Sorption of phosphorus by some surface soils from Quebec in relation to their properties

Abstract

Surface horizons from Podzolic and Gleysolic soils were collected in various parts of the province of Quebec, Canada, and equilibrated with various amounts of KH₂PO₄ in 0.01 M CaCl₂ for 48 hours. P sorption data conformed to the linear form of the Langmuir and Freundlich equations. P solubility isotherms showed evidence of hydroxyapatite formation in most samples studied, whereas equilibration solutions of only few samples were saturated with respect to either dicalcium phoshate dihydrate or octocalcium phosphate. These reaction products were associated to soil pH and levels of added phosphate. The average values of the Langmuir sorption maximum for these studied Gleysolic and Podzolic samples were 763 and 1096 μg/g respectively. These values were higher than those obtained by the segmented and modified Freundlich models.

Relationships between the soil characteristics and P sorption parameters were evaluated by regression analysis. Among all variables, oxalate‐extractable Fe plus Al content of the Podzolic samples and the ratio of oxalate—extractable Al to clay of the Gleysolic samples gave the best significant correlation coefficients. Furthermore, soil pH and various ratios such as pyrophosphate‐extractable Fe and Al, oxalate‐extractable Fe and organic matter to clay were found to be significantly correlated only with the P sorption parameters of the Gleysolic samples.     

Remediation of a Magnesium‐Contaminated Soil by Chemical Amendments and Leaching

The deposition of magnesium (Mg)‐rich dust from magnesite mining activities has resulted in serious land degradation. However, the main factors limiting plant growth in Mg‐contaminated soils are unclear. Moreover, little information is available on the remediation of Mg‐contaminated soils. In this study, remediation of soils contaminated with Mg‐rich dust was investigated in a pot experiment using maize as the indicator plant. There were five treatments: (i) control; (ii) leaching; (iii) application of CaCl₂; (iv) leaching + CaCl₂ application; and (v) application of Ca(H₂PO₄)₂ · H₂O. Soil properties and growth of maize (Zea mays L.) seedlings were measured. Leaching alone significantly decreased soluble Mg concentration. Leaching + CaCl₂ application greatly increased exchangeable Ca concentration and decreased soil pH by 0·3 units. Application of CaCl₂ alone increased soluble Mg concentration sharply, which directly inhibited the germination of maize seeds. Application of Ca(H₂PO₄)₂ · H₂O significantly increased the concentrations of exchangeable Ca and available phosphorus and decreased soil pH by 1·7 units. The biomass of maize seedlings increased in the order of control = leaching < leaching + CaCl₂ < < Ca(H₂PO₄)₂ · H₂O. These results suggested that the plant growth in Mg‐contaminated soils was limited primarily by Ca deficiency and secondarily by high soil pH when exchangeable Ca was sufficient. High soil pH suppressed plant growth probably mainly by inhibiting phosphate uptake from the soil. Applying acid Ca salt with low solubility is an attractive option for the remediation of Mg‐contaminated soils. Copyright © 2015 John Wiley & Sons, Ltd.     

Time‐dependent zinc desorption in soils

Abstract

Time dependent zinc (Zn) desorption in eight benchmark soils of India was studied in relation to various pH values and ionic strengths. Soil samples were equilibrated in solutions containing 10 μg Zn g^‐1 soil at pH 5.5,6.5, and 7.5 for 48 h at 25±2°C, and adsorbed Zn extracted with calcium chloride (CaCl₂) for various periods of time. Desorption of Zn decreased with increasing pH, and the desorption rate decreased abruptly at pH 7.5. In contrast, an increase in the equilibration period and ionic strength of the background electrolyte increased Zn desorption. Four rival kinetic models were fitted and evaluated for their suitability for describing the Zn desorption process. Reaction rate constant (ß) calculated from the Elovich model for the different soils ranged from 9.99 to 25 (mg Zn kg^‐1)^‐1. The different kinetic models tested indicated that Zn desorption in soils was a diffusion controlled process. The desorption was rapid in the first 4 h, followed by slower phase in the rest of the time at all the pH values indicating a biphasic desorption, characteristic of a diffusion controlled process. The ß value for the Elovich equation showed a strong association with soil clay content and cation exchange capacity (CEC). Further, the best prediction of Zn desorption reaction rate constant could be made using multiple‐regression equation with soil clay content and CEC as variables.     

