Iron Oxides In Soils Research Articles

Use of soil amendments to immobilize antimony and lead in moderately contaminated shooting range soils

Shooting ranges are a source of environmental concern around the world as they are a source of toxic antimony (Sb) and lead (Pb). In-situ chemical stabilization is a strategy to reduce metal(loid) leaching and bioavailability. However it is difficult to find the right treatment due to the fact that Pb is a cation and Sb an anion, under oxidised conditions and they often show the opposite mobility in soil, on the application of amendments. A batch experiment was set up with two soils (slightly acidic and alkaline), two red mud based amendments (ViroSoil™ 1 and 2) alone and in combination with two reducing agents (zero valent iron and iron sulphate), to assess the effect of the treatments on metal(loid) leaching and compare it to unamended soil and soil amended with goethite, a known Sb adsorbent. Iron sulphate was effective at reducing Sb leaching due to the reduction of SbV to SbIII which bound more strongly to iron (hyr)oxides in soil. However it had an adverse effect on the leaching of Pb due to its acidifying effect and reductive dissolution of manganese (hyd)roxides. Combining ViroSoil™ amendments with FeSO4 still reduced Sb leaching but also Pb leaching and proved a suitable treatment.

A Detailed Laboratory Scale Feasibility Study of Recovering Metallic Iron and Chromium from Chromium Contaminated Soils

One of potential technologies applicable to chromium-contaminated soils is thermal treatment, for example, the vitrification. Literature showed the reduction of hexavalent to trivalent chromium at high temperature, thus converting highly toxic and water-soluble compound into less toxic and water-insoluble compound. At high temperature, such as that of vitrification, both iron and chromium oxides can experience stepwise reduction to potentially recyclable metallic iron and chromium under reducing environment. Hence the objective of this study is to investigate the feasibility to reduce iron oxides in chromium-contaminated soils. Using solid carbon as reducing agent, the reduction to metallic iron was observable at 1200 °C. At 1400 °C, the addition of 15 % carbon by weight is required for complete reduction. The reduction is very rapid at this temperature. The information on reduction at high temperature should prove useful in providing background information in thermal treatment and also the potential recycling of metal from contaminated soils.

Climatic thresholds for pedogenic iron oxides under aerobic conditions: Processes and their significance in paleoclimate reconstruction

Abstract Iron oxides are widely distributed across the surface of the Earth as a result of the aerobic weathering of primary Fe-bearing minerals. Pedogenic iron oxides which consist mainly of hematite (Hm), goethite (Gt), maghemite (Mgh), are often concentrated synchronously in aerobic soils under low to moderate rainfall regimes. Magnetic susceptibility (χ) and redness, which respectively reflect the content of Mgh and Hm in soils, are considered reasonable pedogenic and climatic indicators in soil taxonomy and paleorainfall reconstruction. However, under high rainfall regimes, the grain growth of Mgh and transformation to Hm, combined with the prior formation of Gt under conditions of high relative humidity (RH), can result in magnetic reduction and dramatic yellowing of soils and sediments, which explains the existence of rainfall thresholds for Mgh and Hm at a large scale even before the pedogenic environment turns anaerobic. In order to capture the rainfall thresholds for Mgh and Hm occurring under aerobic conditions, we explored a tropical transect across a granitic region where the soil color turned from red to yellow under a wide rainfall range of 900–2200 mm/yr and a corresponding mean annual RH range of 77%–85%. We observed a lower rainfall threshold of ∼1500 mm/yr and a corresponding RH ∼80% for Mgh and Hm along this transect, as well as a higher rainfall threshold of ∼1700 mm/yr and a corresponding RH of ∼81% for Gt and total pedogenic iron oxides (citrate/bicarbonate/dithionite-extractable Fe, Fed). Cross-referencing with comparable studies in temperate and subtropical regions, we noted that the rainfall or RH thresholds for Fed and Hm or Mgh likewise increase with temperature. Moreover, the different thresholds for total and individual iron oxide phase indicates that a negative correlation between chemical weathering intensity and redness or χ in sediment sequences can occur under the prevalent climate regime just between their thresholds. Finally, we developed an integrated model to interpret the sequential formation of rainfall thresholds for different pedogenic iron oxides in soils and sediments with conditions from aerobic to anaerobic.

