Fe In Soils Research Articles

A study on heavy metals accumulation and its uptake by Cowpea [Vigna unguiculata (L.) Walp.] fertilized with Sugar mill effluent and DAP treatment in two cropping seasons

A study was performed under natural environment to compare heavy metal accumulation in soil and Vigna unguiculata L. (Cowpea) irrigated with five rates of SME viz. 10, 25, 50, 75 and 100% concentrations and DAP treatment (applied @100Kg/ha i.e. 0.7g / per 5 Kg) and control (Bore well water) separately in both the rainy (Kharif) and summer (Zaid) seasons for 90 days. Results revealed that among various concentration of SME and DAP treatment, irrigation with 100% SME concentration significantly (P<0.001) increased Zn (323.07-341.02 %), Cu (371.23-389.04%), Ni (3666.66-4133.33%), Cd (525.00-725.00%), Cr (1444.4-1477.77%) and Fe (224.08-244.89%) in the soil. In case of V. unguiculata irrigated with different SME concentrations, maximum range of heavy metals such as Zn (2.43-2.98 mg Kg-1), Cu (2.39-2.73 mg Kg-1), Ni (0.55-0.91 mg Kg-1), Cr (1.01-1.21 mg Kg-1), Cd (0.13- 0.17 mg Kg-1), and Fe (5.54-6.18) were observed at 100% concentration of SME than that of DAP treatment in both the cultivated seasons. However, the concentration of all the metals Zn, Cu, Ni, Cd, Cr and Fe in soil and plant were lower than toxicity threshold i.e. within the permissible limit. Enrichment factor (Ef) for soil/V. unguiculata was recorded maximum with Ni (37.66-42.33) / (24-30.33) and minimum with Fe (3.24-3.44) / (2.28-2.52) after 90 days of SME irrigation than DAP in both the cropping seasons of Kharif and Zaid. The minimum accumulation of Fe in both soil and crop showed that metals with completely filled d orbitals (d8, Fe) were least incorporated into the V. unguiculata crop.

Metals in agricultural soils and plants in Egypt

Since analysis of both soil and plants are useful to assess contamination of a geographic area, concentrations of five representative metals: copper (Cu), zinc (Zn), cadmium (Cd), lead (Pb), and iron (Fe) in soil and associated plants were measured by atomic absorption spectroscopy. Samples were collected from four different Egyptian regions (El-mehala El-kobra, Kafr El-Sheikh, Kafr El-zayat, and Al-fayoum) during spring and summer 2010. Concentrations of the selected metals in agricultural soils were significantly different among locations and seasons. Concentrations of Cd and Fe in soils at the four locations exceeded the maximum allowable concentrations for Cd (8 mg/kg, dry mass (dm)) and Fe (1000 mg/kg, dm). Accumulation was different for clover and cotton. Clover blossoms grown in soil from Kafr El-zayat contained the greatest concentrations of Cu, Zn, Pb, and Fe. Cotton flowers from El-mehala El-kobra accumulated the highest levels of Cd. Concentrations of Cd and Pb in both clover and cotton flowers from the four locations exceeded maximum allowable concentrations (3 mg/kg, dm) for both Cd and Pb. Using such agricultural soils for cultivation of edible crops for consumption may result in chronic hazards to human health.

Soil micronutrient availability to crops affected by long-term inorganic and organic fertilizer applications

The effects of mineral and organic fertilization on the contents of Fe, Cu, Zn, Mn, B and Mo in soil and in the soil solution as well as on availability of these elements for crops were investigated in the long-term field trial. The highest contents of Zn, Fe, Mn and Cu in soil and soil solution were observed in the treatment with the lowest pH (NPK). In this same combination the content of B and Mo was the lowest. The concentration of Zn, B and Fe in the soil solution significantly increased under farmyard manure application. Liming significantly decreased contents extractable by 1 mol/L HCl forms of Mn and Zn and significantly increase the content of Mo in the soil. Regardless of fertilization applied, microelement concentrations in the soil solution are sufficient for fulfilling nutritional needs of plants cultivated during the trial.