Sorption of Phosphorus from Swine,Dairy, and Poultry Manures

In most phosphorus (P) sorption studies, P is added as an inorganic salt to a predefined background solution such as calcium chloride (CaCl₂) or potassium chloride (KCl); however, in many regions, the application of P to agricultural fields is in the form of animal manure. The purpose of this study, therefore, was to compare the sorption behavior of dissolved reactive P (DRP) in monopotassium phosphate (KH₂PO₄)–amended CaCl₂ and KCl solutions with sorption behavior of DRP in three different animal manure extracts. Phosphorus single‐point isotherms (PSI) were conducted on eight soils with the following solutions: KH₂PO₄‐amended 0.01 M CaCl₂ solution, KH₂PO₄‐amended 0.03 M KCl solution, water‐extracted dairy manure, water‐extracted poultry litter, and swine lagoon effluent. The PSI values for the dairy manure extract were significantly lower than the CaCl₂ solution for all eight soils and lower than the KCl solution for six soils. The PSI values were significantly higher, on the other hand, for poultry litter extract and swine effluent than the inorganic solutions in four and five of the soils, respectively. Our observations that the sorption of DRP in manure solutions differs significantly from that of KH₂PO₄‐amended CaCl₂ and KCl solutions indicates that manure application rates based on sorption data collected from inorganic P salt experiments may be inaccurate.     

Characterization of sulfur retained by soils exposed to sulfur dioxide

Abstract

Soils have substantial capacity for sorption of sulfur dioxide (SO₂) but little is known about the nature of the sorbed S. Three surface soils varying in pH, organic matter, CaCO₃ equivalent and surface area were exposed to air containing 5% SO₂ and subsequently analyzed by ten different procedures to characterize the sorbed S. Most of the sulfur retained by soils after exposure to SO₂ could be recovered as CaCl₂‐extractable S, Ca(H₂PO₄)₂‐extractable S, or S released as H₂S by hydriodic acid (HI). Only small amounts of sulfur could be recovered as tetrachloromercurate (TCM)‐extractable S, S released as SO₂ by HCl, or S released as H₂S by HCl + Zn, HCl + Sn, or Raney Ni and NaOH. However, large amounts of S released as SO₂ by HCl were recovered from the air‐dry Webster and the moist Storden soils indicating that SO₂ sorption is influenced by organic matter in air‐dry soils and by CaCO₃ in moist soils.     

Effect of liming on phosphate sorption by acid soils

The sorption of phosphate (P) by four strongly acid Fijian soils from 0.01 M CaCl₂ decreased with increasing pH up to pH 5.5–6.0 and then increased again. The initial decrease in P sorption with increasing pH appears to result from an interaction between added P, negative charge, and the electrostatic potential in the plane of sorption. The results of a sorption study, involving KCl or CaCl₂ of varying concentrations as the background electrolyte and using Nadroloulou soil incubated with KOH or Ca(OH)₂, suggested that the increase in P sorption at pH values > 6.0 was caused by the formation of insoluble Ca-P compounds. For some soils this is consistent with the results of an isotopic-exchange study in which incubation with lime caused marked reductions in the amounts of exchangeable P at high pH.     

Phosphate adsorption by soils 1. Influence of time and ionic environment on phosphate adsorption

Abstract

The influence of reaction time and ionic environments, on phosphate adsorption were studied using one calcareous soil from India, and one calcareous and two latosols from Hawaii.

Phosphorus adsorption by soils has a initial rapid phase followed by a slow process. For plant nutrition studies, where emphasis is on P concentration of solutions from which plants derive P, isotherms should be constructed using data obtained after near‐equilibration has been attained. This condition does not obtain in a few hours and may require 6 days or more.