Immobilization of toxic metal cations on goethite-amended soils: a remediation strategy

The study investigates a simple and viable option to reduce toxic metals mobility and availability in four surface (0–30cm) soils with varying physicochemical properties amended by different percentages of goethite. Batch sorption experiments carried out to study the effectiveness of immobilizing Pb2+, Cu2+, Zn2+ and Cd2+ ions on these soils showed that goethite played vital role in the metals adsorption (≥10% increase in adsorption). Removal of soil iron oxides caused reduced Pb2+ adsorption on soils with high organic matter (≤ 10% decrease in adsorption) with no significant increase in adsorption upon amendment, while soils having low organic matter had enhanced adsorption with amendment. Cu2+ and Cd2+ adsorptions were not enhanced even at 10% goethite amendment. However, Zn2+ adsorption was interestingly different: the soils showed ≥55 % increases upon removal of inherent soil iron oxides without goethite amendment. Goethite amendments further enhanced Zn2+ adsorption on these soils. Generally, both whole and amended soils showed higher preference for Pb2+; the sorption trend is – Pb2+ >Cu2+ >Zn2+ >Cd2+. Goethite amendment of these soils improved Pb2+ and Zn2+ adsorption. Hence, goethite amendment may be an effective method for immobilizing Pb2+ and Zn2+ on these soils and thus reducing their availability to biota. The quantity of goethite required by a soil to attain maximum immobilization varies depending on the metal and the soil’s physicochemical properties; however, Cu2+ and Cd2+ may not be effectively immobilized using goethite amendment.Keywords: Soil; Goethite; Toxic metals; Adsorption, Remediation

Distribution and interactions of pentachlorophenol in soils: The roles of soil iron oxides and organic matter

Soil iron oxides (IOs) and organic matter (OM) play varying roles in pentachlorophenol (PCP) retention and mobility, but the extent and mechanism are still unknown. Therefore, in order to have a better understanding of the adsorption of PCP on soils, batch sorption studies were carried out on whole soils and soils selectively treated to remove IOs (IOR) and OM (OMR). The effects of pH, time, and temperature were investigated. Results showed that PCP sorption was temperature and pH dependent; sorption decreased as both temperature and pH increased. Sorption was partly surface adsorption and partly partitioning within voids of IOs components as revealed by the kinetics models. The surface adsorption was multi-layer in nature. Equilibria were faster in the IOR soils than the untreated and OMR soils. IOs played greater roles in PCP sorption than OM. Removal of soil components, especially the IOs, as experienced in soils plagued by soil erosion, may lead to increased risks of PCP pollution of environmental media especially the aquifer.

Remove mechanisms of sulfamethazine by goethite: the contributions of pH and ionic strength

Sulfamethazine (SMT) as an ionic compound can enter the soil environment via the application of livestock wastes in agricultural fields and via the abuse of pharmaceuticals. Goethite as one of the most important iron oxides in soil might interact with SMT and influence its environmental behavior and bioavailability in soil. In this study, the sorption properties of SMT on goethite under different solution conditions were investigated. The sorption isotherm exhibited a significant nonlinear shape and desorption hysteresis, while the data could be fitted well by the Freundlich model with the correlation coefficient R 2 = 0.991. Sorption capacity initially increased and then decreased as pH values increased from 3 to 13, while the strongest uptake occurred in neutral conditions. The sorption increased slightly and then kept relatively constant as the ionic strength of the solution increased. The results indicated that the sorption mechanism would be altered in different solution conditions. In acidic and neutral conditions, the π–π electron donor–acceptor interactions and outer- and inner-sphere complexions might be the dominating sorption mechanisms. The sorption in alkali conditions might be dominated by electrostatic interactions between SMT and goethite. It should be noted that the heterogeneous sorption affinity of SMT on goethite under various solution conditions will influence its environmental fate.

