Aggregate Stability of Tropical Soils in Relation to Their Organic Matter Constituents and Other Soil Properties

This study was carried out to determine the distribution of organic matter and its constituents, as well as other soil properties, in various aggregate size fractions for four soil types in Malaysia, and to investigate the relationship and relative importance of these soil properties on aggregate stability. The four soil series with contrasting particle size distributions used were Munchong (Typic Hapludox), Melaka (Xanthic Hapludox), Rengam (Typic Paleudult), and Bungor (Typic Paleudult). The top soil, i.e. 0-15 cm of the soils of the four soil series was sampled and analyzed for their particle size distribution, aggregation, aggregate stability, organic matter, humic acids (HA), fulvic acids (FA), polysaccharides, functional groups of HA and FA (carboxylic, COOH, and phenolic-OH), and free Fe and Al oxides. Multiple linear regression revealed that silt, followed by free Fe oxides, fine sand, FA-OH, and HA-COOH, were the most important soil constituents to explain the observed differences in the aggregate stability between the four soil types. Generally, as the aggregate size decreased, the amount of clay, silt, OM, and free Fe oxides would also increase, while the aggregation and the amount of sand would decrease. As for the Rengam and Bungor series, the aggregate stability would generally increase with the decreasing aggregate size. Meanwhile, the observed differences in the amounts of HA, FA, and polysaccharides were mainly due to the differences in the soil types