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.     

Chemical Fractions of Mn in Acidic Soils and Selection of Suitable Soil Extractants for Assessing Mn Availability to Maize (Zea Mays L.)

Twenty surface (0–15 cm) samples of acidic soils were analyzed for water soluble (WS), exchangeable (EX), lead displaceable (Pb-disp.), acid soluble (AS), manganese (Mn) oxide occluded (MnOX), organically bound (OB), amorphous Fe oxide occluded (AFeOX), crystalline iron (Fe) oxide occluded (CFeOX) and residual (RES) fractions of Mn, and also for extractable Mn in some common soil extractants: (diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), DTPA (pH 5.3), AB-DTPA (pH 7.6), Mehlich-3 (pH 2.0), Modified Olsen, 0.005 M calcium chloride (CaCl₂), 1 M magnesium chloride (MgCl₂) and ion exchange resins. The WS-Mn fraction showed a significant and positive correlation with Mn extractable in DTPA (pH 5.3) and AB-DTPA (pH 7.6), while both WS-Mn and EX-Mn fractions correlated significantly and positively with Mn concentration and uptake by maize plants grown in these soils. The AB-DTPA (pH 7.6) and DTPA (pH 5.3) appeared suitable to assess the availability of Mn in acidic soils.     

Proposal of a simple screening method for a rapid preliminary evaluation of “heavy metals” mobility in soils of contaminated sites

Purpose  

Risks associated to “heavy metals” (HM) soil contamination depend not only on their total content but, mostly, on their mobility. Many extraction procedures have been developed to evaluate HM mobility in contaminated soils, but they are generally time consuming (especially the sequential extraction procedures (SEPs)) and consequently applicable on a limited number of samples. For this reason, a simple screening method, applicable even “in field”, has been proposed in order to obtain a rapid evaluation of HM mobility in polluted soils, mainly focused on the fraction associated to Fe and Mn oxide/hydroxides.     

Fractionation of tropical soilborne heavy metals—Comparison of two sequential extraction procedures

We compared Cr, Cu, Ni and Zn fractionation patterns in four typical soils naturally containing high levels of these elements on the tropical volcanic island of Réunion. Two sequential chemical extraction procedures were used: the modified four-stage BCR procedure (subsequently called mBCR) and the modified six-stage Geological Survey of Canada procedure (subsequently called mGSC). The results obtained by these two procedures highlighted some similarities. With both approaches, exchangeable fractions were the smallest fractions with respect to the four heavy metal (HM) distributions (< 5% of the total HM quantity), and residual fractions had the highest Cr, Cu, Ni and Zn contents (39.1–97.9%) in the four soils. In contrast, we noted differences in HM fractions bound to organic matter. These differences could be explained by the different reagents and extraction sequences implemented in the two procedures. However, the most marked difference in the results obtained by the two procedures concerned the HM fraction bound to oxyhydroxides, despite the fact that the same reagent was used (hydroxylammonium chloride). Our results revealed that the mBCR procedure underestimated the proportion of HM bound to this fraction. The mGSC procedure therefore seems more suitable for analysing tropical soils which typically contain high levels of Fe and Mn oxyhydroxides.     

Fractionation and colorimetric determination of boron in soils

We attempted to modify and evaluate existing sequential fractionation schemes for B involving the use of chemicals, which subsequently do not interfere with the measurement of B by colorimetry. Also evaluated was the contribution of various soil B fractions to the amount of B extracted by hot CaCl₂, CaCl₂‐mannitol, salicylic acid, ammonium acetate, HCl, and tartaric acid. For this purpose, 17 soils with diverse properties were used. The extraction scheme proposed here partitioned B into five pools, (i) readily soluble, (ii) specifically adsorbed, (iii) oxide bound, (iv) organically bound, and (v) residual boron, respectively extracted with 0.01 M CaCl₂, 0.05 M KH₂PO₄, 0.175 M NH4‐oxalate (pH 3.25), 0.5 M NaOH, and HF + H₂SO₄ + HClO₄. The procedure of elimination of color from extracts of oxide bound, organically bound, and residual B fractions was also evolved. Relationships of individual B fractions with physicochemical properties of the experimental soils confirmed the general validity of the proposed fractionation scheme. The relationships of different B fractions with extractable B in soils suggest that hot CaCl₂ and salicylic acid may be better extractants for available B in soils.     