Immobilization of Cu and As in two contaminated soils with zero-valent iron – Long-term performance and mechanisms

Immobilization of trace elements in contaminated soils by zero-valent iron (ZVI) is a promising remediation method, but questions about its long-term performance remain unanswered. To quantify immobilization and predict possible contaminant remobilization on long timescales detailed knowledge about immobilization mechanisms is needed. This study aimed at assessing the long-term effect of ZVI amendments on dissolved copper and arsenic in contaminated soils, at exploring the immobilization mechanism(s), and at setting up a geochemical model able to estimate dissolved copper and arsenic under different scenarios. Samples from untreated and ZVI-treated plots in two field experiments where ZVI had been added 6 and 15 years ago were investigated by a combination of batch experiments, geochemical modeling and extended X-ray absorption fine structure (EXAFS) spectroscopy. Dissolved copper and arsenic concentrations were described by a multisurface geochemical model with surface complexation reactions, verified by EXAFS. The ZVI remained “reactive” after 6–15 years, i.e. the dissolved concentrations of copper and arsenic were lower in the ZVI-treated than in the untreated soils. There was a shift in copper speciation from organic matter complexes in the untreated soil to surface complexes with iron (hydr)oxides in the ZVI-treated soil. The pH value was important for copper immobilization and ZVI did not have a stabilizing effect if pH was lower than about 6. Immobilization of arsenic was slightly pH-dependent and sensitive to the competition with phosphate. If phosphate was ignored in the modeling, the dissolution of arsenate was greatly underestimated.

Thermal Transformation and Characterization of Synthetic Al-Substituted Maghemites (γ-Fe2-xAlxO3)

Burning is a common practice in tropical areas and related changes in mineralogy might affect the chemical and physical behavior of soils. Maghemite is a common iron oxide in soils formed from basic rocks in tropical regions. This mineral and hematite are the main pigments in these soils and exhibit high magnetization stemming from the precursor magnetite formed during the weathering process of primary minerals. The objective of the present study was to analyze changes in color, magnetic suceptibility values, Fourier transform infrared spectroscopy (FTIR) spectra, and available Fe and Al contents extracted with 1 mol L-1 KCl during the process of thermal transformation of synthetic Al-maghemites into Al-hematites. Synthetic substituted maghemites with different degrees of Al-substitution (0.0, 1.0, 2.0, 2.9, 3.8, 5.6, 6.7, 10.0, 12.0, and 17.1 mol% Al) were subjected to a temperature of 500 ± 10 °C for 0, 5, 10, 16, 64, 128, 192, 360, 720, 2160, 3600, 5040 and 6480 min. The color of the samples was analyzed by a Munsell system in a colorimeter. Mass-specific magnetic susceptibility (χLF) was measured at low-frequency. Available Fe and Al contents were estimated by a 1 mol L-1 KCl solution. Fourier transform infrared spectroscopy (FTIR) spectra were obtained through use of a Bruker Vertex 70X FTIR spectrophotometer at a spectral resolution of 4 cm-1. Contents of Fe and Al extracted by 1 mol L-1 KCl in Al-hematites were not detected. All samples analyzed exhibited YR hue. Hue proportion decreased with increased heating time, and color changed from brown to red. The increase in isomorphic substitution (IS) led to increased hue values from maghemite to hematite, and the latter then became yellower. The χLF values decreased with an increase in heating time, indicating transformation from a ferrimagnetic phase (maghemite) to an antiferrimagnetic phase (hematite). With increasing IS, the maghemite χLF values decreased. Bands of the initial members (time 0) in the FTIR spectra were indexed as maghemites. The end members after completion of the heat treatment were identified as hematites. The IS of Fe by Al in maghemite influenced the thermal transformation to hematite, as well as the color and χLF of the minerals. The χLF proved to be very efficient in detecting maghemites remaining after thermal processing. Fe and/or Al were not ejected from the hematite crystalline structure after heat treatment.

Measurement of Total Free Iron in Soils by H2S Chemisorption and Comparison with the Citrate Bicarbonate Dithionite Method.

Free iron is one of the major analytical items for soil basic properties. It is also an important indicator for understanding the genesis of soil, soil classification, and soil distribution behavior. In this study, an alternative analytical method (chemisorption) based on thermodynamic knowledge was proposed for measurement of total free iron oxides in soils. Several representative soil samples belonging to alfisols, ultisols, inceptisols, and entisols were collected from Taiwan and tested by the chemisorption, and the estimated total free iron oxides were compared with those measured from the traditional citrate bicarbonate dithionite (CBD) method. Experimental results showed that the optimal operating temperature was found to be at 773 K and the carbon monoxide (CO) is the best gaseous reagent to promote the formation of FeS. The estimated total free iron oxides for soil samples determined from the chemisorption in the presence of CO were very close to those from the CBD technique. The result of regression indicates that the estimated total free iron is strongly correlated with the CBD-Fe content (R2 = 0.999) in the presence of CO.

