Internal and External Phosphorus Requirements of Maize Genotypes on Typic Calciargid

External and internal phosphorus (P) requirements of hybrid maize (FHY-396) and indigenous variety (EV-7004) were compared on a Typic Calciargid soil. A sorption isotherm was constructed by equilibrating 2.5 g soil with 25 mL of a 0.01 M calcium chloride (CaCl₂) solution containing 2, 3, 6, 12, 25, 50, and 100 mg P L^–1. Sorption data were fitted to a modified Freundlich equation [x/m = K_f(EPC)^1/n] to compute P rates (0, 30, 60, and 120 mg kg^–1 soil) against solution levels (0, 0.09, 0.26, and 0.76 mg P L^–1) for a pot study. Applied P significantly increased shoot dry matter, P concentration, and P uptake in both the genotypes. For optimum shoot growth, internal P requirement of hybrid (2.51 mg g^–1) was 5% more than variety (2.39 mg g^–1). However, external P requirement of hybrid (0.50 mg L^–1) was remarkably more than variety (0.19 mg L^–1). This strongly advocated greater P rates for the high-yielding hybrid than for the variety.     

Using Soil Potassium Adsorption and Yield Response Models to Determine Potassium Fertilizer Rates for Potato Crop on a Calcareous Soil in Pakistan

Ustochrept soil was collected from a major potato-growing area in Pakistan for a potassium (K) adsorption isotherm experiment. Adsorption data were fitted to Freundlich and Langmuir adsorption models. Results showed that the Freundlich model (R²?=?0.96**) fit the data better than did the Langmuir model. Fertilizer rates were calculated based on the Freundlich model and targeted solution K levels at 0, 3, 6, 9, 12, 15, 18, 21, 24, and 27 mg K L^?1. A field experiment was then conducted on the soil to assess the effect of various soil solution K levels (0–27 mg L^?1, with K fertilizer rates at 0, 24, 49, 75, 101, 128, 155, 182, 210, and 237 kg ha^?1), on tuber yield and quality along with 300 kg N and 250 kg P₂O₅ ha^?1 as basal doses. Yield response models (linear plus plateau, quadratic, square root, quadratic plus plateau, and exponential) were used to calculate the optimal fertilizer rate for potato crop. Linear plus plateau model fit the data with less bias than the other models. There was a significant effect of K use on the yield and quality of potatoes. Potassium fertilizer application at 130 kg K ha^?1, which is equivalent to a soil solution level of 12 mg K L^?1, maximized the tuber yield of potato. However, for the improvement in tuber dry matter, reducing sugars, protein contents, and starch contents, the soil solution K level required was as high as14.62 mg L^?1 (157 kg ha^?1). Even greater rate of K, 17.74 mg L^?1 (190 kg ha^?1), was needed to maximize vitamin C content in potato.     

Phosphorus accumulation and leaching risk of greenhouse vegetable soils in Southeast China

Over-fertilization has caused significant phosphorus(P) accumulation in Chinese greenhouse vegetable production(GVP) soils. This study, for the first time, quantified profile P accumulation directly from soil P measurements, as well as subsoil P immobilization, in three alkaline coarse-textured GVP soil profiles with 5(S5), 15(S15), and 30(S30) years of cultivation in Tongshan, Southeast China. For each profile, soil samples were collected at depths of 0–10(topsoil), 10–20, 20–40, 40–60, 60–80, and 80–100 cm. Phosphorus accumulation was estimated from the difference in P contents between topsoil and parent material(60–100 cm subsoil). Phosphorus mobility was assessed from measurements of water-soluble P concentration(PSol). Finally, P sorption isotherms were produced using a batch sorption experiment and fitted using a modified Langmuir model. High total P contents of 1 980(S5), 3 190(S15), and 2 330(S30) mg kg~(-1) were measured in the topsoils versus lower total P content of approximately 600 mg kg~(-1) in the 80–100 cm subsoils. Likewise, topsoil PSol values were very high, varying from 6.4 to 17.0 mg L~(-1). The estimated annual P accumulations in the topsoils were 397(S5), 212(S15), and 78(S30) kg ha~(-1) year~(-1). Sorption isotherms demonstrated the dominance of P desorption in highly P-saturated topsoils, whereas the amount of adsorbed P increased in the 80–100 cm subsoils with slightly larger P adsorption capacity. The total P adsorption capacity of the 80–100 cm subsoils at a solution P concentration of0.5 mg L~(-1) was 15.7(S5), 8.7(S15), and 6.5(S30) kg ha~(-1), demonstrating that subsoils were unable to secure P concentrations in leaching water below 0.5 mg L~(-1) because of their insufficient P-binding capacity.     