Total and Extractable Manganese and Iron in Some Cultivated Acid Soils of India: Status, Distribution and Relationship with Some Soil Properties

A total of 400 surface soil (0–15 cm) samples were collected from cultivated soils representing four soil series, namely, Hariharapur, Debatoli, Rajpora and Neeleswaram in Orissa, Jharkhand, Himachal Pradesh and Kerala states of India, respectively, and were analyzed to measure the contents of total and extractable Mn and Fe, to establish the relationship among total and extractable Mn and Fe and soil properties, and to characterize the spatial distribution pattern of Mn and Fe in some cultivated acid soils of India. The contents of total as well as extractable Mn and Fe varied widely with extractants and soil series. However, the amounts of Mn or Fe extracted by diethylene triamine penta-acetic acid (DTPA), Mehlich 1, Mehlich 3, 0.1 mol L−1 HCl and ammonium bicarbonate DTPA (ABDTPA) were significantly correlated with each other (P < 0.01). Based on the DTPA-extractable contents and the critical limits (2 mg Mn kg−1 soil and 4.5 mg Fe kg−1 soil) published in the literature, Mn and Fe deficiencies were observed in 7%–23% and 1%–3% of the soil samples, respectively. The content of soil organic carbon (SOC) had greater influence on total and DTPA-extractable Fe than did soil pH. Geostatistical analysis revealed that total and DTPA-extractable Mn and Fe contents in the acid soils were influenced by soil pH, SOC content, and exchangeable cations like potassium, calcium and magnesium. Spatial distribution maps of total and DTPA-extractable Mn and Fe in soil indicated different distribution patterns.

Influence of Humic Acid on Availability of Zn, Cu, Mn, Fe in Soils

Influence of Humic Acid on Availability of Zn, Cu, Mn, Fe in Soils

The Effect of Molybdenum and Iron on Nodulation, Nitrogen Fixation and Yield of Chickpea Genotypes (Cicer Arietinum L)

The present study was based on the hypothesis that the applied molybdenum and iron influence the nodulation, nitrogen fixation and yield by chickpea genotypes. For this purpose a field experiment was conducted to study the influence of different levels of molybdenum and iron on the nodulation, nitrogen fixation and yield of chickpea genotypes (Cicer arietinum L.) growing two different genotypes such as Desi (sheenghar) and Kabuli (Karak-II) during, 2011-12 at Malakandher Farm, The University of Agriculture, Peshawar. Different levels of molybdenum and iron were applied at the rate of 0, 0.25 and 0.50 and 0, 2 and 5.0 kg ha -1 , respectively along with a basal dose of 25 N, 60 P2O5 and 60 K2O in randomized complete block design with split plot arrangement and replicated three times. Results revealed that maximum yield and yield parameters, numbers of root nodules and nitrogen concentration were observed in those treatment plots where Mo 0.5 and Fe 2.0 kg ha -1 were applied simultaneously for both genotypes. The grain yield, nodulation and nitrogen concentration were recorded significantly more in Kabuli (Karak-II) as compared to Desi (sheenghar) of chickpea genotypes, perhaps due to the formation of maximum nodulation and nitrogen concentration by plants. Results revealed that with increasing the levels of Mo and Fe in soil, the concentration of Fe and N in plant leaves were significantly increased in both genotypes at flowering stage. Moreover, in the present study the number of nodules were correlated with N concentration of plants for both genotypes and found as the nodules formation increases the plant N concentration linearly increased and showed close relationship with one another. Similarly, the Fe-concentration increases in plant leaves, N-concentration also increases in a similar fashion, indicated that Fe-played a vital role in N-fixation by chickpea genotypes. The present study suggests that the application of Mo 0.5 and Fe 2.0 kg ha -1 is important which play a significant role in getting the maximum yield, nodules and nitrogen concentration in chickpea genotypes.

