Lateritic soils of Kerala, India: their mineralogy, genesis, and taxonomy

Abstract

In this study, we report the chemical and mineralogical characteristics of 4 benchmark Ultisols of Kerala to elucidate their genesis and taxonomy. The taxonomic rationale of the mineralogy class of Ultisols and other highly weathered soils on the basis of the contemporary pedogenesis is also explained. The Ultisols of Kerala have low pH, low cation exchange capacity, low effective cation exchange capacity and base saturation, with dominant presence of 1 : 1 clays and gibbsite. Presence of gibbsite along with 2 : 1 minerals discounts the hypothesis of anti-gibbsite effect. Since the kaolins are interstratified with hydroxy-interlayered vermiculites (HIV), the formation of gibbsite from kaolinite is not tenable. Thus, gibbsite is formed from primary minerals in an earlier alkaline pedo-environment. Therefore, the presence of gibbsite does not necessarily indicate an advanced stage of weathering. On the basis of a dominant amount of gibbsite, a mineralogy class such as allitic or gibbsitic does not establish a legacy between the contemporary pedogenesis and the mineralogy. The dominance of kaolin–HIV in the fine clays of Ultisols and their persistence, possibly since early Tertiary, suggests that ‘steady state’ may exist in soils developed on long-term weathered saprolite. Since the present acid environment of Ultisols does not allow desilication, the chemical transformation of Ultisols to Oxisols with time is difficult to reconcile as envisaged in the traditional model of tropical soil genesis.

Phosphate sorption and desorption by Thai upland soils

“…Gibbsite is present only in Oxisols derived from limestone (Ak1) and basalt (Ti1, Ti2, Ti3, Nb1 and Nb2) under more humid conditions. The presence of gibbsite along with HIV minerals which has been referred to as the "antigibbsite effect" (Jackson, 1963;Chandran et al, 2005) occurs in Ti1, Ti2, Ti3, Nb1 and Nb2 soils.…”

Rock magnetic properties of lateritic soil profiles from southern India: Evidence for pedogenic processes

“…The laterites seen in Kasaragod District are predominantly ferruginous (Soman, 1997). The lateritic soils of Kerala are grouped as 'ultisols' under the United States Department of Agriculture soil taxonomy with kaolinite, gibbsite and vermiculite as the dominant minerals (Chandran et al, 2005).…”

Soil Classification Following the US Taxonomy: An Indian Commentary

“…The introduction of this subsurface diagnostic horizon and inclusion of “kanhapl” intergrade helped group many low activity clay Inceptisols into Alfisols (>35% base saturation) or Ultisols (<35% base saturation). Although the Inceptisols have been grouped properly as Kandi (c) Alfisols and/or Ultisols, the formation and existence of Oxisols have been debated (Chandran et al, 2005; Pal et al, 2014). The kandic horizon provides a basis for differentiation among soils with clay accumulation in the subsoils.…”

“…⋅ gibbsite content in < 2 mm fraction of soil is > 18%# in the soil control section (Chandran et al , 2005) (Method 2)…”