Genesis and Classification of Sodic Soils in the Northern Pantanal

Abstract

ABSTRACT:The simultaneous occurrence of high levels of exchangeable sodium percentage (ESP) and alkalinity in soils imposes restrictions on plant development and affects physical properties such as porosity, bulk density, permeability, and hydraulic conductivity. Although sodic soils are frequent in the flood plain of the São Lourenço River, northern Pantanal, Brazil, few studies focus on their formation and classification, especially with regard to specific processes and detailed classification into lower categorical levels by the different systems available. The aim of this study was to identify the predominant pedogenetic processes occurring in sodic soils of the flood plain of the São Lourenço River to understand their genesis and assess how taxonomic classification systems contemplate the variations in soil properties. Five profiles were selected in sites with different progressive stages of dissection from erosion (P1, P2, P3, P4, and P5). At each site, a pit was dug for morphological description of the profiles and for collecting samples for chemical, particle size, mineralogical, micromorphological, and chronological analyses. Each profile was classified according to the Soil Taxonomy, World Reference Base (WRB), and Brazilian Soil Classification System (SiBCS/ Sistema Brasileiro de Classificação de Solos). Argilluviation is the predominant process, with a localized and intense ferrolysis action in the E/Bt transition zones in profile P5. Soils showed signs of lithologic discontinuity. This makes it difficult to distinguish how much of the textural gradient is inherited from fluvial sedimentation processes and how much is the result of pedogenetic processes. In the most advanced stage of alteration, P5 had a paler color, thickening of the E horizon, and an abrupt and irregular transition entering the Bt horizon in the form of a "tongue". When passing from the most preserved to the most eroded area, ferrolysis becomes more intense in the E/Bt transition, the electrical conductivity values decrease, and the ESP values increase, suggesting the sodification process. Under Soil Taxonomy criteria, P5 was classified as Natraqualf and the other profiles were classified as Natrudalf; under the WRB, however, all profiles were classified as Solonetz. The SiBCS exhibited variation at the Order level, with P5 classified as Planossolo and the others as Luvissolo. Despite an indication of different processes at the Order level, the SiBCS does not yet contemplate the sodic character in the studied Luvissolos. We propose inclusion of the sodic character at the Great Group level, as has already occurred with other SiBCS classes.

Salt-affected soils on elevated landforms of an alluvial megafan, northern Pantanal, Brazil

“…The studied trench is located in an ancient lobe of the São Lourenço megafan that has experienced intense and regional erosion (Nascimento, 2012), which has probably been magnified in the more humid conditions of the last 2600-3000 years (Bertaux et al, 2002;Whitney et al, 2011;McGlue et al, 2012). Thus, continuous elevated zones formed by paleochannels-paleolevees have been destroyed, connecting the flood drainage, which favors leaching and prevents Na + accumulation through evaporative concentration (Nascimento et al, 2015;Oliveira Junior et al, 2017a, 2017b. Consequently, greater sediment mobilization due to erosion occurred in the sandy areas of the paleochannel-paleolevee complexes, leaving the finer (silty/clayey) and more resistant areas in discontinuous narrow topographical highs (Fig.10c).…”

Epi and endosaturation affecting redoximorphic features and pedogenesis in subtropical soils with high textural contrast developed from sedimentary rocks

“…Textural contrast in soils is usually due to clay illuviation processes (Soil Survey Staff, 1999) or lithologic discontinuity caused by the deposition of coarser sedimentary material on a pre-existing soil (Schaetzl, 1998;Michelon et al, 2010). However, although many of these soils present morphological features and properties indicative of argilluviation processes (Kämpf and Curi, 2012), the hypothesis that high textural contrast can also be formed by the contribution of processes such as ferrolysis (Brinkman, 1970(Brinkman, , 1977(Brinkman, , 1979Jimenez-Rueda and Demattê, 1988;Andrade, 1990;Almeida et al, 1997;Oliveira Junior et al, 2017) is not discarded.…”

Flooding effect on mineralogical and geochemical changes in alkaline‐sodic soil system of northern Pantanal wetlands, Brazil

“…In the sample Btk, calcite peaks were identified at 3.03, 2.28 and 2.09 A d‐spaces. This phase occurs as precipitates, confirmed in the soil morphological description in the field by the reaction with diluted hydrochloric acid (HCl) (Oliveira Junior, Beirigo, et al, ; Oliveira Junior, Chiapini, et al, ).…”

“…The soil distribution in the northern Pantanal is closely associated with the landscape. At the highest altitudes (palaeolevees), Natrustalfs, with a Bt horizon and high exchangeable sodium percentage (ESP) values, prevail; in the lowest altitudes (floodable areas) Plinthaquults are more common, whereas Quatzipsamments occur in the palaeochannels (Nascimento et al, ; Oliveira Junior, Beirigo, et al, ; Oliveira Junior, Chiapini, et al, ). Soils with high ESP and carbonate precipitates have been observed in the highest ground (approximately 3 m above the floodplain) that originated from these elongated palaeolevees (Nascimento et al, ; Oliveira Junior, Beirigo, et al, ; Oliveira Junior, Chiapini, et al, ), but little is known about their mineralogical characteristics.…”