| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1995: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1994: ¥1,800,000 (Direct Cost: ¥1,800,000)
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| Research Abstract |
Crop production in Sakurajima-town has dropped rapidly since 1972 when the volcanic activity of Sakurajima-Minamidake began to be furious. A negative correlation was found between the annual amount of ash vomited from Minamidake and the yield of sweet potato in Sakurajima-town, expressed as the ratio to the overall yield of Kagoshima prefecture. In addition, the cities and towns situated encircling Sakurajima tended to be inferior in crop yield to the municipalities situaed close behind them, but superior to Sakurajima-town. The results suggest that the crop yields in and around Sakurajima is affected by the ash fall.
In order to examine the effect of ash fall upon plugging stomata, the stomatal resistance in several crops was measured at various places within a 40km radius, but the relationship between the stomtal resistance and the distance from a explosion craster was unclear. A considerable rise in leaf temperature was observed in the leaf covered with volcanic ash, because of a dec
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rease in transpiration rate and an increase in the absorption of solar radiation. This suggests that volcanic ash cover on leaves affects photosythesis by not only shading leaf surface but also increasing leaf temperature.
Though it was supposed that the reduction in photosynthesis arises in leaf covered directly with volcanic ash, the reduction in growth was larger in crop grown under glass sheet covered with volcanic ash than it. It seemed that the disagreement depended mainly upon the difference in light conditions on which leaves developed after the treatments were put. In addition, it was suggested that when the volcanic ash is left on covering material for a long term the growth after the remaoval will be also checked.
When volcanic ash is mixed into arable soil, the crop growth and/or yield reduced with an increasing in the percentage of volcanic ash-mixture. It was proved in pot-experiment as well as on-the-spot examination that the crop growth is larger when the mormal soil is arranged concentrically aroud a root than when it is mixed into volcanic soil. A curvillinear relationship was found between the crop growth and both area and depth around a root, replaced by normal soil. The means that there is a optimum area and depth maximizing the replacement-effect. Less
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