Influence of iron oxides on cobalt adsorption by soils

Eleven soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA, and dithionite-EDTA (DE) to fractionate iron (and manganese) oxides. The amounts of cobalt adsorbed and acidity desorbed by the extracted soils as well as by two synthetic iron oxides were determined, using 0.85 mM cobalt in 0.2 m NaNO₃.
No significant correlations were found between cobalt adsorption and the contents of extractable manganese or organic matter, presumably because of their low contents. The major part of the cobalt adsorption (by DE-extracted samples) was due to the clay fraction and was associated with the release of approximately one proton per adsorbed Co. The remaining cobalt adsorption was attributed to the iron oxides. This portion of adsorbed cobalt was well described by considering soil iron oxides composed of only two fractions, an EDTA-extractable fraction of high reactivity and a less reactive fraction corresponding to the difference between DE-extractable iron and EDTA-extractable iron. Approximately 1.7 protons were released per Co adsorbed by these iron oxide fractions and by the synthetic iron oxides.
The amounts of cobalt adsorbed by the soil iron oxides were well predicted from the contents and specific surfaces of the two iron oxide fractions together with the specific cobalt adsorption of synthetic iron oxides.     

Influence of iron oxides on the non-specific anion (chloride) adsorption by soil

Soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite-EDTA (DE) to dissolve crystalline iron oxides. The amounts of chloride adsorbed by the extracted soils from 1 m NaCl at pH 5 and pH 7 were determined. The differences (ΔCl) between chloride adsorption at pH 5 and pH 7, attributed to variably charged groups, decreased when iron oxides were removed by EDTA and DE extraction. Close correlations (P>0.001), with negligible intercepts, were found (i)between EDTA-extractable iron (amorphous iron oxides) and the decrease in ΔCl following EDTA extraction, and (ii) between the difference between DE-extracted iron and EDTA-extractable iron (crystalline iron oxides) and the further decrease in ΔCL following DE extraction. The difference between ΔCl for acetate-extracted and DE-extracted samples was calculated from the contents and specific surfaces of amorphous and crystalline iron oxides, together with ΔCl per m² for synthetic iron oxides. Calculated and measured values were in very good agreement, indicating that soil iron oxides, in relation to chloride adsorption, may be treated as if they consist of only two fractions.     

The influence of iron oxides on phosphate adsorption by soil

Soils from Denmark and Tanzania were extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite-EDTA (DE) to dissolve crystalline iron oxides. The phosphate adsorption capacities of the extracted soils were taken as the maximum quantity of phosphate adsorbed computed from the Langmuir equation. The decreases in the phosphate adsorption capacity following EDTA extraction and DE extraction were attributed to the removal of iron oxides. Close correlations (P<0.001) were found (i) between EDTA-extractable iron (amorphous iron oxides) and the decrease in phosphate adsorption capacity following EDTA extraction, and (ii) between the difference between DE-extractable iron and EDTA-extractable iron (crystalline iron oxides) and the further decrease in phosphate adsorption capacity following DE extraction. The phosphate adsorption capacity, estimated to be approximately 2.5 μmol P m^?2, was in good agreement with the capacity of various synthetic iron oxides. The calculated phosphate adsorption capacity of soil iron oxides, obtained from the contents and specific surfaces of amorphous and crystalline iron oxides together with the phosphate adsorption capacity per m² for synthetic iron oxides, compared favourably with the measured phosphate adsorption capacity.     

