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1.
Behaviour of heavy metals in soils. 1. Heavy metal mobility 158 soil samples with widely varying composition were analysed for their total, EDTA, DTPA and CaCl2 extractable contents of Cd, Zn, Mn, Cu and Pb. By means of single and multiple regressions the relations between the different heavy metal fractions and the pH, organic carbon and clay content were considered. The correlations between the total, EDTA and DTPA extractable contents are very close, whereas the CaCl2 extractable contents are not or only weakly correlated with these fractions. According to these statistical results the former fractions are considered to be the total quantity (total content) and the reactive quantity (EDTA and DTPA extractable contents) of the heavy metals, whereas the CaCl2 extractable fraction represents the mobile fraction of the heavy metals in soils. The multiple regressions show that the mobile content of heavy metals is closely correlated with each of the quantity fractions and with soil pH. In the same way the proportion of the mobile fraction (in %) of the total, EDTA and DTPA extractable heavy metal content of the soil samples is closely related to the soil pH. Hereby the proportion of the mobile content of the various elements increases in the pH range 6,5 - 3 below element-specific threshold pH values (in brackets) in the order Cd (6,5) > Mn (5,7) > Zn (5,3) > Cu (4,5) > Pb (3,5). In the pH range 6,5 - 7,5 mainly Cu and to a lesser degree also Pb show an increasing mobility due to the influence of soluble organic substances.  相似文献   

2.
Human exposure to toxic heavy metals via dietary intake is of increasing concern. Heavy-metal pollution of a rice production system can pose a threat to human health. Thus, it was necessary to develop a suitable extraction procedure that would represent the content of metal available to rice plants (Oryza sativa L.). The aim of this study was to predict, on the basis of single extraction procedures of soil heavy metals, the accumulation of heavy metals (cadium, lead, copper, and zinc) in rice plants. Six extracting agents [Mehlich 1, Mehlich 3, EDTA (ethylenediaminetetraacetic acid), DTPA–TEA (diethylenetriaminepentaacetic acid–triethanolamine), ammonium acetate (NH4OAc), and calcium chloride (CaCl2)] were tested to evaluate the bioavailability of heavy metals from paddy soils contaminated with lead–zinc mine tailings to rice. The extraction capacity of the metals was found to be of the order EDTA > Mehlich 3 > Mehlich 1 > DTPA–TEA > NH4OAc > CaCl2. The correlation analysis between metals extracted with different extractants and concentrations of the metals in the grain and stalk of the plant showed positive correlations with all metals. The greatest values of correlation coefficients were determined between the NH4OAc- and CaCl2-soluble fractions of soil and contents in plants in all four metals studied. Therefore, NH4OAc and CaCl2 were the most suitable extractants for predicting bioavailability of heavy metals in the polluted soils to rice. The results suggested that uptake of heavy metals by rice was mostly from exchangeable and water-soluble fractions of the metals in the soils. Soil-extractable metals were more significantly correlated with metal accumulation in the stalk than in the grain. The pH had more significant influence on availability of heavy metals in the soils than total content of metals and other soil properties. The bioavailability of metals for rice plants would be high in acidic soils.  相似文献   

3.
Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH4NO3) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH4NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘1 d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH4NO3. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.  相似文献   

4.
Abstract

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

5.
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 + NH4OAC, 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.  相似文献   

6.
Abstract

Eighteen soils from northwestern Switzerland were used to study the value of seven universal extractants (CaCl2; DB‐DTPA; Mehlich 1, 2, and 3; Morgan‐Wolf; and NH4OAc‐EDTA) for predicting plant available potassium (K) as compared to a bioassay (a modified Neubauer test with winter rye). These extractants were evaluated on the basis of K uptake by the bioassay test and the soil K status. In order to create the sufficiency level of exchangeable K for plant growth, soils were treated with 0, 20, 40, 80, and 160 mg K/kg of soil. The range of K uptake by the bioassay tests was between 89.2 and 403.0 mg/kg of soil for the control pots, and 136.6 to 495.8 for the K treatments with optimal conditions for plant growth. The average amounts of K extracted by the seven universal extractants, in ascending order, were: CaCl2 < Morgan‐Wolf < Mehlich 1 < Mehlich 2 < NH4OAc‐EDTA < Mehlich 3 < DB‐DTPA. The highest simple correlation with K uptake versus the bioassay test was obtained with the DB‐DTPA (r = 0.89) extractant and the lowest with the Mehlich 1 (r = 0.53) extractant. The DP‐DTPA, NH4OAc‐EDTA and Mehlich 3‐K procedures showed an advantage over K procedures based on water soluble and exchangeable K pools in the investigated soils in order to predict the amount of plant‐available K. A simple regression and the Cate‐Nelson graphic method offer the possibility of assessing the soil‐K status using K values obtained by these universal extractants and to calibrate them against K forms as follows: exchangeable, water soluble, and non‐exchangeable.  相似文献   