Investigation of Heavy Metals using Various Extraction Methods in Livestock Manures

The use of animal waste for a soil amendment is a viable option for waste management. For safe and sustainable management of waste, it is important to assess the concentrations of heavy metals (HM). An experiment was conducted to compare metals [copper (Cu), zinc (Zn), and manganese (Mn)] in cow manure (CM), duck litter (DL), poultry litter (PL), and poultry litter ash (PLA) using eight extraction solutions. Extractability of HM was highly dependent upon the type of waste as well as extracting agent. Manures differed for the release of HM in the order of PL > DL > CM. Marked decreases in extractable trace elements were observed after ashing of PL irrespective of extraction method. Except for water, extractions released HM in the order of Mn > Cu > Zn. For Zn and Mn, the amount extracted varied in the order 1 M nitric acid (HNO₃) > 0.1 M HNO₃ > 0.01 M HNO₃ ≈ ethylenediaminetetraacetic acid (EDTA) > ammonium nitrate (NH₄NO₃) > calcium chloride (CaCl₂) > ammonium acetate (NH₄OAc) > H₂O in PL and PLA. Peak concentration of Cu was achieved in 1 M HNO₃ solution and the lowest Cu was found in NH₄OAc solution. On the basis of these results, the low extractability of HM in ash could suggest that the use of burned PL would be less of a water-pollution problem in the fields.     

Evaluation of the BCR sequential extraction for trace elements in European reference volcanic soils

Trace metal behaviour in volcanic ash soils displays distinctive features related to the soils’ large contents of metal‐binding phases and to the rapid release of trace metals from glasses and weatherable minerals. In this work, the BCR (Community Bureau of Reference) sequential extraction scheme (exchangeable + weak acid soluble, reducible, oxidizable, and non‐extractable metal fractions) was applied to selected COST‐622 European reference volcanic soils to determine partitioning of zinc and copper between various solid‐phase constituents, along with the major elements Al, Fe and Mn. The total extracted Al (ΣAl) was strongly correlated with acid ammonium oxalate extractable Al (Al_o) (ΣAl = 0.985Al_o+ 0.11, R²= 0.98), while the total extracted Fe clearly underestimated the amorphous fraction. Large values for the non‐extractable Al fraction were associated with the presence of gibbsite and phyllosilicates. Although the Zn and Cu contents of the soils were generally large, total amounts extracted (the potentially mobilizable fraction) were small, especially for Zn and for soils with crystalline secondary minerals. The fraction of the total Cu which was potentially mobilizable generally exceeded that of Zn. In the potentially mobilizable Cu the oxidizable fraction was generally dominant. Biocycling appears to play an important role in the surface enrichment of potentially mobilizable Zn and Mn. Although further methodological research seems necessary, the BCR sequential extraction appears to be a valuable tool for studies on metal dynamics in soils with andic properties.     

THE DISTRIBUTION OF IRON, MANGANESE, AND SCOTLAND ALUMINIUM IN SOME SOILS FROM NORTH-EAST SCOTLAND

Twenty-four soils from north-east Scotland have been subjected to differential extraction techniques to determine the effect of hydromorphism on various Fe, Mn, and A1 fractions. There were pronounced losses of dithionite-extractable Fe and Mn from gleyed horizons, but the 'silicate-Fe’fraction appeared to be relatively unaffected. The oxalate-extractable Fe and A1 fractions also decreased in response to gleying. The ratio of the oxalate- to dithionite-extractable Fe fractions (Fe₀/Fe_d) increased in gleyed horizons, presumably due to variations in the rate of ageing and crystallization of amorphous Fe oxides and hydroxides.     