Soil micronutrient contents and relation to other soil properties in Ethiopia

Abstract

Alfisols, Vertisols, Inceptisols, Aridisols, Mollisols, and Entisols were sampled (0–30 cm) from 32 locations across Ethiopia. The soils were analyzed for copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe) contents using 0.005 M diethylene triamine pentaacetic acid (DTPA), 0.05 M hydrochloric acid (HC1), and 0.02 M ethylene diamine tetraacetic acid (EDTA) extractants. EDTA extracted more of each micronutrient than DTPA, which extracted greater amounts than HC1. The quantities of EDTA and DTPA‐extractable micronutrients were significantly correlated, and were in the order: Mn>Fe>Cu>Zn. The order of HCl‐extractable micronutrients was Mn>Fe>Zn>Cu. Micronutrient contents of Mollisols, Vertisols, and Alfisols were usually greater than those of the other soils, and Entisols usually had the lowest micronutrient contents. The contents were mostly positively correlated with clay and Fe₂O₃ contents, but negatively correlated with soil pH and A1₂O₃contents. While comparison of DTPA‐ and EDTA‐extractable micronutrients with critical levels showed that most soils had adequate amounts of the micronutrients for crops, the amounts extracted by HC1 were below critical levels in most soils. Since the critical levels that were used in the comparisons were not established in Ethiopia, calibration of the soil contents of these micronutrients with crops grown in Ethiopia is required to identify the most suitable extractant(s).     

The influence of iron oxides on the surface area of soil

Soils from Denmark and Tanzania have been extracted with ammonium acetate (controls), EDTA to dissolve amorphous iron oxides, and dithionite-EDTA (DE) to dissolve crystalline iron oxides. The surface areas of the extracted soils have been determined by applying the BET equation to nitrogen adsorption and by water adsorption at 19 percent relative humidity. High correlations (P < 0.001) were found (i) between EDTA-extractable iron (amorphous iron oxides) and the decrease in the surface area following EDTA extraction, and (ii) between the difference between DE-extractable iron and EDTA-extractable iron (crystalline iron oxides) and the further decrease in the surface area following DE extraction. The calculated specific surfaces of both the amorphous and the crystalline iron oxides varied from soil to soil but without any definite trend. The means of all the soils investigated may therefore serve as reasonable estimates of the specific surfaces of amorphous and crystalline iron oxides in soil.     

The adsorption of copper by soil samples from scotland at low equilibrium solution concentrations

At low solution concentrations of copper in the presence of 0.05 M CaCl₂, adsorption isotherms for copper on soil samples were essentially linear. Although no direct correlations were found between isotherm gradients and individual soil properties, the gradients were of the same order of magnitude as predictions based on gradients obtained for some specific soil components. The soil components which appear to be most important in copper adsorption and which were used to obtain the predictions were organic matter and iron and manganese oxides. The amounts of adsorbed copper remaining isotopically exchangeable or extractable with EDTA in the short term increased with the amount of copper adsorbed but the proportions of adsorbed copper estimated by each of these techniques remained constant. Concentrations of copper in solution increased (adsorption decreased) at pH values below 4.5 and above 6.5.     

The profile distribution of total and extractable zinc in selected Nigerian soils

Abstract

The profile distribution of total, DTPA‐ and 0.1 N HC1‐extractable Zn was determined in 11 Nigerian soil profiles formed on various parent Materials including the coastal plain sands, shales, basalt, granite and banded gneiss.

The total content ranged from 9 to 84 ppm. Generally soils developed on igneous rocks contained more Zn than those on sedimenatary deposits. Among the soils on sedimentary rocks, those on shale had more total Zn than those on sandstones. Total Zn was weakly correlated with organic matter but strongly associated vith clay content and free oxides of iron and manganese.

The amounts of Zn extracted by DTPA and 0.1 N HC1 ranged from 0.01 to 10.98 and from 0.23 to 6.25 ppm, respectively. The dilute acid generally removed more Zn from the soils than did the DTPA. The amounts extracted generally decreased vith depth especially vith DTFA extractant. Soils developed on basalt and shales contained the highest amounts of 0.1 N HCl‐extractable Zn while those on basement complex rocks gave the highest values of DTPA‐extractable Zn. Extractable Zn from soils on coastal plain sands remained relatively lev. The extractable Zn was more associated vith organic matter than vith clay content.     

The forms of cobalt in some Scottish soils as determined by extraction and isotopic exchange

The results of fractionation and correlation studies provided evidence that cobalt in soils is associated predominantly with the soil oxide fraction, particularly the manganese oxides. Only a small proportion of the total cobalt present in soils was extracted by acetic acid, EDTA, pyrophosphate or hydroxylamine. Cobalt extracted with these reagents was considered to be derived principally from easily reducible manganese oxides, although the origin of the cobalt extracted by acetic acid in particular was not well defined. The bulk of the cobalt present in soils appeared to be occluded by more highly crystalline oxide materials or was present in the structures of primary and secondary minerals. Labile cobalt in soil was assessed by extraction with acetic acid and EDTA and by determination of isotopically exchangeable cobalt. The amounts of cobalt extracted by both EDTA and acetic acid were highly dependent on the length of extraction period and on the temperature of extraction. Neither of these reagents appeared likely to give good estimates of the quantity or intensity factors of soil cobalt supply to plants as defined by the isotopic exchange determinations.     

