Zinc Release Characteristics from Calcareous Soils using Diethylenetriaminepentaacetic Acid and Other Organic Acids

Adsorption and desorption reactions of zinc (Zn) in soils control its availability to plants. In the present investigation, time-dependent Zn release was evaluated using three organic acids [diethylenetriaminepentaacetic acid (DTPA), citric acid, and maleic acid] to depict the Zn fraction controlling Zn release rate from slightly calcareous to calcareous soils. Eight surface and two subsoil samples of selected soil series varied in their physicochemical properties, amount of Zn held in different chemical pools, and Zn-retention capacities (21–61%). Each soil was extracted for a total period of 24 h at 1:10 soil/extractant suspension ratio using 0.005 M DTPA. The time-dependent parabolic diffusion model best described the Zn release in six consecutive extractions. Soils differed in cumulative Zn extracted (1.09–3.81 mg kg^?1 soil) and Zn release rate. Under similar conditions, three soils differing in Zn-retention capacities were also extracted with five different concentrations (0.01–0.0001 M) of citric and maleic acids. Although both maleic and citric acids released soil Zn at greater rates and in greater amounts than DTPA, maleic acid was more efficient. Soil Zn bound to amorphous iron (Fe) + manganese (Mn) oxides was the main Zn pool that controlled Zn release characteristics.     

Kinetics of Iron and Manganese Release from Contaminated Calcareous Soils

Knowledge of the release of heavy metals (HM) and their chemical speciation is necessary for characterizing HM behavior in soils. The kinetics and characteristics of iron (Fe) and manganese (Mn) release were studied in 10 contaminated calcareous soils using 0.01 M calcium chloride (CaCl₂), 0.01 M ethylenediamine tetraacetic acid (EDTA), and 0.01 M malic acid (malic acid) extractions. Iron and Mn in soil samples were fractionated before and after 2084 h kinetic release using a sequential extraction procedure. The proportion of Fe and Mn released by EDTA was greater than that with CaCl₂ and malic acid. A power model satisfactorily described Fe and Mn release from soils. In general, the mean release rate of Fe was greater than that of Mn, indicating a greater rate of Fe release from contaminated soils. It was shown that Fe and Mn distributions were similar in native soils and they were mainly found in Fe-Mn oxides and organic-matter (OM) fractions. There were changes in the proportional distribution of Fe and Mn in all soils during the 2084 h kinetic study with different extraction solutions. In general, the proportions of Fe and Mn associated with carbonate (CARB) and OM fractions tended to decrease, with corresponding increases in the Fe-Mn oxides for Mn and residual (RES) fractions for Fe during the kinetic study with all extraction solutions. The Fe and Mn solubility at the initial and final stages of release was controlled by siderite (FeCO₃), vivianite [(Fe)₃(PO₄)₂·8H₂O], MnCO₃(am), MnHPO₄, and rhodochrosite (MnCO₃) minerals in all extraction solutions. Based on a risk assessment and percentage of release of metals, there is a high potential for Mn release into the food chain from contaminated soils.     

有机酸和磷对两种污染土壤铅的释放作用研究

用土壤培养和化学浸提法研究了不同低分子量有机酸和磷对污染土壤中铅释放的影响。结果表明,随有机酸浓度增加,铅污染红壤、棕壤中可溶出铅量均增加。当供试有机酸浓度≥1mmol·L-1时,相同浓度有机酸溶出铅量为柠檬酸〉乙酸〉草酸;当有机酸浓度≤0.5mmol·L-1时,溶出铅量为草酸〉柠檬酸〉乙酸。将2g·kg-1磷及50mmol·kg-1有机酸与铅污染红壤以不同方式混合后,柠檬酸处理的溶出铅比率（在污染土壤中加入P、有机酸后溶出铅含量与单加有机酸溶出铅含量之比）为66%（先加有机酸再加磷）、58%（有机酸与磷同时加入）、70%（先加磷再加有机酸）,草酸处理（方式同上）的溶出铅比率为90%、89%、94%,乙酸处理（方式同上）的为10%、8%、10%。铅污染棕壤上,以上处理的溶出铅比率分别为106.46%、104.43%、105.19%（柠檬酸）;43%、48%、58%（草酸）;38%、42%、55%（乙酸）。供试条件下,红壤最低溶出铅比率低于棕壤。     

