Availability of Cu,Zn and Mn in soils: I.—Influence of soil pH,organic matter,and extractable phosphorus

Samples from Ap horizons of 36 cultivated Wisconsin fields were tested for concurrent availability of Cu, Zn and Mn. The effects of soil pH, organic matter, and available P were evaluated by using four chemical extract ants. Oats were used as the test crop and were grown using a self-watering pot-culture technique in a plant-growth room. The divergent soils had the following averages: pH, 6–4; organic matter, 2–6%; available P, 37 ppm; total Cu, 20 ppm; total Zn, 35 ppm; and total Mn, 631 ppm. Concentrations of the micronutrient elements in plants and soils were determined by atomic absorption spectrophotometer. NPK fertilisation resulted in greater plant uptake of Cu, Zn and Mn. Significant interactions between the soil properties and the different chemical fractions influenced the plant uptake of each micro-element; interactions between Cu, Zn and Mn in the same chemical fraction also influenced their individual uptake. Copper uptake was best predicted by inclusion particularly of soil pH, or the same chemical fractions of Zn and Mn in the regression equation; Zn uptake by inclusion of soil organic matter and available P, Mn uptake, or the chemical fractions of Cu and Mn; and Mn uptake by inclusion of available P, Cu chemical fraction, or Zn uptake in the equation. The extractants N ammonium acetate (pH 7) 10 · 01 M EDTA and 0·1 N -HCI show promise in soil tests for the simultaneous availability of Cu, Zn and Mn.     

Comparison of chemical tests for estimation of the availability of soil zinc

Tests for determining the availability of soil Zn were evaluated by simple and multiple correlation analysis. The soil tests included total Zn, and Zn extractable from soil by 0.2 M MgSO₄, 0.1 N HCl or dithizone. In simple correlation analyses, each of the tests correlated significantly with the uptake of soil Zn by maize (Zea mays L.) plants grown in the glasshouse. The predictions were improved significantly with all tests by the inclusion of one or more of the soil variables, pH and clay and organic matter contents, in multiple correlation analyses. The plant uptake of soil Zn could best be predicted from a multiple regression equation which included soil pH and logarithmic functions of 0.1 N HCl-extractable Zn and soil clay content as the independent variables.     

A comparison of various extractants for the estimation of extractable zinc in cacao-growing soils of south-western Nigeria

Forty-six soil samples from cacao plantations located in South-western Nigeria were analysed for extractable zinc by four methods, namely, ammonium acetate, dilute hydrochloric acid, magnesium chloride and diethylenetriamine pentaacetic acid (DPTA). Guinea corn (sorghum) was grown as a test crop. Relations among soil test methods, plant zinc uptake, and soil properties were examined by simple and multiple correlation analyses. The Zn extracted was in the following order: 1.0N NH₄OAc>0.1N HCl>2N MgCl₂>0.005M DTPA. The only correlation between extracts that was significant at the 5% level was between NH₄OAc and DTPA extractable Zn. No soil properties except iron and aluminium oxide were significantly correlated with soil test values. Silt, clay and silt plus clay were correlated at 5, 5 and 1% respectively with Zn uptake, but pH was not. Zinc uptake by the plant was more closely correlated with 2N MgCl₂ extractable Zn (r=+0.389) than with 1N NH₄OAc extractable Zn (r=+0.291); 0.1N HCl extractable Zn (r=+0.079); or with DTPA extractable Zn (r=+0.220). The best prediction of uptake by plants was observed in multiple regression analyses involving combination of MgCl₂ extractable Zn, pH, organic matter, and silt plus clay fraction (r=+0.601).     

Availability of Cu,Zn and Mn in Soils: III.—Predictability of plant uptake

The influence of various chemical soil fractions Of Cu, Zn and Mn in conjunction with plant uptake of any one or two of the elements on the variability of plant uptake of one of them was evaluated by correlation and regression analyses. Plant and soil data were obtained from divergent Wisconsin soils. Inclusion of Zn uptake and the HCl-or EDTA-extractable soil Cu fraction in the regression equation resulted in very high predictability of Cu uptake by oats. High predictability of Zn uptake was likewise realized by using the Mg(NO₃)₂ or DTP A soil Zn fraction along with plant Cu uptake as determinants. Manganese uptake was best predicted by using plant Zn uptake and Mg (NO₃)₂-rextractable soil Mn as predictors. The extractant N ammonium acetate (pH 7)/0·01 M EDTA showed promise as a reliable soil test for predicting the concurrent plant availability of Cu, Zn and Mn in Wisconsin soils.     

