Changes in forest soil aggregates under repeated dry-wet moisture conditions

Three, four, and five millimeters soil aggregate samples were collected from the A horizons of a Japanese cypress (Chamaecyparis obtusa Endl) and broad leaf stand and incubated for 14 d under three different moisture conditions: dry, repeated dry-wet cycle, and wet. The 3- and 4-mm aggregates from both stands incubated under repeated dry-wet conditions were easily dispersed by slaking, whereas similarly incubated 5-mm aggregates were not as readily dispersed. The degree of aggregate dispersion varied by aggregate size, with larger aggregates being less readily dispersed than smaller aggregates. Moreover, there was no clear difference in degree of aggregate dispersion between stands. Aggregate dispersion was not observed in aggregates incubated under wet conditions.