Metal Extractability in Binary and Multi-metals Spiked Calcareous Soils

In the present study, a laboratory experiment was designed to compare the 0.01 M calcium chloride (CaCl₂) and diethylenetriaminepentaacetic acid (DTPA) extraction methods for their ability to predict cadmium (Cd), copper (Cu), iron (Fe), Manganese (Mn), nickel (Ni), and zinc (Zn) availability and mobility in five calcareous soils. The soils were spiked with different amounts of metals (0, 50, 100, 200, and 400 mg kg^?1) both in binary (Cu and Zn; Ni and Cd; Fe and Mn) and in multi-systems (Cd, Cu, Fe, Mn, Ni, and Zn) and incubated for 1 months at field capacity. In metal-spiked soils, both extraction methods showed a linear relationship of extractable to total metals for all soils. The fraction of total metals extracted by DTPA was much higher than the fraction extracted by CaCl₂, which was attributed to the formation of soluble metal-complexes in the complexing extracts calculated by the Visual Minteq program. DTPA extraction method showed higher selectivity for Cu over other metals both in binary and in multi-systems. Different order of metals extractability was found in binary and multi-systems for both extraction methods. Solid/solution distribution coefficient (K_d) was calculated by the ratio of the solid phase to soil solution concentration of metals extracted by CaCl₂ or DTPA extraction methods. Both in binary and in multi-systems, the average K_d (l kg^?1) of metals by soils were in the order of Mn (5398) > Fe (4413) > Zn (3376) > Cu (2520) > Ni (969) > Cd (350) in the CaCl₂-extractable metals and Fe (35) ≥ Ni (34) > Zn (18) > Mn (11.2) > Cu (6.3) > Cd (4) in the DTPA-extractable metals. Results showed that among the six studied metals, Cd had the lowest K_d, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that in the CaCl₂-extraction method and in both binary and multi-systems the dominant species for Cu, Mn, Ni, and Zn were Cu²⁺, Mn²⁺, Ni²⁺ and Zn²⁺, respectively, while for Cd and Fe, the dominant species were CdCl⁺ and Fe(OH)²⁺, respectively.     

Effect of pH on Potentially Toxic Trace Elements (Cd,Cu, Ni,and Zn) Solubility in Two Native and Spiked Calcareous Soils: Experimental and Modeling

The effect of soil pH on solubility of the potentially toxic trace elements (PTEs) [cadmium (Cd), copper (Cu), nickel (Ni), zinc (Zn)] was assessed using two native and spiked calcareous soils. Multiple PTEs solutions were added to soils and equilibrated (aged) for 40 days. Then, PTEs solubility was measured at different pH level (1–3 units below and above the pH of native soils). In native soils, all PTEs displayed a V-shaped pH-dependent solubility pattern with important releases at pH 4 and 10 (native soil 1) and 5 and 11 (native soil 2). In spiked soils, the general tendency for the pH where solubility started was in the order Cd > Ni > Zn > Cu. Solubility of added trace elements increased with a decrease in pH. Solubility of PTEs occurred at a lower pH in the soil with a higher carbonate content than the other soil (both native and spiked). In order to predict the effect of soil pH on solubility of PTEs, surface complexation and ions exchange models of PHREEQC program were used. The model simulated the PTEs solubility in soils very well. Comparison of experimental and simulated data indicated that ions exchange and surface complexation were the main mechanisms for predicting PTEs solubility in soils. Environmental implications concerning PTEs mobility might be derived from these findings.     

Role of Phenolics and Organic Acids in Phosphorus Mobilization in Calcareous and Acidic Soils

