Phosphorus sorption maxima and desorbability in selected soils with andic properties from the Azores, Portugal

P sorption and desorption capacities were determined on 30 soil horizons (surface and subsurface) of soils with andic properties from the Azores, Portugal, using the Langmuir equation and successive extractions with dilute calcium chloride (CaCl₂), respectively. The proportion of P recovery (Prec) using distilled water (H₂O), CaCl₂, Bray 2 (B2), Mehlich 3 (M3), Egnér–Riehm (ER) and Olsen (OL) extractants was also determined to assess the extent of P release from soils enriched with P at P sorption maxima (Pm). Soils containing very low amounts of organic C and allophane (Vitrandic Haplustepts and Vitrandic Udorthents) showed the lowest values of Pm (48–565 mg kg^− 1) and the highest values of P desorbability (Pdes) (69–100%), indicating that P can be easily lost from these soils. Application of fertilizers to these soils should be restrained in order to minimize eutrophication risk of nearby water bodies. In contrast, allophanic and non-allophanic horizons of Typic Placudands, Alic Hapludands, Acrudoxic Hapludands and Acrudoxic Hydrudands showed much higher values of Pm (2273–52,400 mg kg^− 1) and lower values of Pdes (4–57%).They also showed low proportions of Prec by the used extractants, indicating that large amounts of P can be sorbed in an unavailable form. Thus, these soils may require large amounts of P fertilizers and an efficient method of P application. Other studied soils with high amounts of 1:1 layer silicate minerals and having weak andic properties (Typic and Andic Haplustepts), showed intermediate Pm (1124–8333 mg kg^− 1) and Pdes values (20–63%).

The values of Pm were positively correlated with Al_d, Al_o, allophane, Fe_o, Fe_d and Al_p contents, and with the values of Al_o + 1/2 Fe_o. In contrast, values of Pdes were negatively correlated with these soil constituents. Of the six extractants, the B2 extractant showed generally higher proportions of Prec than the other extractants in most studied soils. The proportions of Prec by the B2, M3, ER and OL extractants were negatively correlated with contents of Fe_o, Fe_d, Al_d, Al_o, Al_p, and Fe_p, and with the values of Al_o + 1/2 Fe_o and PR.     

Simple phosphorus saturation index to estimate risk of dissolved P in runoff from arable soils

Abstract. There is increasing evidence that phosphorus has been accumulating in the surface horizons of agricultural soils to the extent that some soils represent a potential diffuse source of pollution to surface waters. The relationships between equilibrium phosphorus concentration at zero sorption (EPC ₀) of soil and a number of soil physicochemical variables were investigated in the surface layers of arable and grassland agricultural soils sampled from the Thame catchment, England. Soil EPC₀ could be predicted from an equation including soil test (Olsen) P, soil phosphate sorption index (PSI) and organic matter content (OM) (R²=0.88; P <0.001) across a range of soil types and land use. The simple index Olsen P/PSI was found to be a good predictor of EPC₀ (R²=0.77; P <0.001) and readily desorbable (0.02 m KCl extractable) P (R²=0.73; P <0.001) across a range of soil types under arable having soil organic matter contents of <10%.     

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.     

广东罗浮山土壤颗粒分形维数分布特征

  目的  揭示广东罗浮山不同海拔高度土壤颗粒组成分形维数特征的分布规律。  方法  在广东罗浮山不同海拔高度的10个土壤采样点挖掘剖面,采集各发生层土壤,测定了土壤颗粒组成、有机碳（SOC）、全铁（Fe_t）、游离铁（Fe_d）、无定形铁（Fe_o）、阳离子交换量（CEC）等理化性质,分析了土壤颗粒分形维数与海拔、土壤颗粒分布及化学性质之间的相关关系。  结果  随着土层深度的增加,土壤颗粒分形维数先增加后减小;随着海拔的升高,土壤黏粒含量、颗粒分形维数均呈减小趋势,且与海拔高度均呈极显著相关关系;随土壤质地的变细,分形维数平均值由2.7601上升到了2.8954,即分形维数随土壤质地的变细而增大;颗粒分形维数与砂粒呈极显著负相关关系,与黏粒呈极显著正相关关系;分形维数与SOC、Fe_o、Fe_o/Fe_d、CEC呈极显著或显著负相关关系,与Fe_t、Fe_d含量表现为极显著正相关关系;通径分析表明Fe_t、Fe_o/Fe_d是化学性质中影响颗粒分形维数的主要因素。  结论  土壤颗粒分形维数可以作为土壤质地的重要诊断指标,也可作为不同海拔高度土壤风化成土进程的参考表征指标。     

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.     

Phosphate sorption in some representative soils of Bangladesh

An experiment was conducted to observe the phosphate sorption potential of some soils of Bangladesh. Three soil series of calcareous origin, namely Sara (Aquic Eutrochrept), Gopalpur (Aquic Eutrochrept) and Ishurdi (Aeric Haplaquept), and two soil series of non-calcareous origin, namely Tejgaon (Rhodic Paleustult) and Ghatail (Aeric Haplaquept), were selected. The soils were equilibrated with dilute solution of calcium chloride containing graded concentrations of phosphate (0, 1, 2, 5, 10, 25 and 50?μg?P?mL^?1), and the amount of phosphate sorbed or desorbed was determined. Although all the soils showed potential for sorbing phosphate from applied phosphorus, their ability to sorb phosphorus differed. Increasing rates of phosphate application increased the amount of P sorption but reduced phosphate sorption percentage in all soils except Tejgaon. Phosphate was sorbed by the soils in the order: Tejgaon > Ghatail > Ishurdi > Gopalpur > Sara at 50?μg?P?mL^?1 application. Soils possessing higher amounts of free iron oxide and clay sorbed more phosphate from applied phosphorus.     

