Home Agriculture Farming systems that can offset methane emissions from rice fields

Farming systems that can offset methane emissions from rice fields

by Admin-Phmp

Text and Photos by Henrylito D. Tacio

If the world is serious about avoiding the worst effects of climate change, we need to cut methane emissions from the fossil fuel industry,” said United Nations Environment Program (UNEP) chief Inger Andersen at the launching of the International Methane Emissions Observatory during the United Nations Climate Conference (COP26) held in Glasgow, United Kingdom.

As the fossil fuel industry is responsible for one-third of anthropogenic emissions, it is the sector with the highest potential for reductions, Andersen said, adding that a 30-country-strong effort to slash these emissions by 30% must be accomplished by 2030.

Methane is a greenhouse gas. When released directly into the atmosphere, it is more than 80 times as potent as carbon dioxide over a 20-year period, UNEP explains. However, the atmospheric lifespan of methane is a relatively short 10 to 12 years; thus, emissions-cutting actions can reduce the rate of the world’s warming.

But it’s not only in the fuel industry that methane emissions must be cut extensively; it also needs to cut those emitted methane coming from producing food for the masses.

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 environments such as rice paddies.

“An estimated 19 percent of the 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.”

Now, Filipino farmers can help minimize methane emissions by adopting sustainable – yet profitable – farming systems. This is particularly true among farmers who grow rice on their farms. Rice is the leading source of sustenance for all Filipinos.

“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.”

Estimates of global methane emission rates from rice fields range from 20 to 100 Tg per year (1 Tg is equal to 1 million tons), according to Dr. Heinz-Ulrich Neue in a paper published in BioScience.

Rice-duck system

Rice farmers can help offset the release of methane from irrigated rice fields by raising ducks. The integrated farming of rice and ducks in irrigated fields has long been practiced in China, Japan, and Korea.

Under the system, ducklings/ducks are released to rice fields to graze and feed. The paddling movement of the ducklings/ducks stimulates the rice plants to produce massive tillers, which, in effect, raises annual yield by as much as 10-15 percent. The constant stirring action of the ducklings/ducks on the paddy bottom also suppressed methane emission.

There are several other benefits. Besides their paddling, ducks also eat the insects and unwanted weeds in the rice field, thus eliminating the need for pesticides and herbicides. The elimination of these synthetic inputs improved the farm over time.

Ducks plowing the rice field

The system is also profitable. A 2013 study conducted at the Northern Cagayan Experiment Station of the Department of Agriculture in Cagayan Valley showed that the total cost of production for the rice-duck system (79,507) was 29% higher than that for rice only (P56,614) because of the addition of the ducks. However, the net income from the rice-duck system (P280,492) was 5.2 times more than that from rice alone (P53,886).

Alternate wetting and drying

Filipino rice farmers can also help reduce methane emissions released into the atmosphere by adopting controlled irrigation or alternate wetting and drying (AWD) technology, which the Laguna-based International Rice Research Institute (IRRI) has developed.

AWD is a technology that allows rice fields to dry for a certain period before applying irrigation water. “This technology can actually save farmers almost one-third of irrigation water without sacrificing yield,” IRRI explains. “It also saves farm inputs like oil, fuel, and labor being utilized on the operation of water pumps.”

Rice 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.

In AWD technology, rice fields are alternately flooded and dried. The number of days of non-flooded soil can vary from one day to more than ten 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 technique can be started a few days after transplanting (or with a 10-centimeters tall crop in direct seeding). When many weeds are present, AWD can be postponed for 2-3 weeks until the ponded water has suppressed weeds.

Local fertilizer recommendations as for flooded rice can be used, the rice research institute says. Nitrogen fertilizer may be 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 says. “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 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.”

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

There are three products that come from growing rice: grain, husk, and straw. Among these three products, straw and husks are considered wastes. In most places, these wastes have no commercial value and are disposed of in various ways. “Around 60% of Asia’s rice straw is just burnt in the field,” says Dr. Craig Jamieson, who once worked with the IRRI and the World Agroforestry Center.

Rice stubbles incorporation

In the Philippines, a total of 10,680 gigatons (Gg) of rice straw are produced per year. “Much of this is burnt in open fields or incorporated in the soil in wet conditions during ploughing,” says a brief policy paper published by the Economy and Environment Program for Southeast Asia (EEPSEA).

In addition, burning rice straw is unhealthy – not only to the environment but also to people. “Rice straw burning is also known to emit particulate matter and other chemicals such as dioxins and furans that have negative impact on human health,” the paper said.

A study headed by Cheryll C. Launio of the Philippine Rice Research Institute (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 greenhouse gas emissions.

Also involved with the study were Dr. Constancio Asis Jr., Rowena G. Manalili, and Evelyn F. Javier. The result of the study was published by the EEPSEA under the report, “Economic Analysis of Rice Straw Management Alternatives and Understanding Farmers’ Choices.”

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 the 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 on the five-year study (from 2006 to 2010), it was found that incorporating stubble less than 30 days before crop establishment is responsible for the largest contribution of GHG emissions. But incorporating 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 the 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.

The study also found that incorporating rice stubble more than one month before cultivation and rapidly composting rice straw and applying it back to the field was also a cost-effective option.

“Because this option significantly mitigates greenhouse gas emissions while improving the soil condition, it is cost-effective despite the additional labor cost of piling and composting the rice straw,” the researchers said.

This is good news, indeed. As Dr. Drew Shindell, a climatologist at NASA’s Goddard Institute for Space Studies in Columbia University in New York told reporters: “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.”

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