1. Full name: Ngo Duc Minh                                                       2. Sex: Male

3. Date of birth: 22 October 4, 2018                                           4. Place of birth: Vinh Phuc

5. Admission decision number: Decision No. 3485/QĐ-KHTN-CTSV dated on 14/9/2012 by Rector of the VNU University of Sciences - Vietnam National University, Hanoi.

6. Changes in academic process: Decision No. 2346/QĐ-SDH dated on 28/05/2013 by Rector of the VNU University of Sciences - Vietnam National University, Hanoi on changing supervisors

7. Official thesis title: Modeling greenhouse gas emission (CH4, N2O) from rice-based system in Vu Gia-Thu Bon river basin, Quang Nam province.

8. Major: Soil and Water Environment     9. Code: 62440303

10. Supervisors:

Main supervisor: Assoc. Prof. Dr. Nguyen Manh Khai    

Co-supervisor: Assoc. Prof. Dr. Mai Van Trinh   

11. Summary of the new findings of the thesis

*The major results/new findings from thesis study:

- Dynamics of Eh, pH, soil temperature under field experiments: Soil Eh rapidly decreases to below -100 mV during the 0-20 DAS. In continuos flooding regime, Eh reaches the lowest in the period 30-50 NSS, the panicle and tillering (from -171 mV to -233 mV in winter-spring season and from -158 to -239 mV in summer-autumn season), hen increased slightly until the end of the season. In alternate wetting-dry regime, Eh also decreased rapidly during the period of 20-30 DAS to -145 mV to -190 mV, but increased sharply to 109 mV and 116 mV after drainage. 32-47 DAS in WS and 28-41 DAS in SA crop season, and decreased rapidly when irrigated rice was re-flooded during panicle formation and flowering. The soil pH of paddy field was less volatile and fluctuated in near neutral (6.0-6.2). Daily soil temperature in the SA is higher than in the WS crop season from 3.5-5oC.

- Application of ADW reduced CH4 emissions from 15-45% but increase N2O emissions from 12-32%) as compared with CF regime. The emission rate and seasonal cumulative emissions of CH4 and N2O in SA season were 9-35% higher than in WS season. The highest CH4 emission rate occured at the maximum tillering stage (45-60 DAS). The N2O emission rate varied at period of 25-85 DAS, reaching to the highest level at the mid-season drainage (MD).

- The overall correlation between observed and simulated daily CH4 fluxes was acceptable for both field experiment and both water irrigation regime (R2 ranged from 0.80-0.91, the RMSE coefficient ranged from 0.16-0, 23 and the EF of the model was greater than 0.70). The statistical analysis for comparison of the simulated and observed CH4 and N2O fluxes demonstrated the “goodness of fit” of model prediction.

- The model sensitive test found that temperature, soil texture, SOC content, irrigation regime, organic fertilizer (farm yard manure) are the major factors affecting to CH4 emission rate; and SOC, irrigation regime, nitrogen fertilizer rate, organic fertilizers are the major contributors to N2O emissions.

- Correlation between Eh, soil pH with CH4 emission rate: The CH4 emission rate was negatively and strongly correlated with Eh soil (R index ranged from -0.66 to -0.79, with p <0.05). The correlation between soil pH and CH4 emission rate is negative but weak with R ranging from -0.16 to -0.30. Correlation between Eh and soil pH with N2O emission rate: N2O emission rate and Eh emission of rice paddy is positively correlated with weak correlation (0.30 to 0.52). Eh in both irrigation modes is not within the optimal Eh range for N2O emissions, so the correlation between N2O and Eh emissions is not as clear as for CH4 emissions.

