Abstract
We investigated several properties of water-stable soil aggregates giving special attention to macroaggregation (>0.25 mm), using 3 volcanic (group A) and 3 non-volcanic (group B) ash soils. 1) The contents of organic C (C), hydrolyzable carbohydrate (HC), readily hydrolyzable hexose (RH), and dithionite-citrate-bicarbonate soluble Al and Fe in the bulk soils and the aggregate size fractions were much higher in group A than in group B. 2) Among the macroaggregate size fractions of group A, the contents of the organic components such as C, HC, and RH generally increased with increasing aggregate size. The Al tended to be concentrated in the 0.25 to 1.0 mm size fractions. On the other hand, in group B, the organic and inorgaic components showed decreasing tendency with increasing aggregate size. 3) In group A, larger amounts of C, HC, RH, Al, and Fe were distributed in the macroaggregate than in the microaggregate size fractions. No such trend was observed in group B. 4) The degree of macroaggregation was much higher in group A than in group B. In group A, the higher the RH and Al contents, the higher the degree of macroaggregation. No such relationship was observed in group B. 5) From the results obtained, it was suggested that active Al and microbial polysaccharides merit close attention as the factors in the macroaggregation of group A, although the significant factors in group B remained unclear.