Extractability and bioavailability of zinic,nickle, cadmium and copper in three Danish soils sampled 5 years after application of sewage sludge

Soils from three Danish experiments testing identical quantities of sewage sludge were sampled 5 years after the application of sludge ceased. Chemical studies on the soils involving single and sequential extractions, displaced solution measurements and plant uptake experiments in a glasshouse showed that sludge-added Zn, Ni, Cd and Cu persisted in extractable and bioavailable forms in the topsoils and that soil pH and texture influenced their chemistry and availability. The EDTA-extractabilities of native and of sludge-added Cd were similar, but native Zn, Ni and Cu were less extractable than sludge-added metals. 0.1 M-calcium chloride was the best extractant for predicting plant uptake. In some cases a chelating extractant combined with pH measurements is suitable if a single reagent is to be used for all four metals.     

An appraisal of currently used soil tests for available copper with reference to deficiencies in English soils

Eight soil tests for plant-available copper were used on twenty English soils of moderate to low copper status. The ability of these tests to predict plant copper uptake, tested in a pot trial, was compared using multiple regression analysis including other soil factors such as pH, organic matter and clay content. The EDTA soil test was found to give the best prediction of plant uptake from a regression equation including EDTA extractable soil copper, pH, free Mn and Fe oxide, clay and organic matter content.     

The effects of plants on the mobilization of Cu and Zn in soil columns

Whereas metal effects on plants have been well studied, much less is known about plant effects on metal mobilization in soils. We investigated metal mobilization and speciation with a resolution of a few cm in soil columns planted with willows (Salix viminalis). In the presence of plants, the concentration profiles of dissolved organic carbon (DOC), major ions (e.g., Ca), Cu, and Zn exhibited more variation than in the absence of plants, and both smaller and larger concentrations were observed, indicative of strong local effects. The Cu concentration in the absence and presence of plants was controlled by DOC mobilization and could be described by the same relationship. Zn mobilization was controlled by DOC and Ca in the plant-free system and by pH and Ca in the presence of plants. Cu2+ and labile Zn were reasonably well predicted by the NICA-Donnan model and were influenced by the plant-induced changes of the soil solution composition. Plant uptake reduced the dissolved Zn concentration and transpiration reduced Cu and Zn leaching.     

信阳茶区土壤有效态微量元素含量状况

目的对信阳毛尖茶5个主产区茶园土壤pH、有机质和有效态Zn、Cu、Mn、B和Fe的含量进行调查和分析,为茶园合理施肥提供借鉴。方法分别采用pH计、元素分析仪和等离子体光电直读光谱仪对土壤的pH、有机质和微量元素的含量进行测定。结果信阳毛尖茶5个主产区茶园土壤pH值总体偏酸性,有机质平均含量低于15 g/kg,且地域差异较大。土壤有效态Zn的平均含量处于中等水平,空间分布很不均匀。其中,罗山县和浉河区茶园土壤有效态Zn的含量在中等及中等以上的分别占100%和99.08%,而光山县和新县茶园仅为15.39%和1.92%。土壤有效态土壤Mn和B的含量极其缺乏,均低于土壤缺素临界值,而有效态Fe含量极其丰富。茶园土壤pH值与有效态的Zn和Fe含量呈极显著负相关性,与有效态的Cu、Mn和B的含量呈极显著正相关性;土壤有机质含量和有效态Zn、Cu和Fe的含量呈正相关,与有效态Mn和B呈负相关性。结论信阳毛尖茶茶园需要增施有机肥,同时还要增施Zn、Cu、Mn和B微肥。     