Soybean Seed Nutrition as Affected by Cotton, Wheat, and Fallow Rotation

Limited information is available on the effects of crop rotation on seed nutrition. Therefore, the objective of the current research was to determine whether crop rotations are beneficial to soybean seed nutrition for the first two complete rotation cycles in an experiment conducted from 2007 through 2012. The first complete rotation cycle (experiment one) was conducted in 2009, then repeated in 2010, and the second complete rotation cycle (experiment two) was conducted in 2011, and then repeated in 2012. The rotation sequences were: wheat-late cotton-fallow-soybean (WCFS), fallow-cotton-wheat-soybean (FCWS), and fallow-cotton-fallow-soybean (FCFS). The results showed that WCFS and FCFS resulted in higher seed oil, palmitic and stearic acids, glucose, sucrose, fructose, Fe, P, and B. No consistent effects on seed protein, oleic acid, linoleic acid, linolenic acid, raffinose, stachyose, and Mn contents were observed. These changes were accompanied by higher P, K, B, Fe in soil and N, K, and B in leaves, indicating that soil and leaf nutrients may result in continuous supply and mobility of nutrients from leaves to seed during seed fill. Our research demonstrated that crop rotation management can result in seed nutrient changes, affecting seed quality.

XAS study of iron speciation in soils and waters from a boreal catchment

Iron (Fe) is a key element, strongly influencing the biogeochemistry of soils, sediments and waters, but the knowledge about the variety of Fe species present in these systems is still limited. In this work we have used X-ray absorption spectroscopy (XAS) to study the speciation of Fe in soils and waters from a boreal catchment in northern Sweden. The aim was to better understand the controls of Fe speciation across different, but adjacent landscape elements including soil, soil solution, groundwater and stream water draining catchments with contrasting land characteristics. Our results showed that all samples contained mixtures of Fe(II) and Fe(III). The soils consisted of Fe phyllosilicates, Fe (hydr)oxides and Fe complexed by natural organic matter (NOM). All aqueous samples contained Fe(II)– and Fe(III)–NOM complexes, often in combination with Fe(III) (hydr)oxides that were associated with NOM. The variation in contribution from Fe–NOM and Fe (hydr)oxides was controlled by pH and total concentrations of NOM. The XAS spectra suggested formation of mononuclear Fe–NOM complexes consisting of chelate ring structures, but it could not be determined whether they originated solely from Fe(III)– or from a mixture of Fe(II)/Fe(III)–NOM complexes. Our collective results showed that the Fe speciation was highly variable across the different landscape elements and streams. This variation was manifested both in the distribution between mononuclear Fe–NOM complexes and Fe (hydr)oxides associated with NOM and between Fe(II) and Fe(III). These results highlight the complexity of Fe speciation in natural environmental systems and thus the challenges in interpreting Fe reactivity.

Role of exogenous nitric oxide in alleviating iron deficiency-induced peanut chlorosis on calcareous soil

This study examined the effects of exogenous nitric oxide (NO) on physiological characteristics of peanut (Arachis hypogaea L.) growing on calcareous soil. Sodium nitroprusside (SNP), a NO donor, was root application (directly; slow-release bag; slow-release capsule; slow-release particle) and foliar application. The results showed that SNP application alleviated iron (Fe) deficiency-induced chlorosis, increased the yield of peanut and increased the Fe concentration in peanut grain. SNP, especially supplied by slow-release particle improved the available Fe in soil by reducing pH of soil and increasing available Fe of soil. Furthermore, SNP application significantly increased the H+-ATPase and Fe3+ reductase activities and increased the total Fe concentration in the leaves. Meanwhile, SNP application, especially foliar application enhanced the availability of Fe in the plant by significantly increasing the active Fe content and chlorophyll content in the leaves. In addition, SNP also increased the antioxidant activities, but decreased the superoxide anion (O2•−) generation rate and malondialdehyde content, which protected peanut against the Fe deficiency-induced oxidative stress. Therefore, these results support a physiological action of SNP on the availability, uptake and transport of Fe in the plant and foliar application SNP had the best effects in leaves and SNP supplied by slow-release particle had the best effects in roots. In addition, on the whole, the effects of SNP supplied by slow-release ways were better than directly supplied into the soil.

Effects of the Incorporation of Phosphorus and Iron into Arsenic-Spiked Artificial Soils on Root Growth of Lettuce using Response Surface Methodology

We investigated effects of phosphorus (P) and iron (Fe) on root elongation (RE) of lettuce in arsenic (As)–spiked soils using response surface methodology (RSM). To stabilize interactions between As and Fe in a soil preparation, the sequential incorporation method using Fe and P (SIMFe-P) was applied. From a phytotoxicity assay, As in roots (Asroot) was negatively associated with RE, Fe in soils, and P in roots and soils. The P in roots was also positively related to RE. In a model study, As and interaction factor between P and Fe showed negative coefficients but others showed positive ones. From a confirmation study, RE on exposure to As was verified to be much greater in soils treated by SIMFe-P than in soils separately treated with both elements. These results indicated that application of SIMFe-P to As-contaminated soils might be expected to have an advantage during the early stage of plant root growth.