Calcium chloride as suspending electrolyte always gave lower phosphate solubility than when KC1 was used as electrolyte. Phosphate retention increased with increasing ionic strength. The necessity for obtaining clear supernatant solutions and the desirability for maintaining reasonable constant equilibrium conditions make 0.01 M CaCl₂ a reasonable choice for constructing P sorption isotherms, even though 0.01 M CaCl₂ is not representative of Ca concentrations in many soil solutions. Saturation extracts of soils investigated here were in the range 0.0002 to 0.005 M Ca.

Adsorption of calcium by highly weathered soils was high suggesting specific adsorption. Calcium adsorption was increased by phosphate additions to a Hydrandept.     

Evaluation of calcium dihydrogen phosphate solution as an extractant for inorganic sulfate applied to soils

Abstract

To evaluate conventional calcium dihydrogen phospahte [Ca(H₂PO₄)₂] solution containing 500 mg P/L as an extractant for soluble plus adsorbed sulfate (SO₄), we added known amounts of SO₄ to 10 soil samples differed in clay mineral composition and extracted with Ca(H₂PO₄)₂ solution. The experimental results showed that the five successive extractions at a soihsolution ratio of 1:10 could quantitatively recover the added SO₄, and there was little effect of air‐drying the soils after addition of SO₄. Based upon these experimental results, we concluded that the Ca(H₂PO₄)₂ extraction is an excellent method for determining soluble plus adsorbed inorganic SO₄ in soils.     

Desorption of myo‐inositol hexakisphosphate and phosphate from goethite by different reagents

Inositol phosphates are abundant organic phosphates found widely in the environment. The sorption and desorption of organic phosphate (P_o) are important processes in controlling the mobility, bioavailability and fate of phosphorus (P) in soil and sediment. The desorption characteristics of myo‐inositol hexakisphosphate (IHP) and inorganic phosphate (P_i) from goethite were studied by pre‐sorption of IHP or P_i followed by desorption by KCl, H₂O, and citrate. Batch experiments and in situ attenuated total reflectance Fourier transform infrared (ATR‐FTIR) spectroscopy were used to investigate the desorption of IHP/P_i. The desorption percentage of IHP/P_i by citrate was much higher than that by H₂O/KCl. The desorption of P by citrate was mainly achieved through ligand exchange, and the desorption increased with decreasing pH. Desorption by H₂O was slightly greater than that by 0.02 M KCl because the electrostatic repulsion between the P molecules is larger in H₂O. Due to the higher affinity of IHP for goethite than that of P_i, the maximum desorption of IHP was lower than that of P_i. Desorption curves (desorption concentration in solution vs. sorption density) of IHP or P_i on goethite by KCl or H₂O was well fitted by an exponential equation, while those by citrate were well fitted by a linear equation. The desorption amounts of P in the first cycle account for more than 58% of the total desorption followed by substantial decreases in the second and third cycles. There was a re‐sorption of P_i from solution in the late stage of desorption by KCl and H₂O, resulting in a sharp decrease in desorption. Re‐sorption of IHP did not occur, which is probably due to its poor diffusion into goethite. The initial desorption rate of P_i with KCl and H₂O decreased with increasing pre‐sorption time, whereas that of IHP was opposite. This study indicates that strong sorption on and weak desorption of IHP from iron (hydr)oxides may explain the accumulation of IHP in soils.     

Short‐Term Effect of Lime,Phosphorus, and Iron Amendments on Water‐Extractable Lead and Arsenic in Orchard Soils

Abstract

Lead arsenate was extensively used to control insects in apple and plum orchards in the 1900s. Continuous use of lead arsenate resulted in elevated soil levels of lead (Pb) and arsenic (As). There are concerns that As and Pb will become solubilized upon a change in land use. In situ chemical stabilization practices, such as the use of phosphate‐phosphorus (P), have been investigated as a possible method for reducing the solubility, mobility, and potential toxicity of Pb and As in these soils. The objective of this study was to determine the effectiveness of calcium carbonate (lime), P, and iron (Fe) amendments in reducing the solubility of As and Pb in lead‐arsenate‐treated soils over time. Under controlled conditions, two orchard soils, Thurmont loam (Hapludults) and Burch loam (Haploxerolls), were amended with reagent‐grade calcium carbonate (CaCO₃), iron hydroxide [Fe(OH)₃], and potassium phosphate (KH₂PO₄) and incubated for 16 weeks at 26°C. The experimental results suggested that the inorganic P increased competitive sorption between H₂PO₄ ^? and dihydrogen arsenate (H₂AsO₄ ^?), resulting in greater desorption of As in both Thurmont and Burch soils. Therefore, addition of lime, potassium phosphate, and Fe to lead‐arsenate‐contaminated soils could increase the risk of loss of soluble As and Pb from surface soil and potentially increase these metal species in runoff and movement to groundwater.     

