Dynamics of dissolved-state phosphorus infiltrating agricultural soil

2020 Fiscal Year Final Research Report

• Project/Area Number: 18K05885
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 41030:Rural environmental engineering and planning-related
• Research Institution: Kyoto University (2020); Kumamoto University (2018-2019)
• Principal Investigator: Hama Takehide 京都大学, 農学研究科, 准教授 (30512008)
• Project Period (FY): 2018-04-01 – 2021-03-31
• Keywords: リン / 浸透 / 吸着等温線 / 移流分散方程式 / Hydrusモデル

Outline of Final Research Achievements

In this research, the temporal change of phosphorus concentrations in infiltration process was evaluated. It is confirmed by field investigation that phosphorus concentration of groundwater in agricultural area was high (0.5 mg/L). Therefore, it is suggested that the groundwater received high phosphorus load from the surface land. In addition, the adsorption isotherm of phosphorus, which was estimated from a batch test, was applied to a numerical model to simulate the temporal variations in phosphorus concentration in the effluent of the column test. It is revealed that the dynamics of phosphorus in the infiltration process, even if the infiltration rate was more than 0.3 cm/min, can be simulated on the assumption of the equilibrium adsorption. However, the initial adsorption of phosphorus has large influence on the simulation results of the phosphorus dynamics in the infiltration process.

Free Research Field

農業水文学

Academic Significance and Societal Importance of the Research Achievements

一般的にリンは農地土壌に強く吸着されるため，農地土壌に吸着された懸濁態のリンの移動抑制が従来の水質保全対策の中心であった。しかし近年，海岸部の地下水湧出水に溶存態のリンが高濃度で検出されることが報告され未解明の水質汚染メカニズムとして，土粒子に吸着されずに地下水流動とともに移動する溶存態リンの実態把握が重要になりつつある。本研究は現地観測によって農業地区の地下水にはリンが高濃度で存在することを示した。また，土壌カラムを用いた通水型のリン吸着実験を通じて，土壌浸透過程におけるリンの動態を明らかにし，その数値モデル化を行った。これらの知見は今後の農地からの排出負荷削減対策に有益なものとなる。