Revisiting the fertility of tropical highly weathered soils: Is Oxisols nutrient-poor?

2021 Fiscal Year Final Research Report

• Project/Area Number: 19K15952
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 41050:Environmental agriculture-related
• Research Institution: Kyoto University
• Principal Investigator: SHIBATA MAKOTO 京都大学, 地球環境学堂, 助教 (40799607)
• Project Period (FY): 2019-04-01 – 2022-03-31
• Keywords: Oxisols / Ultisols / ベトナム / 養分循環 / アカシア / 熱帯林 / 硝酸

Outline of Final Research Achievements

In this study, we compared the nutrient cycling pattern of tropical forests on Oxisols and Ultisols, which have been lumped together just as highly weathered tropical soils. We reconsidered the question, "Is the Oxisols nutrient-poor soil as previously thought? The results showed that leaching of nitrate to the lower soil horizons occurred only in Oxisols, and that cations such as calcium and magnesium also moved to the lower soil horizons along with nitrate. Therefore, by focusing not only on the nutrient stock in the soil, but also on the nutrient flow through the soil, i.e., the nutrient cycling mechanism between plant and soil, we clarified the forest ecosystems on Oxisols have a dynamic nutrient cycle pattern.

Free Research Field

土壌学

Academic Significance and Societal Importance of the Research Achievements

本研究によって，土壌-植生間の養分循環を評価することで，従来のように土壌中の養分賦存量のみに焦点を当てた静的な肥沃度評価では見えてこなかった，土壌生態系の姿が明らかになった。すなわち，これまで単に貧しい土壌と考えられてきたオキシソルに成立する森林生態系では養分がダイナミックに循環していた。オキシソル土壌の農業利用を考える上では，樹木作物を活かしたアグロフォレストリー的な利用にはアルティソルよりも適している可能性がある一方で，過度な伐採や単年性作物を主とした常畑利用によっては土壌養分が急速に枯渇する危険性について留意されるべきである。