The effect of pH on zinc transformation in autoclaved soils treated with pyrophosphate

Abstract

Zinc solubility in soils can be affected by both pH and pyrophosphate (PP), yet the reaction of PP is influenced by pH, thus there is a need to evaluate pH effect on Zn transformation in soils treated with PP. Samples of three autoclaved soils, a Dalhousie (DT) clay, a St. Bernard (ST) loam, and an Uplands (UT) sand were equilibrated first with PP (0.0 and 9.0 P mM), then with Zn (0.0, 0.5, 1.0 Zn mM) and followed by 0.03 M KC10₄ solutions at the initial pH of 4.5, 6.0, and 7.5 with constant ionic strength. The first equilibration was for PP sorption, the second for Zn sorption and PP desorption, and the third for Zn desorption and further PP desorption. And finally, Zn of selected samples were extracted with 0.5 M KNO₃ (exchangeable Zn, Zn_KNO3), 0.5 M NaOH (organic and Fe oxides associated Zn, Zn_NaOH) solutions, and concentrated HNO₃+H₂O₂ (residual Zn, ZnHNO₃).

Increases in pH reduced PP sorption in the UT and the ST soils while high or low pH values tended to reduced it in the DT soil, indicating a competition between PP and OH ions for sorption sites. Zinc sorption was linearly related to solution pH, the slopes varied from 0.10 to 1.06, lower values were associated with PP addition, with low Zn rate, with finer textured soils, with high contents of Fe and Al materials, and with high pH buffer capacity. The values of Zn desorption and Zn_KN03 were greater at low than high pH while the reverse was true for Zn_NaOH. The pH effects on Zn sorption‐desorption and fraction distributions were less significant in soil with than without PP. The overall effect of high pH and the presence of the sorbed PP was the increased Zn specific sorption, compared to the pH or PP effect alone.     

Sorption of calcium and sulfate by sandy soils from flue‐gas desulfurization gypsum and phosphogypsum

Abstract

Increasing concern on sulfur dioxide (SO₂) pollution has prompted many coal‐fired electric power generating plants to install SO₂ scrubbing units which generate large amounts of flue‐gas desulfurization gypsum (FGDG). This source of gypsum can be an excellent amendment to supply calcium (Ca) and/or sulfate (SO₄) to sandy soils which are deficient in these nutrients. In this study, reactions of FGDG, phosphogypsum (PG), reagent grade calcium sulfate (CaSO₄), and calcium chloride (CaCl₂) were investigated using a Candler fine sand (uncoated, hyperthermic, Typic Quartzipsamment), a typical well‐drained deep sand, and a Pineda fine sand (loamy, siliceous, hyperthermic, Arenic Glossaqualf), a typical shallow poorly drained sand. Concentrations of various water‐soluble elements were similar in FGDG as well as PG, except the latter contained 11 and 15 g/kg phosphate (PO₄) and fluoride (F), respectively, while these ions were undetectable in the former. In batch‐equilibration (4 h) technique using soilrsolution ratio of 1:2, pH of equilibrium solution decreased by 0.2 and 0.8 units, while ionic strength increased by 5‐ and 15‐fold in the Pineda and Candler sand, respectively, when using FGDG or PG solution as compared to using water for equilibration. Sorption of Ca by the two soils varied from 0.56 to 0.71 Cmolc/kg regardless of source of gypsum. As compared to sorption of SO₄, that of Ca was greater by 2.5‐ and 2.6 to 4.3‐fold by the Candler and Pineda sand, respectively. With the exception of SO4 sorption by the Pineda sand, this study demonstrated that the reactions of FGDG with these sandy soils were very similar to those of PG or reagent grade CaSO4. Since much of the past research on agricultural use of gypsum was done using PG and CaSCU, we could conclude that similar response could be expected with use of FGDG.     

