抄録
Nemuro and Kushiro districts in the eastern part of Hokkaido have unfavorable climate for agriculture. Moreover, they are covered with volcanic ash soils erupted recently from Mt. Mashu. So, Nemuro and Kushiro are representative districts of low productivity in Hokkaido. These districts were appointed repeatedly as sites for proposed reclamation work. But, unfortunately, no good results have been obtained. About 20,000 ha of flat land are left unclaimed. So, authors intended to make clear the characteristics of soil which covers these districts and find out the fundamental idea for the maintenance of the fertility of the soil. These districts are covered with more than ten layers of volcanic ashes erupted from Mt. Mashu. Authors selected four layers from surface which has direct effect on the crops cultivated there, and called them : Mashu-a, M-b, M-c, and M-d from the top layer downward. The soils, derived from layers M-a and M-b, are very young suffering weakly from weathering; and almost all their exchange capacities are due to the humus, not to inorganic colloid. However, the soils, derived from M-c and M-d, have some amounts of inorganic colloid which has exchange capacity. But all in these cases, the soils contain free aluminium of considerable amount. So, in the case of M-a and M-b, we must prevent the soils from the exhaustion of humus; and in the case of M-c and M-d, from the unfavorable influence of free aluminium.