Abstract

Phenolic acids (caffeic, CAF; protocatechuic, PCA; p-coumaric, COU; and vanillic, VAN), catechol (CAT), poly-galacturonic acid (PGA), and citric acid (CIT) were compared for their effectiveness in phosphorus (P) mobilization in three soils differing in chemical properties. The addition of organic ligands at 100 μmol g^{? 1} soil increased the concentrations of resin P (P_r), water-extractable P (P_w), and bicarbonate-extractable inorganic P (P_bi), thus improving the phosphorus availability. The magnitude of P mobilization in the calcareous soil can be expressed in the following order: CAF > CAT > PCA = CIT > VAN > COU > PGA, which was consistent with the number of phenolic hydroxyl groups they contained and the position of carboxyl on the benzoic ring. In the two acid soils tested, the order of P mobilization was CIT > CAT > PCA > CAF after 24 h incubation, and CIT > PCA > CAF > CAT after a 14 d incubation. The mobilized P originated partly from the organic P fractions, which could be extracted by 0.5 M NaHCO₃. In addition, P_r decreased and P_w increased during incubation. The exceptions were that the CAF treatment increased P_r and the CIT treatment did not affect P_w. Calcium extraction from the soils after a 1 d or 14 d incubation could not fully account for the P mobilization. The results suggest that the inorganic P dissolution by the organic ligands was not the only mechanism of P mobilization in the calcareous soil, while in acid soils the chelation of metal cations by organic ligands is likely an important factor in P mobilization.     

Kinetics of Ligand-Controlled Release of Zinc in Acid Sulfate Paddy Soils

The elevated solubility of zinc(Zn) in acid sulfate paddy soils can limit rice production and pose a risk of environmental pollution.However, little attention has been paid to the ligand-controlled release of Zn in these soils. Here we quantified the rate of ligandcontrolled Zn release in Thai acid sulfate paddy soils, using ethylenediaminetetraacetic acid as the extractant. Sequential extractions were performed to obtain quantitative information on Zn fractions contributing to the ligand-controlled mechanisms. The amount of Zn released within 192 h varied significantly(8–43 mg kg~(-1)), which corresponded to 12%–40% of the total soil Zn, indicating that Zn solubility in most soils was relatively low and that Zn mainly occurred as residual phases. The kinetics of Zn release was well described by the power function model(r = 0.65–0.99, median = 0.87). The magnitude of initial Zn release(coefficient a) was significantly(P 0.05) related to the aqua regia-soluble Zn. Easily mobile Zn, organically bound Zn, and Zn associated with Fe and Mn oxides also contributed to the ligand-controlled release mechanisms to various degrees. Our results provide a systematic understanding of Zn fractions and release from acid sulfate paddy soils, the dynamics of which have a significant influence on the availability, phytoextraction, and mobility of Zn in terrestrial and engineered environments.     

Effect of Time of Application of the First Dose of Nitrogen on Yield and Fertilizer Use Efficiency in Maize Grown in Calcareous Soils

Application of a basal dose of fertilizer nitrogen (N) at sowing of maize has been always practiced in general recommendations in Egypt and elsewhere. A field experiment in two consecutive years (2015 and 2016) was conducted to assess the usefulness of application of a dose of N fertilizer at sowing of maize in calcareous soil at West Delta, Egypt. The treatments consisted of N fertilizer levels of 0, 240, 280, and 320 kg N ha^?1 applied in three equal split doses. The first dose for each level was practiced at 0, 7, 14, and 21 days after sowing (DAS). The results indicated that practicing the first dose of N fertilizer at 0 or 7 DAS resulted in highest normalized difference vegetation index (NDVI) at early growth stage. However, the NDVI at later stages dramatically modified to reach highest when practicing the first dose at 14 or 21 DAS. Grain yields of maize when applying the first dose at 14 or 21 DAS were always significantly higher than when applied at 0 or 7 DAS. This was consistent with N fertilizer-use efficiencies. By just postponing the first dose of N from 0 to 14 DAS resulted in an increase of 7.7–13.5% in recovery efficiency and 1.1–2.7 kg grain kg^?1 N in agronomic efficiency in both seasons. This study evidenced that application of N fertilizer early at sowing of maize is not necessary as it could resulted in low N-use efficiency.     