Clay,Organic Carbon,Available P and Calcium Carbonate Effects on Phosphorus Release and Sorption–Desorption Kinetics in Alluvial Soils

Information on phosphorus (P) release kinetics and sorption–desorption in soils is important for understanding how quickly reaction approaches equilibrium and replenishes the depleted soil solution. Laboratory experiments were conducted to study the P release and sorption–desorption kinetics in soils differing in clay, soil organic carbon (SOC), available P, and calcium carbonate (CaCO₃) contents. Phosphorus release from soils proceeded in two phases: initially faster phase followed by a slower phase as equilibration progressed. Elovich equation (R² ≥ 0.97**) described well the P release versus time data. P release coefficients for power function were significantly correlated with available P and SOC. Freundlich sorption constants increased with increase in clay and CaCO₃ content. With increase in SOC and available P concentration in soils, substantial reduction in sorption constants was observed. It was concluded that for efficient P management, it is important to take into account soil texture, the existing soil P level, SOC content, and soil calcareousness.     

Determination of phosphate desorption characteristics in soils using successive resin extractions

Abstract

An alternative method for examining phosphate desorption characteristics in soil was tested. Five tropical soils with very different phosphate sorption capacities were incubated with added phosphate under three different conditions: 2 days at 25°C, 55 days at 25°C, and 2 days at 50°C. After incubation the phosphate was desorbed from the soil using successive cation‐anion resin extractions. The data from these extractions were fitted to a first order rate equation describing desorption. From the equation, an asymptote (B) was found to represent the ultimate amount of phosphate desorbable from each soil after incubation. It was found that increasing the incubation time or increasing the temperature of the incubation lowered this parameter ‘B’ suggesting that the slow reaction of adsorbed phosphate had reduced the amount of readily desorbable phosphate. Differences between soils as reflected in this parameter may indicate differences in the residual value of added phosphate in the field.     

Establishing sorption isotherm to meet phosphorus requirement for tomato seedling growth 1

An Indiana silt loam soil was equilibrated with various amounts of Ca(H₂PO₄)₂ H₂O and a 0.01 M CaCl₂ solution to construct its phosphorus sorption isotherms. Using the isotherms, the P buffering capacity of the soil was calculated and amounts of fertilizer P necessary to give several levels of P in the soil solution, for experiments conducted over a 2 year period, were determined. Twenty‐four day old tomato seedlings were grown and measured for leaf area, root length, dry weights and P concentrations in leaf, petiole, stem and root.

Phosphorus concentration in soil solution increased slowly with the first increment of P added to the soil. Subsequent P additions increased the P concentrations in solution exponentially. The maximum P absorption by the soil was 324 μg P/g soil and the constant related to P binding energy was 1.37. In addition, the soil buffering capacity decreased with an increase in the amount of P in the soil solution.

Plant shoot dry weight increased linearly with P increase in the concentration range 0.65 to 6.5 μM P in soil solution. However, beyond this level the response was low. The leaf area rate of increase in the 0.65 to 6.5 μM P solution concentration range was 75 times that in the 6.5 to 84 μM P. The root length: shoot dry weight ratio decreased with increasing P supply in the soil solution. P uptake by the plants increased with increased P concentration in soil solution. At soil solution concentrations above 6.5 μMP the rate of P uptake in the shoot was 20 times less than the rate for concentrations below 6.5 μM P. Of the P taken up by tomato seedlings about 65% was in the leaf, 13% in the stem, 13% in the petiole and 9% in the root.     

