Seasonal GHG emissions from rice production in the Mekong Delta depend on water management and varietal selection
Thi Bach Thuong Vo1, Reiner Wassmann2, Bjoern Ole Sander3, Folkard Asch1
1University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Germany
In Vietnam rice is produced on 7.7 million ha making Vietnam the world’s 6th largest rice producer. The Mekong River Delta (MRD) comprises lowland rice with providing 55 % of all Vietnamese rice production. Lowland rice production is a source of greenhouse gases (GHG) due to emissions of methane (CH4) and – to a lesser extent nitrous oxide (N2O). Since rice production accounts for 15 % of the national GHG emissions, Vietnam aims at reducing GHG emissions from rice production by changing farming practices. The impact of selecting different rice varieties, however, is still poorly understood. A 2-year field experiment has been conducted in the Mekong Delta, Vietnam, in the early-year seasons of 2020 and 2021 using the closed chamber method to 1) quantify the baseline emissions of 20 selected rice varieties under typical growing conditions; 2) assess interactive impacts of varieties and two different water management practices: Continuous Flooding (CF) and Alternate Wetting and Drying (AWD); and 3) to compare these field emissions against the GHG estimates in the National Communications (IPCC Tier 2 approach). The results confirm pronounced differences between CF and AWD in terms of CH4 emission whereas N2O emission are generally low (< 3 % of GWP). Across all varieties, the reduction potential of AWD was above the IPCC default (45 %), ranging from 59 % and 62 % in seasons 1 and 2, respectively. Thus, in dry seasons that allow control of water tables in the fields, water management determines the magnitude of GHG; under flooded conditions i.e. in the rainy seasons, however, variety selection modulates these emissions within a range of ±16 %, and can thus be regarded either as an additional measure to maximise the AWD effect during the dry season or as a mitigation option in locations or seasons where AWD is not possible.
Keywords: Alternate-wetting-and-drying, IPCC Tier 2, methane
Contact Address: Thi Bach Thuong Vo, University of Hohenheim, Inst. of Agric. Sci. in the Tropics (Hans-Ruthenberg-Institute), Garbenstr. 13, 70599 Stuttgart, Germany, e-mail: thibachthuong.vouni-hohenheim.de