7.
Behaviour of heavy metals in soils. 2. Extraction of mobile heavy metals with CaCl2 and NH4NO3 156 soil samples from arable fields, grassland and forest stands were analysed for the CaCl2? and NH4NO3? extractable contents of Cd, Zn, Mn, Cu and Pb. The average amounts of Cd, Zn, Cu and Pb extracted with CaCl2 are higher compared with NH4NO3 whereas the relation for Mn is vice versa. The proportion of the NH4NO3? extractable contents in percent of the CaCl2? extractable contents of Cd, Zn and Pb decrease with increasing pH, whereas the contents of Mn and Cu increase. Inspite of a differing extraction behaviour of the two salt solutions the CaCl2? and NH4NO3? extractable amounts of Cd, Mn, Zn und Pb are highly correlated and can be converted one into another. The mobile (CaCl2, NH4NO3) proportion of the corresponding total, EDTA and DTPA heavy metal contents is in close relation to the pH of the soils. Using CaCl2 solution the threshold pH values for an increasing mobility decrease in the order Cd > Mn > Zn > Cu > Pb, using NH4NO3 as extractant the order is Mn > Cd > Zn > Cu > Pb. In the case of CaCl2 as extractant soluble chloro-Cd-complexes will be formed so that the Cd mobility in soils will be overestimated in most cases.  相似文献   

8.
Abstract

The accumulation of heavy metals in plants is related to concentrations andchemical fractions of the metals in soils. Understanding chemical fractions and availabilities of the metals in soils is necessary for management of the soils. In this study, the concentrations of copper (Cu), cadmium (Cd), lead (Pb), and zinc (Zn) in tea leaves were compared with the total and extractable contents of these heavy metals in 32 surface soil samples collected from different tea plantations in Zhejiang province, China. The five chemical fractions (exchangeable, carbonate‐bound, organic matter‐bound, oxides‐bound, and residual forms) of the metals in the soils were characterized. Five different extraction methods were also used to extract soil labile metals. Total heavy metal contents of the soils ranged from 17.0 to 84.0 mgCukg?1, 0.03 to 1.09 mg Cd kg?1, 3.43 to 31.2 mg Pb kg?1, and 31.0 to 132.0 mg Zn kg?1. The concentrations of exchangeable and carbonate‐bound fractions of the metals depended mainly on the pH, and those of organic matter‐bound, oxides‐bound, and residual forms of the metals were clearly controlled by their total concentrations in the soils. Extractable fractions may be preferable to total metal content as a predictor of bioconcentrations of the metals in both old and mature tea leaves. The metals in the tea leaves appeared to be mostly from the exchangeable fractions. The amount of available metals extracted by 0.01 mol L?1 CaCl2, NH4OAc, and DTPA‐TEA is appropriate extractants for the prediction of metals uptake into tea plants. The results indicate that long‐term plantation of tea can cause sol acidification and elevated concentrations of bioavailable heavy metals in the soil and, hence, aggravate the risk of heavy metals to tea plants.  相似文献   

9.
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 (Kd) 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 Kd (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 Kd, 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.  相似文献   

10.
Abstract

In order to evaluate the influence of extraction procedure on extractable nitrogen (N) fractions, fresh as well as dried soil samples were extracted with CaCl2 at various temperatures (20,40,60, 80°C) for 30–120 minutes. Data obtained were compared with those from the electro‐ultra‐filtration (EUF) method. Increasing the drying temperature as well as the extraction temperature led to an increase in Norg content. The EUF and CaCl2‐method produced comparable results for all N‐fractions (NO3 ‐, NH4 +, Norg) when an extraction temperature of 80°C was applied for two hours. Data presented suggested that the Norg fraction represented mainly the microbial biomass and may thus be considered as being easily available to plants.  相似文献   

