5. Conclusions
The impacts of contents of SOC and Fe/Al oxides and puddling intensity
on soil aggregate distribution and cracking patterns in two different
paddy soils were investigated. For the young paddy soil (YPF soil), the
Fe/Al oxides were key binding agents for microaggregates and claysized
aggregates, whereas the SOC plays a primary role in stabilizing
macroaggregates. The SOC was dominant agent for stabilizing aggregates
of all sizes in the old paddy soil (OPF soil). The increase of simulated
puddling intensity increased clay- and silt-sized aggregates, and consequently
resulted in an increase in crack area density (Dc) and crack
average width (AW). The removal of SOC and Fe/Al oxides generally
resulted in larger Dc and AW except DCB treatment in the YPF soil. The
physical effect of removal of SOC and Fe/Al oxides contributed more to
Dc and AW than chemical effect. The chemical effect of Fe/Al oxide