Residual heavy metal concentrations in sludge‐amended coastal plain soils ‐ I. Comparison of extractants

Abstract

The purposes for this research were: to examine the long‐term residual effects of farmland applications of municipal sludges from four treatment technologies on the total and extractable Zn, Cu, Mn, Fe, Pb, Ni and Cd concentrations in Coastal Plain soils; to investigate the effects of sludge sources and rates on the effectiveness of soil extractants to remove the various metals; and to determine correlation coefficients for soil extractable versus plant accumulation in tobacco. The extractants evaluated were Mehlich 1 and 3, and DTPA‐pH 7.3. Composite Ap horizon soil samples and tobacco leaf samples were obtained in 1984 from research plots at two sites in Maryland that were established in 1972 and 1976, respectively, using sludge materials from three wastewater treatment facilities in the Washington, D.C. metropolitan region. Similar application rates were used at both sites.

A wide range in soil pH values was found among treatments at each site. Significant (p ≤ 0.05) increases were observed in total Zn, Cu, Fe, Pb, Ni, and Cd for all sludge sources with increased rates; however, values for total soil Mn exhibited high variability in all cases. The rankings among the extractants varied for some elements depending on the sludge sources. For Zn, the rankings were Mehlich 1 > Mechlich 3 > DTPA‐pH 7.3 across all sources and rates. For Cu, Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was found for soils amended with Blue Plains digested (BPD) and Piscataway limeddigested (PLD) sludges but Mehlich 1 ≥ DTPA pH 7.3 > Mehlich 3 for Blue Plains limed compost (BPLC) and Annapolis Fe and heat treated (AFH) sludges. Concerning extractable Mn, Mehlich Mehlich 1 > Mechlich 3 > DTPH pH 7.3 was the order for BPLC and AFH sludges but Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was observed for BPD and PLD sludges. The rankings among extractants for Fe (Mehlich 3 > Mehlich 1 > DTPA‐pH7.3), Ni (Mehlich 3 ≥ Mehlich 1 > DTPA‐pH 7.3), Pb (Mehlich 3 > DTPA‐pH 7.3 > Mehlich 1) and Cd (Mehlich 1 > Mehlich 3 > DPTA‐pH7.3) were somewhat similar across all sludge sources. Significant correlation coefficients were obtained for all three extractants for soil extractable vs. plant Zn, Cu, Ni, and Cd at both sites; however, Mehlich 3 was not significant for Mn. Also, neither of the extractants produced significant coefficients for Fe and Pb.     

Comparison of soil tests to determine micronutrients status in Argentina soils

Abstract

Soil extraction techniques to measure the status of available micronutrients for plants are important in the diagnosis of deficiency or toxicity. Mehlich 3 (M3), EDTA (pH=8.2), DTPA‐TEA, and Soltanpour and Schwab (SS) solutions were confronted for their ability to extract simultaneously copper (Cu), zinc (Zn), manganese (Mn), and iron (Fe). Argentinean soils from different taxonomic orders with widely varying properties were investigated. The values obtained showed that DTPA‐TEA and SS solutions extracted similar amounts of Zn, Fe, and Mn, while EDTA dissolved comparatively higher amounts of Fe and Mn. Mehlich 3 yielded the highest extractions for the four micronutrients. Soil pH not only affected the extraction of Mn by DTPA‐TEA, SS, and EDTA extractions, but also the extraction of Fe by EDTA. The organic carbon affected the determination of Fe and Zn in all cases. The correlations of the different tests for Cu, Zn, Mn, and Fe were significant. The results suggest that for the determination of the bioavailable status of micronutrients, any of the studied tests could be applied using the soil edaphic properties as factors to improve the correlations between them and standardize the methods.     