Iron oxides in soils of different lithological origins in Ferriferous Quadrilateral (Minas Gerais, Brazil)

Different environmental conditions also lead to the formation of different pedogenic iron oxides, influencing soil chemistry. We examined the chemistry and mineralogical composition including various crystallographic parameters of pedogenic iron oxides of soils developed from itabirite, ferruginous dolomite, serpentinite and other parent materials. The low SiO2 contents relative to Al2O3 and Fe2O3 suggest strong desilication by the effect of the environmental conditions for all soils. The main pedogenic iron oxides were hematite and goethite, followed by maghemite. The small crystal size of goethite resulted in an increased specific surface area; also, isomorphic substitution of aluminum in goethite differed with the parent material. The highest content of soil Fe2O3 from sulfuric acid digestion found here was 701gkg−1, which was the highest value registered in the world literature with this methodology, according to the author's knowledge. The Fed content in the soils was strongly influenced by the parent material, with hematite being the more abundant iron oxide. Al-substitution indicated that hematite formation occurred in a different pedoenviroment than for goehtite. These results suggest that the effects of parent material on soil properties are important for both well weathered soils and little-leached soils, determining their drainage, P adsorption and capacity of trace element accumulation.

Occurrence characteristics of free iron oxides in soil microstructure: evidence from XRD, SEM and EDS

Free iron oxides in soils usually have distinct electrochemical properties, relatively high surface energy, a strong ability to adsorb, and provide structural cementation in the soil. Thus, soil properties are influenced by the content, characteristics and occurrence of free iron oxides. This paper reports a study on Zhanjiang clay and Longmen laterite, both of which are rich in free iron oxides, to investigate the occurrence characteristics of free iron oxides in soils. Dithionite-citrate-bicarbonate solution was adopted to remove free iron oxides from the soils, and qualitative filter paper was used to extract particles with size d < 25 μm. X-ray diffraction, scanning electron microscopy, and energy dispersive spectrometry were used to analyze alterations in the physical and chemical properties, mineral composition, and microstructure caused by the removal of free iron oxides. The results obtained in this study show that free iron oxides act as a bridge in Zhanjiang clay and mostly in the form of cladding in Longmen laterite. Both forms enhance the cementation and structural strength of the soils and weaken the swelling-shrinkage capacity. The findings of this paper will contribute to a deeper understanding of the formation and failure of soils.

Iron Oxides Minerals in Soils Derived from Different Parent Materials

The knowledge on soil iron oxides morphology and crystallization is important for the management of nutrients especially phosphorus. The objectives of the study were to determine the iron oxides minerals in Pothwar uplands. In the study one soil from each parent material (loess, alluvium, sandstone and shale) was selected. Selected clay samples suspensions were observed under transmission electron microscope. Ferrihydrite was common iron oxide mineral observed in all selected parent material soils at different level of crystallinity. Ferrihydrite was observed in scattered granules and also as aggregates or clusters. Crystalline iron oxides hematite and lepidocrocite was observed only in shale derived Murree soil. Mica and Rutile were the inorganic crystalline material on which masses of ferrihydrite was scattered. Energy dispersive spectra of scattered ferrihydrite masses show it has more phosphorus than lepidocrocite and hematite. The study concludes that ferrihydrite was the major iron oxides mineral in all selected parent material soils while shale derived soil also had lithogenic hematite and lepidocrocite. Short Research Article Mehmood et al.; IJPSS, 5(2): 110-116, 2015; Article no.IJPSS.2015.065 111

Changes in forms and distribution pattern of soil iron oxides due to long-term cropping in the Northwest of Iran