Genotypic Responses of Corn to Phosphorus Fertilizer Rates in Calcareous Soils

In the Mediterranean region, much emphasis is placed on the role of fertilizers in enhancing crop production to achieve food security. Given the complex nature of phosphorus (P) reactions in soils, considerable research has dealt with fertilizer aspects related to efficient P use, but comparatively less emphasis has been given to plant variation with respect to P efficiency. In this study, selection and adaptation of P‐efficient corn genotypes was seen as one possible approach to enhancing P efficiency. Thus, a greenhouse experiment with 10 corn genotypes (traditional to modern), five P application rates (0–200 mg kg^?1), and four field trials with three genotypes for 2 years were carried out on various calcareous soils (Vertic Torrifluvent, Vertic Calciorthid, Entic Chromoxerert, and Typic Xerofluvent). Measurements were made of root characteristics. Treatments in the field trials were five P application rates as main plots (0–68 P ha^?1) and three corn genotypes as subplots. Genotypes were selected for the field trials from the greenhouse experiment as “efficient‐responsive,” “efficient‐nonresponsive,” and “inefficient‐responsive.” Dry‐matter (DM) yield and plant P uptake by plants increased with P application rates in the greenhouse experiment. Root length and mass were considerably increased by increasing P levels. Genotypes were classified for P efficiency. The studies indicated that because corn genotypes respond to P‐fertilizer application differently, this trait could be utilized to exploit native and applied P more efficiently, especially at low levels of available P and when P‐ fertilizer use is limited. This differential response derives from morphological, physiological, and genetic variability among the genotypes. Although genotypic efficiency is important for fertilizer management, the contribution of the efficiency is not a substitute for fertilizers, especially if high yields are required. Nevertheless, breeding for P‐use efficiency should be a component of any program to improve crop yield potential.     

Copper Release Behavior in Two Calcareous Soils Amended with Three Organic Materials

Understanding time-dependent copper (Cu) desorption behavior is critical for improving the prediction of Cu availability in soils. This study was conducted to evaluate the influence of municipal waste compost, sheep manure, and wheat straw on desorption characteristics of Cu and to evaluate the suitability of different kinetic models to describe the Cu release pattern in two calcareous soils. Diethylenetriaminepentaacetic acid (DTPA) and ethylenediaminetetraacetic acid (EDTA) were employed to extract Cu from soils. Best-fitted kinetic models including Elovich, simple Elovich, two-constant rate, and parabolic diffusion were selected based on their low standard error and high coefficient of determination. Extractable copper significantly decreased with increasing rates of sheep manure and wheat straw but increased with increasing rates of municipal waste compost amendment. Results revealed that copper was more readily desorbed from clay soil compared to silt loam soil. The copper desorption patterns were almost similar for both extractants; however, EDTA extracted more Cu from soils.     

低分子量有机酸对石灰性土壤磷素形态转化及有效性的影响

采用室内培养和化学分析的方法研究了几种低分子量有机酸对石灰性土壤中磷的活化作用。结果表明:供试有机酸通过溶解、螯合等作用均能不同程度地促进合成磷酸盐的磷素释放。活化DCP、ODP、Fe-P、A l-P的能力依次为柠檬酸>草酸>苹果酸>酒石酸>乙酸;活化FA的能力是草酸>柠檬酸>苹果酸>酒石酸>乙酸。同种有机酸作浸提剂时,有机酸浓度越高磷酸盐中磷素释放量也越大。施加各种有机酸可以不同程度地降低土壤中Fe-P、A l-P和Ca10-P,增加Ca2-P、Ca8-P和O-P含量,总的趋势是促进土壤中植物难以利用的无机磷形态向有效性较高的形态转化。这种促进作用大小顺序为草酸>柠檬酸>酒石酸。     

Oxalic Acid Effect on Potassium Release from Typical Rice Soils of Kashmir

Batch experiments were employed to examine the influence of oxalic acid on release kinetics of potassium (K) from soils along with adsorption and desorption of soil K⁺. The soils used were three rice soils from high-, mid-, and low-altitude zones. The results showed that soil K extracted using 0.2 mol L^–1 oxalic acid was similar to that of 1 mol L^–1 boiling nitric acid (HNO₃). The relation between K release (y) and concentrations of oxalic acid (c) could be best described as y = a + b log c, whereas the best-fit kinetic equation of K release was y = a + b √t. The K release for soils was in the order Bonbagh > Ganasthan > Kreeri. An oxalic acid solution with low pH was able to release more K. Oxalic acid decreased soil K⁺ adsorption and increased desorption, the effect of which tended to be greater at lower pH.     

