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.
"on – desorption reactions can be attributed to a shift in the form of P held at the surface from a loosely bound to a more tightly bound type . Mechanisms proposed for this process included precipitation of discrete phosphate minerals ( Van Riemsdijk et al . , 1984 ) , a shift from monodentate to bidentateforms of sorbed P ( Munns and Fox , 1976 ; Wisawapipat et al . , 2009 ) , and diffusive penetration of surface - sorbed P into soil components ( Ryden et al . , 1977 ; Pierzynski , 1991 ) . With increasing paddy cultivation age , greater desorbability of P occurred in surface paddy soils at both sites suggesting a decrease of irreversibility of P sorption in the older paddy soils . The fraction of desorbe"
[Show abstract][Hide abstract] ABSTRACT: Information on the dynamics of phosphorus (P) fraction and sorption–desorption characteristics of paddy soils with long cultivation history is essential to improve our understanding of P transformation and transport in agro-ecosystems and critical for sustainable and environment-friendly soil management. We investigated changes in P fraction and sorption–desorption characteristics in topsoils from two contrasting paddy chronosequences developed on calcareous marine sediments at Cixi and acidic quaternary red clays at Jinxian, respectively, in subtropical China. Both chronosequences showed similar patterns and pedogenetic trends of their topsoil P status. Total P (PT) and various P fractions (calcium-associated P (PCa), organic P (Po), non-occluded and occluded P) accumulated to a maximum after 50-yrs and 150-yrs of cultivation, respectively, at Cixi and Jinxian due to P addition, consistent with the prior agronomic field studies on decadal time scales. However, rapid decrease of PT occurred in the older paddy soils at both sites, despite the continuous P additions, which we attributed to the decline of P sorption capacity since P sorbents (CaCO3, Fe- and Al-oxides, and clay) rapidly decreased. Compared with Walker and Syers’ model of gradual P depletion and decreasing bioavailabity in natural ecosystems, our results show that long-term paddy cultivation alters both the rate and trajectory of topsoil P transformations during agro-ecosystem development. The ability of the topsoil to sorb added P decreased with paddy cultivation history in both chronosequences, due to the decline in the maximum P sorption capacity (Smax); whereas the P release potential increased as a result of paddy cultivation at both sites, as indicated by the higher degree of P saturation (DPS) and greater P desorbability in the paddy soils than the uncultivated soils. Our study suggests that after long-term cultivation paddy soils are getting degraded by lowering their P holding capacity so may enhance the P release potential and lead to increasing environmental risk through P loss.
Soil and Tillage Research 09/2014; 142:32–41. DOI:10.1016/j.still.2014.04.007 · 2.62 Impact Factor
"There are close positive relationships between P sorption and the abundance of crystalline and amorphous Fe and Al oxides in soils from different environments (Nair et al., 1998; Sanyal et al., 1993; Zhou et al., 1997; Agbenin, 2003; Wiriyakitnateekul et al., 2005; Wisawapipat et al., 2009). Various pools of Fe and Al associated with P retention are commonly distinguished by selective dissolution with different extractants. "
[Show abstract][Hide abstract] ABSTRACT: Excessive phosphorus (P) fertilization can lead to eutrophication of surface water. Compositional differences between Alaquod E and Bh, and Paleudult E and Bt horizons are factors affecting sub-surface P transport in these soils. The objective of this study was to relate P sorption characteristics to compositional differences in Alaquod and Paleudult sub-surface horizons and to evaluate implications for risk of P loss via sub-surface flow in these soils. Soils were sampled by horizon from six sites located in Florida. Iron (Fe) and aluminum (Al) were extracted by sodium citrate-bicarbonate-dithionite, ammonium oxalate, and sodium pyrophosphate. The P retention characteristics were determined for all samples using single-point (1,000 mg P kg−1) isotherms and the traditional Langmuir isotherms for 33 Bh and 45 Bt samples. Eluvial horizons of Alaquods have no measurable P retentive capacity, whereas E horizons of Paleudults can retain P because of presence of metal oxides as indicated by oxalate, pyrophosphate, and citrate-bicarbonate-dithionite extractions. The P retention capacities of Bh and Bt horizons are highest among horizons studied. Greater resistance to P desorption for Bt relative to Bh horizons likely relates to the greater abundance of Fe oxides and kaolinite clay in the Bt and to the predominance of organically over inorganically complexed Al in the Bh. Compositional differences between Alaquod and Paleudult sub-surface horizons explain differences in tendencies of P retention and release within Alaquod and Paleudult profiles and within the landscape-hydrologic settings associated with these soils.
"Fe/Al (oxy)hydroxides, especially the less crystalline forms, adsorb more As per unit mass than several clay minerals (Goldberg 2002). However, the Fe/Al (oxy)hydroxide contents in sediments are lower than the clay mineral contents (Wisawapipat et al. 2009), so that the adsorption capacity of sediments must be mainly determined by the number of reactive surface groups that clay minerals expose. During the last few years, a relative large number of studies were performed investigating the arsenate adsorption onto clay minerals such as montmorillonite , kaolinite and illite (Manning and Goldberg 1996; Goldberg 2002). "
[Show abstract][Hide abstract] ABSTRACT: Arsenate adsorption was studied in three clastic sediments, as a function of solution pH (4.0–9.0) and arsenate concentration. Using known mineral values, protolytic constants obtained from the literature and K
ads values (obtained by fitting experimental adsorption data with empirical adsorption model), the constant capacitance surface complexation model was used to explain the adsorption behavior. The experimental and modelling approaches indicate that arsenate adsorption increases with increased pH, exhibiting a maximum adsorption value before decreasing at higher pH. Per unit mass, sample S3 (smectite–quartz/muscovite–illite sample) adsorbs more arsenate in the pH range 5–8.5, with 98% of sites occupied at pH 6. S1 and S2 have less adsorption capacity with maxima adsorption in the pH ranges of 6–8.5 and 4–6, respectively. The calculation of saturation indices by PHREEQC at different pH reveals that the solution was undersaturated with respect to aluminum arsenate (AlAsO42H2O), scorodite (FeAsO42H2O), brucite and silica, and supersaturated with respect to gibbsite, kaolinite, illite and montmorillonite (for S3 sample). Increased arsenate concentration (in isotherm experiments) may not produce new solid phases, such as AlAsO42H2O and/or FeAsO42H2O.
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