11.
Abstract

Individual soil tests are used to assess plant nutrient element needs. Separate soil tests, however, are time consuming and costly. Our objective was to develop a 0.5M sodium bicarbonate (NaHCO3) soil phosphorus (P) test in combination with 0.005M diethylenetriaminepentaacetic acid (DTPA) so macronutrient dements: ammonium‐nitrogen (NH4‐N), nitrate‐nitrogen (NO3‐N), P, potassium (K), calcium (Ca), and magnesium (Mg); and micronutrients: iron (Fe), manganese (Mn), zinc (Zn), and copper (Cu) could be quantified in one extraction. The NaHCO3‐DTPA extracting solution is a combination of 0.5M NaHCO3 and 0.005M DTPA and has a pH of 7.60±0.05. Sodium in the solution enhances the NH4, K, Ca, and Mg extraction; bicarbonate (HCO3) is for P extraction; DTPA chelates Ca, Mg, and micronutrients; and the water is for NO3 extraction. Soil samples (0–15 cm depth) came from two sources. The first set was from 12 N x P dryland proso millet (Panicum miliaceum L.) experiments, conducted from 1985 through 1987 in eastern Colorado. These soils were extracted with potassium chloride (KCl), NaHCO3, ammonium acetate (CH3‐COONH4), DTPA, ammonium bicarbonate DTPA (AB‐DTPA), and with the NaHCO3‐DTPA solutions. The second set included 25 soils from Alabama, Georgia, North Carolina, and South Carolina and were analyzed only for available P with the NaHCO3 and NaHCO3‐DTPA methods. Simple linear correlations for macronutrient elements and micronutrients were highly significant. Critical levels for the macronutrient elements: NO3‐N, P, and K were 27, 11, and 144 mg kg‐1, respectively; and the critical levels for the micronutrients: Fe, Mn, Zn, and Cu were 3.9, 0.35, 0.97, and 0.24 mg kg‐1, respectively.  相似文献   

12.
In this study, complexation extractants ammonium bicarbonate diethylene triamine pentaacetic acid (AB-DTPA), diethylene triamine pentaacetic acid (DTPA), and ethylene diamine tetraacetic acid (EDTA) and mild cation-exchange extractants calcium chloride (CaCl2) and ammonium nitrate (NH4NO3) were used to evaluate the bioavailability of soil cadmium (Cd) to cacao in the field. Among the five extractants, the extractable Cd generally followed the order EDTA > DTPA > AB-DTPA > CaCl2 > NH4NO3. Correlation analysis was done between the extractable Cd in soil and total Cd content of cacao tissues (nibs, shells, leaves, and pods). The Cd extracted by CaCl2 and NH4NO3 was significantly (P < 0.05) correlated with some of the tissues but their Pearson correlation coefficients were weak. In contrast, extractants AB-DTPA, DTPA, and EDTA showed stronger, significant correlations to the Cd concentration in all four tissues. Overall, regression analysis demonstrated that AB-DTPA, DTPA, or EDTA can be used to predict bioavailable Cd in soils for cacao. Of these, AB-DTPA and DTPA both showed the strongest correlations compared to EDTA. However, the ease of preparation and the superior shelf-life of DTPA over AB-DPTA make it the preferred reagent for Cd bioavailability extractions from cacao soils and is currently being used to develop cost-effective soil treatments to reduce bioavailable Cd to cacao plants.  相似文献   

13.
Immobilization of metals by two materials (zeolite, AZ, and a synthetic, carbonate-rich material, “slovakite”, SL) was tested in a pot experiment with two soils from urban areas of Sevilla and two soils affected by a mine spill. Barley (Hordeum vulgare L. Hispanic) was grown in the pots, and metal contents were measured after 31 days in shoots and roots. Available metal was estimated by extraction with CaCl2 (readily soluble), ethylenediaminetetraacetic acid (EDTA; plant available), a mixture of organic acids (soluble by root exudates), and glycine (bioaccessible by ingestion). Neither treatment caused significant differences on plant growth or metal contents of shoots, whereas roots contained more Cu in the SL treatments. Root Zn uptake was reduced in all cases, but reduction of Pb in roots was observed only in AZ treatments of the mine-spill soils. The effects on metal availability were often method-dependent. Decrease of CaCl2 data were observed only in the mine-spill soils. EDTA-soluble metals were clearly decreased by both materials. Bioaccessible Zn were decreased by either material in several cases (but not in the most heavily polluted soil), whereas Cu or Pb data were less conclusive.  相似文献   

