Soil characteristics and clay mineralogy of two subalpine forest spodosols with clay accumulation in taiwan

Two Spodosols with significant spodic morphological characteristics and clay accumulation were selected from a subalpine forest region where the elevation ranges from 2400 to 2700 meters, with high precipitation and low temperatures, and cool and humid weather conditions prevail. The objectives of this study were to investigate the soil characteristics, weathering patterns of clay mineralogy, and genesis of the two Spodosols with clay accumulation in the Chunta Mountain region of central Taiwan. We have also proposed modification of the description of Spodosols in Soil Taxonomy. Soil characteristics, clay distribution, low soil pH, and very low base saturation percentages caused by strongly leaching processes indicate that podzolization and clay illuviation are the pedogenic processes in the study area. The subsurface horizons of the two Spodosols meet the chemical criteria of the spodic horizon defined in Soil Taxonomy, which suggests that translocation of spodic materials has occurred. The value of organic carbon and Fep/Feo or Alp/Alo ratio reaches a profile maximum in the spodic horizon, which suggests that the spodic horizon was formed predominantly by the illuviation of organo-metallic complexes. Soluble organic matter leached with soil solutions along the soil pores from the upper horizons to the spodic horizon. The spodic horizon is characterized by many black and other dark pellets of organic matter. The clay mineralogy of the A and albic horizons is dominanted by illite, vermiculite and vermiculite-illite interstatified minerals (VI), but the Bhs horizons contain mainly vermiculite and hydroxy-interlayer vermiculite (HIV). The clay mineralogy of the eluvial horizons differs somewhat from that in the illuvial horizons as a result of moderate weathering. The weathering sequence of clay minerals in these two loamy Spodosols is: illite → vermiculite (or VI) → HIV. According to the USDA Soil Taxonomy, the two pedons with clay accumulation can be classified as a Typic Haplohumod and a Typic Haplorthod.