The extractable trace element content of acid soils and the influence of pH,organic matter and clay content

Abstract

The analysis of extractable trace elements was carried out on 434 soils using 0.1 N HC1 as the extractant for copper, manganese, iron, zinc and cobalt, 0.2 M ammonium oxalate at pH 3.0 for molybdenum and boiling water for boron. Results indicated that on the average from about 1 to 20 percent of the total element content of the soil uas extractable, the percentage varying with the element. Comparing the amount of extractable elements in the 0–15 cm and 15–30 cm layers indicated that only manganese, zinc and boron were significantly different.

Correlation studies showed that the pH significantly influenced the quantity of manganese, iron, zinc and boron extracted, while organic matter influenced copper, manganese, zinc, cobalt and boron and clay content the copper, manganese, iron, zinc, cobalt and boron.     

Origin of extractable titanium and vanadium in the a horizons of scottish podzols

The A horizons of Scottish podzols often contain unusually high amounts of EDTA-extractable Ti and V. Five such soils developed on different parent materials were studied, total and EDTA-extractable Ti, V and Fe being determined in the samples and their particle size fractions. The fine sand accounts for 50–80% of the total and extractable amounts of all three elements in the total soil although, in general, both the total and extractable Ti and V concentrations increase with decreasing particle size. Thus the clays contain up to 420 ppm Ti and 27 ppm V extractable with EDTA. The main Ti minerals in the samples are anatase, rutile and ilmenite. Observations by scanning electron microscopy of the surfaces of the minerals show clear evidence of chemical, and possibly physical weathering, processes that may lead to the accumulation of Ti in fine fractions, but not to downward translocation. Vanadium is probably associated with iron oxides and ferromagnesian minerals, from which it is released by weathering and subsequently adsorbed by the clay fraction. Electron paramagnetic resonance spectra confirm that most of the V extracted from the samples and their clay fractions is in the vanadyl, (VO)²⁺, form.     

Availability of soil boron fractions to M.26 apple rootstock

The availability of various boron (B) fractions in soil to M.26 apple (Malus spp.) rootstock was examined. The study was carried out in a greenhouse on soils with diverse chemical and physical properties. The following B fractions were determined: (i) B in soil solution, (ii) B non‐specifically adsorbed on soil surface, (iii) B specifically adsorbed on soil colloid surfaces, (iv) B occluded in Mn oxyhydroxides, (v) B occluded in noncrystalline aluminum (Al) and iron (Fe) oxides, (vi) B occluded in crystalline Al and Fe oxides, (vii) B fixed with soil silicates, and (viii) total soil B. In the studied soils there were: 0.07–0.17 mg kg^‐1 B in soil solution, 0.01–0.03 mg kg^‐1 B non‐specifically adsorbed on soil surface, 0.04–0.08 mg kg^‐1 B specifically adsorbed on soil colloid surfaces, 0.28–0.67 mg kg^‐1 B occluded in manganese (Mn) oxides, 4.03–17.22 mg kg^‐1 B occluded in noncrystalline Al and Fe oxides, 8.93–50.62 mg kg^‐1 B occluded in crystalline Al and Fe oxides, 12.2–42.5 mg kg^‐1 B fixed with soil silicate, and 52.9–82.2 mg kg^‐1 total B. Simple correlation analysis showed positive correlation between B contents in M.26 apple rootstocks and amounts of B in soil solution (r=0.77), B non‐specifically adsorbed on soil colloid surfaces (r=0.65), B specifically adsorbed on soil surface (r=0.76) and B occluded in Mn oxyhydroxides (r=0.77). No relation was found between plant B contents and amounts of B occluded in non‐crystalline and crystalline Al and Fe oxides, B fixed with soil silicates and total B. The results indicated that extraction of B by 0.1 M NH₂OH HCl solution adequately represented amounts of B in soil solution, B non‐specifically and specifically adsorbed on soil compound surfaces and B occluded in Mn oxyhydroxides to assess availability of B to apple trees.     