- In the field experiment, there is no difference of rice yield under both the two irrigation systems (ranging from 579-611 g /m2 in WS season and from 502-515 g/m2 in SA season. The application of AWD did not reduce rice yield as comparison with traditional irrigation. The cumulative CH4-SP under AWD treatments were 17-37% lower than CF treatment. The cumulative CH4-SP at the MB1 treatments were 7-16% lower than MB2 treatments. Actual yields of SA were 13-20% lower than in WS season, but the CH4-DT of SA season was 7-26% higher than WS season so the CH4-SP was 21-30 % higher as compared to WS. The cumulative N2O-SP under CF was 21-36% lower than AWD regime but the cumulative N2O-SP was not significantly different between the two fertilizer amount levels. As N2O-DT emissions of SA season were 11-35% higher than WS season, the N2O-SP of SA season were 24-44% higher than WS season.

- At the regional scale/mode: the CH4 emission of the rice-rice system with were estimated at 451 kgCH4/ha/year under CF and reduced by 17-42% when applying the mid-season drainage (MD or RN) regime. In contrast, N2O emission increased by 8% -32% (by number of drainage) at MD. Fluvisols emitted more N2O than Acrisols, while Acrisols emitted more CH4 than Fluvisols.

- As applying MD at least one time during rice season, the total CH4 emission of the entire catchment were decreased by 4,300 tons/year (107,530 tons of CO2e/year), while total N2O emission increased by 22.8 tons/year (6,735 tons CO2e/year). The highest total emission of CH4 and N2O was found in the main rice regions of Quang Nam, including Dien Ban, Duy Xuyen, Thang Binh, Dai Loc, Phu Ninh districts.

- Application of 1MD increased by 12% of total N2O emission/year but with small amount (228 tons of N2O/year or 6735 tons of CO2e/year), the GWP of the entire basin was still decreased by nearly 100,000 tons of CO2e, equivalent to 1.5 tons of CO2e/ha of rice land per year.

- Emission factor of CH4 using in GHG inventory under the IPCC Tier 2 was proposed by 1.8 kg CH4/ha/day (midland) and 3.3 kg CH4/ha/day (plain/delta lowland) for countinuos flooding; The scaling factors for different irrigation regimes (SFw): 0.66 (midland) and 0.58 (delta lowland) for 1 MD; 0.56 (midland) and 0.47 (delta) for > 1 MD.

In general, this study represents the first attempt to combines three components in a case study in Central region of Vietnam: (i) field data on GHG emissions under different farming management practices (water management, fertilizer application…) conducted in study site; (ii) Technical Coefficients and GHGs simulation results using the models that have been calibrated and validated for these field conditions and (iii) farmer surveys on acceptability of different farming management practices. Furthermore, the study initially predict dynamic of CH4 and N2O fluxes from paddy soil in 2 different landscapes of Vu Gia-Thu Bon river basin (delta lowland and hilly midland) under different season, soil properties and farming practices. In addition, through compilation of GIS database with GHG emission inventories into map at regional scale, the hot-spot of GHGs fluxes from rice field at different scenarioswas identified and accessed. Lastly, the study proposed CH4 emission factor and scaling factor of different irrigation regimes for the study area and a roadmap of adoption of feasible/appropriate water-saving practice for farmer that not only can potentially mitigate GHGs fluxes but also still obtain rice yield in the case study and regional context.  This is a considerable contribution to the national database on GHG emissions from agriculture sector.

12. Paratical applicability, if any:

This is one of the first studies in Vietnam to employ a detailed process based model integrating existing databases of the farming-practices with quantitative soil characteristics important in influencing the production and emission of CH4 and N2O. This approach allows evaluating the effects of various rice management strategies on mitigation of CH4 and N2O emissions not only at the field site but also at regional levels, of which we have considered water management, fertilizer application during the season.

Furthermore, the use of DNDC simulation models and spatial databases to upscale measurements made in field experiments to higher levels of river basin is an evolving science, and we hope that this study can be used as a baseline for next studies, in which some of the current limitations are addressed, so that increasingly better predictions can be made. The insights gained from this study will be made available and transferable to other similar regions. The research results can be additionally applied within land management plans with emphasis on mitigation strategies in Central Vietnam.

13. Further research directions, if any

- Study on the relation/correlation between dynamics of inorganic ions (Fe and Mn) in paddy soil environment for CH4 formation and emission at the field condition of study site.

