**Acknowledgements**

We are deeply grateful to the staff members of the Akita Prefectural Agricultural Experiment Station (especially Mr. Kazuki Sekiguchi and Mr. Keiji Sasaki) and the Center of Field Education and the Research, Faculty of Bioresource Sciences (present: Agri-Innovation Education and Research Center), Akita Prefectural University for their support in the management of the experimental fields. We also thank Ms. Emiko Sato, Ms. Keiko Hatakeyama, Ms. Tomoko Suzuki, and the students of the Laboratory of Soil Science, Faculty of Bioresource Sciences, Akita Prefectural University for their great help with the field survey and laboratory analyses. We also thank Ms. Hiroko Sato (Akita Prefectural Livestock Experiment Station) for providing the livestock manure compost.
