Effects of different forms of Fe and Al oxides on soil aggregate stability in midsubtropical mountainous area of southern China

Soil aggregation is an important soil physical property that controls water storage,aeration,fertility,plant growth,and biological activity. Soil aggregates are formed as a result of rearrangement,flocculation,and cementation of particles. They are controlled by soil organic carbon,biota,and mineral particles( clay and oxides). Fe and Al oxides,as important inorganic binding agents for aggregates,have attracted increasing attention in tropic and sub-tropic areas where soils are rich in oxides. Oxides can contribute to aggregation in three ways: Oxides as a flocculant in soil solution; organic materials adsorbed on oxide surfaces; and a coat of oxides formed on the surface of minerals that creates bridges between primary and secondary particles. However,owing to the difference in degree of crystallinity,particle size,and distributionof oxides,the debate on the effect of oxides on aggregate formation and stability has continued. The subtropical mountainous area of southern China is a major timber plantation reg