Effect of Rock Phosphate on Zn and Fe Bioavailability and Accumulation bySalix smithianain Heavily Contaminated Soil

High biomass production Salix smithiana was proved as the plant able to accumulate substantial amount of Cd and Zn in aboveground biomass. Nevertheless, in heavily contaminated soils (mainly by Zn) willows can suffer from chlorosis because of Fe deficiency induced by excess of Zn amount. Method such as chemophytostabilization seems like very good measure for planting willows in such heavily contaminated soil. In our experiments we evaluated effect of rock phosphate on changes in Zn and Fe bioavailability and accumulation of these elements by willows together with the willows growth on heavily contaminated soil. Addition of rock phosphate reduced plant-available Zn concentrations in soils resulting in significant decrease of Zn content in leaves. In the case of Fe, however, its contents in the leaves significantly decreased as well, although the mobile portion of Fe in soil remained unchanged. Yield of aboveground biomass in rock phosphate treatment was not significantly different in comparison to the control. After the first vegetation period, we can conclude that reduction of Zn contents in willows after rock phosphate application did not lead to suppress of Fe deficiency and improvement of willow growth in heavily contaminated soil.

Assessing the hydrogeochemical impact and distribution of acid sulphate soils, Heart Morass, West Gippsland, Victoria

The hydrogeochemical processes associated with the precipitation and oxidation of pyrite during the development of acid sulphate soils was investigated in the coastal floodplain environment of the Heart Morass, Victoria, Australia. During drought conditions in 2009, low-lying areas of the floodplain (0–2 m elevation) were the most affected by acid sulphate soils, with a median soil pH (pHF) of 3.56 to approximately 50 cm depth. Soils below ∼100 cm depth in these areas contain pyrite and have reduced inorganic S concentrations of up to 0.85 wt%. Higher areas of the floodplain (2–6 m) do not contain acid sulphate soils, with a median pH of 4.74 to approximately 50 cm depth, an average neutralising capacity of 3.87 kg H2SO4/t, and no appreciable unoxidised pyrite. In low-lying areas concentrations of Co, Ni, Zn, Mn and Fe in soil increased from <2.0, 4.0, 10, 20 and 2000 mg/kg, respectively, at 56 cm depth to 10, 20, 45, 152 and 15,000 mg/kg at 221 cm depth. In areas of higher elevation, concentrations of Co, Ni, Zn and Fe increased from 6, 11, 21 and 12,500 mg/kg at 44 cm depth to 10, 19, 47 and 19,400 mg/kg at 239 cm depth. These data indicate acidic leaching of metals from the upper soil profile in both low-lying and more elevated areas. The lowest concentrations of Al, Co, Fe, Mn and Ni in surface water or pit water from low-lying areas were 2.43, 0.06, 2.90, 2.89 and 0.09 mg/L, respectively. These concentrations are 1–2 orders of magnitude higher than in any potential water sources around the morass and are higher than can be accounted for by evapotranspiration, indicating the leaching of metals into surface water and groundwater. Excess SO42- from pyrite oxidation in the central low-lying area of the morass was characterised by molar Cl:SO4 ratios <5 and δ34S values <10‰. The Cl:SO4 ratios combined with δ34S values define zones of SO42- depletion during reduction (Cl:SO4 ∼ 24, δ34S = 22.7‰) and contemporary SO4 reduction of water enriched with oxidised pyritic SO42- (Cl:SO4 = 9.9, δ34S = 26.2‰). Average concentrations of Fe in the upper soil profile decreased from 129 g/kg during drought conditions to 15.2 g/kg after flooding in 2011, suggesting the dissolution of Fe mineral salts accumulated in the upper soil profile. Average concentrations of Al, Ni, Cr and Cu increased in the upper soil profile from 9,522, 18.4, 17.0 and 14.4 mg/kg during drought to 12,800, 22.4, 22.6 and 22.4 mg/kg after flooding, suggesting that metal precipitation and dissolution is the result of changing pH and redox chemistry during flooding. This highlights the need for continuous measurement and sampling during flood events in order to better constrain these processes.

