Abstract
　Physical soybean damages caused by fall of scoria with eruption of a volcano were experimentally studied. Scoriae were divided into three sizes. The small scoria is smaller than l.5cmφ: the middle is l.5 to 2.5: the large is 2.5 to 3.5. These scoriae were fallen to soybean canopy from 5m above ground surface at three growth stages of soybean.
　Results are as follows.
l. Yield of all the damaged soybean decreased in comparison with the normal soybean.
2. The influence of the small scoria was less. The fall of leaves by the small scoria was hardly recognized in the late stage of growth. Damages by the middle scoria were especially large in the early stage of growth. Numerous leaves were fallen by the large scoria in the late stage of growth. When the pod is large the yield is directly reduced by fall and injury of the pod in the stage.
3. Total fallen dry weight of soybean become very large by the large scoria in comparison with the middle scoria of the same weight.
4. Visible injuries of leaves in this experiment were similar to that observed in Izu Oshima just after the eruption of volcano in 1986.

【キーワード】：スコリア，ダイズ，作物被害，伊豆大島火山
Key words: scoria, soybean, crop damage, Izu Oshima Volcano

*千葉大学園芸学部
Faculty of Horticulture, Chiba University