Micronutrients distribution in salt-affected soils of the Punjab in relation to soil properties

Salt-affected soils in arid and semi-arid tracts of the Indian Punjab are prone to deficiency of micronutrients. Nine profiles from alluvial terraces, sand dunes and palaeochannels in the southwestern Punjab were investigated for total and diethylenetriamine-penta-acetic acid (DTPA) extractable Zn, Cu, Mn and Fe. Soil physiography exerted significant influence on the spatial distribution of micronutrients. Total contents varied from 20–78 for Zn, 8–32 for Cu, and 88–466 mg kg^?1 for Mn and 0.82–2.53% for Fe. DTPA-extractable contents varied from 0.10–0.98 for Zn, 0.14–1.02 for Cu, 0.54–13.02 for Fe and 0.82–9.4 mg kg^?1 for Mn. Total contents were higher in fine-textured soil than in coarse-textured soils. Concentration of micronutrients in the surface layer was low and there occurred more accumulation in the Cambic horizon. Organic carbon, pH, clay, silt and calcium carbonate exerted strong influence on the distribution of micronutrients. DTPA extractable Zn, Cu, Mn and Fe increased with increasing organic carbon but decreased with increase in pH and calcium carbonate content. Total micronutrient contents increased with increase in clay, silt and calcium carbonate contents and decreased with increase in sand content.     

Metal Extractability in Binary and Multi-metals Spiked Calcareous Soils

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

Comparison of routine soil tests and EPA method 3050 as extractants for heavy metals in Delaware soils

Abstract

Agricultural use of sewage sludges can be limited by heavy metal accumulations in soils and crops. Information on background levels of total heavy metals in soils and changes in soil metal content due to sludge application are; therefore, critical aspects of long‐term sludge monitoring programs. As soil testing laboratories routinely, and rapidly, determine, in a wide variety of agricultural soils, the levels of some heavy metals and soil properties related to plant availability of these metals (e.g. Cu, Fe, Mn, Zn, pH, organic matter, texture), these labs could participate actively in the development and monitoring of environmentally sound sludge application programs. Consequently, the objective of this study was to compare three soil tests (Mehlich 1, Mehlich 3, and DTP A) and an USEPA approved method for measuring heavy metals in soils (EPA Method 3050), as extractants for Cd, Cu, Ni, Pb and Zn in representative agricultural soils of Delaware and in soils from five sites involved in a state‐monitored sludge application program.

Soil tests extracted less than 30% of total (EPA 3050) metals from most soils, with average percentages of total metal extracted (across all soils and metals) of 15%, 32%, and 11% for the Mehlich 1, Mehlich 3, and DTPA, respectively. Statistically significant correlations between total and soil test extractable metal content were obtained with all extractants for Cu, Pb, and Zn, but not Cd and Ni. The Mehlich 1 soil test was best correlated with total Cu and Zn (r=0.78***, 0.60***, respectively), while the chelate‐based extractants (DTPA and Mehlich 3) were better correlated with total Pb (r=0.85***, 0.63***). Multiple regression equations for the prediction of total Cu, Ni, Pb, and Zn, from soil test extractable metal in combination with easily measured soil properties (pH, organic matter by loss on ignition, soil volume weight) had R² values ranging from 0.41*** to 0.85***, suggesting that it may be possible to monitor, with reasonable success, heavy metal accumulations in soils using the results of a routine soil test.     

印度酸性耕作土中总锰、铁以及可提取态锰、铁的水平、分布及其与土壤性质的关系研究

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-1soil 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.     

Micronutrient status of calcareous paddy soils and rice products: implication for human health

