Joint Research on Evaluating Rice Cultivation in the Kikuchi River Basin from Historical, Cultural, Natural, and Taste Perspectives

Terraced rice fields in Ryumon, Kikuchi City, Kumamoto Prefecture

International Research Center for Biological and Environmental Agriculture, Graduate School of Advanced Science, Kumamoto University

Kumamoto Gohan LLC

Kumamoto Gohan LLC (Kumamoto Prefecture, Representative: Yozo Tomioka) has started a joint research project with the International Research Center for Biological and Environmental Agriculture, Graduate School of Advanced Science, Kumamoto University (Center Director: Professor Shinichiro Saw) on the correlation between historical and cultural value and natural environment and taste in the Kikuchi River basin.

This research aims to integrate natural science and cultural history to evaluate the unique natural conditions, cultural history, and taste correlation of the Kikuchi River basin, and to record and disseminate their value academically. Based on the research results, we aim to construct an academic index called 'Kikuchi Terroir Index (KTI)' to comprehensively organize and evaluate the unique characteristics of rice-producing regions.

I. Background of the Research - Why the Kikuchi River Basin?

The Kikuchi River basin (Kikuchi City, Yamaga City, Tamana City, Mizuma Town, Kumamoto Prefecture) has continued rice cultivation for approximately 2,000 years from the Yayoi period to the present. In 2017, it was recognized as a 'Japanese Heritage' by the Agency for Cultural Affairs, with 33 constituent cultural properties related to rice proving the depth of its historical and cultural value.

However, on the other hand

Limitations of Existing Evaluations

Current rice evaluations focus on taste, yield, and appearance, and do not reflect the relationship with the land and historical and cultural value.

Lack of International Context

Unlike wine terroir research, there is no established framework in Japan that scientifically demonstrates the characteristics of the producing region.

Challenges in Succession

Academic records and information related to 2,000 years of rice cultivation culture, agricultural environment, and taste have not been sufficiently conducted from the perspective of adding value to agricultural products.

This research will address these challenges as an interdisciplinary study that integrates natural science and cultural history research. The purpose is to clarify the unique natural conditions, cultural history, and taste correlation of the Kikuchi River basin and to record and disseminate their value academically.

II. Overview of the Research

Research Title: Research on the Correlation between Historical and Cultural Value and Natural Environment and Taste in the Kikuchi River Basin

Research Institution: International Research Center for Biological and Environmental Agriculture, Graduate School of Advanced Science, Kumamoto University

Principal Investigator: Professor Shinichiro Saw (Center Director)

Co-Investigator: Kumamoto Gohan LLC Representative Yozo Tomioka

Contract Conclusion: April 2026

Research Area: Kikuchi River Basin, Kumamoto Prefecture (Kikuchi City, Yamaga City, Tamana City, Mizuma Town)

Research Direction: Scientific Evaluation and Dissemination of Kikuchi Terroir Index (KTI)

III. Three Steps of the Research - Integration of History, Science, and Evaluation System

STEP 1 Visualizing Regions with High Historical and Cultural Value (History and Culture Research)

Organize the historical accumulation of rice cultivation in the Kikuchi River basin (tangible and intangible heritage) through literature research and GIS maps.

Academically visualize the location information and relationship with rice cultivation of the 33 constituent cultural properties of Japanese Heritage.

Verify the correlation between historical water systems and modern soil and water quality.

STEP 2 Analyzing the Relationship between Natural Conditions and Quality (Terroir Research)

Analyze soil and water quality by geology, including granite, sandy soil, volcanic ash soil, and silica content.

Scientifically analyze the mineral components (Ca, Mg, Si, etc.) of the Kikuchi River system.

Analyze the correlation between ripening period temperature, day-night temperature difference, altitude, terrain, and taste.

Conduct sample surveys in multiple paddy fields within the basin.

STEP 3 Organizing the Foundation of a New Rice Evaluation System (Evaluation System Research)

Design a rice evaluation system based on four axes: historical and cultural value, terroir, quality, and sustainability.

Construct the academic foundation of the Kikuchi Terroir Index (KTI) by categorizing each axis into four levels.

