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ABSTRACT: Surface charge characteristics were investigated using a charge fingerprinting procedure for 90 samples from
32 profiles of highly weathered Oxisols and Ultisols derived from shale/limestone, basalt, granite, local alluvium,
sedimentary, and metasedimentary rocks under tropical savanna and tropical monsoonal climates in Thailand. The charge
fingerprints of 5 whole soils, after removal of organic matter and of kaolin and ion oxides from these soils, were also
measured to clarify factors contributing to the variable charge behaviour. Phosphate sorption was determined and related to
charge properties. Kaolin was the dominant mineral of the clay fraction with moderate amounts of goethite and hematite.
Gibbsite was present in Oxisols formed on limestone and basalt under more humid conditions. All soils exhibited variable
charge behaviour but the magnitude and rate of change in variable charge with pH varied greatly between Oxisols and
Ultisols. Oxisols had higher amounts of variable charge than Ultisols, reflecting the differences in amounts of clay and
extractable Fe and Al. Oxisols formed on basalt and limestone under more humid conditions had high values of anion
exchange capacity (AEC) due to the contributions of goethite, gibbsite, and boehmite. The relationships of base cation
exchange capacity (CECB) and AEC with pH were linear. Rates of change with pH of both negative and positive variable
charge (Ac, Aa) were closely related to CEC, specific surface area (SSA), pH(NaF), and various forms of extractable Fe, Al,
and Mn. The charge fingerprints of soil after removal of organic matter indicated that organic matter exerted a strong
influence on both the magnitude of negative charge and rate of change with pH. Kaolin had permanent and variable charge,
with SSA and crystal size (MCD001) being highly predictive of the rate of change in variable negative charge with pH. Iron
oxide concentrates exhibited strongly pH-dependent charge and the mean coherently diffracting length (MCD110) of
hematite was highly predictive of both the magnitude and rate of change in variable positive charge with pH. Charge
coefficients (Ac, Ba) had highly significant (P = 0.005) positive relationships with Langmuir and Freundlich phosphate
sorption maximum coefficients (Xm, k), indicating that the surfaces of amorphous, poorly ordered, and crystalline Fe and Al
oxides are prime sites for both P sorption and variable charge.
Australian Journal of Soil Research. 01/2010; 48:337-354.
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ABSTRACT: Phosphate (P) sorption and desorption characteristics have been investigated for sixty-two representative
samples of the major Thai upland agricultural soils which are Oxisols and Ultisols formed on diverse parent
materials and under various climatic conditions. P sorption characteristics are well described by Langmuir and
Freundlich equations. Values of Langmuir P sorption maximum (Xm) and b coefficient range from 47 to
1250 μg g−1 soil and 0.5 to 30 mL μg−1, respectively and the Freundlich k varies between 12 and 1694 μg g−1
and B coefficient 0.09 and 0.67. Soils derived from basalt have larger values of P sorption maximum than soils
on other parent materials. Both P sorption maximum and Freundlich k are closely related to pH (NaF), SSA,
total titanium, aluminum and iron, dithionite and oxalate extractable Fe and Al, and other soil properties that
reflect specific surface area. Soil pH in NaF is highly effective in predicting the P sorption capacity of Thai upland
soils explaining 79% of the variation in P sorption by these soils. P desorption curves for adsorbed P are well
described by the Freundlich equation. The Freundlich kd coefficient for P desorption is highly, linearly related to
the Freundlich k coefficient of P sorption indicating that the above soil factors that contribute to P sorption
similarly affect P desorption.
Geoderma. 01/2009; 153:408-415.
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ABSTRACT: Phosphate sorption characteristics of 28 samples of red Oxisols and red Ultisols from agricultural areas of Thailand were described by using Langmuir and Freundlich equations. The soils were three Typic Kandiudults, a Typic Paleustult, a Typic Kandiustult, a Typic Kandiustox, three Rhodic Kandiustox, two Rhodic Kandiudox, two Typic Kandiudox, and a Kandiudalfic Eutrudox. Values of Langmuir P maximum (Xm) ranged from 18 to 1111 mg kg-1 soil and the Freundlich k coefficient varied between 9 and 652 mg kg-1. Many soil properties were closely correlated with these measures of P sorption capacity including total titanium, goethite, total iron, amorphous aluminum, and specific surface area. Goethite, microcrystalline kaolin, and amorphous forms of Fe and Al oxides were major contributors to P sorption by these soils. The Freundlich B coefficient, which is a measure of P bonding energy, was weakly related to clay content but there were no close relationships between the equivalent Langmuir b coefficient and soil properties. Soil pH in 1 M NaF (pH 8.0) was highly predictive of P sorption and may therefore be used as a quick economical field test for evaluating P fertilizer requirement.