Modern agricultural systems have to provide enough micronutrient output to meet all the nutritional needs of people. Accordingly, knowledge on micronutrient status in soil and crop edible tissues is necessary. This study was carried out to investigate zinc (Zn), iron (Fe), manganese (Mn), and copper (Cu) concentration of calcareous paddy soil and the relative rice grain. Rice crops (straw, hull, and grain) and associated surface soils (0–25 cm) were collected from 136 fields and analyzed for total and diethylene triamine pentaacetic acid (DTPA) available Zn, Fe, Mn, and Cu. The DTPA-Zn concentration in more than 50% of paddy soils was less than its critical deficiency concentration (2 mg kg⁻¹), while the concentrations of DTPA Fe, Mn, and Cu were sufficient. The grain Zn concentration of more than 54% of the rice samples was less than 20 mg kg⁻¹. About 55% and 49% of the rice samples were deficient in Mn and Cu, respectively, while the Fe concentration in rice grains was sufficient. A significant negative correlation was found between the CaCO₃ content and soil DTPA-extractable Zn, Fe, Mn, and Cu. There were significant relationships between the total soil phosphorus and DTPA-extractable micronutrient concentrations. By considering the average daily rice consumption of 110 g per capita, the Zn, Fe, Mn, and Cu intake from rice consumption was estimated to be 2.4, 7.7, 1.6, and 0.7 mg for adults, respectively.     

Micronutrient Soil-Test Levels and Eucalyptus Foliar Contents

Eucalyptus is the most widely planted forest species in Brazil (～3.4 million hectares). Ongoing rotations and high yields lead to the occurrence of copper (Cu), manganese (Mn), iron (Fe), and zinc (Zn) deficiency symptoms. The objectives of this work were to identify the most appropriate extractant for evaluating micronutrient availability in commercial Eucalyptus plantations and to evaluate the influence of soil properties on Eucalyptus foliar micronutrient contents. Soil micronutrient contents were extracted by Mehlich 1, Mehlich 3, and diethylenetriaminepentaacetic acid (DTPA). Mehlich 1 and Mehlich 3 extracted the greatest amounts for all micronutrients analyzed. Foliar Cu, Mn, and Zn contents showed significant and positive relationships with soil Cu, Mn, and Zn contents extracted by the three solutions. Soil organic carbon (SOC), soil clay content, and soil pH improved significantly the power of regression models in estimating foliar micronutrient contents. The improvement was greater for Mehlich 3 and DTPA extractants than for Mehlich 1.     

Evaluation of Mehlich 3 as a Universal Nutrient Extractant for Australian Sugarcane Soils

This study evaluated the suitability of the Mehlic h3 universal extractant as a part of a multielement test to assess the nutrient status of Australian sugarcane soils. Soil samples from BSES Soil Exchange Programs, representing all major soil types and geographic sugarcane-growing regions, were analyzed using existing BSES, acid-based extraction methods for calcium (Ca), magnesium (Mg), sodium (Na), potassium (K), copper (Cu), zinc (Zn), iron (Fe), manganese (Mn), and phosphorus (P) and the ASPAC 10B3 method for sulfur (S). These were compared with the Mehlich 3 procedure. Mehlich 3 results for Ca, Mg, Na, S, and Mn correlated highly with the BSES procedures (R² = 0.95, 0.98, 0.99, 0.91, and 0.91, respectively). Satisfactory correlations were also obtained with 0.1 M HCl–extracted Zn, Cu, and Fe (R² = 0.89, 0.85, and 0.85, respectively) and with the BSES sulfuric acid (H₂SO₄)–extracted P (R² = 0.81). The poorest correlation (R² = 0.79) was observed for K. In conclusion, the Mehlich 3 procedure is suitable as a diagnostic tool to assess the basic nutrient status of Australian sugarcane soils.     

Distribution of Total and DTPA‐Extractable Zinc,Copper, Manganese,and Iron in Vertisols of India

