Ferrolysis induced soil transformation by natural drainage in Vertisols of sub-humid South India

Abstract

In sub-humid South India, recent studies have shown that black soil areas (Vertisols and vertic Intergrades), located on flat valley bottoms, have been rejuvenated through the incision of streambeds, inducing changes in the pedoclimate and soil transformation. Joint pedological, geochemical and geophysical investigations were performed in order to better understand the ongoing processes and their contribution to the chemistry of local rivers. The seasonal rainfall causes cycles of oxidation and reduction in a perched watertable at the base of the black soil, while the reduced solutions are exported through a loamy sand network. This framework favours a ferrolysis process, which causes low base saturation and protonation of clay, leading to the weathering of 2:1 then 1:1 clay minerals. Maximum weathering conditions occur at the very end of the wet season, just before disappearance of the perched watertable. Therefore, the by-products of soil transformation are partially drained off and calcareous nodules, then further downslope, amorphous silica precipitate upon soil dehydration. The ferrolysed area is fringing the drainage system indicating that its development has been induced by the streambed incision. The distribution of 14 C ages of CaCO 3 nodules suggests that the ferrolysis process started during the late Holocene, only about 2 kyr B.P. at the studied site and about 5 kyr B.P. at the watershed outlet. The results of this study are applied to an assessment of the physical erosion rate (4.8 × 10 − 3 m/kyr) since the recent reactivation of the erosion process.

Formation and preservation of pedogenic carbonates in South India, links with paleo-monsoon and pedological conditions: Clues from Sr isotopes, U–Th series and REEs

“…Both watersheds have similar substratum, saprolite and soil cover which have been studied in detail for the Mule Hole watershed (Barbiéro et al, 2007(Barbiéro et al, , 2010Braun et al, 2009;Violette et al, 2010). The parent material is composed of the Peninsular gneiss of the >2.8 Ga West Dharwar craton (Naqvi and Rogers, 1987) intermingled with much less abundant mafic to ultramafic rocks, mostly amphibolite, of the Sargur series (Shadakshara Swamy et al, 1995).…”

“…The pedogenic carbonate sampling is based on previous pedological studies carried out within both Mule Hole and Maddur watersheds (Barbiéro et al, 2007(Barbiéro et al, , 2010. Two soil sequences and an erosion spoon at Mule Hole (Fig.…”

Revisiting ferrolysis processes in the formation of Planosols for rationalizing the soils with stagnic properties in WRB

“…The soil-forming process, termed ferrolysis, was proposed by Brinkman (1970), to explain clay decomposition and interlayering in acid, seasonally wet soils. Ferrolysis involves cyclic reduction and oxidation of iron in an open system that allows evacuation of the reduced solution from the ferrolysed area (Barbiero et al, 2010). During the reduction phase, iron (III) oxides are reduced and the ferrous iron formed displaces exchangeable cations, including Al, on the silicates with surface charge.…”

“…Since the eighties, several studies also have questioned the incidence of ferrolysis and indicated that ferrolysis as process to destroy open 2:1 clay minerals and to form soils with contrasting texture has been overestimated (Boivin et al, 2004;Eaqub and Blume, 1982;Favre et al, 2002;Montagne et al, 2008;Van Ranst and De Coninck, 2002). Meanwhile, few studies are based on the monitoring of the physicochemical characteristics of the soil solutions to validate or not the occurrence of ferrolysis as the transformation process (Barbiero et al, 2010;Boivin et al, 2002;Hobson and Dahlgren, 1998).…”

Influence of redox processes on clay mineral transformation in Retisols in the Carpathian Foothills in Poland. Is a ferrolysis process present?

“…It involves destruction of clay minerals due to cyclic reduction and oxidation in acidic and periodically wet soils (Brinkman 1970;Barbiero et al 2010). Ferrolysis involves biochemical reduction of Fe 3+ taking place during wet seasons and leading to mobilization of Fe and substitution of exchangeable cations within clay minerals with Fe 2+ .…”