1999 Volume 81 Pages 23-33
For conservation of a valuable land with high-moor peat soil where the main vegetation is sphagnum, it is very important to make an index of the qualitative change of the soil due to the change in soil moisture. Therefore, in the present study, the moisture tension-moisture relation and the shrinkage-restoration characteristics due to the change in soil moisture as well as the fundamental physical-chemical properties of the Akaiyachi high-moor peat soil were attempted to be clarified. Especially, the shrinkage-restoration of soil is a conspicuous physical behavior due to the change in soil moisture. The principal results are as follows : The method followed in the study, namely, the pressure plate method is very useful to determine the moisture tension-moisture relation for low and medium moisture tension ranged from 0.981 kPa (pF 1.0) to 981 kPa (pF 4.0) in drying process. The changes of horizontal, vertical and volume shrinkage percentages of the high-moor peat soil consisting mainly of living sphagnum are small in the stage of low moisture tension and large in that of high one. Moreover, the change of its vertical shrinkage percentage is larger than that of its horizontal one in all stages of the moisture tension because of its subsidence by dead weight. The changes of the shrinkage percentages of the high-moor peat soil containing much inorganic dressing materials are large in the stage of the low moisture tension and small in that of the high one, while in the same soil under natural condition, the changes are large in both the stages of the low and the high moisture tension. Moreover, in these high-moor peat soils, the changes of their vertical shrinkage percentages are also larger than those of their horizontal ones in all stages of the moisture tension because of their subsidences by dead weight. To protect the land with high-moor peat soil from the qualitative change due to the shrinkage, it must be managed so that the moisture tension does not exceed about 41.8 kPa (pF 2.6) where the restoration after the shrinkage is perfect, namely, the moisture content is about more than the capillary one.