石灰土壤原状土柱上硼和锌的迁移

Leaching of boron （B） and zinc （Zn） can be significant in some pedomorphic conditions, which can cause contamination of shallow groundwater and economic losses. Boron and Zn adsorption and transport was studied using 8.4 cm diameter × 28 cm long intact columns from two calcareous soil series with differing clay contents and vadose zone structures： Lyallpur soil series, clay loam （fine-silty, mixed, hyperthermic Ustalfic Haplargid）, and Sultanpur soil series, sandy loam （coarse-silty, mixed, hyperthermic Ustollic Camborthid）. The adsorption isotherms were developed by equilibrating soil with 0.01 tool L^-1 CaCl2 aqueous solution containing varying amounts of B and Zn and were fitted to the Langmuir equation. The B and Zn breakthrough curves were fitted to the two-domain convective-dispersive equation. At the end of the leaching experiment, 0.11 L 10 g L^-1 blue dye solution was also applied to each column to mark the flow paths. The Lyallpur soil columns had a slightly greater adsorption partition coefficient both for B and Zn than the Sultanpur soil columns. In the Lyallpur soil columns, B arrival was immediate but the peak concentration ratio （the concentration in solution at equilibrium/concentration applied） was lower than that in the Sultanpur soil columns. The breakthrough of B in the Sultanpur soil columns occurred after about 10 cm of cumulative drainage in both the columns; the rise in effluent concentration was fast and the peak concentration ratio was almost 1. Zinc leaching through the soil columns was very limited as only one column from the Lyallpur soil series showed Zn breakthrough in the effluent where the peak concentration ratio was only 0.05. This study demonstrates the effect of soil structure on B transport and has implications for the nutrient management in field soils.     

Zinc Transformation in a Calcareous Soil as Affected by Applied Zinc Sulfate,Vermicompost, and Incubation Time

An experiment was conducted to evaluate the effect of zinc (Zn) rates and vermicompost levels on distribution of Zn forms of a calcareous soil. After incubation periods, soil samples were air dried, and a sequential extraction scheme was used to fractionate Zn into soluble and exchangeable, bound to carbonate, organically bound, bound to manganese (Mn) oxide, bound to amorphous iron (Fe) oxide, bound to crystalline Fe oxide, and residual forms. In untreated soil, Zn was mainly in the residual fraction. Increasing rates of applied Zn significantly increased all forms of Zn. Carbonate and residual forms showed the greatest increase. Application of vermicompost significantly increased all fractions except Mn-oxide form. This increase was more pronounced for organically bound, soluble, and exchangeable forms, indicating an increase in bioavailability of soil Zn. Incubation time significantly decreased soluble, exchangeable, and organically bound forms but increased other forms of Zn, meaning a significant reduction in Zn phytoavailability in soil with time.     

低分子量有机酸对土壤中铝的化学行为的影响

本文从Al在土壤中的水解-沉淀、吸附-解吸、活化、迁移、降低毒性以及对含Al矿物的表面性质的影响等方面综述了低分子量有机酸对Al的化学行为的影响,并提出了今后需要进一步加强研究的一些方面。     

秸秆添加对石灰性土壤有机与无机碳释放的影响

在富含碳酸盐的石灰性土壤上,土壤本身CO2释放不仅来自土壤有机碳（SOC）的分解,也源于无机碳（SIC）的溶解。在秸秆还田下,石灰性土壤CO2释放来源达到三个（秸秆碳、SOC和SIC）,由于区分技术的限制,当前区分CO2释放三源的研究,尚少见报道。以华北石灰性农田土壤为研究对象,采用13C标记玉米秸秆添加土壤进行室内培养32周,设置4个处理,分别为无添加对照（CK）、低量秸秆添加（S1,相当于田间秸秆还田量9.6 t?hm-2）、中量秸秆添加（S2,秸秆还田量28.8 t?hm-2）和高量秸秆添加（S3,秸秆还田量48.0 t?hm-2）,利用秸秆碳、SOC与SIC之间的δ13C差异,借助稳定同位素溯源模型IsoSource,区分土壤CO2的释放来源,明确秸秆添加对石灰性土壤有机与无机碳释放的影响。结果表明,随着培养时间的进行,土壤释放CO2中源于秸秆的贡献呈下降趋势;秸秆分解对土壤CO2释放的贡献随着秸秆添加量增加而增加,对于S1、S2和S3处理,土壤释放CO2中源于秸秆、SOC和SIC的贡献比值约分别为3:3:4、5:2:3和6:2:2;与CK相比,S1处理降低SOC分解的激发效应（程度为9%）,S2和S3处理反而增加了SOC分解的激发效应（程度分别为22%和57%）;秸秆和SOC矿化增加SIC溶解的释放,随秸秆添加量增加而增加,S1、S2和S3处理提高SIC源CO2的释放程度分别为368%、561%和652%。因此,秸秆添加不仅影响SOC源CO2的释放,也增加了SIC源CO2的释放,若忽略SIC溶解对土壤CO2释放的贡献,可能导致SOC矿化量的高估,进而影响SOC激发效应评估的准确度。     

