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Greenhouse gas emissions from a continuously and intermittently flooded Bangladeshi paddy field in relation to redox potential, soil moisture and soil solution chemistry depth profiles

Author
Organization
Project
GA.0101.14N GreenRice - JPI FACCE
Abstract
Introduction: The emission of green house gases (CH4, CO2 and N2O) from rice paddy fields is influenced greatly by several factors like soil redox potential (Eh), availability of labile organic carbon and oxidants for soil organic matter (SOM) degradation.The alternate aerobic and anaerobic cycling of rice fields declines CH4 emission and enhances N2O emission, often in contrast to continuously flooded fields. In irrigated rice soils, soil moisture level, Eh and levels of dissolved organic carbon (DOC) and reduced species like NO3-, Mn2+, Fe2+ etc. differs strongly between depth increments soil layers. But relation of these dynamic depth profiles with bulk soil CH4 and N2O emissions have not been resolved. Objectives: The evidence of an integrated beneficial effect of water saving irrigation management on GHG emission is still lacking for young floodplain paddy soils in Bangladesh. Our objective is to understand how depth distributed Eh, moisture, DOC, Fe and Mn content drive CH4, N2O and CO2 emissions. We set up a paddy field experiment at the Bangladesh Agricultural University in the 2015 Boro season. We hypothesize that green house gas emission from paddy soils are mostly governed by soil moisture profiles and Eh profiles, rather than bulk soil levels of DOC or NO3-. Materials and methods: The cultivated rice variety (BRRI dhan28) was grown for 14 weeks under three water management practices (continuous flooding (CF), Alternate wetting and drying (AWD) and dry seeding (DS)). To explore our main hypothesis, we compared global warming potential (GWP) based on cumulative emissions of CH4, CO2 and N2O at several sampling events (closed chamber/GC).The soil Eh at four different depths was measured continuously by a HYPNOS III data logger an Eh-probes system. Soil moisture tension was monitored regularly via Electronic Tensiometers with hypodermic needle (SMS 25000 S). DOC, Fe and Mn in soil solution, collected from three depths with rhizon solution samplers, were measured at regular interval. Results: The Eh(mV) decreased sharply in both AWD and CF plots within 1st week and stabilized near -600mV in both CF and AWD treatments over all soil depths. Eh peaked for several days close to 0mV at drainage events in AWD mostly at 5cm and several times also at 12.5 and 20.5cm depth. After 70DAT, reductive conditions (-300 to -400mv) in AWD and CF and even in DS (so as to 84DAS) due to continuous flooding resulted in CH4 fluxes (10-30 mg m-2 h-1) in case of the AWD and CF treatments. Between 14-70DAT CH4 emission rate of 0-20 mg m-2 h-1 was irregular in the AWD plots and progressive under CF. During the drainage and re-flooding events both CH4 emission and Eh at different depths fluctuates abruptly in AWD treatments. Mean CH4 fluxes in DS plots are lower than AWD and CF plots throughout the season. Analysis of N2O, CO2, DOC, Fe and Mn and volumetric soil moisture levels are on-going and will be presented in detail at the workshop. Conclusion: Most strikingly, both rate and magnitude of the drop of Eh in the Mymensingh floodplain soil was unusually large. Even under AWD, strong reducing conditions are seen at times even at 5cm depth and continuously at 30cm depth. We therefore also anticipate fast preferential reduction of NO3-, Mn4+ and Fe3+, preceding methanogenesis under both CF and AWD. The young age of non-calcareous Bangladeshi floodplain soils developed from Ganges and Brahmaputra alluvial sediments with low pedogenic Fe content may explain these observations. Our partial results already indicate that GWP-benefits of water reducing management may be less than anticipated in these floodplain soils, when compared to studies in other areas. The analysis of remaining soil chemical parameters will provide a more process-oriented insight in the biogeochemistry of non-continuously flooded paddy soil systems.