Phosphate sorption by red mediterranean soils from Greece

Abstract

In nineteen surface horizons of red Mediterranean soils from various locations of Greece, phosphorus (P) sorption experiments were conducted and the sorption characteristics were studied in relation to soil properties. Phosphate sorption data were fitted both to the Langmuir and Freundlich equations. From these equations, the following P sorption parameters were determined from the Freundlich equation, X = ACⁿ, the parameters A (the phosphate sorbed at C = 1 mg P/L), n (the P sorption intensity), the P sorption index (PS = X/log C) and maximum P sorption (Xmfr). From the Langmuir equation, C/X = 1/KXm + C/Xm, the parameters K (showing the bonding energy), maximum P sorption (Xmla), the quantity of P adsorbed at a standard concentration of 0.2 mg P/L (P0.2), and P maximum buffering capacity (PMBC). The Freundlich parameter A was strongly correlated to the clay and sesquioxides ("free”; iron and aluminum oxides and amorphous iron oxides) content. Seventy‐four percent of the variance of this parameter was explained by clay and “free”; iron (Fe) content. The Freundlich parameter n was significantly correlated with pH and amorphous iron oxides content, while 52% of its variance was explained by amorphous Fe and dithionite extrac‐table aluminum (Al). The P sorption maxima calculated from the Freundlich equation were in general lower than those calculated by the Langmuir equation. Both these parameters were strongly correlated with clay and more slightly with sesquioxides content. About 50% of their variance was explained by clay content of the soils. The P sorption index was strongly correlated with the clay content and less strongly with dithionite‐extractable Fe and Al. The P‐buffering capacity calculated from the data of Langmuir equation was also strongly correlated with these two parameters. In addition, clay content and dithionite‐extractable Fe and Al were well correlated to the amounts of P required to obtain an equilibrium concentration of 0.2 mg P/L while 61% of the variation of this parameter was explained by the clay and the dithionite‐extractable Fe content. From these findings, it seems that for the red Mediterranean soils from Greece, P sorption is affected by clay content and iron and aluminum oxide contents.     

Evaluation of phosphorus sorption by an allophanic soil

Solutions containing different P concentrations were equilibrated with samples of an allophanic soil from Navarra (Spain) to determine whether P sorption conformed qualitatively and quantitatively to the Langmuir, Freundlich and Sokolowska isotherms.Phosphorus sorption conformed to the Langmuir isotherm. When the sorption d data were plotted according to the conventional and Hofstee forms, two linear relationships were obtained. At the lower equilibrium P concentrations the K₁ parameter determined by regression analysis was higher than those corresponding to higher equilibrium P concentrations. The values obtained for K₁ and K₂ by the conventional and Hofstee equations were different. A procedure for evaluating the coefficients for higher equilibrium P concentrations was proposed. The K₁ and K₂ values so obtained allowed us to generate an experimental curve by addition of calculated adsorption data. This suggests that the curve-splitting technique is satisfactory.The sorption data also conformed to the Freundlich and Sokolowska equations, but in the latter it was necessary to evaluate two different sets of parameters.The same experimental data can be adjusted to the three different equations, in one case with only one set of constants and in the other two cases with two different sets of parameters, one for the lower P concentrations and the other for the higher ones. Besides, to fit the experimental data to the Langmuir and Sokolowska equations, it was necessary to split the isotherm into two regions and these two regions were different for the Langmuir and the Sokolowska equations. This suggests that the parameters do not have any chemical signification and that they are only “curve fitting”.A study of the effect of pH on the P sorption indicated that low pH notably increased the P sorption.The soil samples had very high phosphate sorption capacity probably due to the very large specific surface and reactivity of the allophane.     