Geochemical Fractionation and Adsorption Characteristics of Zinc in Thai Major Calcareous Soils

Zinc (Zn) is a vital plant nutrient that is widely deficient in Thai cultivated calcareous soils. The chemical fractionation and adsorption of Zn are among the most important solid- and liquid-phase interactions that determine the retention of Zn in the soils. This study aimed to investigate the fractionation and adsorption isotherms of Zn in cultivated Thai calcareous soils. The results of sequential extractions showed that Zn is mainly distributed in residual fractions followed by organic-bound, iron and manganese oxides-bound, carbonate-bound, and exchangeable Zn, respectively. Zinc adsorption was well fitted by the Langmuir and Freundlich isotherms. Thai calcareous soils had high Zn adsorption capacity. Soil pH, organic carbon, calcium carbonate, cation exchange capacity, and extractable calcium were the major soil properties that affected the Zn adsorption isotherms in these soils. Zinc hydroxide was the solid precipitate and the Zn hydroxide ion (ZnOH⁺) was the dominant Zn ion in alkaline equilibrium solution.     

有机酸对石灰性潮土有机磷组分的影响

采用小麦盆栽试验的方法,研究了有机酸对石灰性潮土有机 P 组分含量及土壤 P 有效性的影响.结果表明:石灰性潮土的 4 种有机 P 组分中,以中度活性有机 P 为主,其次为高稳性有机 P 和中稳性有机 P ,活性有机P的含量最低;施用磷酸二氢钾和氟磷灰石后,土壤有机P总量和有机P各组分发生了变化;土壤经有机酸处理后,有机P总量增加,有机P总量的增加主要是中度活性有机P和活性有机P的增加.而中稳性有机P和高稳性有机P主要表现为下降,说明有机酸能够促进土壤有机P由有效性较低的形态逐步向有效性高的形态转化,从而进一步矿化为无机P或者被植物根系直接吸收,其中草酸的作用效果总体上较腐殖酸强;在P素供应不足的情况下,有机酸(草酸和腐殖酸)能够提高石灰性潮土中P的有效性,促进植物的正常生长.     

玉米生长对石灰性土壤无机碳与有机碳释放的根际效应

利用IsoSource模型三源区分玉米根际土壤CO2释放来源(根源呼吸、土壤无机碳与有机碳释放),研究玉米根际效应对石灰性土壤无机碳与有机碳释放的影响.在玉米拔节期(24～53 d)、抽穗期(54～66 d)和灌浆期(67～99 d)末分别破坏性取样,测定根系、土壤有机碳和无机碳的13C含量等指标;自拔节期开始至生育期...     

Zinc Desorption of Calcareous Soils as Influenced by Applied Zinc and Phosphorus and Described by Eight Kinetic Models

The activity of zinc (Zn) ions in the soil solution bathing plant roots is controlled by the simultaneous equilibrium of several competing reactions, such as surface exchange, specific bonding, lattice penetration, precipitation reactions, and the processes leading to the desorption of surface and lattice-bound ions. Desorption of Zn in 15 calcareous soils from southern Iran, treated with 10 mg Zn kg^?1 soil as zinc sulfate (ZnSO₄·7H₂O) and 100 mg phosphorus (P) kg^?1 soil as calcium phosphate [Ca(H₂PO₄)₂H₂O] and then equilibrated and extracted with diethylentriaminepentaacetic acid (DTPA), was studied in this experiment. The results were fitted to zero-order, first-order, second-order, third-order, parabolic diffusion, two-constant rate, Elovich, and simple Elovich kinetic models. Two-constant rate, simple Elovich, and parabolic diffusion models were determined to best describe Zn-desorption kinetics. Zinc desorption increased as Zn was applied but decreased with applied P.