Aggregate stability and size distribution of red soils under different land uses integrally regulated by soil organic matter, and iron and aluminum oxides

The stability and size distribution of soil aggregates is profoundly affected by land use, but the influencing mechanisms of land use are not clear. A study was carried out to investigate and attempted to interpret the effects of land use on soil aggregates from types of land use and soil properties in soil samples and size fractions of soil aggregates. Soil samples were taken from 9 sites under paddy, forest, and upland in southern China. The wet-sieving method was used to obtain 6 size fractions of soil aggregates: >5, 5-2, 2-1, 1-0.5, 0.5-0.25, and <0.25 mm. The stability and size distribution of soil aggregates was measured as mean weight diameter (MWD), the percentage of water-stable aggregate (WSA) and the percentage of each size fraction (PSA). The quantities of soil organic carbon (SOC), humic substances, dithionite-citrate-bicarbonate (DCB) and oxalate extractable iron (Fe) and aluminum (Al) oxides were also measured. The results showed that types of land use solely explained 66.6% variation of soil aggregates; SOC, DCB-extractable Fe and Al oxides, and oxalate-extractable Al oxide caused 84.3% variation, in which SOC contributed 29.0%, Fe and Al oxides contributed 33.8%, and their interactions contributed 21.4%. The multiple linear regression and partial correlation analysis showed that soil organic matter and Fe and Al oxides had significant effects but played different roles on the stability and size distribution of soil aggregates. The study suggests that land use affects the stability and size distribution of soil aggregates through the integration of soil organic matter and Fe and Al oxides.