Don’t burn rice straw

Text and Photos by Henrylito D. Tacio
Not too many Filipino farmers are aware that burning rice straw, locally known as “dayami,” can contribute to the warming of the world. 
“Rice production also contributes to global warming as it emits methane,” said Dr. Constancio Asis, Jr. supervising science research specialist at the Philippine Rice Research Institute (PhilRice) in Muñoz, Nueva Ecija.
After carbon dioxide, methane is the second most important greenhouse gas, which 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.
It wasn’t until in 2001, when the United Nation’s Intergovernmental Panel on Climate Change (IPCC) submitted its report that methane was given much attention. “One of the most potent greenhouse gases on Earth,” the report said.
“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. Asis, Jr., a recipient of the 2011 Norman E. Borlaug International Agricultural Science and Technology Fellowship Award.
The Journal Science reported that atmospheric concentration of methane has more than doubled during the last 300 years and is increasing at an annual rate of about 1% each year.
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.
Growing rice is one of the main culprits in why the world has become inhospitable to living, according to a paper released during the Economics on Climate Change in Southeast Asia in Siem Reap, Cambodia two years ago.
The Philippines, being of the world’s top producers of rice, is a biggest contributor.  “From 2006 to 2010, the Philippines harvested around 16 million tons of rice each year on average,” said the policy brief paper published by the Economy and Environment Program for Southeast Asia (EEPSEA).  “Most of the country’s production (57%) came from the wet season harvest.”
“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.”
In fact, 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.”
Oftentimes, Filipino farmers burn rice straw to discard them from the rice fields.  Doing so, as stated earlier, is not good for the environment, according to the PhilRice experts.
“Burning of rice straws, generally practiced during the harvest season, causes air pollutants such as carbon dioxide, carbon monoxide, nitrogen oxide, and sulphur dioxide,” the government rice agency says. “If continually done, it will decrease soil’s nitrogen, 25% of phosphorus, 20% of potassium, and 5-60% of sulfur. The practice also damages food resources of beneficial insects in the rice field.”
In addition, burning rice straw is unhealthy.  “Rice straw burning is also known to emit particulate matters and other chemicals such as dioxins and furans that have negative impact on human health,” the paper said.
The Philippines produces 15.2 million tons of rice that leave 11.3 million tons of rice straw every year.
To minimize postharvest waste, PhilRice urges farmers to use rice straws as organic fertilizer and primary material for mushroom production.  Rice straw and other biomass from farm by-products can help farmers save expenses from chemical fertilizer inputs. 
Recycling farm wastes can also keep their environment clean and free of pollutants. “When straws are scattered in the field during land preparation, they maintain soil’s nutrients and moisture,” said Evelyn J. Javier, supervising science research specialist of PhilRice’s Agronomy, Soil, and Plant Physiology Division.
According to Javier, every 5 tons of rice straws can increase soil’s nutrients such as nitrogen, phosphorus, potassium, sulfur, silicon, and carbon. They also preserve the biodiversity of microorganisms that helps in nutrient cycling and efficient fertilizer utilization.
Rice straws can also be used as mulch to protect the roots of the plants from heat and cold and reduce the evaporation rate, the PhilRice experts say. They also prevent weeds to grow in the paddy field.
On the other hand,  Rizal G. Corales of PhilRice’s Palayamanan Plus recommended the use of rice straws as substrate for oyster mushroom (Pleurotus spp.) production.
“Bulk of the rice biomass produced is still being disposed indiscriminately despite its many known uses. Using rice straw as mushroom substrate is economically profitable for farmers and people engaged in agribusiness,” Corales said.
“The waste from mushroom production is also the main substrate for vermicomposting, one of the best organic fertilizers produced,” Corales added.
With such negative effects, farmers in the Philippines are encouraged to stop burning rice straw and adopt more environmentally-friendly rice straw management practices.
Meanwhile, a study headed by Cheryll C. Launio, also of PhilRice, found out that early incorporation of both stubble and straw into the soil is “the most cost-effective way of disposing rice straw.”  More importantly, it can help reduce GHG emissions.
The study was done in the rice growing areas of Central Luzon, Western Visayas, Cagayan Valley, and Ilocos regions, where around 30% of farmers burnt their rice straw.  The rest of farmers adopted any of the following practices: scattered it in their fields, incorporated it into the soil during land preparation, or just left it in their threshing areas for incorporation in the next cropping season.
Based from the study, it was found that incorporating stubble less than 30 days before crop establishment is responsible for the largest contribution of GHG emissions.  But incorporation rice stubble more than 30 days before crop establishment and incorporating composted rice straw into the field “yielded the lowest cumulative levels of methane and nitrous oxide.”
However, “simply shifting from the baseline approach of late stubble incorporation and straw burning to early incorporation of both stubble and straw also gave good results and led to reduction in GHG emissions of around 80%.  This was mainly due to reductions in methane emissions.”
The researchers’ conclusion: “Shifting from rice straw burning to rice straw incorporation will not necessarily reduce global warming potential if straw is incorporated less than 30 days before cultivation, especially in flooded conditions.”
In terms of monetary benefits, early incorporation of both stubble and rice straw into the soil more than 30 days before cultivation is more profitable.  “This option gave a net benefit of P21 or around $0.50 per ton of carbon dioxide equivalent reduction,” the paper said.