Abstract
The authors studied the stability of aggregates due to soil humus of volcanic and nonvolcanic ash organic soils, so-called Kuroboku soil, through analysis of water-stable aggregates, water holding capacity and penetrated depth by kneading.
The results obtained are summarized as follows:
1) The aggregates of each soil are reduced in size by kneading. However, coarse aggregates of nonvolcanic ash organic soil become smaller than those of volcanic ash organic soil.
2) The difference between volcanic and nonvolcanic ash organic soil are observed in the low region of soil moisture suction. In case of volcanic ash organic soil, pF increases due to kneading. On the other hand, in case of nonvolcanic ash organic soil, pF decreases as a result of kneading.
3) The penetrated depth by kneading of volcanic ash organic soil is much the same as that for nonkneading. But the penetrated depth due to kneading of nonvolcanic ash organic soil remarkably increases.
From the above results, we considered that coarse aggregates of volcanic ash organic soil are more stable than those of nonvolcanic ash organic soil.
