Soil properties of Hachijo-Kojima island in concern of self-sustenance in a remote island

It is reported that many local governments are dismissed in near future in Japan. Then it is meaningful to look back past case study whose village has already been deleted almost half century ago. Many case studies of deletion of local government can be triggered by not just socio-economic reason but also natural disaster. In 1969, all citizen left from their island, Hachijo-Kojima Island (hereinafter The Island) which is study site of this report, and the people moving might be thought that it includes same problem as region abandonment occurred in recent year. Thus deep understanding of people moving happened in 1969 in The Island, can support to stmggle to same phenomena which people discard their habitat these years.

Extraordinary, The Islands ware abandoned even the possibility of self-sufficiency was existed. In this point, The Island is underlined. In that time, elementary school girl from The Island wrote her mind about The Island like below. “—Ош Island never erupts and sinks down, but people will not exist, then The Island will not exist as well”.

For some hundred years, how land use was managed with limited and angled area until 1969 when last citizen left The Island, ft is said that deeply considered land use way which grown up in local area might not give big impact on the ecology system and last for long term.

In this article, agricultural land use of The Island and process of dismissing The Island is studied, through field work and interview to citizen from The Island. Additionally consideration about self-sufficiency from soil management point of view is discussed.

The Island has 3.2km2 square which is constructed with solo volcano. The longest diameter of The Island is 3.1km, and shortest of that is 1.0km. The highest summit is reaching to 616.8m sea level above.

Neighbor Island called Hachijo-Island has more than 3,200mm precipitation per year which record almost twice of that of Tokyo. However even a small currents have not existed, and historically people living there have used rainfall water or exuded water from rock. Two villages, Toriuchi and Utsuki had been existed till 1969. So the location of the settlements might not be influenced to water resources, ft can be said that it is curious even in all over the world.

In 1840, the population of the Island was 513, and the high population density was one of the social problems at that time. Finally in 31st March 1969, extraordinary all citizen moved out from The Island depend on their will and cooperation of local government.

ft was said that the reason for leaving was gap of quality of life between The Island and Hachijo-Island or main land. In The Island, it was lack of electricity, water supply, medical care and income. Moreover the low population was another reason. After finish of basement education, all students ware flowed to Hachijo-Island or main land for extend education or job.

Methodology

Because The Island territory was registered as national park, plant or soil sample ware not anowed to be taken to outside of The Island, easy way date sets ware corrected in the field.

Study point 1 to 8 ware corrected on 12th August 2016 and the points 9 to 16 ware on 18th November 2016. In each point, 6 kinds of date ware gathered below.

• 1)    Penetration test: The deepest score was 100cm underground. More than 3 times was tested in 1 point. The hardness was surveyed till 2 MPa.

• 2)    Simplified Soil profile survey: Layering soil profile by soil color until 100cm depth by small tubed sample corrected by penetrator. Soil textures ware recorded depend on Soil Survey Handbook[l],

• 3)    Colometric test on soil surface: Color of Surface soil was recorded quantitively by spectrophotometer SPAD-503(Konica Minolta).

• 4)    Moisture content: Recorded by moisture meter SM200(DELTA-T) (v/v%).

• 5)    pH(H2O): By water resist pH meter PH-6011A(Horiba). The sample was supernatant of mixed water from each top soil and purified water. The mix weight ratio was 1:2.5 (top soil: purified water).

• 6)    Volume ratio of cray and sand: The number was taken form mixed water which was prepared for calculating pH.

In addition, land features including length of crop field and angle ware recorded.

Through 2 staying periods in The Island, interview researches ware implemented with 4 persons from The Island, a person from government of town and prefecture, journalist and several persons who know about The Island.

Conclusions

• 1.    Vertical hardness of the soil was cleared by penetration test. Effective soil suitable for agriculture was reaching 40cm depth at point 1 and 2 where ware used as step field. The points where ware not used as cropping field ware reaching to mother rock at 30cm depth depend on not just soil hardness but also soil texture. Thus it is suggested that long period as cropping field made the area to deepen their effective soil. Munsell denotation value (brightness) of top soil was 2 or 3 in all of the study points. The value has positive correlation with organic carbon contentr. (Shields et al. 1968). According to the article, soil of all study point contain organic matter from 3~5%. Overall tip soils of all the study points contain approximately 5% of organic matter, and the number means there are high potential for productivity.

• 2.    It was suggested that the higher of Munsell value, the more bigger value of cray and sand ratio. Because much cray or silt bury small gap and it makes top soil surface to be higher of albedo. At the result Munsell value is getting to be higher or brighter.

• 3.    Each retrieved date set can be indicator for evaluating whether the point is adoptive for cropping use or not. Then 4 indicators, namely, 1) soil hardness vertical distribution, 2) value ratio of cray and sand, 3) pH, and 4) organic matter contents, ware set for the check test. Finally all points can be divided to 5groups. The points passed for all tests can be guessed as higher

• 4.    Economical relation of The Island with Hachijo-island and main land had been getting stronger year by year and The Island’ self-sufficiency had been getting weaker and weaker. Depend on memory of The Island citizen, there was no self-sufficiency life in 1960s. Life in The Island after Second world War was never tough, because land rice which is high productivity, was introduced into the system of slash and burn agriculture. Moreover scheduled ship had started running between The Island and Hachijo-island per a week. However there are no records which prove that the citizen quit their cropping field. They did not stop making their effort to crop.

• 5.    Through field work, self-sufficiency, land use and soil productivity in The Island ware considered. To evaluate soil productivity, field works ware implemented 2 times. According to easy way survey of the soil samples, all the study points ware distinguished to 5 groups by 4 check tests. In addition, it was suggested that half of the all points marked as high productivity.

• 6.    Originally The Island has kept high productivity, and sustainable agriculture had been conserved till in 1969. Thus limit of land use was not the reason for citizen leaving. But social reason which includes increasing cash income and detachment from self-sufficiency, in considered as trigger for withdrawing from The Island.

potential for cropping. The first check point is effective soil or not. If soil hardness is lower than 2MPa until 30cm depth, the point can be effective soil. Only the points with effective soil can go next check teat 2), if the volume ratio of cray and sand is higher than 1 (cray contents is higher than that of sand) or not. The points which fulfil 1) and 2) are evaluated by 3) test, whether pH is higher than 5 and lower than 6.5. For the last 4) test, Munsell value is key. If the value is lower than 30 out of 100. At the result, only point 5, 11 and 12 passed all tests. And 8 points passed until 3) test. It can be concluded that half of study points are possibly covered with high productivity soil.