Kunisaki Peninsula Usa area
The deep valleys and ridges extending outward from the Futago mountain system to become the Kunisaki Peninsula
A natural environment that is tough on rice paddy agriculture
The Kunisaki Peninsula Usa area is situated in northeast Kyushu, south of the Seto Inland Sea. It is formed by four cities and one village, with the round peninsula at their center. The geographical terrain features mountain ridges and deep valleys extending out radially from the Mt. Futago mountain ranges at the centre of the peninsula. Plain lands are narrow and there are many short and steep rivers. Due to its low precipitation and volcanic soil that quickly absorbs any rainfall this region has struggled with the difficulties of securing water since ancient times.
- 180,572. Total of 14,842 people in agriculture, forestry and fisheries (as of March 2010)
- Humid, temperate climate (Seto Inland Sea climate)
- Main industries
- Agriculture, forestry and fisheries, precision instruments manufacturing
- Average precipitation comparison
Irrigation water supply system of multiple interlinked irrigation ponds born from the geographical constraints of the region
On top of stably running rice paddy agriculture, it is estimated that the history of the indispensable irrigation ponds began in the period in the 11th Century when the fields were opened up and crop cultivation began. Most of these were established in accordance with the population increase of the 19th Century. Given that the construction of large scale irrigation ponds was not possible due to the area’s geographical conditions our ancestors established the techniques to secure the necessary amount of water using multiple interlinked small scale irrigation ponds. Through this, reciprocally beneficial water supplies were equalized and the precious water was efficiently distributed and the water shortage issue was resolved. In addition by having open waterways between the irrigation ponds, the water catchment area was increased so that more rainfall entered the irrigation ponds and a stable water supply is attained.
The management system of the multiple, interlinked irrigation ponds
The Tsunai region of Kunisaki City currently uses an interlinked system of six ponds which was established in the Edo Period. Takao pond, which is the furthest upstream pond, is kept for use in the latter period of wet-land rice production. Until then, the three mid-stream ponds and the two downstream ponds are fed into one another and supply the water for production.
In this region the knowledge and experience needed for continuing the irrigation water supply system is passed down through generations. There is a position called the “Ikemori” (pond manager) who is entrusted with the operations and management of the irrigation ponds. Water withdrawal management is conducted so that rice paddy water rations are equalized and so that water is used effectively and fairly. The fact that this system is maintained and managed for each of the rivers spreading outward from the Mt. Futago ranges is a feature of the rice paddy agriculture of this region.
The Sawtooth Oak circulation system and food production system
Japan’s largest Sawtooth Oak forests and their multiple functions
The cumulative total of Sawtooth Oak trees in Oita Prefecture accounts for around 24% of the total nationwide, making it the largest amount in Japan. The proportion of the region’s forest area covered by Sawtooth Oak forests is 11.5%, which exceeds the prefectural average. This is due to the geographical characteristics of the area which make the natural environment well suited to Sawtooth Oaks. From this stemmed the active planting of trees in the Satoyama areas for use as Shiitake cultivation log wood as well as wood and charcoal fuel materials so that residents could make a living.
Preservation of Sawtooth Oak forests and the cultivation of log wood cultivated Shiitake
Even when chopped down, the Sawtooth Oak sprouts from the stump and has the fantastic characteristic of being a cyclical source of timber. Through appropriate management, planted Sawtooth Oak forests will grow to the suitable size needed for use in log wood cultivated Shiitake production after around fifteen years. The fully grown Sawtooth Oak trees are cut down in autumn and supply Shiitake production. After the Sawtooth Oak trees are cut down, new shoots sprout from the stump the following spring.
In order to ensure the necessary amount of sunlight and nutrients for growth, undergrowth and weeds are trimmed back. The trimmed undergrowth then not only holds back the growth of future undergrowth, but as it slowly decomposes it also assists the growth of the Sawtooth Oaks and provides them with nourishment. Furthermore, the fallen leaves and old logs that have been used for Shiitake cultivation humify and turn into mineral rich soil, forming a soft, swollen water retention layer. Two to three years after sprouting, the stumps are cleared to leave only two to three shoots which accelerates their growth. Before long, around 15 years after being cut down, the Sawtooth Oak trees regrow to a size that allows them to be used as log wood for Shiitake cultivation.
- Log wood cross cutting
- 1-2 months after cutting down the trees, they are trimmed to 1-1.2m in length.
- Preparing the logs (January to March)
- Holes are drilled into the trimmed logs with an electric drill and wood chips containing shiitake fungal filaments are inserted into the holes.
- Resting period (January to March)
- The logs inoculated with Shiitake fungus are left to rest in an area that will allow the fungus to spread. To provide good ventilation and shelter them from direct light, the logs are covered in Sawtooth Oak branches. This is called ‘Kasagi’.
- Relocation to the Hoda-ba
- After resting, in the autumn of the second year, the log wood is moved to a location suited to Shiitake sprouting called a ‘Hoda-ba’ (where log wood cultivated Shiitake are grown).When Shiitake begin to sprout from the log wood, the logs are then called ‘Hoda-gi’.
- Growth and harvesting
- Shiitake predominantly sprout in spring and autumn. Once they grow to the appropriate size, they are harvested by lightly twisting the base of the mushroom.
Unique Hoda-ba management for growing log wood cultivated Shiitake
The key points for growing top quality log wood cultivated Shiitake mushrooms are the Hoda-ba that are used, and the water sprinkling. During winter this area receives little rainfall and experiences low temperatures. Therefore in the period when water is needed for Shiitake to sprout, log wood cultivated Shiitake are produced with methods such as using irrigation pond water for water sprinkling. The Hoda-ba here are not in the commonly used cedar coniferous forests, but instead in broad leaf forests called “bright Hoda-ba” where the lighting and temperature can be suitably controlled.
Dried log wood cultivated Shiitake are log wood cultivated Shiitake that have been dried in sunlight or using a drying machine. Depending on their shape, luster and color they are divided into categories such as “Donko”, “Koko” and “Koshin”. In this region, valuable, high quality dried log wood cultivated Shiitake such as the “Chabadonko” and “Koko” varieties can be grown using superior cultivation techniques. Oita Prefecture holds many shining accolades for its Shiitake and has been awarded the prestigious Grand Prize at the National Dried Shiitake Competition 20 years in a row, and has won a total of 52 times (as of 2018).