Japan Geoscience Union Meeting 2015

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International Session (Oral)

Symbol A (Atmospheric and Hydrospheric Sciences) » A-GE Geological & Soil Environment

[A-GE04] Subsurface Mass Transport and Environmental Assessment

Sun. May 24, 2015 11:00 AM - 12:45 PM 301A (3F)

Convener:*Yasushi Mori(Graduate School of Environmental and Life Science, Okayama University), Hirotaka Saito(Department of Ecoregion Science, Tokyo University of Agriculture and Technology), Ken Kawamoto(Graduate School of Science and Engineering, Saitama University), Shoichiro Hamamoto(Department of Biological and Environmental Engineering, The University of Tokyo), Ming Zhang(Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology), Chair:Hirotaka Saito(Department of Ecoregion Science, Tokyo University of Agriculture and Technology), Shoichiro Hamamoto(Department of Biological and Environmental Engineering, The University of Tokyo)

11:45 AM - 12:00 PM

★ [AGE04-07] Interactive effects of EC and pH on nitrous oxide emissions and denitrification

*Thi kim thanh HA1, Morihiro MAEDA1 (1.Graduate School of Environmental and Life Science, Okayama University)

Keywords:Denitrification, EC, nitrous oxide, paddy soil, pH

Long-term fertilizer applications and saline water irrigation lead to the accumulation of salts and changes in soil pH. These changes may in turn affect N2O emissions from soil. Interactive effects of EC and pH on N2O emissions were studied by using paddy soil in Ushimado, Okayama Prefecture, Japan. Closed incubation experiments were conducted in 100-mL glass bottles for 72 h at 25oC. Each bottle contained 5 g of air-dried soil and 25 mL of solution, which includes KNO3 (10 mg NO3-N L-1) and NaCl (0 M, 0.005 M, 0.01 M, 0.05 M, 0.1 M, 0.2 M) for adjusting different electric conductivity (EC) levels under different pH: acid (HCl 0.005 M), neutral (no adjustment), and alkaline (NaHCO3 0.005 M). Nitrous oxide concentration in the headspace of the bottle was measured 3 h, 24 h, 48 h, and 72 h after incubation with gas chromatograph (GC-8A, Shimadzu, Kyoto, Japan). After gas collection, the solution was taken out for measuring pH, EC and concentrations of NH4+ and NO3-. Results indicated that pH was a significant factor controlling N2O emissions (P < 0.05). Nitrous oxide emissions were greater in higher EC treatments under the acid treatment. Nitrous oxide emissions peaked at 24 h of incubation and fell sharply afterwards due to further dentrification process. At 24 h, the highest N2O emissions was measured in 0.2 M NaCl (7.5 mg kg soil-1), followed by in 0.1 M, 0.05 M, 0.01 M, 0.005 M and 0 M treatments, which were 6.7, 5.1, 3.8, 2.0, and 1.2 mg N kg soil-1, respectively. Nitrous oxide reductase was sensitive to both high EC and low pH condition. In neutral and alkaline treatments, there was no significant effect of EC on N2O emissions during 72 h incubation (P > 0.05). The N2O emissions were 0 mg kg soil-1 at 3 h after incubation then ranged from 0.02 to 0.11 mg N kg soil-1. Ammonium concentration increased over the incubation periods. Higher EC promote NH4+ release. There was no significant difference in NO3- removal among treatments at different EC levels (P > 0.05). We conclude that low pH increased N2O emissions and higher EC under acid conditions promoted N2O emissions.