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231. Reducing Greenhouse Gas Emissions from Rice Fields

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Rice is a staple food that is eaten everyday. Actually, greenhouse gases (GHG), which cause global warming, are emitted to make rice. The amount varies depending on how rice is cultivated (amount of fertilizer, whether rice straw is added to the rice field etc.), but more than half is methane (one of the GHG) generated from the rice fields. When the rice fields are flooded (filling the rice fields with water) and the oxygen level is low, the microorganisms in the soil produce large amounts of methane.

The concentration of methane in the earth’s atmosphere increased by 150% between 1750 before industrialization and 2011, and about 11% of methane derived from anthropogenic activities is generated from paddy fields (annual methane generation rate is 33-40 × 1012 g methane, 1012 = Tg, Ciais et al., 2013). About 90% of the world's rice is produced in Asia (FAOSTAT, 2018), and 90% of the methane produced in the world's paddy fields comes from this region (Smith et al., 2014). 

One way to reduce methane is to use Alternate Wetting and Drying (AWD) method. AWD is an irrigation method in which rice paddies are intermittently irrigated and water is not added until the soil is dry. When it dries, oxygen is distributed to the soil and the action of microorganisms that produce methane is suppressed. Many cases have been reported by JIRCAS and others that AWD can reduce the amount of methane that comes out compared to conventional water management called constant flooding, in which water is kept in the rice fields throughout the cultivation period. In addition, it has been reported that AWD has benefits to farmers in terms of increased yields.

In this way, JIRCAS is working on the development and demonstration of various cultivation techniques such as AWD to reduce GHG emissions from agriculture. We are investigating whether these cultivation techniques can increase farmers' profits (total profits minus costs) and their impact on the environment. This time, we would like to introduce the survey of paddy farms in Vietnam.

Vietnam is the fifth largest rice producer in the world. The main production area is located in the Mekong Delta region in the south. This region has a warm and rainy climate so that rice can be grown 2-3 times a year. However, because the region is low and flat, the sea level rises due to climate change, and there are concerns about the impact of salt water running up the Mekong River, floods, and water shortages on agriculture. AWD has also been introduced in the Mekong Delta region and is becoming more widespread.

For the farmer survey in the Mekong Delta, we prepared a questionnaire in English and the interview of farmers is conducted by the staff of Can Tho University. In the rural areas, it is possible to go by car and drive to the main road. In narrow roads where cars cannot enter, the local people has to carry the investigators one by one to the farmers’ house using motorcycles. In Vietnam, motorcycles are the main means of transportation, and it is common to see a large number of motorcycles occupying the road. Everyone wears colorful helmets and masks. It is a very different scene from Japan and motorcycles move all at once when the traffic signal changes. It is also very common to see a motorbike carrying a whole family with the father, mother and small children, or a motorbike carrying loads of goods and merchandise.

The farm surveys are still in progress, and these surveys are designed not just to find out if cultivation methods that reduce GHGs are also increasing farmers' profits. The current state of farmer's cultivation management will be shared to researchers who are developing the technology, and we are aiming to develop a system that efficiently connects farmers and researchers so that we can develop and propose better cultivation techniques based on the current situation.



Ciais, P. et al., 2013: Carbon and Other Biogeochemical Cycles. In: Cli¬mate Change 2013: The Physical Science Basis. Contribution of Working Group I to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Stocker, T.F., D. Qin, G.-K. Plattner, M. Tignor, S.K. Allen, J. Boschung, A. Nauels, Y. Xia, V. Bex and P.M. Midgley (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

FAO (2018). “FAOSTAT statistical database”, http://www.fao.org/faostat/en/#home. 

Smith P. et al., 2014: Agriculture, Forestry and Other Land Use (AFOLU). In: Climate Change 2014: Mitigation of Climate Change. Contribution of Working Group III to the Fifth Assessment Report of the Intergovernmental Panel on Climate Change [Edenhofer, O., R. Pichs-Madruga, Y. Sokona, E. Farahani, S. Kadner, K. Seyboth, A. Adler, I. Baum, S. Brunner, P. Eickemeier, B. Kriemann, J. Savolainen, S. Schlomer, C. von Stechow, T. Zwickel and J.C. Minx (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.

Contributor: LEON Ai (Social Sciences Division)