Sawdust: Cost Effective Scavenger for the Removal of Chromium(III) Ions from Aqueous Solutions

Cr(III) ions sorption onto sawdust of spruce (Picea smithiana) has been studied thoroughly using radiotracer technique. Maximum sorption (94%) of Cr(III) ions (8.98×10^?5 M) onto sorbent surface is achieved from deionized water in 20 min agitation time using 200 mg of sawdust. The sorption data followed the Freundlich, Dubinin-Radushkevich (D-R) and Langmuir isotherms. Freundlich constants l/n = 0.86 ± 0.07 and C _e = 85.0 ± 25.8 mmole g^?1 have been estimated. Sorption capacity, X _m = 0.82± 0.3 mmole g^?1, β = ?0.00356± 0.00017 kJ² mole^?2 and energy, E = 11.9± 0.3 kJ mole^?1 have been evaluated using D-R isotherm. The Langmuir constants Q = 5.8± 0.2 μmole g^?1 and b = (7.4± 0.5)×10⁴ dm³ mole^?1 have been calculated. The variation of sorption with temperature yields thermodynamic parameters Δ H = ?11.6± 0.3 kJ mole^?1, Δ S = ?16.2± 0.9 J mole^?1 K^?1 and Δ G = ?6.8± 0.3 kJ mole^?1 at 298 K. The negative value of enthalpy and free energy reflect the exothermic and spontaneous nature of sorption respectively. Among the anions studied oxalate, citrate, carbonate and borate have reduced the sorption. The cations Y(III), Ce(II) and Ca(II) suppressed sorption. The sawdust column can be used to separate Cr(III) ion from Cs(I), I(I),Tc (VII) and Se (IV).     

Equilibrium, Kinetics and Mechanism of Removal of Methylene Blue from Aqueous Solution by Adsorption onto Pine Cone Biomass of Pinus radiata

The kinetics and mechanism of methylene blue adsorption onto raw pine cone biomass (Pinus radiata) was investigated under various physicochemical parameters. The extent of the methylene blue dye adsorption increased with increases in initial dye concentration, contact time and solution pH but decreases with the amount of adsorbent, salt concentration and temperature of the system. Overall the kinetic studies showed that the methylene blue adsorption process followed pseudo-second-order kinetics among various kinetic models tested. The different kinetic parameters including rate constant, half-adsorption time and diffusion coefficient are determined at different physicochemical conditions. Equilibrium data were best represented by Langmuir isotherm among Langmuir and Freundlich adsorption isotherm. The maximum monolayer adsorption capacity of pine cone biomass was 109.89 mg/g at 30°C. The value of separation factor, R _L, from Langmuir equation and Freundlich constant, n, both give an indication of favourable adsorption. Thermodynamic parameters such as standard Gibbs free energy (?G ⁰), standard enthalpy (?H ⁰), standard entropy (?S ⁰) and the activation energy (A) were calculated. A single-stage batch absorber design for the methylene blue adsorption onto pine cone biomass has been presented based on the Langmuir isotherm model equation.     

Effect of coffee husk and cocoa pods biochar on phosphorus fixation and release processes in acid soils from West Cameroon

Acid soil in West Cameroon has limited phosphorus (P) availability which limits plant growth. This is mainly because of low pH, high levels of exchangeable aluminium (Al) and iron (Fe) and fixation of P. In this study, acid soils, sampled in Bafang, were amended with biochar produced from coffee husks (CH) and cocoa pod husks (CP) at two different temperatures (350 and 550 °C) in other to evaluate the effect on the physicochemical properties of the acid soil and the effect on P sorption and desorption. The soil was amended with biochar at a rate of 0, 20, 40 and 80 g/kg and incubated for 7 and 60 days. Physicochemical properties of all soil–biochar samples were determined followed by sorption experiments and data fitted in the Langmuir and Freundlich isotherm models in other to evaluate soil P sorption capacity and its affinity to soil amended with biochar. Moreover, desorption studies were done to evaluate the availability of P in soil amended with biochar after sorption. The outcomes of this study reveal an increase in soil pH, electrical conductivity (EC), available P, soil organic carbon and a drastic decrease in exchangeable Al and Fe. The point of zero charge of biochar-amended soil was higher than the control and increased with amendment rate. The experimental data of the sorption of P on soils and soil–biochar samples fits into Langmuir and Freundlich models (R² > 0.9) suggesting that the P adsorption is controlled by both model mechanisms. Soil–biochar mixture results in a decrease in the sorption capacity as compared with the control and the decrease was predominant with increasing amendment rate. At amendment rates of 20, 40 and 80 g/kg after 7 days of incubation, $Q_{\max }$ for SCH350 were 2267, 2048 and 1823 mg/kg which increased to 2407, 2112 and 1990 mg/kg after 60 days of incubation. This tendency was observed for all biochar inputs with respect to the increase in incubation days. Furthermore, desorption of P from soil–biochar mixtures was enhanced with biochar added at greater rate and produced at higher temperature. The desorption percentage was increased by more than around 10% for all biochar types from 20 mg/kg to 80 mg/kg amendment. Thus, biochar addition to acid soils reduces P fixation to acid soil and improves P desorption to soil solution, thereby providing more available P in the soil solution and better conditions for plant growth.     

