fields also produces methane, which then escapes to the atmosphere during the growing season.  “Traditionally, farmers flood their rice fields continuously and incorporate 4-5 tons of rice straw per hectare at land preparation,” says a report released by the Philippine Council for Agriculture, Aquatic, and Natural Resources Research and Development (PCAARRD). “Every year, these practices release 5,883 tons of methane to the atmosphere.”

Second most important

After carbon dioxide, methane is the second most important greenhouse gas.  Like carbon dioxide, the levels of methane released into the atmosphere has also reached new highs in 2011: at 1,813 parts per billion.  This is 259 percent of the pre-industrial level, according to the UN World Meteorological Organization, blaming mainly human activities.

About 12 percent of global warming is attributed to increases of methane in the world’s atmosphere.  The journal Science reported that atmospheric concentration of methane has more than doubled during the last 300 years and is increasing at annual rate of about one percent each year.

“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,” says Dr. Constancio Asis Jr., a recipient of the 2011 Norman E. Borlaug International Agricultural Science and Technology Fellowship Award.

But there’s good news. Filipino rice farmers 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), AWD is a technology which 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.

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.

Silicate fertilizer

On the other hand, Dr. Asis headed a study, conducted by the Philippine Rice Research Institute (PhilRice) and funded by Global Research Alliance Program on Agricultural Greenhouse Gases, which showed that calcium silicate can potentially reduce methane emission from rice.

The study titled, “Effect of silicate fertilizer application on methane emission from rice,” showed that applying calcium silicate slag significantly reduced methane emission by 17-22 percent owing to the release of active iron oxide, a source of electron acceptor.

Dr. Asis compared the effect of applying different sources of silicon (Si) including carbonized rice hull (CRH), carbonized sugarcane trash, and calcium silicate on methane emission from rice. Studies have shown that Si can substantially increase tolerance of rice to environmental stresses and aid its growth.

“While calcium silicate has reduced methane emission, CRH, despite having high amount of carbon, neither contributed to the concentration of methane in the atmosphere nor significantly decreased emission,” PhilRice said in a statement.

Methane-belching animals

Livestock are another major contributor of methane.  The digestive system of ruminant animals such as cattle and goats contain anaerobic bacteria and thus produce methane gas.  A single cow belches out 100 gallons of methane gas a day.

In 2006, the amount of methane emitted by farm animals alone exceeded that of the iron, steel, and cement industries combined. “Livestock are one of the most significant contributors to today’s most serious environmental problems,” said Henning Steinfeld, a senior UN official.

President of the National Academy of Sciences Ralph Cicerone said that the contribution of methane by livestock flatulence and eructation to global warming is a “serious topic.” Cicerone, an atmospheric scientist, said: “The population of beef cattle and dairy cattle has grown so much that methane from cows now is big. This is not a trivial issue.”

A recent study showed that emissions of methane from livestock are larger than previously thought.  An Agence France Presse report said: “Revised calculations of methane produced per head of cattle show that global livestock emissions in 2011 were 11% higher than estimates based on data from Intergovernmental Panel on Climate Change.”

Prof. Dave Reay, from the University of Edinburgh, was quoted as saying: “As our diets become more meat- and dairy-rich, so the hidden climate cost of our food tends to mount up.” He added: “Cows belching less methane may not be as eye-catching as wind turbines and solar panels, but they are just as vital for addressing climate change.”

Dr. Nicholas Stern, author of the 2006 Stern Review on Climate Change, also suggested: ““People will need to turn vegetarian if the world is to conquer climate change.”

End of the world

Although non-toxic, colorless and odorless gas, methane is highly combustible.  At room temperature, methane is a gas less dense than air.  It melts at –183°C and boils at –164°C.  It is not very soluble in water. Methane is combustible, and mixtures of about 5%-15% in air are explosive.

Some scientists claim that a holocaust is likely to happen should methane violently reactive with oxidizers, halogens and some halogen-containing compounds.  Earth’s atmosphere is made up of 21% free oxygen, and some 2% of halogen and halogen compounds.

One environmentalist post this alarming information in his blog: “If global warming continues unchecked, and the regions of the earth where there is a 5-15% concentrations of methane gas in the atmosphere reaches the temperature of 53 degrees Celsius, which is the flash point of methane gas, it could result in a spontaneous ignition of atmospheric gases and wreak unimaginable destruction to our planet.”