Use of Single Extraction Methods to Predict Bioavailability of Heavy Metals in Polluted Soils to Rice

Human exposure to toxic heavy metals via dietary intake is of increasing concern. Heavy-metal pollution of a rice production system can pose a threat to human health. Thus, it was necessary to develop a suitable extraction procedure that would represent the content of metal available to rice plants (Oryza sativa L.). The aim of this study was to predict, on the basis of single extraction procedures of soil heavy metals, the accumulation of heavy metals (cadium, lead, copper, and zinc) in rice plants. Six extracting agents [Mehlich 1, Mehlich 3, EDTA (ethylenediaminetetraacetic acid), DTPA–TEA (diethylenetriaminepentaacetic acid–triethanolamine), ammonium acetate (NH₄OAc), and calcium chloride (CaCl₂)] were tested to evaluate the bioavailability of heavy metals from paddy soils contaminated with lead–zinc mine tailings to rice. The extraction capacity of the metals was found to be of the order EDTA > Mehlich 3 > Mehlich 1 > DTPA–TEA > NH₄OAc > CaCl₂. The correlation analysis between metals extracted with different extractants and concentrations of the metals in the grain and stalk of the plant showed positive correlations with all metals. The greatest values of correlation coefficients were determined between the NH₄OAc- and CaCl₂-soluble fractions of soil and contents in plants in all four metals studied. Therefore, NH₄OAc and CaCl₂ were the most suitable extractants for predicting bioavailability of heavy metals in the polluted soils to rice. The results suggested that uptake of heavy metals by rice was mostly from exchangeable and water-soluble fractions of the metals in the soils. Soil-extractable metals were more significantly correlated with metal accumulation in the stalk than in the grain. The pH had more significant influence on availability of heavy metals in the soils than total content of metals and other soil properties. The bioavailability of metals for rice plants would be high in acidic soils.     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

Assessment of Metal Availability in a Contaminated Soil by Sequential Extraction

A contaminated soil from Pieve Vergonte (Piedmont, Italy) has been investigated in order to point out the availability and extractability of a series of metal ions and consequently their potential release into other environmental compartments. A sequential extraction procedure has been adopted in order to subdivide total concentrations into five operational fractions with different potential toxicity. A chemometric analysis has been used for the characterization of similarities or differences of behaviour. High concentrations of the main pollutants, namely Cu, Pb and Zn, were extracted into the exchangeable, carbonate-bound/specifically adsorbed and Fe-Mn oxide bound fractions, showing the risk of release of these metals into the environment. A remobilization of Cr, Mn and Ni could also take place, but to a lesser extent. The other investigated metals (Al, Fe, La, Sc, V, Ti and Y) were mainly bound to the residual and, in some samples, to the Fe-Mn oxide bound fractions. The high availability of several potentially toxic metals shows that the soil needs remediation.     

Assessment of trace element phytoavailability in compost amended soils using different methodologies

Purpose

This study evaluates the effects of two soil amendments and the growth of two plant species on labile trace element (TE) fractions in two different contaminated soils.

Materials and methods

We studied the effects of two organic amendments (biosolid compost and alperujo compost) and two plant species (Medicago polymorpha and Poa annua) on pH, total organic carbon (TOC), and TE availability, by three extraction methods (CaCl₂ aqueous solution, soil pore water (SPW), and diffusive gradient in thin film (DGT)), in two contaminated soils with contrasting pH values (Aznalcázar, 6.53, and Vicario, 3.48) in a 118-day pot experiment. The effects of the composts on labile TE fractions were compared with element concentrations in plants.

Results and discussion

No relevant effects of amendments and plants were found on the physical and chemical characteristics of the Aznalcázar soil. However, the addition of amendments was essential for plant species growing in the acid Vicario soil. In this soil, amendments and plant growth increased pH and TOC and reduced substantially TE bioavailability. Although absolute values of bioavailable TE contents obtained by the three methods were very different and followed the trend CaCl₂ extraction?>?SPW?>?DGT, these values follow a similar behavior in the two studied soils and for the two species.