Removal of Heavy Metals in Storm Water Runoff Using Porous Vermiculite Expanded by Microwave Preparation

The main objective of this study was to examine the effectiveness of vermiculite for removing heavy metals from water. Vermiculite components were analyzed by X-ray fluorescence, and the concentrations of metal ions were measured by inductively coupled plasma spectrometry. Serial batch kinetic tests and batch sorption tests were conducted to determine the removal characteristics for heavy metals in aqueous solutions. Solution pH values of tests with the inflated vermiculites generally increased and then stabilized. Equilibrium pH was generally established within 5?h. Removal rates of inflated vermiculite were tested at the initial concentration of 3?mg/L. At equilibrium concentrations, except for chromium (36.23%), most heavy metals were effectively removed (96.08?C98.54%). Finally, sorption data were correlated with both Langmuir and Freundlich isotherms. For each metal, the Q _max obtained using the Langmuir isotherm was as follows: lead, 725.4?mg?kg^?1; cadmium, 568.8?mg?kg^?1; zinc, 540.2?mg?kg^?1; copper, 457.2?mg?kg^?1; and chromium, 0.9?mg?kg^?1. The study results indicate that inflated vermiculite has outstanding removal rates and therefore can be used as an adsorbent for various heavy metals.     

Comparison of Adsorption Isotherm Equations to Describe Boron Behavior in Soils Affected by Organic and Mineral Fertilization

The effects of different fertilization techniques—mineral [21% nitrogen (N)], organomineral (10% N), mycorrhiza inoculumns, wine-producing residues (three different formulas: distiller's residue, 2.2% N; anaerobic digestate, 2.8% N; and the same plus mycorrhizas inoculum), and compost by farm residues (2.0% N)—on adsorption of boron (B) were investigated. The soils, collected after a triennial lettuce (Lactuca sativa L. cv. ‘Bacio’) cultivation, were equilibrated using six B concentrations [0, 1, 5, 20, 50, and 100 mg B L^?1, as boric acid (H₃BO₃)]. The B adsorption was studied at two soil mass (m_s) to solution volume (v_s) ratios, m_s/v_s = 0.5 and 1, and the Langmuir, Eadie–Hofstee, Freundlich, and Temkin adsorption equations were fitted to the B adsorption data. The proportion of adsorbed B was gradually less in the more concentrated solutions, with differences in m_s/v_s ratio and in treatments: the percentage of B adsorbed was greater for m_s/v_s = 0.5 and for distiller's residue and mineral fertilizer. The Freundlich isotherm represented the measured B adsorption data well; at m_s/v_s = 0.5, the values of Freundlich adsorption maxima Xm varied from 93.14 to 111.88 mg kg^?1 (organomineral fertilizer and distiller's residue, respectively; at m_s/v_s = 0.5) and from 32.14 to 40.32 mg kg^?1 (mineral fertilizer and control, respectively; at m_s/v_s = 1). In our study, generally the B adsorption was greater with mineral fertilizers and distiller's residue, whereas the organomineral fertilizer led to a decrease in B adsorption. The parameters of adsorption isotherms were significantly correlated, at various degrees, with the exchangeable cation sodium. The adsorption isotherms were well explained by the lower soil mass to volume solution ratio in the order Freundlich > Temkin ≌ Langmuir > Headie–Hofstee.     

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.     

