Factors influencing the carbon footprint of rice production in Northeastern Vietnam

Purpose Rice production in Northeastern Vietnam is livelihood-oriented with a small farm size in the northern mountainous and midlands region. This study aims to determine the contribution of agronomic and input factors to the total carbon (C) footprint of rice production to identify solutions that can reduce greenhouse gas (GHG) emissions in agriculture in this region. Methods We used a life cycle assessment method for the C footprint of rice production from planting to harvesting. Agronomic parameters and input data in both spring and summer crops were collected through interviews conducted with 50 rice-farming households in the Quang Minh commune, Viet Yen district, Bac Giang province, using questionnaires. Additionally, in-depth interviews were conducted to gather information on energy used for land preparation and harvesting. Results and discussion The C footprint per hectare and per tonne of grain of the summer rice crop (15.6 ± 3.3 t CO 2 -eq/ha, 2.34 ± 0.54 t CO 2 -eq/t) was significantly higher than that of the spring crop (9.5 ± 1.8 t CO 2 -eq/ha, 1.3 ± 0.26 t CO 2 -eq/t). GHG emissions were due mainly to direct methane emissions during rice growth, accounting for 89.5% of the total C footprint of the summer crop and 80.5% of that of the spring crop. Fertilizer emissions also contributed significantly, accounting for 5.4% and 10.4%, respectively, nearly 75% from N-fertilizer emissions. A higher C footprint (per grain basis) was generally associated with straw incorporation, continuous flooded irrigation, longer rice growth duration, and lower rice yield, indicating the importance of agronomic management of crop residues, water and nutrients, choice of varieties, and growing seasons. Small farm size did not lead to higher carbon intensity. Conclusions The solutions to avoid direct incorporation of rice straw, to conduct intermittent irrigation, to reduce the amount of N-fertilizer, and to use short-duration rice varieties (especially for summer crop) with high yield potential along with optimal agronomic management practices should be highlighted. Greater adoption of these measures will contribute significantly to reducing the C footprint of rice production in Northeastern Vietnam.