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Summary of Paper Submitted to Journal of Soil Science and Plant Nutrition

This paper examines the impacts of alternate wetting and drying (AWD) on greenhouse gas (GHG) emissions from paddy fields in Central Vietnam. The study aims to establish baseline GHG emissions, investigate the feasibility of AWD in terms of GHG emissions, rice productivity, and water use. Results show that AWD reduces CH4 emissions and is effective in mitigating GHG emissions from paddy fields. The study provides valuable insights for sustainable rice cultivation in Vietnam.

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Summary of Paper Submitted to Journal of Soil Science and Plant Nutrition

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  1. Summary of Paper Submitted to Journal of Soil Science and Plant Nutrition Japan, 2017

  2. Impacts of alternate wetting and drying on greenhouse gas emission from paddy field in Central Vietnam Dang Hoa Tran, Trong Nghia Hoang, Takeshi Tokida, Agnes Tirol-Padre, Kazunori Minamikawa

  3. Progress • Submitted to the Journal: 16 May 2017 • Reviewed: 2 August 2017 • Reviewer response: on going; 15 September 2017

  4. Introduction • Global warming: big issue for the human • Major attributor: C02, CH4, N20 emissions from land use including agriculture • Rice cultivation: a major CH4 source https://www.google.com.vn/search?biw=1364&bih=681&tbm=isch&q=global+warming+causes&sa=X&ved=0ahUKEwj38YbT94TWAhVHxLwKHYUeDSQQhyYIKA#imgrc=xRZxRWtkwOEe1M:

  5. CF is a traditional rice cultivation, enhance CH4 emission • AWD: reduced water input, kept grain yield, reduced CH4 emission

  6. Vietnam • The world’s fifth largest rice producer • Rice cultivation is the largest GHG source in agriculture. CH4 emission from paddy fields was estimated to be 50.5% of the agricultural GHG emission • AWD adoption: contribute to the reduction of GHG emission • Some researches on GHG emission from paddy fields in the Northern and Southern areas were reported • Limited data for Central region

  7. Objectives • To establish the baseline GHG emission from a paddy field in Central Vietnam • To investigate the feasibility of AWD in term of GHG emission, rice productivity and water use.

  8. Material and method

  9. Site and experiment description 16˚28’16’’N; 107˚31’26’’E - Huong An commune, Huong Tra district, ThuaThien Hue Province, Central Vietnam during six consecutive cropping seasons from 2013 to 2016

  10. Experimental layout Soil: classified as Fluvisol (Table 1) Area: 30 m2(5 m x 6 m) Bank: 30 cm Harvest area: 5 m2

  11. Table 1.Soil properties of the experimental site

  12. Treatments • CF: Conventional flooding, floodwater depth 3 - 5 cm • AWD: Safe AWD (Irrigate when water level is at 15 cm below soil surface) • AWDS: Site specific AWD (flexible, AWD that is more adapted to specific site)

  13. Table 2. Rice cropping calendar in the winter-spring (WS) and summer-autumn (SA) seasons DAS, days after sowing. In parentheses for chemical fertilizer, the application rates of urea (kg N ha-1), super phosphate (kg P2O5 ha-1), and potassium chloride (kg K2O ha-1).

  14. Measurements Closed chamber • Base • - Diameter: 50 cm, • - Height: 30 cm • Top chamber has Volume: 120 litters; height: 70cm • Thermometer, fan

  15. Measurements • Gas sampling: • - Weekly in mid-morning (8:00-10:00 AM). • 1, 2, 3, 4, and 5 days after nitrogen (N) fertilizer application. • The gas samples were collected using a 60-mL syringe fitted with a stopcock at 0, 6, 12, 20, and 30 min after chamber closure and used a 19-mL evacuated glass vials

  16. Analysis gas sampling • Gas chromatograph (8610C, SRI Instruments, CA, USA) equipped with a flame ionization detector (FID) for the analysis of CH4 and an electron capture detector (ECD) for the analysis of N2O. • The columns for the analysis of CH4 and N2O were packed with Porapak Q (50-80 mesh) and the carrier gas was nitrogen (N2) • N2O and GWP were recorded for WS3 and SA3. Only 2 years (4 seasons) data

  17. Statistical analysis • ANOVA using a split-plot design, where cropping season (CS) was treated as the whole-plot factor and treatment (water management: CF, AWD, AWDS) as the split-plot factor, with three replications. • Using the Box-Cox transformation was conducted for CH4, N2O, GWP and yield-scaled GWP using the "powerTransform" function in the "car" package of R. • To test differences among water managements, Tukey's HSD test was performed with a significance level of 0.05.

  18. RESULTS

  19. Fig 1. CH4 and N2O emission in Winter – Spring season

  20. Fig 2. CH4 and N2O emission in Summer – Autumn season

  21. Table 3. Seasonal CH4 and N2O emissions, GWP, rice grain yield, yield-scaled GWP, total water use, and water productivity as affected by cropping season and water management

  22. Discussion • The magnitude of CH4 emission observed in our study was relatively high (351-644 kg CH4 ha-1) The magnitude of GHG emission in this site • The application of organic fertilizer may have enhanced the CH4 emission irrespective of treatment • The CH4 emission was variability between WS and SA in Vietnam, although not statistically significant due to difference in air temperature and short fallow period between WS and SA • The N2O emission played a negligible role in terms of the GWP of CH4 and N2O because of the relatively large CH4 emission in this site.

  23. Effects of cropping season and water management on GHG emission • The effect of cropping season on the CH4 emission was mainly attributed to the change in rice stubble management between the first two seasons and the later four seasons • AWD is effective in reducing the CH4 emission. • CH4 fluxes did not sharply decline to be negligible level after drainage events. • Water management showed no significant effect on N2O emission

  24. Feasibility and limitations of AWD in Central Vietnam • AWD did not reduce rice grain yield (rather tended to increase), and water saving was achieved as expected • The GWP of CH4 and N2O was reduced by 26-29% under AWD and AWDS compared to that under CF. AWD is a powerful tool in reducing CH4 emission. • The response of CH4 flux to it was not distinct throughout the six cropping seasons differed between AWD and AWDS. • The development of mitigation options for the GHG emission in fallow seasons will contribute to the reduction in anthropogenic GHG emission in Vietnam.

  25. Conclusion • CH4 emission ranged from 500 kg CH4 ha-1 in WS to 644 kg CH4 ha-1 in SA. Rice paddy in Central Vietnam can contribute to the national GHG budget. • GWP of CH4 and N2O of AWD reduced 26-29% compared to CF • A possibility of AWD’s performance on increasing rice productivity. Thus, it will be key to spread AWD to local farmer

  26. Acknowledge • We would like thank: • The Ministry of Agriculture Forestry and Fisheries (MAFF) of Japan through MIRSA 2 project • Prof. Kazuyuki Inubushi (Chiba University, Japan), Dr. Reiner Wassmann, Dr. Bjorn Ole Sander (IRRI, Philippines), and Dr. Kazuyuki Yagi (NIAES, Japan) for their valuable comments

  27. Thanks for your attention

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