Genesis of soils across a late Quaternary volcanic landscape in the humid tropical island of Leyte, Philippines

Abstract

This study evaluated the characteristics and genesis of soils across a young volcanic landscape in the humid tropical island of Leyte, Philippines. Five representative soil pedons (P1–P5) derived from late Quaternary volcanoclastics (i.e. fragmental) on a hillslope sequence were examined and sampled. Results revealed that the soils have generally similar morphological characteristics particularly in terms of soil colour (10YR 3/3–10YR 5/6) and soil structure (granular to subangular blocky), but differed in terms of soil thickness and clay content, which was higher in P3 than the other pedons across the landscape. The high porosities of the soils were the results of high organic matter, the dominance of noncrystalline (short-range order) minerals, as well as the isovolumetric weathering in the subsoils. All soils have very similar chemical properties (e.g. acidic, high organic carbon, low exchangeable bases), except soils from the middle backslope position (P3), which have high cation exchange capacity because higher exchangeable Ca and K result in a higher base saturation. Allophane, goethite, ferrihydrite, and gibbsite are the dominant clay minerals in the soils. Principal component analysis revealed that P3 was distinct from pedons P1, P2, P4, and P5, suggesting that it was substantially different from all other soils across the landscape. Soil formation was relatively fast due to the easy weatherability of the parent materials, high rainfall, and good drainage of the soils along the landscape. This study revealed that on young volcanic soils under humid tropical condition, topography greatly influenced soil development.