2022 Fiscal Year Final Research Report
Environmental factors determining nitrogen removal rate in rice paddy and their modeling
| Project/Area Number |
19K06332
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Multi-year Fund |
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| Section | 一般 |
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| Review Section |
Basic Section 41050:Environmental agriculture-related
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| Research Institution | Utsunomiya University |
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Principal Investigator |
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| Project Period (FY) |
2019-04-01 – 2023-03-31
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| Keywords | 脱窒 / 硝酸態窒素除去速度 / 添加有機物 / 温度依存性 |
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| Outline of Final Research Achievements |
To develop a model that enables estimation of nitrogen removal rate in a rice paddy, I first derived an equation for the nitrogen concentration changes considering the nitrogen load changes due to infiltration of ponding water and the substance concentration due to evaporation of water. Secondly, I confirmed the temperature dependence of denitrifying bacteria through laboratory experiments, and found that the activity of the denitrifying bacteria was maximum at around 30 degree Celsius. Thirdly, It was found that high evaporation promoted convection in the ponding water and increased the nitrate nitrogen removal rate. Furthermore, comparison between nitrogen removal rates by microorganisms suspended in ponding water and by algae settled on the soil surface suggests that removal by algae settled on the soil surface may be greater.
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| Free Research Field |
水利環境工学
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| Academic Significance and Societal Importance of the Research Achievements |
水田における硝酸態窒素除去量については現地での観測結果が多く，モデル開発への期待があるものの，現象の把握が容易でないため，あまり進んでいない。本研究において導出した硝酸態窒素濃度の濃度変化を表す推定式は，田面水の浸透による湛水中の負荷量変化や水の蒸発に伴う濃縮を考慮しており，水田のみならず比較的水深の浅い流水中での予測にも援用することができる。次に，田面水の蒸発が湛水中の対流を生み，硝酸態窒素除去速度と蒸発量が比例関係にあることは新しい知見であると考えており，今後の研究への貢献が期待される。
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