Conclusions

The results demonstrate that the application of organic amendments are suitable for remediating acid TE-contaminated soils, for the establishment of a vegetation cover on previously bare soils for reducing wind and water erosion and for reducing labile TE fractions to prevent leaching of pollutants into subsoil or groundwater layers. Moreover, the results obtained in this study pointed out that under microcosm conditions, the three methods tested (CaCl₂ extraction, SPW, and DGT) to predict TE bioavailability were highly correlated.

     

低分子量有机酸对土壤磷活化影响的研究

研究两种低分子量有机酸（柠檬酸和苹果酸）对土壤磷活化影响,并用修正的Hedley法测定土壤磷活化前后磷组分的变化。结果表明,低分子量有机酸能持续活化土壤磷,活化强度随低分子量有机酸浓度的增大而增强,并且柠檬酸活化土壤磷的能力强于苹果酸。低分子量有机酸能促进作物有效态无机磷组分（H2O-P和NaHCO3-Pi）的释放;同时还促进有机磷组分（NaHCO3-Po和NaOH-Po）的矿化。在低分子量有机酸浓度达到0.5 mmol/L以上时,其对土壤磷组分的活化量的顺序为:NaOH-Pi HCl-P NaHCO3-Pi H2O-P,即铁铝结合态磷 钙结合态磷 作物有效态磷。低分子量有机酸活化土壤磷的过程中伴有大量铁、铝释放,且铁或铝的释放量与磷活化量之间显著正相关（P0.05）。说明铁、铝结合态磷是低分子量有机酸活化土壤磷的主要磷源,并且其活化机制可能与铁、铝结合态磷的螯合溶解有关。     

Remediation of Lead Contaminated Soil by EDTA. I. Batch and Column Studies

Extraction using ethylenediaminetetraacetic acid (EDTA), and other chelates has been demonstrated to be an effective method of removal of Pb from many contaminated soils. However, column leaching of Pb from alkaline soils with EDTA has been problematic due to extremely low soil permeability. The first purpose of this study was to develop batch extraction procedures and methods of analysis of batch extraction data to provide Pb solubility information which can be used to model the column extraction of Pb from soils. The second purpose was to determine the effect of the addition of KOH and CaCl₂ to K₂H₂EDTA extract solution on both hydraulic conductivity and Pb removal. A Pb-contaminated soil sample was collected from an abandoned battery recycling facility. Both batch shaker extractions and column leaching experiments were completed using 5 different EDTA extract solutions. When only CaCl₂ was added to EDTA no change in the amount of Pb removed by batch extraction was observed. As expected, lead solubility was observed to decrease as pH was increased by the addition of KOH. However, Pb solubility was only slightly decreased by the addition of both CaCl₂ and KOH. The amount of time required to leach 6.0 L of extraction solution through the soil columns varied from 2 to 33 days. The addition of CaCl₂ and/or KOH resulted in increased soil hydraulic conductivity relative to the EDTA-only solution. The hydraulic conductivity was related to residual calcium carbonate content, suggesting that dissolution of CaCO₃ and subsequent production of CO₂ gas in the soil pores was partially responsible for the observed reductions in soil permeability. However, Pb removal was diminished with the addition of CaCl₂ and KOH because of the decreased Pb solubility and also kinetic limitations associated with the shorter residence time of the extract solution in the column.     

Assessment of Heavy Metal Bioavailability in Contaminated Soils from a Former Mining Area (La Union, Spain) Using a Rhizospheric Test

