Changes of Soil Aggregation Structure in the Subsurface Andosols after Being Reclaimed for Arable Land

Abstract

Wet-sieving test in combined with disaggregating pre-treatments (from gentle to vigorous) were applied to investigate the change in soil structure of subsurface Andosols after being reclaimed for arable land. Aggregates of subsurface soil under natural condition was utterly stable to slaking, and stable to oscillation disruption to some extent. In contrast, the aggregates in the reclaimed soils appeared to break down gradually into smaller aggregates as pre-treatment being intensified. These facts indicated that the aggregate hierarchy existed in the reclaimed soil, while in the natural subsurface soil, structure characteristic was more like clod. Soil organic C was showed to be increased with cropping and fertilization practice, while free iron oxides in the soil was decreased. Iron oxides contents in the aggregates and result of deferration experiment indicated that the iron oxides was the predominate stabilizing agent of the natural subsurface soil. However, the role of iron oxides on the stabilization was very weak in the reclaimed soil. Organic C content was constantly high for the small aggregates, which suggests the increase of smaller aggregates in the reclaimed soil may be attributed to the increase in organic matter in the soil. It was concluded that by reclamation, natural subsurface soil which contained large amount of iron oxide cemented clod could be turned into well aggregated soil.