14.
Model experiments on the potassium release of soils with higher electric conductivities by electro-ultrafiltration (EUF) For investigations on the effects of higher ion concentrations in soils on results of EUF (electro-ultrafiltration), performed at constant current, a light soil (12% clay) was analyzed by adding increasing amounts of a NaCl solution to the soil slurry in the EUF middle cell. Recording the course of voltage and current through the EUF cell, it was found, that,
  • 1) a continuous decrease of electrode voltage occurs over extended time periods, when the electric conductivity of the soil was increased.
  • 2) As a function of this voltage decline, the potassium concentration in the EUF-20°C fraction was reduced, whereas in the EUF-80°C fraction higher amounts of potassium could be found.
  • 3) Unlike at very high levels of electric conductivity, the total K extraction by EUF was nearly unaffected, because losses in K content in the fraction EUF-20°C could be compensated by the fraction EUF-80°C.
  • 4) According to Németh and Ziegler (1988) the ratio of EUF-K-80°C to EUF-K-20°C should be between 0.1 and 0.2 for light, but about 0.6 for heavy soils. Under the influence of higher electric conductivities this figure for light soils, however, approached values for heavy soils.
  • 5) Also, the contents of magnesium and calcium showed marked decreases at higher electric conductivities in the EUF-fractions a and b (= EUF-20°C). Contrary to the total amount of extractable potassium, the total contents of magnesium and calcium, extract-able by EUF, were markedly decreased by higher electric conductivities in the light soil.
It is recommended, that the parameters voltage and current should be considered in interpretations of EUF-fractions from soils with higher levels of electric conductivity.  相似文献   

15.
Abstract

A study was carried out to investigate the status of four micronutrients, iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn), and five other trace elements, cobalt (Co), chromium (Cr), nickel (Ni), lead (Pb), and strontium (Sr), in paddy soils of Bangladesh. Soil samples were digested by hydrofluoric acid (HF)‐nitric acid (HNO3)‐perchloric acid (HClO4) for determination of total contents of the nine elements, while DTPA, ASI and 0.1 Mhydrochloric acid (HC1) methods were used for determination of available Fe, Cu, Mn, and Zn. Total trace element contents were found to vary with physiography on which soils are distributed. In general, Ganges Tidal Floodplain soils had the highest content, whereas terrace soils had the lower content. Among the soil properties examined, clay content had a good relation with total trace element contents in the topsoil, except for Sr. Based on the variation with physiography or clay content, the nine trace elements could be grouped into six groups: Cu, Fe and Zn, Pb, Co and Cr and Ni, Mn, Sr. According to the extractable levels of four micronutrients, Bangladesh paddy soils had the medium to optimum amounts of Fe and Cu, but were deficient sporadically in Mn and extensively in Zn. It was indicated that paddy soils of Bangladesh are yet to be polluted with heavy metals.  相似文献   

16.
Zinc was extracted from seven soils collected from Haryana state (India), representing the tropical region of the country, to predict the availability of Zn to crops. Weakly adsorbed Zn extracted by 0.05 M CaCl2 was almost negligible. Similarly 1 M MgCl2, designated to extract the lattice Zn, extracted small quantities of Zn indicating that no Zn was substituted for any other cation in clay lattice. Maximum zinc was extracted by chelating agents like DTPA and EDTA and were correlated significantly among themselves. None of the methods tested was significantly correlated to plant Zn indicating that in addition to crop requirement, other soil factors play a major role in determining the Zn availability. Equilibrium Zn values in all except a sandy soil, were less than 1 μg Zn/ml indicating the possibility of moderate to severe Zn deficiency in these soils.  相似文献   

17.
Abstract

A trial was carried out with compost and compost/peat mixtures to test several extraction methods for the estimation of availability of phosphorus (P). The test plant was Dendranthema grandiflorum All composts had a high pH and salt content. Amounts of P extracted by different extraction methods decreased in the order: Formate < CAL < NH4‐acetate < CaCl2/DTPA < CaCl2. Dilution of compost with peat decreased pH and increased availability of P. The better availability of P caused by dilution with peat was not reflected by the Formate‐, CAL‐, and NH4‐acetate method. These acid and well‐buffered extraction solutions overestimate P, and are therefore not suited to estimate availability of P in composts and compost/peat mixtures. Weak extraction solutions, like CaCl2 and CaCl2/DTPA, gave results which showed a good correlation with P content of plants and P uptake. The advantage of the latter method compared with CaCl2 is the extraction of amounts of P comparable to amounts taken up by the plants. Therefore of all the extraction methods tested, the CaCl2/DTPA method showed the best suitability to estimate the availability of P in composts and compost/peat mixtures.  相似文献   