Fractionation of zinc in some New Zealand soils

Abstract

The amounts and forms of zinc in twenty surface soils from Canterbury and Southland, New Zealand were determined using a sequential fractionation scheme. Total soil zinc concentrations ranged from 38.1 mg#lbkg^‐1 to 113.8 mg#lbkg^‐1. Although the proportions of zinc found in individual fractions varied between soils, on average approximately 3% occurred as exchangeable zinc, 5% as organic‐bound zinc, 9%, 18%, 24% was associated with manganese, amorphous iron and crystalline iron oxides, respectively, and 40% was in the residual fraction. In a group of soils formed in greywacke alluvium or loess, exchangeable zinc was inversely related to soil pH. Within the same group of soils, those of similar age with greater concentrations of total and organic‐bound zinc were present in imperfectly‐ and poorly‐drained soils compared with well‐drained soils. Zinc extracted from the soils with a range of reagents used to assess ‘plant available’ zinc was correlated strongly with the concentrations of zinc present in the exchangeable and organic‐bound zinc fractions.     

Forms and extractability of manganese in potting media

Abstract

Sequential extraction of pine bark medium alone and after amendment with either manganese sulfate (MnSO₄), composted rice hulls, or soil showed that at pH 5.5–7.0 most of the manganese (Mn) exists in a form that is extracted by acidic hydroxylamine hydrochloride, and which could therefore be in oxide or strongly‐bound forms. Acidification to pH 4.5–5.0 transferred large amounts of this ‘oxide’ Mn into ‘readily available’ and ‘weakly adsorbed’ fractions. Similar extractions of Sitka spruce bark showed that most of its Mn was extracted by weak cationic reagents ('readily available’ and ‘weakly adsorbed’ fractions). Growth of oats in pine bark, peat, and eucalypt sawdust media, with and without MnSO₄ amendment, lowered the amounts of Mn in ‘readily soluble’ and ‘weakly adsorbed’ fractions and caused some loss of ‘oxide’ Mn. Comparison of data for Mn extracted by 2 mM DTPA (1:1.5 v/v) with Mn in sequential fractions showed that DTPA dissolves some ‘oxide’ Mn. The data further suggest that up to about 36 mg/L DTPA‐extractable Mn would not be toxic to most plants growing in media of pH 6.0, but 60 mg/L DTPA‐extractable Mn may be if the medium pH falls below 5.5.     

Behavior of soil boron and boron uptake by M.26 apple rootstock as affected by application of different forms and nitrogen rates

Abstract

The changes in availability and uptake of boron (B) by M.26 apple rootstocks as affected by applications of different forms and rates of nitrogen (N) were examined. The study was carried out in a greenhouse using soil with low contents of organic matter, clay, calcium carbonate, NH₄‐oxalate soluble aluminum (Al) and iron (Fe), NH₂OH·HCl extractable manganese (Mn), poor cation exchange capacity and low pH. Soil N application was in the form of urea, calcium nitrate, ammonium sulphate, or ammonium nitrate at rates of 0, 17, 34, and 51 mg N kg^?1. After 1, 3, and 5 days of N application, soil B fractions were determined: B in soil solution, B specifically and non‐specifically adsorbed on soil surfaces, B occluded in Mn oxyhydroxides, and B occluded in crystalline Al and Fe oxides. The results showed that N as calcium nitrate and ammonium nitrate increased B both in soil solution and non‐specifically adsorbed on soil surface and decreased B concentration on Al and Fe oxides. This indicates that N‐NO₃ inhibited B sorption on Fe and Al oxides. Maximum B desorption from Fe and Al oxides was obtained within one day after N‐NO₃ was supplied. Nitrogen application as calcium nitrate and ammonium nitrate increased availability and uptake of B by plant roots. Thus, it was concluded that apple trees planted on coarse‐textured soils where risk of B deficiency is high, calcium nitrate or ammonium nitrates would be appropriately to apply to keep B more available.     