Abstract

Vertisols of India are developed over isohyets of 600 to 1500 mm, and their chemical cycles are set by drainage, landforms, and particle size, which results in variable pedogenic development within the otherwise homogeneous soils. The purpose of this study was to identify pedogenic processes in the distribution of total and DTPA‐extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The soils are developed over basaltic parent material of Cretaceous age. Soil samples were drawn from genetic horizons of the 13 benchmark profiles and analyzed by using HF–HClO₄ acid for total and DTPA extraction. Correlation coefficients were calculated taking all samples together. The total concentration varied from 24 to 102 mg kg^?1 for Zn, 21 to 148 mg kg^?1 for Cu, 387 to 1396 mg kg^?1 for Mn, and 2.36 to 9.50% for Fe. Their variability was proisotropic and haplodized, and their concentrations increased with advancing isohyets. Within the isohyets, hindrance in drainage caused retention of Zn and Cu but loss of Fe. The piedmont soils had more Fe than alluvium soils. The spatial distribution of total contents of Zn, Cu, and Fe was influenced by the pedogenic processes associated with Haplusterts but not with provenance materials. Surface concentrations of the elements by biotic lifting and/or harvest removal were negated by the pedoturbation that further contributed to the irregular distribution of the elements in the profiles. Total Zn and total Cu had positive coefficients of correlations with coarse clay, whereas total Mn and total Fe were positively correlated with fine clay. The DTPA‐extractable forms were functions of isohyets and drainage and showed association with organic carbon content and coarse clay.     

Comparison of Multi-element to Single‐Element Extractants for Macro‐ and Micronutrients in Acid Soils from Spain

Abstract

Different chemical reagents are used to assess plant‐available nutrients from soils with similar properties. The use of different extractants is a serious limitation when comparing results between different soil‐testing laboratories, often leading to large differences in fertilizer recommendations for similar crops.

In this study, 80 samples from acid soils from Galicia (Spain) were used to compare several soil nutrient extractants. Traditional and tested extractants for acid soil such as Bray 2 and ammonium acetate were used to evaluate multielement extractants such as ethylenediaminetetraacetic acid–ammonium acetate (EDTA‐aa), ammonium bicarbonate–diethylenetriaminepentaacetic acid (AB‐DTPA), and Mehlich 3.

Linear regression analyses were performed to relate the amount of each nutrient obtained by traditional soil extractants to the amount obtained by multielement extractants. Strong correlation was found between extractable Bray 2 P and Mehlich 3 P (r²=0.97, slope=0.87, and intercept=?0.48). The slope of the regression line between EDTA‐aa‐extractable calcium (Ca) and that from ammonium acetate (Aa) approached 1∶1 (r²=0.86). Similar results were obtained for magnesium (Mg) (r²=0.99). Soil zinc (Zn) concentrations extracted by Mehlich 3 and EDTA‐aa were similar; slope of the regression line was 0.95 (r²=0.88). With regard to copper (Cu), Mehlich 3 extracted approximately 20% more Cu than EDTA‐aa.

The results showed that Mehlich 3 and EDTA‐aa are suitable for assessment of plant available phosphorus (P), potassium (K), Ca, Mg, Cu, Zn, and iron (Fe) in acid soils.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Extractable Micronutrients Status of Soils in a Plinthitic Landscape at Zaria,Nigeria

Desilication and leaching are processes that accompany plinthilization, leading to nutrient depletion. Soils from 12 profiles in a plinthitic landscape were analyzed for extractable micronutrients [iron (Fe), zinc (Zn), manganese (Mn), and copper (Cu)]. Soils of the landscape from crestal to lower‐slope position contain plinthite in the profile, whereas those of the valley floor are devoid of plinthite. The micronutrients were extracted using diethylenetriaminepentaacetic acid (DTPA) and 0.1 M hydrochloric acid (HCl). The results showed that 0.1 M HCl extracted more of the micronutrients than DTPA. The DTPA‐extractable Fe, Zn, Mn, and Cu in all the soils ranged from 1.15 to 12.44 (mean, 3.69); 0.71 to 2.75 (mean, 1.86); trace 12.44 (mean, 3.35), and trace 3.76 (mean, 0.63) mg kg^?1, respectively. The DTPA‐extractable micronutrient contents were generally greater than the critical available level (4.5 mg kg^?1 for Fe, 0.8 mg kg^?1 for Zn, 1.0 mg kg^?1 for Mn, and 0.2 mg kg^?1 for Cu). The 0.1 M HCl‐extractable micronutrients in the landscape ranged from 8.00 to 30.40 (mean, 15.19); 0.30 to 6.49 (mean, 1.35); 1.00 to 27.20 (mean, 7.74); and 0.26 to 15.0 (mean, 2.77) mg kg^?1 for Fe, Zn, Mn, and Cu, respectively. Both DTPA‐ and 0.1 M HCl‐extractable micronutrients were generally lower in the plinthitic horizons than in the nonplinthitic horizons and higher in the Ap than the subsoil horizons. Correlation analysis showed a significant relationship between DTPA‐Fe and DTPA‐Mn, Cu, and organic carbon (r = 0.913**, 0.411**, and 0.385**). There was a significant and positive relationship between 0.1 M HCl‐extractable Mn and organic carbon (C), total nitrogen (N), and available phosphorus (P) (r = 0.413**, 0.337**, and 0.350**, respectively).     

