Using rice straw as organic fertilizer

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Sunday, June 29, 2014


A STUDY headed by Cheryll C. Launio of the Philippine Rice Research Institute (PhilRice) found out that early incorporation of both rice stubble and straw into the soil is "the most cost-effective way of disposing rice straw."

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 in disposing rice straw: 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 rice stubble less than 30 days before crop establishment is responsible for the largest contribution of greenhouse gas (GHG) emissions. But incorporating rice stubbles more than 30 days before crop establishment and incorporating composted rice straws into the field "yielded the lowest cumulative levels of methane and nitrous oxide."

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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 study said.

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 per ton of carbon dioxide equivalent reduction," the study said.

"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."

Studies have shown that one ton of rice grain produces one ton of rice straw.

In the Philippines, a total of 10,680 gigatons of rice straw are produced per year. "Much of this is burnt in open fields or incorporated in the soil in wet condition during ploughing," which causes the emission of methane and other greenhouse gases.

PhilRice's Engr. Rosanna Espiritu of Integrated Systems and Standards Office said that burning rice straws is hazardous to people's health. When rice straws are burned, air pollutants like suspended particulate matter, carbon monoxide, hydrocarbons, nitrogen oxide, and sulfur dioxide are generated.

Also released are the airborne silica fibers or small particles of straw ash, dioxins and furans, which have been found to have negative impact on human health.

What most farmers don't know is that rice straw can help cut fertilizer costs. According to PhilRice, 5 tons of rice straw is equivalent to 1-2 bags of urea, 2-3 bags of muriate of potash and half bag of solophos.
In Biliran, Bohol, the Bureau of Agricultural Research conducted a study on using rice straw as fertilizer among farmer cooperators. They were taught to use the would-be waste rice straw materials as compost via modified rapid composting method, instead of burning them to the ground and purchasing inorganic fertilizer for their crop.

Rapid composting is made with the use of compost fungus activator like Trichoderma sp. Soon after the implementation of the project, progress in rice production among farmers who followed the technology became apparent.

Expenses of farmer cooperators on fertilizer were reduced to more than half (from P,700 to P4,700) as portions of commercial fertilizers were replaced with rice straw organic fertilizer.

But farmers should not solely rely on organic fertilizer from rice straw if they want to achieve high yields. "Organic fertilizer alone is not sufficient to feed the rice crop, but it enhances soil fertility and productivity through years of usage," reminds PhilRice soil expert Evelyn Javier.

Published in the Sun.Star Davao newspaper on June 30, 2014.

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