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Processes of CH4 emission in paddy soil under water-saving irrigation management

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Abstract
Owing to the dominant anaerobic conditions in irrigated rice fields, considerable methane (CH4) production in soil (with either acetate or CO2 as substrate) can result in substantial CH4 emission to the atmosphere. Management to limit such CH4 emissions during the rice growing season is possible, provided that the controlling processes are understood. In particular, it is not clear to what extent a reduction of CH4 emissions under water-saving irrigation management may be the resultant of enhanced CH4 oxidation, due to the difficulty to reliably quantify CH4 oxidation. We assessed relative contributions of CH4 production and oxidation to its emission in rice fields under water-saving Alternate Wetting and Drying irrigation (AWD) in comparison with the conventional Continuous Flooding (CF) in an Italian rice field in 2015 and 2016. Therefore, we measured soil CH4 emission using closed flux chambers in the field alongside in situ assessment of CH4 oxidation by two distinct methods. Firstly, CH4 oxidation was measured through selective inhibition of CH4 oxidisers with difluoromethane (CH2F2). Secondly, CH4 oxidation and contributions of both CH4 production pathways were estimated by means of stable C isotope measurements in aerobic and anaerobic incubations, plant aerenchym and emitted CH4. As it turns out, acetate was the main substrate for CH4 production in the end of the season (theoretical 2:1 ratio), with the contribution of this pathway being significantly lower under AWD in the beginning of the growing season. Furthermore lower CH4 emissions in fields under AWD (in average 2.9 mg CH4 h-1 m-2 versus 14.0 under CF in 2015; and 5.4 versus 9.3 under CF in 2016) result mainly from lower CH4 production, and to a lesser extent from probably higher relative CH4 oxidation in the beginning of the cropping season. Caution is required in the interpretation of CH4 oxidation results though, since both methods were biased. For the first method, we assume that CH2F2 interacted unintentionally with CH4 production, as often CH4 emissions were higher without than with addition of the CH4 oxidation inhibitor to the closed chambers’ headspace. Concerning the isotope method, several incubation samples were probably too much disturbed – as indicated by their often physically impossible results. In conclusion, water-saving irrigation management leads to lower CH4 production, and maybe – but to a lesser degree – to higher CH4 oxidation in the beginning of the season.

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Chicago
Deroo, Heleen, Masuda Akter, Elizabeth Verhoeven, Daniel Said-Pullicino, Marco Romani, Pascal Boeckx, and Steven Sleutel. 2018. “Processes of CH4 Emission in Paddy Soil Under Water-saving Irrigation Management.” In Applied Biological Sciences, 23rd National Symposium, Abstracts.
APA
Deroo, H., Akter, M., Verhoeven, E., Said-Pullicino, D., Romani, M., Boeckx, P., & Sleutel, S. (2018). Processes of CH4 emission in paddy soil under water-saving irrigation management. Applied Biological Sciences, 23rd National symposium, Abstracts. Presented at the 23rd National symposium on Applied Biological Sciences.
Vancouver
1.
Deroo H, Akter M, Verhoeven E, Said-Pullicino D, Romani M, Boeckx P, et al. Processes of CH4 emission in paddy soil under water-saving irrigation management. Applied Biological Sciences, 23rd National symposium, Abstracts. 2018.
MLA
Deroo, Heleen et al. “Processes of CH4 Emission in Paddy Soil Under Water-saving Irrigation Management.” Applied Biological Sciences, 23rd National Symposium, Abstracts. 2018. Print.
@inproceedings{8609896,
  abstract     = {Owing to the dominant anaerobic conditions in irrigated rice fields, considerable methane (CH4) production in soil (with either acetate or CO2 as substrate) can result in substantial CH4 emission to the atmosphere. Management to limit such CH4 emissions during the rice growing season is possible, provided that the controlling processes are understood. In particular, it is not clear to what extent a reduction of CH4 emissions under water-saving irrigation management may be the resultant of enhanced CH4 oxidation, due to the difficulty to reliably quantify CH4 oxidation. We assessed relative contributions of CH4 production and oxidation to its emission in rice fields under water-saving Alternate Wetting and Drying irrigation (AWD) in comparison with the conventional Continuous Flooding (CF) in an Italian rice field in 2015 and 2016. Therefore, we measured soil CH4 emission using closed flux chambers in the field alongside in situ assessment of CH4 oxidation by two distinct methods. Firstly, CH4 oxidation was measured through selective inhibition of CH4 oxidisers with difluoromethane (CH2F2). Secondly, CH4 oxidation and contributions of both CH4 production pathways were estimated by means of stable C isotope measurements in aerobic and anaerobic incubations, plant aerenchym and emitted CH4. 
As it turns out, acetate was the main substrate for CH4 production in the end of the season (theoretical 2:1 ratio), with the contribution of this pathway being significantly lower under AWD in the beginning of the growing season. Furthermore lower CH4 emissions in fields under AWD (in average 2.9 mg CH4 h-1 m-2 versus 14.0 under CF in 2015; and 5.4 versus 9.3 under CF in 2016) result mainly from lower CH4 production, and to a lesser extent from probably higher relative CH4 oxidation in the beginning of the cropping season. Caution is required in the interpretation of CH4 oxidation results though, since both methods were biased. For the first method, we assume that CH2F2 interacted unintentionally with CH4 production, as often CH4 emissions were higher without than with addition of the CH4 oxidation inhibitor to the closed chambers’ headspace. Concerning the isotope method, several incubation samples were probably too much disturbed – as indicated by their often physically impossible results. In conclusion, water-saving irrigation management leads to lower CH4 production, and maybe – but to a lesser degree – to higher CH4 oxidation in the beginning of the season.},
  author       = {Deroo, Heleen and Akter, Masuda and Verhoeven, Elizabeth and Said-Pullicino, Daniel and Romani, Marco and Boeckx, Pascal and Sleutel, Steven},
  booktitle    = {Applied Biological Sciences, 23rd National symposium, Abstracts},
  language     = {eng},
  location     = {Brussels, Belgium},
  title        = {Processes of CH4 emission in paddy soil under water-saving irrigation management},
  year         = {2018},
}