Abstract
Clay minerals are intermediate products generated during soil development, and their neoformation and transformation are closely related to pedogenesis. Here we aimed at identifying the difference in the clay mineral composition of upland soils derived from different parent materials and different soil-forming environments and exploring the importance of clay mineral composition in pedogenesis and soil taxonomy. We sampled 60 soil B horizons in Hunan Province of subtropical China by digging soils derived from granite (GR), slate and shale (SS), Quaternary red clay (QRC), limestone (LS), and sandstone (SDS). The clay mineral composition and its correlation with parent materials, elevation, micro-topography, and pedogenic processes were investigated using X-ray diffraction and Pearson’s correlation analysis. The clay mineral was dominated by kaolinite, followed by 2:1-type minerals (illite and vermiculite), and a small fraction of mixed-layer minerals. The composition of soil clay minerals varied with parent materials. Kaolinite was predominant in soils derived from GR and LS; mixed-layer minerals prevailed in QRC, whereas illite and vermiculite were prevalent in SDS. In addition, elevation and micro-climate could also explain the variations in clay mineral composition. Increase in elevation was associated with decreased 1:1 clay mineral content and increased 2:1 clay mineral content, especially in soils developed from LS. The composition and content of clay minerals indicated that Ferrosols, Ultisols, and Acrisols had undergone intense weathering; Primosols, Entisols, and Leptosols were characterised by weak weathering, and Plinthic Ali-Udic Cambosols, Plinthudults, and Plinthosols were characterised by strong redox status. This study suggests that clay mineral composition is related to the parent material, climate, and micro-topography, and that it can serve as an indicator of pedogenesis and soil type in subtropical China.
Highlights
Clay minerals are among the essential components of the solid soil phase, and their composition and relative content can affect many physical and chemical properties and the nutrient status of the s oil[1]
The clay minerals in upland soils were composed of 1:1-type clay minerals kaolinite (0.71–0.73 nm, 0.35–0.36 nm), 2:1type clay minerals illite (1.0–1.03 nm), vermiculite (1.42–1.49 nm shifting to 1.0–1.03 nm after heating), and mixed-layer minerals illite/vermiculite (I/V), and illite/smectite (I/S) (1.45–1.66 nm shifted to 1.0–1.02 nm after heating) (Fig. 2)
The relative content of clay minerals varied among upland soils derived from different parent materials (Fig. 3)
Summary
Clay minerals are among the essential components of the solid soil phase, and their composition and relative content can affect many physical and chemical properties and the nutrient status of the s oil[1]. Studies on the effects of different parent materials and pedogenic environments on the composition and content of clay minerals and their dynamic variation among different soil types are of theoretical importance. A few studies have investigated the variation in the composition of clay minerals derived from diverse parent materials (more than three parent materials) and the effects of comprehensive environmental factors (e.g., elevation and micro-topography) on clay minerals in the subtropics. In the present study, we selected 60 upland soils derived from five parent materials in the Hunan Province and analysed the effect of different parent materials, soil environments, diagnostic horizons, and soil types on clay mineral types and contents using X-ray diffraction. The goals of this study were to (i) investigate the effects of diverse parent materials and environmental factors (elevation and micro-topography) on soil clay mineral composition and (ii) explore the evolution of clay minerals during soil development and its implications for soil taxonomy
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