Integrate the sensory evaluation by rice taste appraisal experts and the production area evaluation criteria by top hotel chefs and renowned restaurant chefs.

Disseminate information through international academic journals, etc.

IV. Kikuchi Terroir Index (KTI) / Kikuchi Terroir Index (Tentative)

The 'Kikuchi Terroir Index (KTI) (Tentative)' aimed to be constructed in this research is an academic index case that organizes and evaluates the unique characteristics of rice-producing regions from the perspectives of agricultural science and cultural history research, referring to the terroir concept used in the wine field. We aim to present a new perspective to explain the value of Japanese rice by evaluating the characteristics of rice-producing regions and paddy fields in the Kikuchi River basin from four axes: historical and cultural value, terroir, rice quality, and sustainability.

Axis I: Historical and Cultural Value / Historical & Cultural Value

Evaluation Index: Years of continuous rice cultivation, water utilization records, and association with existing tangible and intangible historical heritage.

Special Notes: Visualization of historical accumulation through documents, GIS, and folklore surveys.

Axis II: Terroir / Terroir

Evaluation Index: Soil parent material, pH, organic matter, silica, water quality minerals (Ca, Mg, Si), ripening period temperature, day-night temperature difference, altitude.

Special Notes: Includes comparative analysis by geology such as granite, sandy soil, and volcanic ash soil.

Axis III: Quality / Quality

Evaluation Index: Amylose, protein, taste value, sensory evaluation by rice taste appraisal experts, evaluation by top hotel chefs, etc.

Special Notes: Sensory evaluation with reproducibility based on standardized protocols.

Axis IV: Sustainability / Sustainability

Evaluation Index: Consistency with GIAHS, satoyama, biodiversity, classification of pesticide and chemical fertilizer use.

Special Notes: Consistency with international certification standards such as FAO and GIAHS.

Image of Stage Evaluation (S, A, B, C four stages)

We will consider constructing an evaluation model for paddy fields and production areas by classifying each axis into four stages of S, A, B, and C. As in the French wine 'Grand Cru' (first-class vineyard) classification, which is granted to specific vineyards, KTI aims to clearly visualize the unique value held by rice-producing regions and paddy fields and to create a framework that leads to the creation of brand value.

V. Research Structure

Principal Investigator and Academic Supervisor: Professor Shinichiro Saw (Director, International Research Center for Biological and Environmental Agriculture, Kumamoto University)

Co-Investigator and Field Coordinator: Yozo Tomioka (Representative, Kumamoto Gohan LLC)

Collection of historical and cultural information in the Kikuchi River basin, coordination of industry-academia collaboration, coordination of interviews with hotels, and improvement of map data.

Sensory Evaluation Responsible: Rice Taste Appraisal Experts (Research Collaborators)

Conduct blind tests based on standardized protocols to obtain reproducible data.

Responsible for Restaurant Field Evaluation: Conduct interviews with chefs and food-related personnel who handle domestic and international rice.

Historical and Cultural Information Liaison: Boards of Education and Cultural Property Protection Divisions of Kikuchi City, Yamaga City, Tamana City, and Mizuma Town.

Geological and Map Information: Geological Survey Center (Geological Map Navi) of the National Institute of Advanced Industrial Science and Technology, and the Geospatial Information Authority of Japan (altitude and terrain data).

■ VI. Future Schedule

April 2026~: Contract conclusion and start of STEP 2 (Terroir Research)

May 2026~: GIS mapping of historical and cultural information and selection of sampling paddy fields (Full-scale implementation of STEP 1)

Autumn 2026: Final field sampling survey, taste analysis, and implementation of sensory evaluation.

Summer to Autumn 2026: Conduct structured interviews with top hotel chefs.

March 2027: Interim report of research results and creation of draft of KTI evaluation system.

March 2027 and beyond: Dissemination of information related to KTI through domestic and international academic journals, etc.

VII. Significance to the Region, Society, and Industry

In this research, we will accumulate academic insights on the rice cultivation culture, natural environment, and rice quality of the Kikuchi River basin, and scientifically record and disseminate the region's agriculture and food culture. This will contribute to the following aspects of the Kikuchi River basin and Japanese agriculture and food.

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