To assess effects of long-term agricultural practices on iron (Fe) oxide forms, 12 soil pedons belonging to six soil subgroups from the cultivated soils and the adjoining uncultivated soils were described and sampled. Soil samples were analyzed for physicochemical properties, mineralogical compounds, and different status of Fe oxides including free Fe oxides (Fed), crystalline Fe oxides (Fecry), poor crystalline Fe oxides (Feo), and organic complex Fe (Fep). For most of the examined soils, long-term cropping caused a considerable drop in organic carbon (12–64 %), electrical conductivity (3–18 %), exchangeable and soluble cations (2–96 %), and calcium carbonates (20–52 %) along with a noticeable rise in the values of clay and cation exchange capacity (3–23 %) as a result of accelerated alteration by farming activities and interaction between the used irrigation water and its receiving soils. X-ray diffraction pattern revealed that the soils were similar in mineralogical compositions, consisting of Fe-bearing minerals (such as mica, pyroxene, amphibole, and feldspars), goethite, hematite, illite, chlorite, smectite, kaolinite, and mixed minerals for both cultivated and uncultivated soils but some changes were observed in peak intensity, position, and figure mainly due to increasing the number of wetting–drying periods induced by irrigation practices as well as cropping and the dynamic of Fe and K. A relative enrichment (RE) in Fe oxide forms was highlighted with cultivation which could be attributed to the variation of weathering rate, pedogenic accumulation, and daily and seasonal fluctuations in temperature and moisture. For instance, long-term continuous cultivation led to an improvement in Fed from 2.1 % (RE of 1.02) to 181 % (RE of 2.81), Fecry from 52 % (RE of 1.53) to 667 % (RE of 7.7), crystalline index from 14 % (RE of 1.14) to 134 % (RE of 2.34), Feo from 2 % (RE of 1.02) to 18 % (RE of 1.18), and Fep from 23 % (RE of 1.23) to 500 % (RE of 6) as compared to the adjacent uncultivated soils. Soil pH, organic matter, active and equivalent of calcium carbonates were found to be the major agents in controlling the dynamic, nature, and distribution of Fe oxide status as appeared in significant correlation among the physicochemical properties and the evaluated Fe oxide forms.

Porosity and pore size distribution of Ultisols and correlations to soil iron oxides

The pore structure of soils greatly influences soil functions and processes. The Ultisols developed on Quaternary red clay in the subtropical China were collected to characterize the porosity and pore size distribution (PSD). Mercury intrusion porosimetry (MIP) and nitrogen adsorption/desorption (NAD) methods were used to quantitatively describe the PSD of soil in the range of equivalent pore diameter of 100–0.003 and 0.1–0.001μm, respectively. The total MIP porosity of Ultisols ranged from 33.0% to 44.9% with a mean value of 36.5%. The soils exhibited three-modal PSDs with peaks at the pore diameter of about 0.01–0.05μm, 0.1–2μm, and >70μm, indicating the heterogeneous nature of the pore system. The ultramicropores (0.1–5μm) and cryptopores (<0.1μm) were dominant pore classes representing an average of 35% and 30% of total pore fraction, respectively. Among the different land use types, bare land (BL) had significantly higher cryptopore (0.01–0.1μm) volume compared with forest land (FL) and orchard land (OL). Higher volume of cryptopores under BL could be attributed to the higher iron oxide and low organic matter contents. The free iron oxide (Fed) and clay contents were positively and significantly correlated with crytoporosity (<0.1μm) while negatively correlated with ultramicroposity. The pores with 0.001–0.1μm diameter were mainly attributed to the pores associated with the structure of clay and iron oxides. The ultramicroporosity (0.1–5μm) increased with increasing soil aggregation index: mean weight diameter (MWD) and geometric mean diameter (GMD). No significant correlation was observed between soil porosity and soil organic matter and macro-, meso-, and microporosity were independent of soil components. Our data suggest that high Fed and clay contents lead to increase <0.1μm pore volume. The Fed and clay contents played an important role in determining the pore structure of Ultisols.

