Indications of ferrolysis and structure degradation in an Estcourt soil and possible relationships with plinthite formation

Abstract

Geographic associations of duplex soils, like the Estcourt form, and plinthic soils, like the Avalon and Westleigh forms, such as are found in the Eastern Free State, are recognised worldwide. These soils share redox morphology. In duplex soils, the redox morphology is dominated by a contrast in clay content between the A or E horizon and the B horizon, indicating that degradation of silicate clay minerals dominates. In plinthic soils, mottling due to redistributed Fe-Mn dominates. Both features can be the result of ferrolysis. In order to research this relatiC?nship, an Estcourt profile with degrading peds was sampled and analysed. Undisturbed peds of the Bhorizon were subdivided for analysis, together with disturbed samples of the A, E and C horizons. The spatial variation of the colours, Fe, Mn, clay content and mineralogy in the profile indicates that both ferrolysis and redistribution of Fe-Mn are active during short periods of reduction in the E and interpedal pores of the B horizon. Degradation of the silicate clay minerals results in ped degradation visible as rounded ped tops and grey material interfingering the B horizon. In this landscape, in soils of the Avalon and Westleigh forms, degraded peds are also present in the lower soft plinthic B horizons and underlying material with the degree of ped degradation visibly associated with the degree of redistribution of Fe-Mn in mottles and nodules. In this landscape, a transitional horizon with properties of both plinthic and degrading structured B horizons cov~rs large areas. This indi-. cates that plinthic and/or E horizons can develop from structured horizons under the current climate.

Selected soil properties as indicators of soil water regime in the Cathedral Peak VI catchment of KwaZulu-Natal, South Africa

“…The increase in pH water with depth may further be a sign of ferrolysis. Ferrolysis is the result of alternating reducing conditions, resulting in redoximorphic features, commonly found in these subsoils (Brinkman 1979, Le Roux et al 2005. Long durations of water saturation above drained upper limit (Kuenene 2007, Kuenene et al 2011) are an indication that reducing conditions occur in these subsoils and consequent oxidation may be responsible for the low subsoil pH water .…”

Interactions between stream channel incision, soil water levels and soil morphology in a wetland in the Hogsback area, South Africa

“…grey pore linings as recorded in observation groups 5, 6, 7 and 8 where root residues enhance microbiological activity in root pores, reduce the environment, dissolve and deplete the iron to form bleached pore linings to precipitate in an oxygenated soil matrix. The duration of the process limits the pronounced presence of iron precipitation as a quasi-ferran recorded in mature soils (Le Roux and du Preez 2004).…”

Formação e degradação de feições redoximórficas em solos do Pantanal - MT

“…Nesta área há maior ocorrência de ciclos de oxi-redução favorecendo o processo de ferrólise causando destruição de argilominerais (BRINKMAN, 1979;BOIXADERA et. al., 2003;LE ROUX, DU PREEZ, BÜHMANN, 2005 10 -5,0 3,9 2,8 0,2 0,6 1,3 0,5 11,4 17,4 2,6 19,9 12,9 57,1 1,1 Franco-argilosa Prof. = profundidade; AMG = areia muito grossa; AG = areia grossa; AM = areia média; AF = areia fina; AMF = areia muito fina; ADA = argila dispera em água e GF = grau de floculação Os processos argiluviação e ferrólise geram perdas no conteúdo de argila dos horizontes Bt, causando a degradação do topo destes horizontes que evoluem para um horizonte BE e com o avanço desses processos ocorre finalmente a transformação do BE em horizonte E (BULLOCK; MILFORD;CLINE, 1974;BRINKMAN, 1979;LINDBO et al, 2000;VAN RANST et al, 2011)…”