- Study on the integrated effect of rice farming practices (land preparation, straw management, fertilizer application, water regime/management…) to GHG emission (emission rate and total emission) at different agro-ecological areas in Vu Gia-Thu Bon river basin.

- Complete the low-emission rice farming practice/technique in Vu Gia-Thu Bon river basin.

14. Thesis-related publications:

[1]. Ngo Duc Minh, Mai Van Trinh, Reiner Wassmann, Tran Dang Hoa, Nguyen Manh Khai (2014), “Farmer’s Perception and Farming Practices in Rice Production under Changing Climate: Case Study in Quang Nam Province”, VNU Journal of Science: Earth and Environmental Sciences (2014), 30 (4), 25-40.

[2]. Ngo Duc Minh, Mai Van Trinh,  Reiner Wassmann, Bjorn Ole Sander, Tran Dang Hoa, Nguyen Le Trang, Nguyen Manh Khai (2015), “Simulation of Methane Emission from Rice Paddy Fields in Vu Gia-Thu Bon River Basin of Vietnam with the DNDC Model: Field Validation and Sensitivity Analysis”, VNU Journal of Science: Earth and Environmental Sciences (2015), 31 (1), 36-48.

[3]. Ngo Duc Minh, Mai Van Trinh,  Reiner Wassmann, Nguyen Manh Khai, Bjorn Ole Sander, Tran Dang Hoa (2015), “Application of the ORYZA2000 model for rice-yield change assessment and yield gap analysis in the Vu Gia-Thu Bon river basin, Vietnam”, VNU Journal of Science: Natural Sciences and Technology (2015), 31 (1S),  56-70.

[4]. Ngo Duc Minh, Mai Van Trinh, Tran Dang Hoa, Hoang Trong Nghia, Nguyen Manh Khai, Nguyen Le Trang, Bjorn Ole Sander, Reiner Wassmann (2016), “Modelling Nitơ-ôxít (N2O) emission from rice field in impacts of farming practices: A case study in Duy Xuyen district, Quang Nam province (Central Vietnam)”, Journal of Vietnamese Environment (J. Viet. Env) – Special Issue (2016). 8 (4), pp.223-228. DOI: 10.13141/jve.vol8.no4.pp223-228. Published online by Technische Universität Dresden. ISSN 2193-6471. https://oa.slub-dresden.de/ejournals/jve.

[5]. Ho Quang Duc, Nguyen Quang Hai, Tran Minh Tien, Ngo Duc Minh (2011), “Overview of nitrogen circulation and mitigation of nitrogen emissions from rice production in Vietnam”, Proceedings of International Seminar on Increased Agricultural Nitrogen Circulation in Asia: Technological Challenge to Mitigate Agricultural Nitrogen Emissions, GIS Convention Center of National Taiwan University September 27-28 (2011) - Taipei, Taiwan. pp115-120.

[6]. Leocadio Sebastian, Ngo Duc  Minh (2016), “Doing it Right - Up-scaling Alternate Wetting and Drying (AWD) Technology in Vietnam”, In “Reaching more farmers – innovative approaches to scaling up climate smart agriculture” - CCAFS Working Paper 135 (2016), Copenhagen, Denmark: CGIAR Research Program on Climate Change, Agriculture and Food Security (CCAFS), edited by Westermann O, Thornton P, Förch W..

[7]. Agnes Tirol-Padre, Ngo Duc Minh, Tran Dang Hoa, Hoang Trong Nghia, Le Van An, Reiner Wassmann, Bjoern Ole Sander (2016), “Carbon Footprint Analysis of Rice Production in Quang Nam Province (Central Vietnam): Greenhouse Gas Emissions in Different Landscapes and Impacts of Alternate Wetting and Drying”, In Land Use and Climate Change Interactions in Central Vietnam - Springer Book Series on Water Resources Development and Management (2016), edited by  Alexandra Nauditt, Lars Ribbe.  ISBN 978-981-10-2623-2.