Dynamics of clay-fixed ammonium as a sink or source of exchangeable ammonium in a paddy soil(Soil chemistry and soil mineralogy)

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概要

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• Clay-fixed ammonium (NH^+_4) plays an important role in the dynamics and availability of soil nitrogen (N), acting as a sink or source of exchangeable NH^+_4. However, quantitative information about NH^+_4 exchange processes between exchangeable and fixed NH^+_4 is limited. In this study, we developed a method to sequentially extract exchangeable NH^+_4 and fixed NH^+_4, and evaluated whether fixed NH^+_4 acts as a sink or source of exchangeable NH^+_4 in a paddy soil. A paddy soil was subjected to anaerobic incubation for 70 days with and without the application of powdered rice (Oryza sativa L. cv. Hinohikari) straw as a pre-treatment, and with and without air-drying as a post-treatment. By the anaerobic incubation, the content of weakly fixed NH^+_4 increased significantly with a significant increase in exchangeable NH^+_4, implying that exchangeable NH^+_4 in the paddy soil is the main pool as a source of weakly fixed NH^+_4. On the other hand, a significant decrease in the exchangeable NH^+_4 content by rice straw application before the incubation slightly lowered the content of weakly fixed NH^+_4. Air-drying after the incubation caused the fixation of exchangeable NH^+_4. Overall, the contents of exchangeable NH^+_4 and weakly fixed NH^+_4 were positively correlated (r=0.58; p<0.05), indicating that weakly fixed NH^+_4 acted as a transitory pool between strongly fixed NH^+_4 and exchangeable NH^+_4. The proposed sequential extraction method was effective to evaluate the interaction between exchangeable and fixed NH^+_4. Combining this method with an incubation experiment, it was demonstrated that fixed NH^+_4, especially weakly fixed NH^+_4, in the paddy soil can be released or retained in quantities sufficient to affect the dynamics of exchangeable NH^+_4.

著者

• Moritsuka Naoki

  Laboratory Of Plant Production Systems Graduate School Of Agriculture Kyoto University

• Matsuoka Kaori

  Department Of Symbiotic Science Of Environment And Natural Resources United Graduate School Of Agric

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• Non-Destructive Method for Determining Temporal and Spatial Changes of the Soil Solution Chemistry in the Rhizosphere
• Effect of Plant Growth on the Distribution and Forms of Soil Nutrients in the Rhizosphere
• Dynamics of clay-fixed ammonium as a sink or source of exchangeable ammonium in a paddy soil(Soil chemistry and soil mineralogy)

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