The effect of soil flooding on the transformation of Fe oxides and the adsorption/desorption behavior of phosphate

As repeatedly reported, soil flooding improves the availability of P to rice. This is in contrast with an increased P sorption in paddy soils. The effects of soil flooding on the transformation of Fe oxides and the adsorption/desorption of P of two paddy soils of Zhejiang Province in Southeast‐China were studied in anaerobic incubation experiments (submerging with water in N₂ atmosphere). Soil flooding significantly increased oxalate‐extractable Fe (Fe_ox), mainly at the expense of dithionite‐soluble Fe (Fe_DCB), as well as oxalate‐extractable P (P_ox), but decreased the ratio of P_ox/Fe_ox. Flooding largely increased both, P adsorption and the maximum P adsorption capacity. The majority of newly sorbed P in the soils was P_ox, but also more newly retained P was found to be not extractable by oxalate. Flooding also changed the characteristics of P desorption in the soils. Due to a decrease of the saturation index of the P sorption capacity, P adsorbed by flooded soils was much less desorbable than that from non‐flooded soils. There are obviously significant differences in the nature of both, the Fe_ox and P_ox fractions under non‐flooded and flooded conditions. The degree of the changes in Fe_ox, P_ox, P adsorption and P desorption by flooding depended on the contents of amorphous and total Fe oxides in non‐flooded soils. Our results confirm that the adsorption and desorption behavior of P in paddy soils is largely controlled by the transformation of the Fe oxides. The reasons of the often‐reported improved P availability to rice induced by flooding, in spite of the unfavorable effect on P desorbability, are discussed.     

Molybdenum Determination in Mehlich‐1 and Mehlich‐3 Soil Test Extracts and Molybdenum Adsorption in Brazilian Soils

Abstract

The extractant Mehlich‐1 is routinely used in Brazil for determination of soil nutrients, whereas Mehlich‐3 has been suggested as a promising extractor for soil fertility evaluation. Both were used for extraction of molybdenum (Mo) in Brazilian soils with Mo dosage by the KI+H₂O₂ method. The Langmuir and Freundlich isotherms were used to study soil Mo adsorption. Mehlich‐1 extracted more Mo than Mehlich‐3 in soils with high contents of organic matter, clay, and iron (Fe) oxides. Mehlich‐3 and Mehlich‐1 extractions correlated positively and significantly with amorphous Fe oxides, crystalline Fe oxides, and organic matter. Molybdenum recovering rates correlated to crystalline Fe oxides and clay contents but not to organic matter, pH, and Mo adsorption capacity. Amorphous and crystalline Fe oxides, clay, and organic matter were responsible for most of the Mo adsorption. The Langmuir isotherm described better the Mo adsorption to soil amorphous Fe oxides and organic matter than the Freundlich isotherm.     

Forms of Iron and Their Association with Soil Properties in Four Soil Taxonomic Orders of Arid and Semi‐arid Soils of Punjab,India

Profiles of arid and semi‐arid zones soils of Punjab, northwestern India, were investigated for different forms of iron (Fe): total Fe, diethylenetriamine penta‐acetic acid (DTPA)–extractable Fe, soil solution plus exchangeable Fe, Fe adsorbed onto inorganic sites and oxide surfaces, and Fe bound by organic sites. Irrespective of the different fractions of Fe present, its content was higher in the fine‐textured Alfisols and Inceptisols than in the coarse‐textured Entisols and Aridisols. Lower content of total Fe was observed in the surface horizon and then increased in the subsurface horizons, whereas no set pattern was observed in Entisols. Also, irrespective of the soil orders, the contents of different forms of Fe were higher in the surface horizon and then decreased by depth. None of the forms of Fe exhibited any consistent pattern of distribution.

Organic matter and the content of clay and silt fractions had a strong bearing on the distribution of forms of Fe. Based on a linear coefficient of correlation, the soil solution plus exchangeable Fe adsorbed onto inorganic sites and DTPA‐extractable Fe increased with increase in soil organic carbon but decreased with increase in soil pH and calcium carbonate content. Total Fe increased with increase in cation exchange capacity (CEC) and clay and silt content. The results also revealed that there was equilibrium in different fractions of this element. Among the different Fe forms, Fe bound by organic sites, water‐soluble plus exchangeable Fe, and Fe adsorbed onto oxides (amorphous surfaces) were positively correlated with the DTPA‐extractable Fe. Though some forms are interrelated, none of the forms had any relationship with the total Fe.     

