Geochemistry in relation to soil colour, physicochemical properties, weathering pattern and metal contamination of laterite-associated soils of Kerala, India
Year: 2026
Type: preprint
Abstract: Geochemical indicators provide valuable insights into the degree of weathering/laterization and help to elucidate the relationships between pedogenic processes with the physicochemical properties of rubified soils of Malabar region. This study investigated five representative laterite-associated soil series—Madgaon, Darbandora, Kinalur, Kanjirapalli and Athirampuzha—from the southern midland zone of Kerala, India, to assess their morphological, physical, chemical and elemental characteristics in relation to weathering intensity and metal contamination. The soils were characterized by high organic carbon (>1.5%) and very dark reddish-brown to dark reddish-brown Ap horizons, whereas the subsurface horizons exhibited dark red to red with a 2.5YR hue and clay enrichment. These soils have argillic/kandic horizons and classified in the subgroup of the Ultisols and Alfisols orders. Significant relationships were observed between CIE L a b* colour parameters and selected soil properties, with regression models providing reasonable estimates of organic carbon (R² = 0.78, P < 0.01) and Al₂O₃ (R² = 0.67, P < 0.01). The Kanjirapalli and Athirampuzha series contained >20% Al₂O₃ and exhibited a high degree of weathering based on the Chemical Index of Alteration, Index of Laterization, Mafic Index of Alteration and other diagnostic weathering indices. Harker and ternary diagrams indicated intense in situ weathering, preferential enrichment of Al-bearing minerals and relatively weak laterization, as reflected by the SiO₂–Al₂O₃–Fe₂O₃ (SAF). The A–CN–K diagram indicated progressive loss of base cations and development of a kaolinitic to kaolinite–smectite mineral assemblage, while the ALF and AF–CNK–M diagrams further supported extensive desilication and base depletion during pedogenesis. Assessment of metal contamination indicated moderate enrichment of Fe and Al, whereas Cd showed high to extremely high contamination based on the geo-accumulation index (Igeo) and enrichment factor. In contrast, Cu, Zn, Cr and Ni remained within baseline levels and exhibited low potential ecological risk, with a pollution load index (PLI) < 1. The results demonstrate the value of series-level geochemical datasets for characterizing spatial variability in weathering intensity, identifying pedogenic thresholds and interpreting the influence of parent material and climatic conditions on soil development. Such information provides a useful basis for understanding soil evolution and supporting sustainable land-use and soil management in the rubber-growing regions of Kerala. Clinical Trial Registration This study is not a clinical trial. It involved field-based and laboratory investigations of laterite-associated soils and did not involve human participants, patients, clinical interventions, or medical treatments. Therefore, clinical trial registration is not applicable.
Source: Research Square
Language: English
Subfield: Soil Science
Domain: Life Sciences
SDGs: Life on land, Zero hunger
Open Access status: green
OpenAlex ID: W7225163664