印度Chattisgarh州两种新开发土和一种淋溶土中磷酸盐吸附-解析特征研究

Two Inceptisols and an Alfisol of the Indravati Catchment area in Chattisgarh, India, comprising several gradients in physical and chemical properties were studied to relate phosphate sorption and desorption to soil properties. From the P isotherm curve, the standard P requirement （SPR） of the soils was determined. Phosphate sorption data were also fitted both to the Langmuir and Freundlich Equations. The mean sorption maximum values for three different soil series were： Bastar 〉 Geedam 〉 Mosodi. The fraction of added phosphate sorbed for the 3 series followed this same trend as did SPR; the phosphate sorption maximum and the maximum phosphate buffering capacity, which were estimated by the Langmuir isotherm; and the Freundlich constant 1/n. However, phosphate desorption, as well as the maximum recovery percent did not follow this order. The phosphate affinity constant （K） was also different following the same progression for the 3 soil series as the Freundlich constant K＇, which measured sorption strength. Meanwhile, an inverse order existed for K and K＇ versus the percent desorbed relative to the sorbed as well as the maximum recovery percent. In addition, significant correlation coefficients among sorption parameters of P and soil factors were found.     

Phosphorus Management of Lucerne Grown on Calcareous Soil in Turkey

ABSTRACT

Lucerne or alfalfa (Medicago sativa L.) is grown as a forage crop on many livestock farms. In calcareous soils in eastern Turkey, lucerne production requires phosphorus (P) additions as the soils are naturally P deficient. Phosphorus sorption isotherms were used to estimate P fertilizer needs for lucerne grown for two years in a 3-cut system on a calcareous P deficient Aridisol in eastern Anatolia, Erzurum province, Turkey. Annual P applications ranged from 0–1200 kg P ha^?1. The Langmuir two-surface adsorption equation was used to derive the maximum P sorption capacity of unamended soil and to determine soil solution P, maximum buffer capacity (MBC), equilibrium buffer capacity (EBC), and P saturation at the optimum economic P rate (OEPR) for dry matter (DM) production. Soils were tested for Olson P at the onset of the study and after two years of P applications. In both years, tissue was analyzed for P content at flowering prior to first cutting. The OEPR (2-year average) was 754 kg P ha^?1 yr^?1 corresponding with a soil solution P concentration of 0.30 mg L^?1, a DM yield of 8725 kg DM ha^?1, and $528 ha^?1 annual profit. The P content of leaves at flowering increased linearly with P application beyond 100 kg P ha^?1 and was 3.2 g kg^?1 P at the OEPR. The unfertilized soil had an EBC, MBC, P saturation, and X_max of 3304 mL g^?1, 3401 mL g^?1, 6%, and 1086 mL g^?1, respectively, whereas two years of fertilization to the OEPR decreased EBC and MBC to 358 mL g^?1 and 540 mL g^?1, and increased P saturation and Olsen P to 56% and 32 mg kg^?1, respectively. These results suggest a P saturation >50% or Olsen P >30 mg kg^?1 are needed to maintain an optimum soil solution concentration of 0.30 mg L^?1 in this calcareous Aridisol. Similar studies with different soils and initial soil test P levels are needed to conclude if these critical soil test values can be applied across the region.     

Phosphate sorption characteristics of major soils in Okinawa,Japan

Abstract

Phosphate sorption isotherms were determined for 16 representative major soils developed from different parent materials on Okinawa. Phosphate sorption characteristics were satisfactorily described by the Langmuir equation, which was used to determine phosphorus (P) sorption maxima of the soils. Phosphate sorption maxima ranged from 630 to 2208 mg P kg^‐1 soil (mean 1,362 mg P kg^‐1). The standard P requirement (i.e., the amount of P required to attain 0.2 mg P L^‐1 equilibrium solution) followed the same trend as sorption maximum (r =0.94***), with values ranging from 132 to 1,020 mg P kg^‐1 soil (mean 615 mg P kg^‐1). This mean value corresponds to fertilizer addition of 923 kg P ha^‐1 indicating that the soils have high P fertilizer requirements. Results of simple linear regression analysis indicated that sorption maximum was significantly correlated with clay content, organic matter, oxalate iron (Fe), pyrophosphate Fe, DCB aluminum (Al), oxalate Al, and pyrophosphate Al, but not with DCB Fe, pH, or available P content. The best regression model for predicting sorption maximum was the combination of clay, organic matter, pyrophosphate Fe, and DCB Al which altogether explained 79% of the variance in sorption maximum. The equation obtained could offer a rapid estimation of P sorption in Okinawan soils.     