The influence of vegetation and soil type on the speciation of iron in soil water

Soluble organic matter derived from exotic Pinus species has been shown to form stronger complexes with iron (Fe) than that derived from most native Australian species. It has also been proposed that the establishment of exotic Pinus plantations in coastal southeast Queensland may have enhanced the solubility of Fe in soils by increasing the amount of organically complexed Fe, but this remains inconclusive. In this study we test whether the concentration and speciation of Fe in soil water from Pinus plantations differs significantly from soil water from native vegetation areas. Both Fe redox speciation and the interaction between Fe and dissolved organic matter (DOM) were considered; Fe – DOM interaction was assessed using the Stockholm Humic Model. Iron concentrations (mainly Fe2+) were greatest in the soil waters with the greatest DOM content collected from sandy podosols (Podzols), where they are largely controlled by redox potential. Iron concentrations were small in soil waters from clay and iron oxide‐rich soils, in spite of similar redox potentials. This condition is related to stronger sorption on to the reactive clay and iron oxide mineral surfaces in these soils, which reduces the amount of DOM available for electron shuttling and microbial metabolism, restricting reductive dissolution of Fe. Vegetation type had no significant influence on the concentration and speciation of iron in soil waters, although DOM from Pinus sites had greater acidic functional group site densities than DOM from native vegetation sites. This is because Fe is mainly in the ferrous form, even in samples from the relatively well‐drained podosols. However, modelling suggests that Pinus DOM can significantly increase the amount of truly dissolved ferric iron remaining in solution in oxic conditions. Therefore, the input of ferrous iron together with Pinus DOM to surface waters may reduce precipitation of hydrous ferric oxides (ferrihydrite) and increase the flux of dissolved Fe out of the catchment. Such inputs of iron are most probably derived from podosols planted with Pinus.

A review of the effects of iron redox cycles on smectite properties

The oxidation state of Fe in soils is one of the few properties that can be altered in situ and is known to have a large effect on chemical and physical properties. Understanding this phenomenon enables the possible manipulation or management of the soil in such a way as to maximize the benefit of such changes in properties. The effects of redox cycles, however, are less understood because most studies have focused only on a single reduction event. The purpose of this report is to review the current state of knowledge of the effects of redox cycles on clay and soil behavior, with the hope that this background will encourage further investigations of these processes. Evidence clearly indicates that the means by which reduction of Fe in clay minerals occurs significantly influences the potential reversibility of the process.

Fractions of Iron in Soil under a Long-Term Experiment and Their Contribution to Iron Availability and Uptake by Maize–Wheat Cropping Sequence

Soil and plant samples were collected from an ongoing long-term experiment (LTE) at the Indian Agricultural Research Institute farm, New Delhi, to study the distribution of various fractions of iron (Fe) and their contribution to availability and plant uptake in a maize–wheat sequence. The optimum dose-based treatments adopted for the study were nitrogen (N), nitrogen–phosphorus (NP), nitrogen–phosphorus–potassium (NPK), NPK + farmyard manure (FYM), NPK+ zinc (Zn), and control (no fertilizer or manure). Different fractions of Fe in the soil were sequentially extracted using different extractants. Diethylenetriaminepentaacetic acid (DTPA)–extractable Fe did not differ significantly among the treatments as a result of continuous cropping for more than three decades. The overall mean total iron (Fe) content varied from 2.36 to 2.61% under different treatments. Residual Fe constitutes a major portion of total Fe in all four layers of soil. The Fe associated with easily reducible Mn and organic matter contributed directly to DTPA-extractable Fe both in pre-maize and post-wheat soil. Residual Fe contributed directly to uptake Fe by maize and wheat crops.