Diagnosis of Micronutrient Imbalance in Lime Crop in Semi-arid Region of Rajasthan,India

Low and unstable fruit yield, poor quality of fruits, and excessive fruit dropping are major problems in a lime crop and are due to either micronutrient deficiencies or nutrient imbalance. A study was conducted to assess the micronutrient status in a lime orchard at the Central Soil and Water Conservation Research and Training Institute (CSWCRTI)’s research farm in Kota, Rajasthan, India. Plant and soil samples were collected during September and October in 2006–2007. The micronutrients extracted with diethylenetriaminepentaacetic acid (DTPA) in soils were in the order of manganese (Mn) > iron (Fe) > zinc (Zn) > copper (Cu). The mean values of DTPA Mn, Fe, Zn, and Cu in surface soils varied from 13.98 to 22.70, 2.48 to 8.66, 0.79 to 1.19, and 0.14 to 0.46 mg kg^?1, respectively, whereas in subsurface soils they varied from 12.94 to 23.06, 4.84 to 6.52, 0.51 to 0.83, and 0.07 to 0.20 mg kg^?1, respectively. Results reveal that except for Fe, the other DTPA-extractable micronutrients decreased with depth. Total Mn, Fe, Zn, and Cu in plant leaves varied from 22 to 83, 70 to 630, 40 to 932, and 37 to 3057 mg kg^?1, respectively, indicating greater or toxic concentrations of total micronutrient in leaf samples. Total Mn, Fe, Zn, and Cu in petiole samples varied from 7 to 60, 235 to 574, 70 to 827, and 101 to 2623 mg kg^?1, respectively. High concentration of Cu and Zn in leaves resulted in Fe and Mn deficiencies (exhibited as leaf chlorosis) in lime plants. Results of the study indicated that Fe and Mn deficiencies are major disorders in lime plantation. Similarly, the measure of DTPA-extractable micronutrients showed the low statuses of Fe and Cu and marginal status of Zn in soils along the Chambal region.     

Effect of Citrate Concentration on the Extraction Efficiency of Selected Micronutrients from Soil

This study was carried out with the objective of evaluating the effect of citrate concentration on the extraction efficiency of some micronutrients from soil. Composite surface soil samples (0–20 cm) were collected from Eastern Harage Zone (Babile and Haramaya Districts), Wolaita Zone (Damot Sore, Boloso Bombe, Damot Pulasa and Humbo Districts) and Dire Dawa Administrative Council in purposive sampling. The treatments were arranged in completely randomized design (CRD) with three replications. A greenhouse pot experiment with soybean plant was conducted to determine the correlation between soil test methods and the selected micronutrients, such as iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn) in the leaves of the plant. The results showed that, among the different citrate concentrations with strontium chloride (SrCl₂) tested for the determination of available Fe, Mn and Zn, the highest correlation coefficients (r = 0.82, p < 0.05), (r = 0.96, p < 0.001) and (r = 0.98, p < 0.001) were found between the diethylenetriamine pentaacetic acid (DTPA) method and 0.02 M strontium chloride (SrCl₂)-0.025 M citric acid extractant, respectively. Therefore, 0.02 M SrCl₂-0.025 M citric acid extractant is considered to be the most effective for the determination of Fe, Mn and Zn in soils of the studied areas. Similarly, high correlation coefficients (r = 0.97, p < 0.001) were found between DTPA and 0.02 M SrCl₂-0.05 M citric acid and (r = 0.88, p < 0.01) between DTPA and 0.02 M SrCl₂-0.025 M citric acid extractants for the determination of available Cu from soils. Hence, the 0.02 M SrCl₂-0.05 M citric acid extractant was shown to be the best for the determination of Cu in soils of the studied areas. However, considering the use of universal extractant, the 0.02 M SrCl₂-0.025 M citric acid extractant could easily be adopted as a procedure for the determination of Fe, Cu, Mn and Zn for both agricultural and environmental purposes. The greenhouse experiment confirmed the result.     