Phosphate sorption by calcium‐bentonite as described by commonly used isotherms

Abstract

The one and two Langmuir, the Freundlich, and the Temkin isotherms were fitted to phsophorus (P) sorption data for P sorption by calcium (Ca)‐bentonite at different initial concentration and pH values of 3.8, 4.8, 6.0, 7.0, 8.0, and 9.0. Each was found to describe P sorption by Ca‐bentonite with comparable success. The effect of pH on P adsorption by Ca‐bentonite was studied and Langmuir, Temkin, and Freundlich isotherms were converted to the forms:

Langmuir: (Co‐X)X= 1/(0.0275–0.0025pH)(12.323–1.061pH) + (Co‐X)(12.323–1.016pH) Temkin: X = (2.45–0.211pH)In(AC) Freundlich: X = (1.324–0.146pH)C(^0.172+0044 _P ^H) where: X = (mmol P/kg) the amount of P sorbed per unit weight of soil, C = (μmol P/L) the P concentration in the equilibrium solution, and Co = ((μmol P/L) initial P concentration. It is noteworthy, that the maximum amount (Xm) of P that can be sorbed in a monolayer decreases by increasing of pH. Finally, the B constant of Temkin isotherms is indepented from pH changes.     

Fate of phosphorus in soil during a long‐term fertilization experiment in Finland

Accumulation and depletion of soil phosphorus (P) was studied in a long‐term (37 y) field experiment in Southern Finland. The loam soil had a high pH (7.5–7.7) due to an earlier liming. Spring barley, spring wheat, oat, and ryegrass, grown in rotation, were annually fertilized with 0, 32, or 67 kg P ha^?1 y^?1 (P₀, P₁, and P₂K) and sufficient N. The average dry matter grain yield 2,600 kg ha^?1 of the P₀ plots increased by about 500 kg ha^?1 at P₁ treatment and another 600 kg ha^?1 by P₂K. Soil samples were collected in 1978 (beginning), 1995, 2005, and 2015. According to the Chang and Jackson sequential extraction, the P₂K and P₁ treatments increased the inorganic soil P by 732 and 32 kg P ha ^?1 in 37 years, respectively, while the P₀ plots were depleted by –459 kg P ha ^?1. The P₂K treatment increased all four P fractions, extracted with NH₄Cl (easily soluble), NH₄F (Al‐P), NaOH (Fe‐P), and H₂SO₄ (Ca‐P). Continuous depletion (P₀) decreased the NH₄Cl‐P and NH₄F‐P pools, NaOH‐P and H₂SO₄‐P pools remaining stable. None of the P pools changed significantly at P₁. The remarkable gap between the measured change and the balance for the P₂K and P₁ treatments cannot be explained solely by lateral soil movement, meaning that a significant proportion of the applied P was lost either in surface runoff or transported below the investigated depth of 40 cm. Despite large P applications, the degree of P saturation reached only 20% in the P₂K topsoil, assuming a 50% reactivity of Fe and Al oxides. As derived from sorption isotherms, a high EPC₀ (i.e., equilibrium P concentration at zero net P sorption or desorption) of 1.30 mg L^?1 had been built up in the P₂K treatment, while in the P₁ treatment EPC₀ (0.33 mg L^?1) had remained unchanged and P depletion (P₀) had caused a decrease to 0.12 mg L^?1. These results demonstrate that P sorption and desorption properties respond strongly to both P fertilization and null fertilization treatments and that in a long‐term field experiment only a low proportion of the residual fertilizer P can be recovered from soil.     