Effect of Manure Types and Period of Incubation on Phosphorus-Sorption Indices of a Weathered Tropical Soil

Application of animal manures with inorganic phosphate (PO₄) fertilizer is proposed as one of the management options to improve availability and solubility of applied phosphate in weathered soil. We studied the effects of poultry, cattle, and goat manures at different incubation periods (0 to 120 days) on phosphorus (P) sorption indices of a weathered sandy clay loam soil. The soil P adsorption isotherms conformed to the H curve. Generally, the soil P-sorption efficiency decreased as the number of days of incubation increased irrespective of manure amendments. Manure application reduced the P-sorption efficiency of the soil; the lowest P-sorption efficiency was observed after 30 days of incubation. The data conformed to adsorption models in the order Temkin > Freundlich > Langmuir. Cattle, goat, and poultry manures reduced the adsorption constants in all models. Standard phosphate requirement and P-buffering capacity were also reduced with the application of the manures.     

Zinc sorption–desorption by sand,silt and clay fractions in calcareous soils of Iran

Zinc sorption–desorption by sand, silt and clay fractions of six representative calcareous soils of Iran were measured. Sand, silt and clay particles were fractionated after dispersion of soils with an ultrasonic probe. Zinc sorption analysis was performed by adding eight rates of Zn from 6 to 120 μmol g^?1. For the desorption experiment, samples retained after the measurement of Zn sorption were resuspended sequentially in 0.01 M NaNO₃ solution and shaken for 24 h. Results indicated that Zn sorption by soil fractions increased in the order clay > silt > sand, and correlated negatively with CaCO₃ content and positively with cation exchange capacity (CEC) and smectite content. Results indicated that for all fractions, the Langmuir equation described the sorption rates fairly well. In contrast to sorption, Zn desorption from soil fractions increased in the order sand > silt > clay, and correlated positively with CaCO₃ content, CEC and smectite content. Results showed that parabolic diffusion and two constant equations adequately described the reaction rates of Zn desorption. In general, for all soils studied, the coarser the particle size, the less Zn sorption and more Zn desorption, and this reflects much higher risk of Zn leaching into groundwater or plant uptake in contaminated soils.     

Influence of phosphate on cadmium sorption by calcium carbonate

Laboratory investigation was conducted to investigate the mechanism of cadmium sorption by pure calcium carbonate and to examine whether, reaction products of phosphate with calcium carbonate serve as a sink for sorption of toxic heavy metal cations like cadmium. The phosphatization of calcium carbonate (G.R) was carried out by treating it with orthophosphoric acid in Ca:P ratio of 5:3, 3:2, 4:3 and 1:1, representing the Ca–P ratios of carbonate apatite, tricalcium phosphate, octacalcium phosphate and dicalcium phosphate and then equilibrated for two months. The X-ray diffraction of the phosphate reaction products revealed that calcite along with monetite, brushite and carbonate apatite were present in each case. The cadmium was effectively retained on CaCO₃ by the mechanism of chemisorption at lower Cd²⁺ concentrations as the pH of the equilibrium system remained constant (8.6) up to initial Cd²⁺ concentrations of 10⁻⁴ mol, coinciding to 100% sorption of Cd²⁺ from the solution. At higher concentrations, precipitation of CdCO₃ on CaCO₃ surface or as a separate phase predominated. Enrichment of CaCO₃ with P reduced the Cd-sorption. The chemisorption of Cd probably involved the exchange of Ca²⁺ by Cd²⁺ from CaCO₃ surface. The Cd²⁺ concentration in equilibrium solution followed the solubility diagram of CdCO₃ at pH ≤ 8.6, whereas the concentration of Ca²⁺ started deviating from the solubility line at pH ≤ 8.2.     

Particle size and free iron oxide distribution in some latosols and groundwater laterites of Ghana

The distribution of particle size and Na-dithionite-extractable (di-Fe₂ O₃) and NH₄-oxalate-extractable (ox-Fe₂O₃) iron oxides were investigated in twelve soil profiles representing latosols and groundwater laterites. Soil profiles studied were selected from the major ecological zones of Ghana. The pattern of distribution of free Fe₂O₃ was closely related to that of clay (< 2μ) in soil profiles of the humid forest zones where clay content was more than 40% in the B horizons. In soil profiles of the relatively dry savannah zones with less than 40% clay in the B horizon, the pattern of distribution of free Fe₂O₃ was closely related to that of silt (2–20 μ). The amount of free Fe₂O₃ in the soils appeared to be related to kind of parent rock or parent material and to climatic factors operating in the various ecological zones. Using the amount of di-Fe₂O₃ in the B horizon as a basis for assessing the relative degrees of pedogenesis in soil profiles developed from the same kind of parent material, it was concluded that soil profile development had progressed most in the rain forest zone. Free Fe₂O₃ was considered as having reached an advanced stage of crystallinity or aging in most of the soils because of the low ox-Fe₂O₃/di-Fe₂O₃ ratios in the solums of most of the soil profiles. Soils studied were placed in the ferrallitic and ferruginous soil classes of D'Hoore. The great soil groups could not be characterized by depth function curves of free Fe₂O₃. However, it was proposed that the relative amounts of di-Fe₂O₃ in the B horizons of the soil profiles could be used as a basis for classifying these soils at the family level.