Plant Fe status affects the composition of siderophore-secreting microbes in the rhizosphere

Soil microbes have been demonstrated to play an important role in favouring plant iron (Fe) uptake under Fe-limiting conditions. However, the mechanisms involved are still unclear. This present study reported the effects of plant Fe status on the composition of siderophore-secreting microbes in the rhizosphere, and their potential function in improving plant Fe nutrition. An Fe-efficient plant, red clover (Trifolium pratense 'Kenland') was cultured in a calcareous soil to obtain rhizosphere soils with (Fe-sufficient) or without (Fe-stressed) foliar FeEDTA spraying. The siderophore-producing ability of rhizospheric microbes was measured. The bioavailability of the siderophore-solubilized Fe from iron oxides/hydroxides was tested in hydroponic culture. In rhizosphere soil, the number of microbes that secreted siderophores quickly was more in the Fe-stressed treatment than in the Fe-sufficient one, while the number of microbes that did not secret siderophores was the opposite. A significantly higher concentration of phenolics was detected in the rhizosphere soil of Fe-stressed plants. Moreover, after the soil was incubated with phenolic root exudates, the composition of the siderophore-secreting microbial community was similar with that of the rhizosphere of Fe-stressed plant. Additionally, the siderophores produced by a rhizospheric microbe isolated from the Fe-stressed treatment can well solubilize iron oxides/hydroxides, and the utilization of the siderophore-solubilized Fe by plant was even more efficient than EDTA-Fe. Iron-deficiency stress of red clover would alter the composition of siderophore-secreting microbes in the rhizosphere, which is probably due to the phenolics secretion of the root, and may in turn help to improve the solubility of Fe in soils and plant Fe nutrition via elevated microbial siderophore secretion.

Iron occurrence in soils and sediments of a coastal catchment: A multivariate approach using self organising maps

The processes controlling the distribution and phases of Fe in soils and sediments of a forested coastal catchment in southeast Queensland, Australia are identified. The physicochemical attributes of 120 spatially distributed soil and sediment samples, along with geomorphic, geological and land-use characteristics were analysed using Kohonen's self organising maps (SOM) methodology. The SOM-based data analysis approach permits the analysis of complex multivariate datasets that are not well suited to traditional statistical methods. Across the catchment readily extractable Fe concentrations are low overall, despite a high proportion of Fe-concretions in many soils. However, two processes associated with elevated Fe occurrences are identified. Firstly, seasonal water-logging leads to the accumulation of Fe in clay-rich soils on lower slope positions. Mottling and the presence of lepidocrocite indicate cyclical redox conditions. Secondly, a high proportion of total readily extractable Fe is present in organically complexed form in the stream sediments. It is suggested that an accumulation of Fe-rich sediment and organic detritus in streams permits the release of Fe under anoxic conditions, which is then bound by organic material. Contrary to the findings of previous studies, vegetation type does not affect Fe; there is no major difference between the concentrations of Fe of soils under pine plantation and native vegetation. Landform, however, does play an important role. Local depressions on gentle-sloped, low-lying terrain and associated with high topographic wetness indices were found to enhance seasonal redox processes. The groupings obtained from the SOM analyses were internally consistent and can be regarded as ‘process groups’. The results show that SOM is a tool that can aid in the interpretation of complex datasets and help identify geochemical processes operating on a catchment scale.

Effect of Al and heavy metals on enzymes of nitrogen metabolism of fast and slow growing rhizobia under explanta conditions

Most of the legume crops are affected by metal stress present in the soil mainly due to contaminated agrochemicals and sewage sludge. The effect of aluminium, and heavy metals copper, iron and molybdenum on growth and activity of enzymes of fast and slow growing rhizobial sps. was studied. Sinorhizobium meliloti RMP5 was found to be more tolerant to metal stress than Bradyrhizobium BMP1. Both the strains were extremely sensitive to Al than other metals. Al was much more deleterious for the enzymatic activities (nitrate reduction, nitrite reduction, nitrogenase and uptake hydrogenase) of strain RMP5 and BMP1. Cu showed inhibitory effect on growth and enzyme activities of Bradyrhizobium strain at all concentrations. However, in S. meliloti RMP5 all the tested enzymatic activities increased up to the concentration of 0.1 mM Cu. Fe enhanced the growth and enzyme activities of S. meliloti RMP5 and Bradyrhizobium BMP1 up to 100 mM concentration. Mo enhanced all the tested enzymatic activities of S. meliloti RMP5 up to 1 mM. Nitrate and nitrite reduction activities of Bradyrhizobium BMP1 increased up to 1 mM concentration. However, nitrogenase and hydrogenase activities of Bradyrhizobium BMP1 got enhanced only up to 0.5 mM Mo. Both Fe and Mo are the key components of the enzyme nitrogenase and nitrate reductase and enhanced the growth and enzyme activities of both the sps. The study of physiology of nitrogen fixing ability of both fast and slow growing rhizobial strains reported that the supplementation of Mo and Fe in soils along with the biological formulations will enhance the process of symbiotic nitrogen fixation.