Chemical and mineralogical changes in a Brazilian Rhodic Paleudult under different land use and managements

Changes in land use and management can affect the dynamic equilibrium of soil systems and induce chemical and mineralogical alterations. This study was based on two long-term experiments (10 and 27 years) to evaluate soil used for no-tillage maize cultivation, with and without poultry litter application (NTPL and NTM), and with grazed native pasture fertilized with cattle droppings (GrP), on the chemical and mineralogical characteristics of a Rhodic Paleudult in Southern Brazil, in comparison with the same soil under native grassland (NGr). In the four treatments, soil was sampled from the 0.0-2.5 and 2.5-5.0 cm layers. In the air-dried fine soil (ADFS) fraction (∅ &lt; 2 mm), chemical characteristics of solid and liquid phases and the specific surface area (SSA) were evaluated. The clay fraction (∅ &lt; 0.002 mm) in the 0.0-2.5 cm layer was analyzed by X-ray diffraction (XRD) after treatments for identification and characterization of 2:1 clay minerals. Animal waste application increased the total organic C concentration (COT) and specific surface area (SSA) in the 0.0-2.5 cm layer. In comparison to NGr, poultry litter application (NTPL) increased the concentrations of Ca and CECpH7, while cattle droppings (GrP) increased the P and K concentrations. In the soil solution, the concentration of dissolved organic C was positively related with COT levels. With regard to NGr, the soil use with crops (NTM and NTPL) had practically no effect on the chemical elements in solution. On the other hand, the concentrations of most chemical elements in solution were higher in GrP, especially of Fe, Al and Si. The Fe and Al concentrations in the soil iron oxides were lower, indicating reductive/complexive dissolution of crystalline forms. The X-ray diffraction (XRD) patterns of clay in the GrP environment showed a decrease in intensity and reflection area of the 2:1 clay minerals. This fact, along with the intensified Al and Si activity in soil solution indicate dissolution of clay minerals in soil under cattle-grazed pasture fertilized with animal droppings.

Iron oxides as proxies for characterizing anisotropy in soil CO2 emission in sugarcane areas under green harvest

Soil CO2 emission (FCO2) is a main contributor of atmospheric carbon transfer and is the subject of research aimed at developing effective methods for characterizing and mitigating CO2 emissions. The FCO2 is related to various soil properties including porosity, density and moisture, which are in turn related to gas transfer, O2 uptake and CO2 release, as well as mineralogical components (particularly iron oxides, which are closely associated with aggregation and protection of soil organic matter). As estimated by diffuse reflectance spectroscopy (DRS), soil iron oxides such as hematite (Hm) and goethite (Gt) can be useful in determining FCO2. The main objective of this experiment was to assess the usefulness of the mineralogical properties Hm, Gt, and iron oxides extracted by dithionite–citrate–bicarbonate (Fed) to estimate the FCO2 in a sugarcane area under green harvest in southeastern Brazil. The experiment was conducted using an irregular 50m×50m grid containing 89 sampling points 0.50–10m apart to assess the soil properties. The FCO2 at each sampling point was measured at the beginning of crop growth and 54 days after planting with the use of two portable LI-COR LI-8100 Soil CO2 Flux Systems. The soil properties studied were found to be spatially dependent and exhibited well-defined anisotropy (particularly the mineralogical properties Hm, Gt and Fed). The first two components of a principal component analysis (PC1 and PC2) jointly accounted for 73.4% of the overall result variability with PC1 essentially related to the physical and mineralogical properties of the soil. Based on a multiple linear regression analysis, free water porosity (FWP) and Hm accounted for 71% of the FCO2 variability. Our results indicate that soil preparation and management practices in mechanically harvested sugarcane affect some factors inherent in the soil forming processes, including physical and mineralogical properties, which in turn affect FCO2. These results affirm the potential of DRS as an auxiliary tool for determination of properties that are typically associated with FCO2. In addition, the ensuing method allows for large-area FCO2 mapping to developing greenhouse gas emission inventories for agricultural soils.

Effect Of The Sequential Application Of Liquid Organic Manure And Phosphorus On Maize Agronomic Traits And P Uptake In Some Tropical Soils

Improving phosphorus (P) fertility is challenging in tropical soils because of the fixation of P by soil components. The trial investigated the effect of the sequential application of poultry manure extract (tea) and P fertilizer on maize agronomy and P uptake, through screen house and field experiments. Results indicated that poultry manure tea is rich in nutrients but low in P and could be applied with phosphorus fertilizer to enhance P availability and reduce fixation. Application of P before manure tea produced taller maize plant on the field and the highest P uptake in the screen house and on the field. Manure tea also increased maize dry matter and grain yield. Combined application of poultry manure tea and P fertilizer had positive complementary and synergistic effects. It was concluded that manure tea enhances P availability and reduces P fixation by soil aluminum (Al) and iron (Fe) oxides irrespective of the sequence of application.

