Long-term monitoring and improvement of soil potassium availability under continuous cropping of forage rice

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K05766
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 38010:Plant nutrition and soil science-related
• Research Institution: Kochi University
• Principal Investigator: Moritsuka Naoki 高知大学, 教育研究部総合科学系生命環境医学部門, 准教授 (10554975)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 飼料イネ / カリウム / 水田生態系 / 土壌診断 / 長期持続性評価

Outline of Final Research Achievements

In Mifune town, Kumamoto prefecture, Japan, the production of rice for whole crop silage (WCS rice) started in around 2000. After the 2016 Kumamoto earthquake, however, the production of WCS rice in Mifune town was returned to the production of edible rice. Since 2014, we have conducted a monitoring survey by evaluating soil fertility in four WCS rice fields and four edible rice fields. In this study, we evaluated the changes of soil K fertility following the land use change from WCS rice to edible rice. Soon after the land use change, the concentration of exchangeable K in the surface soil (0-15 cm) increased and the concentration of nonexchangeable K tended to decrease. Similar trends were observed in the subsoil (15-30 cm), suggesting the leaching of K from the surface to the subsurface layer by the edible rice production. Besides these results, we developed a simple method for estimating the content of nonexchangeable K in paddy soil using extraction with sodium tetraphenylborate.

Free Research Field

土壌肥料学、植物生育環境学、持続的農業科学

Academic Significance and Societal Importance of the Research Achievements

本研究では、全国に先駆けて飼料イネ栽培を導入した圃場を用いて、長期間の飼料イネ栽培を止めて食用米に作付を戻した時に土壌のK肥沃度が回復するのかどうかを評価した。飼料イネ連作で粗放的な管理を続けると、土壌中のK含量が低下し、その後の食用米の収量を制限しうると予想していたが、土壌の交換態K含量は速やかに回復し、逆に非交換態K含量は減少するという予想外の結果が得られた。さらに下層土も表層土と同様に、飼料イネ連作水田の交換態Kと非交換態Kが食用米水田より低い値を示した。そのため土壌のK肥沃度診断では交換態Kだけでなく非交換態Kの評価、また作土だけでなく下層土の評価も重要であることが明らかとなった。