Determination of phytoextraction potential of plant species for toxic elements in soils of abandoned sulphide-mining areas

This study has determined contamination levels in soils and plants from the Sao Domingos mining area, Portugal, by k 0-INAA. Total concentrations of As, Sb, Cr, Hg, Cu, Zn and Fe in soils were very high, exceeding the maximum limits in Portuguese legislation. Concentrations of toxic elements like As, Sb and Zn were highest in roots of Erica andevalensis, Juncus acutus, Agrostis castellana and Nicotiana glauca. Additionally, As, Br, Cr, Fe, Sb and Zn in all organs of most plants were above toxicity levels. Those species that accumulated relatively high concentrations of toxic elements in roots (and tops) may be cultivated for phytostabilisation of similar areas.

Interlaboratory Validation of the Mehlich 3 Method as a Universal Extractant for Plant Nutrients

The Mehlich 3 (M3) method is widely used to extract plant-available phosphorus from soil over a wide range of pH values. The method is also used by many laboratories to determine multiple plant-available nutrients simultaneously. However, except for P, this method has not been statistically validated within and among laboratories. The objective of this study was to determine the repeatability (within-laboratory performance) and reproducibility (among-laboratories performance) of the M3 method for several different nutrients by using a wide variety of soils. An in-house homogeneity test was conducted for 11 soils. Three replicates of each of the 11 soils were sent to 23 domestic and international laboratories for analyses primarily for K, Ca, Mg, Zn, Mn, Fe, and Cu. Samples were scooped, weighed, or both scooped and weighed for extraction. The various nutrients in the extracts were quantified by the participating laboratories by using inductively coupled plasma-atomic emission spectrometry. Ranges (in parentheses) of the repeatability relative standard deviation (RSDr) values for the scooped samples were K (3.88-6.14%), Ca (2.19-10.6%), Mg (2.27-5.73%), Zn (4.11-42.7%), Mn (3.15-8.53%), Fe (2.32-7.74%), and Cu (3.65-11.2%). For the weighed samples, the ranges (in parentheses) of the RSDr values were K (1.65-4.65%), Ca (1.43-16.9%), Mg (1.37-9.83%), Zn (2.60-33.0%), Mn (1.61-4.90%), Fe (1.56-4.47%), and Cu (2.95-17.9%). Ranges (in parentheses) of the reproducibility relative standard deviation (RSDR) values for the scooped samples were K (7.44-20.0%), Ca (7.10-33.5%), Mg (7.63-26.4%), Zn (11.6-48.7%), Mn (10.5-19.7%), Fe (12.4-22.0%), and Cu (8.86-45.3%). Ranges (in parentheses) of the RSDR values for the weighed samples were K (3.47-12.7%), Ca (7.61-34.6%), Mg (7.53-29.0%), Zn (10.6-49.2%), Mn (6.54-20.7%), Fe (11.0-21.5%), and Cu (9.73-43.0%). The Horwitz ratios (HorRat) were also used to evaluate the repeatability, HorRatr, and the reproducibility, HorRatR. Overall, the M3 method appears to be both repeatable and reproducible across the two categories for K, Mg, Zn, Mn, and Cu, and the vast majority of the HorRat values for both repeatability and reproducibility were within the acceptable range. However, a large number of soils in both the weighed and scooped categories displayed unacceptable HorRat values for the reproducibility of Ca and Fe, indicating that the M3 is not suitable for the extraction and quantitation of Ca and Fe in soils. The results of this study indicate that the M3 method for the determination of K, Mg, Zn, Mn, and Cu in soils is both accurate and precise when standardized procedures are used. The method has been proven to be suitable for use as a reference method for testing soil materials for extractable P, K, Mg, Zn, Mn, and Cu. Further study may be needed to confirm the suitability of the M3 method for Ca and Fe.