A rhizospheric biotest, consisting of a thin layer of substratum in close contact with roots of Lolium multiflorum, was used on two contrasting contaminated soils (Cabezo and Brunita) issued from a former mining area in La Union (Spain). On top of this biotest, soil characterisation, including CaCl₂ selective extractions, was performed. Total heavy metal concentrations were the highest in the soil from Cabezo, but CaCl₂ extractions indicated higher heavy metal mobilities in Brunita soil. On the base of heavy metal concentrations and biomass production in L. multiflorum seedlings, availability assessed by the rhizospheric biotest was higher than the values obtained from CaCl₂ extraction, except for Mn and Pb. Rhizospheric biotest also revealed higher heavy metal bioavailability for Cabezo. The low pH of Brunita (3.47) could explain the high CaCl₂-extractable heavy metal concentrations as well as the high transfer factor found for Cu, Mn and Zn in this substrate. Cu, Mn and Zn toxicities were also detected for shoot tissues. Transpiration rates were clearly lower for seedlings exposed to Brunita than for those exposed to Cabezo, while water use efficiency was higher for the former (4.8 mg?DW?ml^?1) than for the latter (3.8 mg?DW?ml^?1). Iron nutrition was found to interfere with heavy metal root absorption, mainly through negative interactions during root absorption. It is concluded that rhizospheric test offers the advantage to consider the root?Csoil interactions in a dynamic perspective and constitutes a useful tool for the assessment of heavy metal availability on contaminated soils. Heavy metal bioavailability assessment should not be based on only one measure alone, but on different and complementary approaches.     

Micrometer-scale internal structure and element distribution of Fe-Mn nodules in Quaternary red earth of Eastern China

Purpose

Fe-Mn nodules are the common feature of tropical and subtropical soils and contain abundant information of pedogenic processes, palaeoenvironmental changes, and element geochemistry. The main aim of the present study was to determine the internal structure and spatial distribution of elements in the Fe-Mn nodules to better understand the 3D internal structure, enrichment, and dynamics of heavy metals in nodules and to provide more aspects to explore the possible heavy metal sequestration and pedoenvironmental implications of Fe-Mn nodules in soils.

Materials and methods

The studied Typic Plinthudult was developed on Quaternary red earths in Èastern China. The Fe-Mn nodules in the Bs horizon of soil were separated and classified into four size fractions (5–8, 3–5, 2–3, and 1–2 mm). The 3D microstructure of Fe-Mn nodules was examined by means of synchrotron radiation-based X-ray microcomputed tomography (SR-mCT), and the spatial distribution of Fe and Mn in nodules was studied by scanning electron microscopy (SEM) equipped with an energy-dispersive X-ray spectrometer (EDS). The association of heavy metals with Fe and Mn oxides in nodules was described by selective chemical dissolution, SEM/EDS, and principal component analysis.

Results and discussion

The SR-mCT images indicated that the 5–8, 3–5, and 2–3 mm nodules exhibited well-defined ring structures, while the 1–2 mm nodule exhibited homogeneous fabric. The internal microstructures of nodules could be divided into four parts: Fe-rich ring, Mn-rich ring, Fe and Mn overlapped ring, and the gap between ring structures. The Fe-Mn nodules were significantly enriched in Mn, Pb, Ni, Cu, and Zn relative to the soil matrix. In particular, the concentrations of Mn and Pb in the nodules were 150 and 90 times greater than those in the soil matrix, respectively. A clear partitioning of heavy metals between Mn and Fe oxide phases was observed in the nodules, indicating that Pb was mainly present in Fe oxides, while Ni, Cu, and Zn were mainly associated with Mn oxide phases.

Conclusions

The SR-mCT and SEM-EDS revealed the detailed internal microstructure of the Fe-Mn nodules and geochemical dynamics of heavy metals in the soil system. The Fe-Mn nodules have very high scavenging ability in sequestrating toxic heavy metals in soils, such as Pb and Ni. The microstructure and spatial distribution of Fe and Mn in nodules reflected the cycle of alternating drying and wetting conditions and served as an important basis for inferring the pedogenic processes and pedoenvironmental conditions.

     

Optimization of DTPA and calcium chloride extractants for assessing extractable metal fraction in polluted soils

Abstract

Metal availability in soils is often assessed by means of extraction with chemical solutions, among others the chelating agent DTPA (diethylenetriaminepentaacetic acid) and the non‐buffered salt calcium chloride (CaCl₂). The same procedures are used for polluted soils that were originally created to assess the nutrient status of arable soils. We studied the influence of various parameters (type of shaker, shaking time, soil to solution ratio, and concentration of chemical extractant) and modify the DTPA and CaCl₂ extraction procedures to make them suitable for the study of polluted soils. The chosen extraction ratio and extractant concentration were the followings: 8 g/20 mL of 0.1 MCaCl₂ and 2 g/20 mL of 0.005 M DTPA. The optimized procedures were applied to nine soil samples affected by different sources of pollution (mine works, vehicle emissions, and various industries). Cadmium (Cd) showed the highest extractability with both extractants. Depending on the soil, copper (Cu) and zinc (Zn) (using DPTA) and Cu and manganese (Mn) (using CaCl₂) were the followings in the extractable amounts. Cadmium, Cu, and Zn were highly correlated in both extractions and with total contents.     

