Clay Mineralogy of Spodosols with High Clay Contents in the Subalpine Forests of Taiwan

Abstract

Three Ultic Haplorthods with significant illuviation of clay and spodic materials in the subalpine forests located in the Alishan area of central Taiwan were selected to identify the clay mineral compositions by X-ray diffraction (XRD) and to explain the transformation of the clay minerals. The three pedons are dominated by vermiculite and vermiculite-illite interstratified minerals, and they have minor kaolinite, quartz and gibbsite. No hydroxy interlayered vermiculite (HIV) was found in the E horizon of the three pedons because the forest soils are very acidic and have very low Al contents. The presence of HIV in the spodic (Bhs) and argillic horizons (Bt) of the three pedons was associated with greater free Fe and Al contents (Fe d and Al d ), more favorable pH ranges, and coatings of organo-metallic complexes which prevented continuous weathering. The specific pedogenic process, clay illuviation and podzolization occurred sequentially in the Alishan area, and induced the unusual clay mineral distribution and transformation. The largest amounts of illite are in the C horizon and the amounts of vermiculite increased with decreasing soil depths. A reverse distribution between illite and vermiculite through the soil profile was observed. Illite was transformed to vermiculite due to the strong weathering environment associated with extremely low exchangeable K contents. The weathering sequence of clay minerals of Spodosols with fine textures in the study area is proposed as: illite ? vermiculite (or interstratified vermiculite-illite minerals) ? HIV and vermiculite.

Review Article. What are the nature and formation conditions of hydroxy‐interlayered minerals (HIMs) in soil?

“…In addition, the increase of pH in illuvial horizons favors precipitation of oxides, hydroxides and allophane‐like compounds. This is reflected in larger contents of oxalate‐ and dithionite‐extractable Al and Fe in illuvial than in eluvial horizons ( Lin et al, ; Bonifacio et al, ). Thus, it is not obvious that dissolved Al 3+ is available for intercalation in illuvial horizons.…”

“…Egli et al (2001) detected HIV in the Bhs and Bw horizons of a 11-kyr-old Haplic Podzol. The accumulation of HIMs in illuvial soil horizons was reported several times (e.g., Lin et al, 2002;Liu and Chen, 2004;Skiba, 2007;Nakao et al, 2009). Lin et al (2002) detected HIV in Bt and Bhs horizons of Spodosols in Taiwan, but not in E horizons.…”

Hydroxy‐Al polymers block the frayed edge sites of illitic minerals in acid soils: studies in southwestern Japan at various weathering stages

“…Hydroxy-interlayered vermiculite (HIV) is a common 2:1 phyllosilicate occurring in moderately acidic soils in humid temperate regions (Bain et al, 1990;Funakawa et al, 1993;Carnicelli et al, 1997;Lin et al, 2002). The pillared hydroxy-Al polymers reduce the cation-exchange capacity of 2:1 phyllosilicate, as well as its expandability, which may markedly affect the availability and dynamics of plant nutrients and pollutants.…”

Mineralogy and Genesis of Mixed-Layer Illite-Vermiculite in the Homogeneous Red Soil and the Net-Like Red Soil of Xuancheng, China

“…In acidic soil of New Zealand and Scotland, mixed-layer illite-vermiculite is considered to be the weathering product of dioctahedral mica (Bain et al, 1990;Churchman, 1980). Mixed-layer illite-vermiculite in Taiwan was originated from the weathering of illite (Lin et al, 2002). Therefore, the occurrence of mixed-layer illite-vermiculite indicated that the weathering was intensified.…”

“…Vermiculite is usually formed in the relatively warm climate from illite under the environment of PH<6. When illite is incompletely transformed to vermiculite, mixed-layer illite-vermiculite might be formed (Lin et al, 2002). Compared to homogeneous red soil samples, the clay mineral layers net-like red soil samples were more significantly tortuous (Fig.3a, b …”