土壤组分对广东省酸性水稻土磷吸附参数的影响

Soil components affecting phosphate sorption parameters were studied using acid paddy soils derived from basalt, granite, sand-shale and the Pearl River Delta sediments, respectively, in Guangdong Province.For each soil, seven 2.50 g subsamples were equilibrated with 50 mL 0.02 mol L-1 (pH=7.0) of KCl containing 0, 5, 10, 15, 25, 50 and 100 ng P kg-1, respectively, in order to derive P sorption parameters (P sorption maximum, P sorption intensity factor and maximum buffer capacity) by Langmuir isotherm equation. It was shown that the main soil components influencing phosphate sorption maximum (Xm) included soil clay, pH,amorphous iron oxide (Feo) and amorphous aluminum oxide (Alo), with their effects in the order of Alo ＞Feo ＞ pH ＞ clay. Among these components, pH had a negative effect, and the others had a positive effect.Organic matter (OM) was the only soil component influencing P sorption intensity factor (K). The main components influencing maximum phosphate buffer capacity (MBC) consisted of soil clay, OM, pH, Feo and Alo, with their effects in the order of Alo ＞ OM ＞ pH ＞ Feo ＞ clay. Path analysis indicated that among the components with positive effects on maximum phosphate buffer capacity (MBC), the effect was in the order of Alo ＞ Feo ＞ Clay, while among the components with negative effects, OM ＞ pH. OM played an important role in mobilizing phosphate in acid paddy soils mainly through decreasing the sorption intensity of phosphate by soil particles.     

Adsorption of Copper in the Different Sorbent/Water Ratios of Soil Systems

While sorbate/sorbent, sorbate/water, and sorbent/water (S/W)ratios in a batch system are known to affect the adsorption ofsorbate, the effect of different S/W ratios on the adsorptionof inorganic sorbates has seldom been addressed. This studyinvestigates the adsorption phenomena of Cu²⁺ in differentsorbate/sorbent/water ratios in a batch system. Batch experimentsare performed to examine the adsorption, and the linear (K _D), Langmuir (K _L), and Freundlich (K _F) adsorption coefficients of Cu²⁺ in lateritic soil. These experiments are conducted using solutions with initial concentrations of 0.5 to 50 mg Cu²⁺ L^-1 equilibratedwith an appropriate amount of soil to give S/W ratios of 0.1 to 2 g mL^-1. Although the variations in the sorbed amountand adsorption coefficients apparently originate from a changein the sorbate/sorbent/water ratio, only the equilibrium concentration significantly affects adsorption. On the otherhand, the linear and Langmuir isotherm cannot adequately describethe adsorption data. In this study, the Freundlich equation gavean excellent fit to the adsorption data with a goodness-of-fit(R²) > 0.984. However, adsorption isotherms should be regarded as only a curve-fitting model or a mathematical tool and cannot be employed to interpret any particular adsorptionmechanism. Meanwhile, the solids effect reveals that K _F andmaximum adsorption (b) of the Langmuir equation increase when S/W ratio decreases. The sorbate in the stagnant phase must beconsidered as part of the equilibrium concentration in the solidphase to avoid underestimating the sorbed amount at a lower S/Wratio and/or a higher sorbate concentration level.     

Retention of Cd, Cu, Pb and Zn by Wood Ash, Lime and Fume Dust

Heavy metals are of interest due to their deleterious impacts on both human and ecosystem health. This study investigated the effectiveness of wood ash in immobilizing the heavy metals Pb, Cd, Cu and Zn from aqueous solutions. The effects of initial metal concentrations, solution pH, ash dose and reaction time on metal sorption, as well as the metal sorption mechanisms were studied. To investigate the effect of initial metal concentrations, solutions containing Cd, Zn (25, 50, 75, 100 or 125 mg L^?1), Cu (25, 50, 75, 100, 125, 150 or 175 mg L^?1) or Pb (250, 500, 750, 1000, 1250, or 1500 mg L^?1) were reacted with 10 g L^?1 ash for two hours. For the effect of pH, solutions containing 100 mg L^?1 of Cd, Cu or Zn or 1500 mg L^?1 of Pb were reacted with 15 g L^?1 ash over a pH range of 4 to 7. The wood ash was effective in immobilizing the four metals with a sorption range of 41–100 %. The amounts of metals retained by the ash followed the order of Pb > Cu > Cd > Zn. As expected, absolute metal retention increased with increasing initial metal concentrations, solution pH and ash dose. Metal retention by the ash exhibited a two-phase step: an initial rapid uptake of the metal followed by a period of relatively slow removal of metal from solution. Metal retention by the ash could be described by the Langmuir and Freundlich isotherms, with the latter providing a better fit for the data. Dissolution of calcite /gypsum minerals and precipitation of metal carbonate/sulfate like minerals were probably responsible for metal immobilization by the ash in addition to adsorption.