Driving factors determining the occurrence of sodic soils in dry subhumid Mediterranean areas

Abstract

An evaluation of the factors determining the occurrence and the properties of soils with low permeability occurring in vast areas in S Portugal was carried out taking into account the terrain morphology and the geology of the region. This paper deals with the variation patterns of the physical and chemical characteristics of soils from several soil toposequences that occur under different gradient slopes and on different parent rocks. Spatial variation of soil properties mainly depends on the composition of their cation-exchange complex, as the role of other factors, such as the mineralogy of the clay fraction, were of minor importance. There is often a stronger increment of Na and/or Mg than of Ca with depth, causing a variable degree of sodicity in some of these soils, to which waterlogging tendency of their upper horizons is related. Though the occurrence of these features is determined by the nature of the parent rock, their degree of expression varies primarily according to the topographic position of soils. Therefore, a catenary distribution including nonsodic Cambisols or Luvisols in the hillcrests and Stagnic Solonetz or Sodic Luvisols or Sodic Stagnosols in the topographic lows is common. Such soil characteristics are of utmost importance for irrigation suitability and management of these soils, and for environmental impacts assessment, as the region is vulnerable to desertification.

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

“…The limitation of water flow, trigged by the combination of shallow water table and/or near-impervious subsurface horizons/layers with locally depressed topography, is responsible for water confinement and low levels of salt leaching, which may increase evaporation rates and aggregate instability (Westin, 1953;USSL Staff, 1954;Munn and Boehm, 1983;Indorante, 2006). Commonly, local maximum ion accumulation, expressed by the highest EC and/or ESP values, occurs in slight depressions of near-flat landscapes, floodplains, low terraces or footslope positions (Whittig, 1959;USSL, 1954;Fehrenbacher et al, 1963;Sandoval and Reichman, 1971;Abtahi, 1977;Abtahi, 1980;Fanning and Fanning, 1989;Heck and Mermut, 1992;Singh and Kar, 2001;Monteiro et al, 2012). To a much lesser extent, Saline, Sodic and Saline-Sodic soils are registered on topographical highs, such as summits, upper slopes or micro-elevations.…”

Phosphorus sorption and desorption properties of soils developed on basic rocks under a subhumid Mediterranean climate

“…Despite their high base saturation, the studied soils show a large difference between pH in water and KCl, which cannot be ascribed to exchangeable Al. Monteiro et al. (2012) suggested that it can result either from the replacement of the nonexchangeable component of acidity by K + , or from the suppression of Na hydrolysis in the presence of KCl.…”

“…Despite their high base saturation, the studied soils show a large difference between pH in water and KCl, which cannot be ascribed to exchangeable Al. Monteiro et al (2012) suggested that it can result either from the replacement of the nonexchangeable component of acidity by K + , or from the suppression of Na hydrolysis in the presence of KCl. On average, the contents in clay, crystalline Fe oxides (as measured by Fe d ) and poorly crystalline forms of Al (as measured by Al ox ) significantly increase from the A to the B horizons (Table 3).…”

Paleoenvironmental Conditions during the Paleocene–Eocene Transition Imprinted within the Glauconitic Giral Member of the Barmer Basin, India

“…Such abnormally high Na 2 O content in glauconite is rarely addressed [69][70][71]. The high Na content in glauconite may indicate the dissolution of volcaniclastic constituents, enriching the porewater [72]. Alternately, the chemical interaction with Na-rich groundwater can form Na-rich glauconite [73].…”

“…Thus, the dissolution of volcaniclastics seems to be the most plausible source of high Na + within the Giral glauconites. The Na-rich porewater possibly led to the incorporation of Na + into the glauconite structure [72,75].…”