AGRITRENDS: The grass that feeds Filipinos

(Last of Five Parts)

“Ten thousand years have passed since the current pleasantly temperate period began, so another sudden shift is overdue. The notion that greenhouse gases could trigger such a rapid change keeps serious scientists up at night… And since scientists today have little understanding of past climate flips, it’s impossible to say when the next one will start.” — Gregg Easterbrook in A Skeptical Guide to Doomsday


Rice production in the Philippines and those in other parts of the world will greatly be affected by climate, experts claim.

“Increasing carbon dioxide leads to increased photosynthesis and potentially, more rice biomass. But concurrent increases in global temperatures could also potentially limit rice harvests by increasing spikelet sterility,” explained Dr. Lewis H. Ziska of the Crop Systems and Global Change Laboratory at the United States Department of Agriculture. “More carbon dioxide could also increase the biomass of known weeds when compared with that of rice, which could limit rice growth in the future.”

“Higher temperature, especially in tropical areas that are already near or above the optimum temperature for rice, will reduce growth and yields,” noted Dr. Keith Ingram, former global climate change coordinator at the International Rice Research Institute (IRRI).

Rising temperatures during the past 25 years have already cut the yield growth rate by 10–20% in several locations, according to a study published in the Proceedings of the National Academy of Sciences (PNAS), a peer-reviewed, scientific journal from the United States.

As nights get hotter, as predicted with climate change, rice yields will drop. “We found that as the daily minimum temperature increases, or as nights get hotter, rice yields drop,” said Jarrod Welch, lead author of the report and graduate student of economics at the University of California, San Diego.

The report analyzed 6 years of data from 227 irrigated rice farms in 6 major rice-growing countries in Asia, which produces more than 90% of the world’s rice. “Our study is unique because it uses data collected in farmers’ fields, under real-world conditions,” said Welch. “This is an important addition to what we already know from controlled experiments.”

The problem is just the tip of an iceberg. Recent studies have shown that should farmers grow more rice, it means more methane will be emitted into the atmosphere. “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.

“Rice is a plant that grows best in wet soil, with its roots flooded,” says 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 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 (PCARRD). “Every year, these practices release 5,883 tons of methane to the atmosphere.”

In Isabela State University, a study funded by PCARRD showed that by using simple science-based strategies, farmers can contribute significantly to the reduction of methane emissions. For instance, mid-season drainage of irrigation water reduced methane emission by 48 percent. This emission is valued at P34.16 million, based on the 2009 World Bank price of US$12 per ton of carbon dioxide and exchange rate of P48 per US$1.

Meanwhile, composting of rice straw resulted in 64 percent less methane emission released in the air. By combining mid-season drainage and application ofrice straw compost, methane emission is further reduced by 81 percent.

“By shifting to climate-change friendly farming practices, as what was done in the 7,789.34 hectares of lowland irrigated rice in Isabela, farmers can get incremental benefits amounting to as high as P138.95 million per year,” the PCARRD report points out.

Rice farmers can also 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.

On an 8-season field experiment conducted at IRRI, it was found that AWD “has real potential to reduce the global warming impact of paddy fields to one-third of the conventional continuously-flooded field water management.”

In a paper presented during the international workshop on “Water Management and Technology for Crop Production under Climate Change” in Suwon, Korea, the authors claimed AWD “can reduce methane emissions by over 40%.”

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 2-3 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 5 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 5 centimeters depth to avoid any water stress that would result in severe loss in rice grain yield. The threshold of water level at 15centimeters 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 IRRI points out. As such, the AWD technology does not only save water but can greatly reduce emissions of methane.

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.”