Abstract
The author made a study on the humus of volcanic ach soil which was originated from Mt. Sakurajima's ash, erupted in 1914. The results obtained may be summarized as follows. 1) In the forest, large amount of humus was accumulated, but its humification degree was low. On the other hand, in the virgin grassland the amount and humification degree of humus were varied according to the texture of ash and the location of its deposition. And a large amount of humus whose humification degree was very high, was accumulated under the grass vegetation dominated by Sasa (Pleioblastus communis) or Susuki (Miscant hus sinensis). 2) On the surface soil of virgin grass land, in general, a) increasing of the amount of humus, b) proceeding humification of humic acids, c) the disintegration of labradorite in the parent rock, d) intensifying of the allophanic character of clay fraction and e) increasing of the amount of the free alumina, these above mentioned phenomena, affecting mutually, seemed to go on towards the same direction.