18.
Abstract

A new soil test procedure using 1M NH4Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH4Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH4Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl2, NH4OAc, and NH4NO3, the 1M NH4Cl‐extracted Cd from soils was found to be a better index of Cd availability.  相似文献   

19.
Abstract

The suitability of the “iron‐impregnated paper‐strip”; (Pi) methodology for the assessment of phosphate (P) availability in soils has been tested on the basis of a comparison with the classical Olsen method as well as with the new‐generation electro‐ultrafiltration (EUF) and Mehlich No. 3 (M3) extraction procedure. The EUF extractions were performed by a first 30 min run at low (L) energy conditions (20°C, max 15 mA, and 200V), followed by a 10 min run at high (H) energy conditions (80°C, max 150 mA, and 400V). The total EUF‐P extracted (T‐EUF‐P), given by the sum L‐EUF‐P + H‐EUF‐P, was also considered. The investigation was carried out on twenty samples of representative Alfisols ("Terra Rossa") from the pedoclimatic environments of the Mediterranean area. The soil samples were characterized by a large variability of their available‐P values, whose ranges were, as mg‐kg‐1 soil, 0.1–34.0 for L‐EUF‐P, 0.2–39.3 for HEUF‐P, 0.3–73.3 for T‐EUF‐P, 0.8–113.6 for Olsen‐P, 1.0–122.4 for Pi‐P, 1.1–224.6 for M3‐P. The respective mean values were 4.6, 5.1, 9.6, 17.2, 20.1, and 29.7 mg P/kg soil, with ratios L‐EUF‐P:H‐EUF‐P:T‐EUF‐P:Olsen‐P:Pi‐P:M3‐P increasing as 0.27:0.29:0.56: 1.00:1.17:1.73. A good compliance among all methods was verified; the most significant correlations were determined for Pi‐P versus M3‐P (R2=0.993***) and for Pi‐P versus Olsen‐P (R2=0.988***), clearly indicating the liability of the Pi procedure for the assessment of the P fertility in Alfisols. A multiple linear regression analysis revealed that all the available P values, afar from the individual procedure, were significantly (P<0.01) dependent on M3 exchangeable iron (Fe) (positively) and aluminum (Al) (negatively). This could lead one to argue that the prevailing available soil P source in the investigated Alfisol samples was that connected with the labile Fe‐P pool. Withal, one could infer that the A1‐M3 and Fe‐M3 parameters should also be considered for the making of P fertilizer recommendations. From this standpoint, the M3 is a well‐proved multielement extractant suitable for the simultaneous determination of available P and exchangeable Fe and Al as well.  相似文献   

20.
Although Ni is officially recognized as an essential micronutrient for all higher plants, the majority of the published research on soil availability of Ni focuses on its hazardous role as a heavy metal. The objective of the study was to evaluate certain Ni soil tests in uncontaminated soils for an initial estimation of its sufficiency critical levels. Nickel was extracted from 30 cultivated soils employing the following extraction methods: DTPA, AB‐DTPA, AAAc‐EDTA, Mehlich‐3, 0.1 M HCl, and 0.1 M HNO3. Ryegrass (Lolium perenne L.) was grown in pots containing the soils, harvested five times, certain plant parameters were determined, and the Cate–Nelson procedures were used for Ni critical levels determination. Among the six methods, HCl was the least reliable extractant for the evaluation of soil available Ni, whereas the most significant (p ≤ 5%) relationships between Ni concentration or Ni uptake by ryegrass and Ni soil tests were consistently obtained for AAAc‐EDTA or Mehlich‐3 extractable Ni. In many cases, > 80% of the variability of Ni concentration or uptake by ryegrass was explained by these two soil tests without the inclusion of other soil properties that affect Ni bioavailability. Sufficiency critical levels of Ni in soil were ≈ 2 mg kg–1 for both methods. Consequently, as an initial approach, concentrations of AAAc‐EDTA or Mehlich‐3 extractable Ni < 2 mg kg–1 are probably a good guide to indicate soils that will respond to Ni fertilization.  相似文献   

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