Surface and Charge Characteristics of Selected Soils in the Tropics

Abstract

Specific surface area and surface charge characteristics of some Alfisols and Ultisols from Nigeria were studied. Specific surface are measured by ethylene glycole retention was generally 2 to 3 times greater than the specific surface area measured by N2 adsorption for both surface and subsoil samples. Soils derived from basalt had the greatest surface area per gram of clay as measured by both methods.The surface charge‐pH curves of the soils bear the characteristic features of metallic oxides, indicating that surface charge behaviour of the soils studied follows the constant potential model. Values of PZC for Alfisol and Ultisol samples ranged from pH 3.0 to 3.9. Subsoils generally have higher PZC than corresponding surface horizons. Specific adsorption of sulfate resulted in a shift of the PZC to a higher value and an increase in the magnitude of positive charge.Cation and anion retention measurements showed that soils derived from basement complex rocks and sandstones contain negligible amount of positive charge while soils from basalts bear moderate amount of positive charge at their natural pH condition. Evidence also indicated that the Alfisols and Ultisols bear a small amount of permanent negative charge ranging from 1 to 4 meq/100 g.The limitation of using CEC value determined by conventional procedures as a criteria for soil taxonomy is discussed.

Effect of Selective Dissolution on Charge and Surface Properties of an Acid Soil Clay

“…Surface areas calculated for the dissolved minerals based on weight loss due to the treatments agree well with surface areas of oxides from several different soil types studied by Gallez et al (1976) and Greenland et al (1968), who estimated surface areas both by surface-area reduction following dithionite treatment (100--400 m2/g) and from electron micrographs of the untreated soils (150-300 m2/g). One possible error in the assumption that all of the loss in surface area upon chemical treatment could be attributed to the dissolved oxides is the likely improved efficiency of stacking of layer silicate plates, reducing Figure 2.…”

“…This sort of behavior was reported for the titration curves of spodosols (Laverdiere and Weaver, 1977) and of an aluminum peat (Bloom, 1979). All of the crossover points are at pH values above those at which Ca2+-exchange capacity was equal to the C1--exchange Units of meq/100 g, estimated error limits of + 0.2 meq/100 g. capacity; this difference between the crossover pH and the pH of ZPC has been noted by several authors (Gallez et al, 1976;Parker et al, 1979;Gillman and Uehara, 1980). The difference may be attributed to the specific sorption of Ca 2+ in the CEC measurements or simply to a greater ability of Ca ions to displace sorbed A1 species.…”

Pedogenesis significantly decreases the stability of water-dispersible soil colloids in a humid tropical region

“…0.001 to 0.1 mol l −1 ) intersected one another (Fig. 2) in accord with the prior studies of kaolinitic tropical soils from Hawaii (Chorover and Sposito, 1995) and some Alfisols and Ultisols from Nigeria (Gallez et al, 1976). The pH PZC of the surface charge-pH curves was on the acid side of the zero point of titration (where equal quantities of HCl and NaOH were added), which was attributed to the presence of permanent negative charge (Van Raij and Peech, 1972).…”

The cation‐ and anion exchange characteristics of soils with a large sesquioxide surface area

“…The regression coefficients of Eqs. 1 and 2 were calculated by the method of least squares for the soils of Table 2, and the data of Gallez et al (1976) and van Ray & Peech (1972).…”