Calcium‐ and iron‐related phosphorus in calcareous and calcareous marsh soils: Sequential chemical fractionation and 31p nuclear magnetic resonance study

Abstract

Phosphorus (P) forms in soils determine the amount of P available for crops and the potential for this element to be released to water. Sequential chemical fractionation can provide some information about major P forms in soils, and allow one to distinguish iron (Fe)‐related phosphorus from calcium (Ca)‐bound P. The ³¹P nuclear magnetic resonance (NMR) spectroscopy has been used in the identification of organic P, precipitated Ca‐phosphates, and aluminum (Al)‐related P in acid soils. Three calcareous soils and four calcareous marsh soils were used in this study. These two types of soils differ in the nature of iron oxides, which are the main P sorbent surfaces. The ratio of low crystalline to high crystalline iron oxides is higher in marsh soils than in calcareous soils as a consequence of the special genesis and conditions of the soil (reduction‐oxidation cycles). Such a ratio is related to the proportion of occluded P in low crystalline oxides relative to that of high crystalline oxides. Citrate‐bicarbonate extractable P (CB‐P) in the fractionation schemes can be ascribed to adsorbed P and high soluble calcium phosphates. CB‐P is correlated with the sum of P fractions in all the soils, thus indicating that the amount of the P that can be easily released is related to the rate of P enrichment of the soil. The ³¹P NMR spectral data reveal that hydroxyapatite is the dominant P form in the soils studied. This is consistent with the fractionation data, where acid‐extractable P is the main P fraction. The spectra also provide some information about the amount of total inorganic P and Ca‐phosphates in calcareous soils.     

Effect of Grinding on Soil Extraction by Aqua Regia, 2 M Nitric Acid,and Mehlich 3

Abstract

The effect of grinding on soil extraction was determined for two soil fractions and three extractants. Arsenic (As), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) were extracted by aqua regia and 2 M nitric acid. Mehlich 3 extractant was used for determination of potassium (K), magnesium (Mg), calcium (Ca), phosphorus (P), iron (Fe), and aluminum (Al). One hundred forty‐seven agricultural soil samples representing all major soil types, climatic regions, and proportions of agronomic cultures in the Czech Republic were collected for the study. Particle size fractions smaller than 2 mm and smaller than 0.150 mm were chosen for investigation. Extraction of elements by aqua regia was similar for both size fractions of soil. Cold 2 M nitric acid is a weaker extractant than aqua regia, and a statistically significant increase in extractable Be (5%), Cd (6%), Co (11%), Cu (5%), Ni (5%), and V (2%) was measured with the finely ground soils. An increase for the finer fraction for K (10%) and Mn (25%) was found for Mehlich 3. A more complex nonlinear relationship was found for Mehlich 3 extractable Al and Fe. This was probably caused by a more intensive re‐adsorption of Fe and Al to the finely ground soils.     

Sequential cold and hot water extract of boron from soils and re‐extraction after adsorption by bentonite,kaolinite, iron,and aluminum hydrous oxides over a range of pH values

Abstract

The relative amounts of boron re‐extracted by cold and hot water sequentially after adsorption, over a range of pH values, onto bentonite, kaolinite, precipitated iron, and aluminum (AI) hydrous oxides have been examined, in an attempt to understand why hot water especially is successful as an extractant to indicate plant availability of boron (B). The relative ability of cold and hot water to extract boron was also tested on some Scottish soils. The recovery of boron adsorbed by bentonite, by extraction with cold water compared with that extracted by hot water, was related to pH, but this was not the case for kaolinite. Comparison of the results for the minerals and soil systems indicates that mineral composition and pH in combination probably regulate the relative extraction power of cold and hot water for soil B. It may be assumed, therefore, that hot water better reflects the capability of plant roots to access B from different adsorption sites than cold water does.