0.01molL-1CaCl2作为土壤不同N素形态浸提剂的研究

本文用荷兰8种表土测试不同温度下0.01molL^-1CaCl₂提取液和淋滤液中N素各形态。试验结果表明温度对NO₃^--N提取量和淋滤量无影响,但对NH₄⁺-N、可溶性总N和还原态N影响显著;可溶性有机态N的释放服从一级动力学方程:N_t=N₀(1-e^-kt),非线性最小二乘法能满意地拟合动力学实验结果。测定0.01molL^-1CaCl₂提取液中的可溶性有机态N对预测土壤N素矿化、合理推荐施肥及防止N素污染可能是一个很有前途的指标。     

Length of Incubation for the Estimation of the Most Probable Number of Nitrifying Bacteria in Soil

Abstract

The Zn content in 8 soil chemical fractions was determined for 21 greenhouse soils and for 8 reference (open field) soils from Kochi Prefecture, Japan to investigate the forms of spontaneously accumulated Zn in the greenhouse soils associated with heavy application of fertilizers and manures. Sequential extraction method was applied to every soil and each Zn fraction was designated as exchangeable (Ex-Zn), Pb-displaceable (Pb-Zn), acid soluble (Aci-Zn), Mn oxide-occluded (MnO-Zn), organically bound (OM-Zn), amorphous Fe oxide-occluded (AFeO-Zn), crystalline Fe oxide-occluded (CFeO-Zn), and residual (Res-Zn) fractions. The Zn content of the greenhouse soils was significantly higher than that of the reference soils in every fraction, except for the CFeO-Zn, and Res-Zn fractions. The Pb-Zn, Aci-Zn, and MnO-Zn fractions showed a difference of more than 60% in the total Zn content between the two soil groups. The amounts of Zn extracted in the Pb-Zn, Aci-Zn, MnO-Zn, AFeO-Zn, and CFeO-Zn fractions of the greenhouse soils increased con-comitantly with the accumulation of applied macro-nutrients. These results indicated that the accumulation of Zn in greenhouse soils caused by intensive fertilization had proceeded through specific adsorption onto or occlusion by the oxides and hydroxides of Fe and Mn in soils.     

Kinetics of phosphorus release from calcareous soils under different land use in Iran

The rate of phosporus (P) release from soils can significantly influence P fertility of soils. The objectives of this study were to investigate the effects of land‐use types on the kinetics of P release under different management practices and the relationship between kinetic parameters and soil physical and chemical properties from calcareous soils. The kinetics of P release in 0.01 M CaCl₂ was studied in surface samples of 30 calcareous soils planted to garlic, garden, pasture, potato, vegetables, and wheat. Trend in P‐release kinetics was similar between land‐use types. Significantly different quantities of P were released under different land use. The maximum amount (average of five soils) (46.4 mg kg^–1) of P was released in soil under potato and the minimum amount (10.4 mg kg^–1) under pasture. The kinetics of P release from soils can be described as an initial rapid rate followed by a slower rate. Different models were used to describe P release. In general, parabolic diffusion and power equation were found to be appropriate for modeling P release. The P‐release rate for the soils was estimated by parabolic equation for the studied land‐use types. The constant b was lower for pasture and wheat than for garlic and potato. The relationship between the rate of P release with Olsen‐P was linear, while it was curved with respect to the CaCl₂‐P, indicating that release of P was diffusion‐controlled. When the kinetic parameters of models were regressed on soil properties, CaCl₂‐P and CaCO₃ appeared to be the most important soil properties influencing P‐release rates in these soils.