Citation

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Chicago
Akter, Masuda, Mohammed Abdul Kader, Sofie Pierreux, Pascal Boeckx, Ahammad Mostafa Kamal, and Steven Sleutel. 2015. “Greenhouse Gas Emissions from a Continuously and Intermittently Flooded Bangladeshi Paddy Field in Relation to Redox Potential, Soil Moisture and Soil Solution Chemistry Depth Profiles.” In Soil Organic Matter, 5th International Symposium, Abstracts, 93–93.
APA
Akter, M., Kader, M. A., Pierreux, S., Boeckx, P., Kamal, A. M., & Sleutel, S. (2015). Greenhouse gas emissions from a continuously and intermittently flooded Bangladeshi paddy field in relation to redox potential, soil moisture and soil solution chemistry depth profiles. Soil Organic Matter, 5th International symposium, Abstracts (pp. 93–93). Presented at the 5th International symposium on Soil Organic Matter.
Vancouver
1.
Akter M, Kader MA, Pierreux S, Boeckx P, Kamal AM, Sleutel S. Greenhouse gas emissions from a continuously and intermittently flooded Bangladeshi paddy field in relation to redox potential, soil moisture and soil solution chemistry depth profiles. Soil Organic Matter, 5th International symposium, Abstracts. 2015. p. 93–93.
MLA
Akter, Masuda, Mohammed Abdul Kader, Sofie Pierreux, et al. “Greenhouse Gas Emissions from a Continuously and Intermittently Flooded Bangladeshi Paddy Field in Relation to Redox Potential, Soil Moisture and Soil Solution Chemistry Depth Profiles.” Soil Organic Matter, 5th International Symposium, Abstracts. 2015. 93–93. Print.
@inproceedings{7205723,
  abstract     = {Introduction: The emission of green house gases (CH4, CO2 and N2O) from rice paddy fields is influenced greatly by several factors like soil redox potential (Eh), availability of labile organic carbon and oxidants for soil organic matter (SOM) degradation.The alternate aerobic and anaerobic cycling of rice fields declines CH4 emission and enhances N2O emission, often in contrast to continuously flooded fields. In irrigated rice soils, soil moisture level, Eh and levels of dissolved organic carbon (DOC) and reduced species like NO3-, Mn2+, Fe2+ etc. differs strongly between depth increments soil layers. But relation of these dynamic depth profiles with bulk soil CH4 and N2O emissions have not been resolved.  
Objectives: The evidence of an integrated beneficial effect of water saving irrigation management on GHG emission is still lacking for young floodplain paddy soils in Bangladesh. Our objective is to understand how depth distributed Eh, moisture, DOC, Fe and Mn content drive CH4, N2O and CO2 emissions. We set up a paddy field experiment at the Bangladesh Agricultural University in the 2015 Boro season. We hypothesize that green house gas emission from paddy soils are mostly governed by soil moisture profiles and Eh profiles, rather than bulk soil levels of DOC or NO3-. 
Materials and methods: The cultivated rice variety (BRRI dhan28) was grown for 14 weeks under three water management practices (continuous flooding (CF), Alternate wetting and drying (AWD) and dry seeding (DS)). To explore our main hypothesis, we compared global warming potential (GWP) based on cumulative emissions of CH4, CO2 and N2O at several sampling events (closed chamber/GC).The soil Eh at four different depths was measured continuously by a HYPNOS III data logger an Eh-probes system. Soil moisture tension was monitored regularly via Electronic Tensiometers with hypodermic needle (SMS 25000 S). DOC, Fe and Mn in soil solution, collected from three depths with rhizon solution samplers, were measured at regular interval. 
Results: The Eh(mV) decreased sharply in both AWD and CF plots within 1st week and stabilized near -600mV in both CF and AWD treatments over all soil depths. Eh peaked for several days close to 0mV at drainage events in AWD mostly at 5cm and several times also at 12.5 and 20.5cm depth. After 70DAT, reductive conditions (-300 to -400mv) in AWD and CF and even in DS (so as to 84DAS) due to continuous flooding resulted in CH4 fluxes (10-30 mg m-2 h-1) in case of the AWD and CF treatments. Between 14-70DAT CH4 emission rate of 0-20 mg m-2 h-1 was irregular in the AWD plots and progressive under CF. During the drainage and re-flooding events both CH4 emission and Eh at different depths fluctuates abruptly in AWD treatments. Mean CH4 fluxes in DS plots are lower than AWD and CF plots throughout the season. Analysis of N2O, CO2, DOC, Fe and Mn and volumetric soil moisture levels are on-going and will be presented in detail at the workshop. 
Conclusion: Most strikingly, both rate and magnitude of the drop of Eh in the Mymensingh floodplain soil was unusually large. Even under AWD, strong reducing conditions are seen at times even at 5cm depth and continuously at 30cm depth. We therefore also anticipate fast preferential reduction of NO3-, Mn4+ and Fe3+, preceding methanogenesis under both CF and AWD. The young age of non-calcareous Bangladeshi floodplain soils developed from Ganges and Brahmaputra alluvial sediments with low pedogenic Fe content may explain these observations. Our partial results already indicate that GWP-benefits of water reducing management may be less than anticipated in these floodplain soils, when compared to studies in other areas. The analysis of remaining soil chemical parameters will provide a more process-oriented insight in the biogeochemistry of non-continuously flooded paddy soil systems.},
  author       = {Akter, Masuda and Kader, Mohammed Abdul and Pierreux, Sofie and Boeckx, Pascal and Kamal, Ahammad Mostafa and Sleutel, Steven},
  booktitle    = {Soil Organic Matter, 5th International symposium, Abstracts},
  language     = {eng},
  location     = {G{\"o}ttingen, Germany},
  pages        = {93--93},
  title        = {Greenhouse gas emissions from a continuously and intermittently flooded Bangladeshi paddy field in relation to redox potential, soil moisture and soil solution chemistry depth profiles},
  year         = {2015},
}