Soil Science 08/2005; 170(9):716-725. · 1.14 Impact Factor
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ABSTRACT: An analysis of properties of red Oxisols on calcareous sedimentary rocks under different climatic regimes in Thailand was carried out to ascertain their similarities and differences. These soils are Kandiustox in Northeast Plateau and Kandiudox in Peninsular Thailand and have characteristics typical of highly weathered soils. They are very deep (> 2 m depth), are generally acidic (pH 5–6), clayey, have low cation exchange capacity and negative ΔpH values. Their profile development illustrates some differences being Ap(A)–Bt–Bto for Kandiustox and Ap–Bto or Ap–Bto–Bo for the Kandiudox which can be due to differences in leaching conditions under different moisture regimes and a more favourable natural condition for iron oxide accumulation in the Kandiudox. These soils generally have low bulk densities (0.77–1.36 Mg m− 3) and low available water for plants (5.0–9.3 wt.%). The fabric of the soils indicates that there are more well rounded micropeds in Kandiudox than in Kandiustox and the sizes of microaggregates in these soils are somewhat different ranging from 10 to 1000 μm in Kandiustox and 50–1400 μm in Kandiudox. The iron oxide concentration in microaggregates is more variable in the Kandiudox possibly indicating a more complex pedogenesis in these soils as compared to the Kandiustox. Kaolin, quartz and hematite are the dominant minerals in all these Oxisols, gibbsite and goethite are major minerals only in the Kandiudox and boehmite occurred in only one Kandiudox in tropical rainforest environment. Differences in mineralogy also indicate the influence of parent material composition. Soil properties that relate to soil fertility status particularly organic matter concentration (2.1–34.5 g kg− 1), available phosphorus (0.3–47.5 mg kg− 1) and available potassium (5–233 mg kg− 1) are poor and similar for the Kandiustox and Kandiudox profiles. Both groups of Oxisols have low values of cation exchange capacity which is in consistent with the dominance of low activity clays (kaolin, sesquioxides) with the Kandiudox profiles having lower mean CEC (6.7–10.2 cmol kg− 1) than the Kandiustox (11.5–16.3 cmol kg− 1) profiles.
Geoderma 136:477-493. · 2.32 Impact Factor
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ABSTRACT: Purified samples of kaolin group minerals [kaolins] from red Oxisols and red Ultisols from 14 sites on diverse parent materials and under various climatic conditions in Thailand were characterized using analytical transmission electron microscopy, X-ray powder diffraction and chemical analysis. The kaolins show a variety of crystal morphologies including euhedral hexagonal to subhedral platy crystals, tubes and partly rolled tubes. Tubes and partly rolled tubes occur in soils under both udic and ustic moisture regimes (i.e. Rhodic Kandiudox, Typic Kandiudox, Typic Kandiudults, Rhodic Kandiustox). The lowest kaolin HB crystallinity index (3.3–5.3) and smallest size (9–11 nm) are for kaolins consisting of anhedral plates, tubes and partly rolled tubes in a soil on basalt under very high rainfall. This kaolin has the highest specific surface area (SSA) (35–64 m2 g− 1), cation exchange capacity (CEC) (16–23 cmol kg− 1) and Fe2O3 content (1.99–3.62%). The trend of increasing kaolin crystal size with associated decreasing CEC and SSA in these soils is in the sequence red Oxisols on limestone under ustic moisture regime < red Ultisols on old alluvium < red Oxisols on basalt under ustic moisture regime < red Oxisols on limestone under udic moisture regime < red Oxisols on limestone under udic moisture regime < red Ultisols on sedimentary rock under udic moisture regime.
Applied Clay Science 32:25-39. · 2.47 Impact Factor