Evaluation of available boron content using eight methods of extraction in different soils from Córdoba and sucre in Colombia

The aim was to evaluate eight methods of boron (B) extraction in different soils from Córdoba and Sucre, Colombia. 37 samples were collected at a depth of 0–20 cm and carried to Soil and Water Laboratory of University of Córdoba for its chemical characterization. The available boron was extracted with the following methods: modified hot water, calcium chloride (CaCl₂) 0.05, hydrochloric acid (HCl) 0.05, barium chloride (BaCl₂) 0.006, manitol 0.05 + CaCl₂ 0.01, Ca(H₂PO₄)₂H₂O 0.008 in mol L^?1, mehlich-1 and ammonium acetate (NH₄OAc) (1.0 mol L^?1, pH = 7.0). The major quantity of boron was extracted with mehlich-1, HCl 0.05 mol L^?1 and hot water, extracting 0.36, 0.29 and 0.26 mg kg^?1, respectively. The extracting solution that correlated with the hot water method was HCl 0.05 mol L^?1 (r = 0.81); followed by Ca(H₂PO₄)₂H₂O 0.008 mol L^?1 (r = 0.62) and mehlich-1 (r = 0.54). According to characteristic and heterogeneity of soils, we recommend HCl method to extract available boron.     

Ionic equilibria,selectivity and diffusion of cations in soil as influenced by anion additions

Abstract

An experiment was carried under controlled conditions to investigate the influence of the anions, H₂PO₄ ^‐. and Cl on the ionic equilibria, selectivity and effective diffusion of Rb, K, Na, Ca, Mg in two Indiana soils.

Additon of anions to the soils increased the concentration of cations in soil solution. In both the soils receiving H₂PO₄ ^‐, lower cation concentrations were found in the soil solution than in those receiving Cl^‐ . Additon of H₂PO₄ ^‐and Cl^‐ reduced the ion selectivity coefficient, k, for various homovalent (Rb/K, Rb/Na, K/Na, Ca/Mg) and mono‐divalent ion pairs (Rb/Ca, Rb/Mg, K/Ca, K/Mg). In Zanesville soil treatments receiving H₂PO₄ ^‐ had lower k values for mono‐divalent cations than treatments receiving Cl^‐. However, no such conclusions could be drawn for Raub soil. Soils treated with H₂PO₄ ^‐ had higher k values for homovalent cations than Cl^‐ treated soils. The differences in the selectivity of adsorption in these two soils might be attributable to the differences in the type and nature of exchange materials and cation concentrations on the exchange phase.

Addition of H₂PO₄ ^‐ or Cl^‐ enhanced the magnitude of effective diffusion coefficient. (De) of all the cations under considerations. The magnitude of effective diffusion coefficient for cations was lower for H₂PO₄ ^‐ treated soils than Cl^‐ treated soils. Such a reduction in De is related to the reduction in cation concentration in soil solution thereby increasing the buffer capacity for the ions under consideration.     

Effects of equilibrating salt solutions on phosphate sorption by soils

Abstract

Several equilibrating salt solutions have been used in the studies of P sorption by soils and sediments. This study was conducted to evaluate the effects of 10 salt solutions on estimation of P sorption by soils. Results obtained showed that, when the equilibrating solution was made to contain 0.01M with respect to CaCl₂, Ca(NO₃)₂, CaSO₄, MgCl₂, KCl, LiCl, Nacl, or KHCO₃, the amount of P sorbed by soil always exceeded the amount sorbed from the soil‐water system. In comparison with the amount of P sorbed from water, 0.01M NaHCO₃ reduced P sorption by soils. Use of THAM buffer (0.05M pH 7.0) to control the pH increased P sorption by some soils and decreased P sorption by others, relative to that sorbed from the soil‐water system. The results indicated that inclusion of salts in the equilibrating solution for P‐sorption studies should be avoided, especially in studies related to water quality.     

Effect of temperature on EDTA‐extractable copper in soils

Abstract

Two contrasting soils were extracted with 0.05 M EDTA in 1 M CH₃ COONH₄ at pH 6, before and after incubation for 4 weeks at constant (10, 20 or 30°C) or fluctuating (10/30, mean 20°C) temperatures. Less copper was extracted from soils which were incubated at fluctuating temperature than from those maintained at a constant 20 C. Where incubation temperature was constant, extractable copper increased or decreased with increasing temperature depending on the soil and how it was treated. Recovery of added copper was low initially but increased during the incubation. Maximum recovery was associated with low incubation temperature in one soil, but high temperature in the other. The amounts of copper extracted were slightly increased by γ‐irradiation of the soils. Extractable copper was also increased by increasing the temperature at which the extraction was performed.