Evaluation of four chemical extractants for metal determinations in wetland soils

Abstract

Wetland soils (hydric soils) are unique in their chemical characteristics compared to upland soils. It is known that they are capable of removing a variety of wastes from polluted water entering the wetland including metals and potentially toxic heavy metals. When these metals are determined in wetland soils, it is necessary to use the proper chemical extractant(s). Four commonly used chemical extractants (Mehlich 1, Mehlich 3, 0.1M HCl, and DTPA) for soil fertility evaluation were selected to measure metal concentrations of three different wetland soils/spoils. Soil samples were collected from the constructed wetland cells which were lined with Abernathy silt loam topsoil and two different mine spoil materials [collected from active coal strip‐mined sites in Alabama (pH 5.9) and Tennessee (pH 3.2)]. Mehlich 3 extracted the most zinc (Zn), iron (Fe), manganese (Mn), calcium (Ca), magnesium (Mg), potassium (K), sodiumm (Na), and aluminum (Al), while 0.1M HC1 extracted more cadmium (Cd), copper (Cu), and lead (Pb). Extractants followed the same trend in removing quantities of the metals from the three soil/spoil materials, with DTPA generally extracting the least amount of the metal (the trend was Mehlich 3 > 0.1N HCl > Mehlich 1 > DTPA). However, DTPA removed larger quantities of metals from Tennessee spoil compared to Alabama spoil and topsoil, suggesting the higher effectiveness of DTPA under acidic conditions. Metal concentrations in plant tissue did not show a definite trend in correlation with metals extracted by the four chemical extractants.     

Effect of Application of Chromium Feedstock Compost on the Growth and Bioavailability of Some Trace Elements in Lettuce

A pot experiment was conducted to investigate the effect of chromium compost (0, 10, 30, and 50%) on the growth and the concentrations of some trace elements in lettuce (Lactuca sativa L.) and in the amended soils. Compost addition to the soil (up to 30%) increased dry matter yield (DMY); more than 30% decreased DMY slightly. The application of compost increased soil pH; nitric acid (HNO₃)–extractable copper (Cu), chromium (Cr), lead (Pb), and zinc (Zn); and diethylenetriaminepentaacetic acid (DTPA)–, Mehlich 3 (M3)–, and ammonium acetate (AAc)–extractable soil Cr and Zn. The addition of Cr compost to the soil increased tissue Cr and Zn but did not alter tissue cadmium (Cd), Cu, iron (Fe), manganese (Mn), nickel (Ni), and Pb. The Cr content in the lettuce tissue reached 5.6 mg kg^?1 in the 50% compost (326 mg kg^?1) treatment, which is less than the toxic level in plants. Our results imply that compost with high Cr could be used safely as a soil conditioner to agricultural crops.     

