Abstract
Rice production is a significant source of greenhouse gas (GHG) emissions in the national budget of many Asian countries, but the extent of emissions varies strongly across agro-environmental zones. It is important to understand these differences in order to improve the national GHG inventory and effectively target mitigation options. This study presents a meta-analysis of CH4 database emission factors (EFs) from 36 field sites across the rice growing areas of Vietnam and covering 73 cropping seasons. The EFs were developed from field measurements using the closed chamber technique. The analysis for calculating baseline EFs in North, Central and South Vietnam in line with the Intergovernmental Panel on Climate Change (IPCC) Tier 2 methodology was specified for the three cropping seasons being early-(E), mid-(M) and late-year (L) seasons. Calculated average CH4 EFs are given in kg ha−1 d−1 and reflect the distinct seasons in North (E: 2.21; L: 3.89), Central (E: 2.84; M+L: 3.13) and South Vietnam (E: 1.72; M: 2.80; L: 3.58). Derived from the available data of the edapho-hydrological zones of the Mekong River Delta, season-based EFs are more useful than zone-based EFs. In totality, these average EFs indicate an enormous variability of GHG emissions in Vietnamese rice production and represent much higher values than the IPCC default. Seasonal EFs from Vietnam exceeded IPCC defaults given for Southeast Asia corresponding to 160% (E), 240% (M) and 290% (L) of the medium value, respectively.
Highlights
In Vietnam, rice is produced on 7.7 million ha with a total production of 43 million tons in 2017 [1], making Vietnam the world’s 6th largest rice producer and the 3rd largest rice exporting country
Even though our database does not cover all agro-ecological zones (AEZ), we feel that the distinction into three regions can be seen as a reasonable resolution for greenhouse gases (GHG) estimates at a national scale
The database reflects an enormous variability in emission factors (EFs) for the country as a whole as well as within individual AEZs; Inter-comparisons among AEZs revealed distinct seasonal patterns, but – by and large – all EFs of CH4 are in a similar order of magnitude (1.83–3.6 kg ha−1 d−1 ) with only smaller differences among individual AEZs; The different edapho-hydrological zones within the Mekong River Delta (MRD) showed a lower impact on determining
Summary
In Vietnam, rice is produced on 7.7 million ha with a total production of 43 million tons in 2017 [1], making Vietnam the world’s 6th largest rice producer and the 3rd largest rice exporting country (afterIndia and Thailand). In Vietnam, rice is produced on 7.7 million ha with a total production of 43 million tons in 2017 [1], making Vietnam the world’s 6th largest rice producer and the 3rd largest rice exporting country Vietnam’s rice exports account for 6.61 million tons per year Of the global rice trade) [2] and represent a major source of revenue for the population and the national economy. Lowland rice production has been known to be a source of greenhouse gases (GHG) due to emissions of methane (CH4 ) and, to a lesser extent, nitrous oxide (N2 O). CH4 emissions from rice accounts for less than 1.5% of all GHG emissions globally [3], but these percentages could be fairly high at the national scale for rice-growing countries [4]. The official figures on total emissions per country can be obtained from the most recent national communications (NC) submitted to the United Nations
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