Specific property of nitrogen discharge in clayey ex-paddy fields related with decline of soil nitrogen fertility

2016 Fiscal Year Final Research Report

• Project/Area Number: 26450083
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Plant nutrition/Soil science
• Research Institution: National Agriculture and Food Research Organization
• Principal Investigator: SUZUKI Katsuhiro 国立研究開発法人農業・食品産業技術総合研究機構, 中央農業研究センター 水田利用研究領域, 上級研究員 (90354068)
• Project Period (FY): 2014-04-01 – 2017-03-31
• Keywords: 粘土質転換畑 / 窒素流出 / 脱窒 / 溶存有機態窒素 / 窒素・酸素安定同位体比 / 窒素肥沃度

Outline of Final Research Achievements

Recently, declining yields are of concern in the ex-paddy fields, that were previously used to cultivate paddy. We investigated the specific properties of nitrogen (N) discharge in clayey ex-paddy fields related with decline of soil N fertility.
Nitrate was the main form of N in tile drainage. Nitrate concentrations decreased gradually during each rainfall event, with loss of more than 20% nitrate in the fields with conventional drainage. Stable isotope studies of N and O in the form of nitrate ion suggested that the decline of nitrate is caused by denitrification. Additionally, dissolved organic N (DON) was found in the drainage water, and the DON concentration was up to 70% of nitrate. Water-extractable N in the topsoil was primarily in the organic form and represented up to 30% of the available N.
From these results, we concluded that the nitrate loss by denitrification and discharge as DON seemed to affect the soil nitrogen fertility in the clayey ex-paddy fields.

Free Research Field

土壌学