Agriculture is one of the major sources of methane and nitrous oxide gases, produced in the course of livestock raising, rice cultivation and soil management. Around 83.5 percent of methane emission in Nepal is from agriculture, including rice production. Our rice fields are flooded with irrigation water, up to four to six centimeters deep. But irrigated rice cultivation is considered among the highest sources of atmospheric methane worldwide. Since rice is staple food, we cannot minimize its production to cut down on greenhouse gas emissions. But proper understanding of microbial processes and turnover of carbon and nitrogen in soil could help us reduce greenhouse gases.
Rice is cultivated in all districts of Nepal, except Manang and Mustang. Plantation normally begins from the second week of June in the hills and last week of the same month in Tarai plains and concludes by the first week of September. In Nepal, rice is cultivated in 1.5 million hectares of arable land, with average productivity of 3 ton/ha. Rice contributes around 50 percent of total cereal crop production in Nepal.
Decomposition of organic material in flooded rice fields produces methane, which escapes to the atmosphere primarily by diffusive transport through rice plants during the growing season. But rice roots could absorb methane in the gas phase. Moreover, periodic drainage of irrigated rice paddies can result in significant decrease in methane emissions. There are reports of a single midseason drainage reducing seasonal emission by up to 50 percent. In addition, multiple short periods of drainage (two to three days) approximately every three weeks during growing season can significantly reduce methane emissions without decreasing rice yield.
USAID's Low Emissions Asian Development (LEAD) program focuses on emission factor identification as a key area of technical assistance. The LEAD provides training and technical assistance on the development of reliable country specific GHG emission factors. In this context, this author along with two other colleagues had an opportunity to participate in a regional workshop held in Pati of Indonesia from February 1 to 4, 2016 on improvement and development of emission factors for methane from rice cultivation.
Participants were taken on a visit to Indonesian Agricultural Environment Research Institute, located at 27 kilometers south-east of Pati city. This institute carries research into agricultural land. The institute has developed good facilities for researches on sustainable agriculture including methane gas emission. We witnessed various activities in the laboratory as well as on the field. The collection and utilization of rain water for various purposes, remedies to pollution control and environment-friendly agricultural cultivation impressed us.
The institute has adopted the innovative practice of bio-fencing and planting mango trees along the ridge of rice field. According to the director of the farm, bio-fencing helps control pests.
Rice farming in Nepal is mostly monsoon-based. Flooding is neither possible due to limited water available, nor is it feasible in hilly terrains. In some places rice is even grown without any irrigation. Methane emission from such rice fields is low. However, monsoon rain is high on some years, leading to more water of Tarai soils, where rice is mainly grown. This means higher emissions. Therefore, Nepal, like Indonesia, needs to now develop its own country specific emission factor (CSEF).
Currently, Nepal uses Intergovernmental Panel on Climate Change (IPCC) data to estimate methane emission from rice fields. IPCC encourages countries to submit CSEF developed under local conditions. IPCC's Emission Factor Database (EFDB) recommends three approaches for developing CSEF: (a) experimentation and measurement, (b) mining of scientific publications, journal, and internet ressources and (c) organizing regular meetings of scientific researchers.
For this the Nepal Agricultural Research Center (NARC) needs to start a field experiment like the one being undertaken by its Indonesian counterpart immediately.
Bhairabr@gmail.com
The author was formerly with the Nepal Agricultural Research Center