Evaluation of soil extractants to estimate available micronutrients under wheat‐field conditions

Abstract

Three extracting reagents were evaluated by correlation analyses to provide the best index of Zn, Cu, Mn and Fe availability to wheat (Triticum aestivum L.) plants growing under open field conditions. Twenty one soils were selected to obtain the widest range in properties of soils of the land wheat cultivated. The magnitude of the extractive power varied in the following order: 6NHCl ? EDTA + NH₄OA_C, pH4.65 > DTPA‐TEA, pH 7.3. The mild extractants, EDTA and DTPA, gave the same order of removal of micronutrients being Zn < Cu < Fe < Mn. The acid extractant was on the contrast more effective on Cu and Fe with respect to Zn and Mn, respectively. Wheat concentrations of Zn, Mn and Fe were significantly correlated to soil micronutrients. Highly significant relationships were found for Zn extracted by DTPA solution (r = 0.737***) and for Mn and Fe extracted by EDTA solution (r = 0.710*** and r = 0.564**). Plant Zn and Mn were also well predicted by the acid extraction. The absence of correlation for plant Cu vs. soil Cu occurred probably because of wheat concentrations almost constant, ranging from 5.0 to 8.0 mg/kg.     

Micronutrient Levels in Sugar Beet in Soils of Greece

A survey was conducted in order to estimate micronutrient levels in plants and soils of 215 farms in Greece cultivated with sugar beet. Soils were analyzed for particle-size distribution, pH, organic carbon (C), CaCO₃, and DTPA-extractable copper (Cu), zinc (Zn), iron (Fe), and manganese (Mn). Sugar beet leaves were analyzed for the same metals. Also, aboveground biomass (top), root, and raw sugar yields were recorded. DTPA-extractable Fe and Mn were above critical levels in all cases, whereas Cu and Zn were above critical levels in 49% and 24% of the soil samples, respectively. Concentrations of the four metals in plant tissue were similar or higher than the sufficiency range. Concentrations of DTPA-extractable Fe and Mn, and plant Zn and Mn, were significantly and negatively correlated with soil pH. Soil pH and DTPA-extractable Fe seemed to have a significant positive impact on root, top, and raw sugar yields. However, in all cases, less than 14% of the variance of the sugar beet parameters was explained by soil characteristics.     

Comparison of Three Micronutrient Soil-Test Extractants in Three Greek Soil Types

The purpose of the present study was to compare the ability of three micronutrient soil-test extractants [diethylenetriaminepentaacetic acid (DTPA), Mehlich 3, and Soltanpour and Schwab] to determine plant-available concentrations of manganese (Mn), iron (Fe), and zinc (Zn) in three soils (from parent material Marl, Gneiss schist, and Peridotite) from central Macedonia, northern Greece. In black plastic bags containing 3 kg of air-dried soil, self-rooted olive plants (cv. Chondrolia Chalkidikis) were grown for about 5 months and irrigated with distilled water during the experimental period. At the end of the experimental period, the three extractants were evaluated, based on correlation analysis among leaf micronutrient concentrations, total plant micronutrient content of olive plants, and soil micronutrient concentrations determined by each extractant. The largest extractable concentrations of Mn, Fe, and Zn were determined by Mehlich 3, compared to the other two soil-test extractants. However, for the correlation analysis, the greatest correlation coefficient between leaf Mn (and total plant Mn content) and soil extractable Mn was achieved when DTPA was used (varying from 0.76 to 0.88, depending on soil type). Therefore, it is concluded that DTPA was a better extractant to determine plant-available Mn than the other extractants for the three soils studied. For correlations between leaf Fe and Zn concentrations and also for total plant Fe and Zn content, and soil extractable concentrations, the type of extractant and soil type play a very important role in determining the best correlation. This means that in each soil type the greatest correlation was achieved with the use of other extractant. For example, for Fe in the Marl and Peridotite soils the best correlation was found for Mehlich 3, whereas in the Gneiss schist the best correlation was achieved for DTPA (R = 0.72–0.94). For Zn, in the Gneiss schist soil the best extractant in determining plant available concentration was Soltanpour and Schwab (R = 0.49–0.60), whereas in the other two soil types DTPA was found to be the most reliable extractant (R = 0.51–0.78). Therefore, soil type should be carefully and thoroughly studied by the researchers in similar future experiments.