The severity of iron chlorosis in sensitive plants is related to soil phosphorus levels.

Iron (Fe) deficiency chlorosis, a major nutritional problem in plants growing on calcareous soils, is related to the content and reactivity of soil iron oxides and carbonates. The effects of other soil components, however, need elucidation. In this paper we tested the hypothesis that application of high doses of phosphorus (P) to the soil can aggravate Fe chlorosis. Lupin and sorghum were grown on 24 calcareous soils. Leaf chlorophyll concentration (LCC) in lupin decreased with increasing available P/available Fe ratio in the native soil but LCC in sorghum was unaffected by that ratio. Application of P to the soil resulted in significant reduction of LCC and dry weight in lupin. In sorghum, LCC and dry weight were positively affected by P fertilisation for soils poor in available P whereas the opposite effect was generally observed for the P-rich soils. In another experiment where olive plants were pot-grown on two soils during the 2009–2011 period, P fertilisation affected LCC negatively only in 2009 and 2011 and in the soil that was poorer in iron oxides. Application of fertiliser P to Fe chlorosis-inducing soils is likely to aggravate this deficiency. However, this effect depends on the plant and the Fe and P statuses of the soil.

Association of trace elements and dissolution rates of soil iron oxides

In this study, nine Oxisols and five Ultisols from Thailand were used to determine the association of major and trace elements with iron (Fe) oxides. The Fe oxides were concentrated and the association of elements (Al, Ca, Cu, Cr, Mg, Mn, Ni, Pb, P, Si, V, Ti, Zn) with Fe was evaluated using batch dissolution in 1 m HCl at 20°C. The dissolution behaviour of Fe oxide concentrates was determined using batch dissolution and flow-through reactors. In addition to Fe, both Al and Ti were present in significant amounts in the Fe oxide concentrates. Manganese was the most abundant trace element, and Cu, Zn, Pb and As concentrations were &lt;250 mg kg–1 in most samples. The dissolution behaviour of Fe-oxide concentrates indicated that Al, Cr and V were mostly substituted for Fe3+ in the structure of goethite and hematite. A significant proportion of Mn, Ni, Co, Pb and Si was also present within the structure of these minerals. Some Mg, Cu, Zn, Ti and Ca was also associated with Fe oxides. The dissolution kinetics of Fe oxide concentrates was well described by three models, i.e. the cube root law, Avrami–Erofejev equation and Kabai equation, with the dissolution rate constants (103k) corresponding to the three models ranging from 0.44 to 6.11 h–1, from 1.01 to 4.40 h–1 and from 0.03 to 4.12 h–1, respectively. The k constants of Fe oxide concentrates in this study were significantly and negatively correlated with the mean crystal dimension derived from [110] and [104] of hematite, the dominant mineral in most samples. The steady-state dissolution rate of a soil Fe-oxide concentrate (sample Kk) was substantially higher than for synthetic goethite under highly acidic conditions; this is possibly due to the greater specific surface area of sample Kk than the synthetic goethite.

EVALUATION OF TOPSOIL IRON OXIDE FROM VISIBLE SPECTROSCOPY

Conventional methods of soil iron oxide estimation are laborious and costly. Reflectance spectroscopy provides a good alternative that may be used to replace conventiona l methods of soil analysis. Most of the studies are concentrated on near infrared region of the spectrum. But in developing countries like India affording for wider range spec troscopy is a costly affair. Hence this study was conducted to establish relatio nship between topsoil iron oxide and their visible reflectance spectra in lateritic type of soils. Visible reflectance spectra of the soil samples were measured by a spectrorad iometer in the range of 325 to 1100nm with a 1nm increment. Multivariate PLSR meth od was used to predict iron oxide from reflectance which resulted in moderate prediction of R 2 0.71 and 0.62 for calibration and validation respe ctively. It can be inferred that visible spectroscopy can be effectively used for topsoil iron oxide pred iction with an acceptable level of accuracy.