毕节地区植烟土壤有效态微量元素含量评价

对毕节地区298个植烟土壤样品的有效态微量元素Cu、Zn、Fe、Mn、B和Mo的含量及丰缺特性进行了分析,以期为毕节烟区平衡施肥及提高烟叶品质提供依据。试验结果表明,毕节地区植烟土壤中有效态Cu、Fe、Mn含量极丰富,Zn含量丰富,有效硼和有效钼的含量比较缺乏,超过1/2的土壤缺硼,超过2/5的土壤缺钼。土壤中有效态Zn、Fe和Mn的含量与pH呈显著性负相关,有效钼含量与pH呈显著性正相关。土壤中有效Fe、Zn、Mn和B的含量与有机质含量呈显著性正相关。综上所述,毕节烟区要适当补充B肥和Mo肥,对Cu、Zn、Fe和Mn等元素要通过控制施入量或土壤改良来降低其有效含量,防止土壤重金属污染。     

Solid-solution speciation and phytoavailability of copper and zinc in soils

The soil solution speciation and solid-phase fractionation of copper (Cu) and zinc (Zn) in 11 typical uncontaminated soils of South Australia were assessed in relation to heavy metal phytoavailability. The soils were analyzed for pH (4.9-8.4), soil organic matter content (3.5 to 23.8 g of C kg(-1)), total soil solution metal concentrations, Cu8 (49-358 microg kg(-1)) and Zn8 (121-582 microg kg(-1)), and dissolved organic matter (DOM) (69-827 mg of C L(-1)). The solid-liquid partition coefficient (Kd) ranged from between 13.9 and 152.4 L kg(-1) for Cu and 22.6 to 266.3 L kg(-1) for Zn. The phytoavailability of Cu and Zn could be predicted significantly using an empirical model with the solid-phase fractions of Cu and Zn, as obtained from selective sequential extraction scheme, as components. Phytoavailable Cu and Zn were found to significantly correlate with fulvic complex Cu (r= 0.944, P < 0.0001) and exchangeable Zn (r = 0.832, P = 0.002), respectively. The fulvic complex Cu was found to explain 89.2% of the variation in phytoavailable Cu, where as, the exchangeable Zn together with fulvic complex Zn could explain 78.9% of the variation in phytoavailable Zn. The data presented demonstrate the role of solid-phase metal fractions in understanding the heavy metal phytoavailability. The assessment of the role of solid-phase fractions in heavy metal phytoavailability is a neglected area of study and deserves close attention.     

Fractions affected and probabilistic risk assessment of Cu, Zn, Cd, and Pb in soils using the free ion approach

The free ion approach quantifies the toxic effects of cationic metals on soil biota as a function of chemistry. The approach is here extended to calculate the general relationship among toxic effects as the Fraction Affected (FA), soil solution pH, and soil organic matter content (SOM) for Cu, Zn, Cd, and Pb within toxicity data sets from literature. The dependence of FA on SOM is strong, with the FA decreasing as the SOM increases. The dependence of FA upon pH varies; Cd and Zn show strong dependences while for Cu and Pb dependences are weaker. The FA usually decreases as the soil pH increases. When the free ion approach is applied, risks across soils due to different metals can be compared using the FA. The free ion approach may also be applied to probabilistic risk assessment. Risk values, using the joint probability curve approach, were derived for Pb using two field soil data sets. One data set, with higher SOM than that of the Pb toxicity data set, gave a lower risk with the free ion approach than that when the soil chemistry was not considered. The other data set had lower SOM than that of the toxicity data set and gave a higher risk with the free ion approach. Since literature toxicity tests are biased toward low SOM soils of circumneutral pH, using such data to perform classical risk assessment for soils of differing chemical composition can lead to misestimation of risk due to neglecting soil chemistry, especially in soils with extreme pH and/or SOM.     

Uptake of metals during chelant-assisted phytoextraction with EDDS related to the solubilized metal concentration

The use of chelants to enhance phytoextraction is one method being tested to make phytoextraction efficient enough to be used as a remediation technique for heavy metal pollution in the field. We performed pot experiments with sunflowers in order to investigate the use of the biodegradable chelating agent SS-EDDS for this purpose. We used singly and combined contaminated soils (Cu, Zn) and multimetal contaminated field soils (Cu, Zn, Cd, Pb). EDDS (10 mmol kg(-10 soil) increased soil solution metals greatly for Cu (factor 840-4260) and Pb (factor 100-315), and to a lesser extent for Zn (factor 23-50). It was found that Zn (when present as the sole metal), Cu, and Pb uptake by sunflowers was increased by EDDS, butin multimetal contaminated soil Zn and Cd were not. EDDS was observed in the sunflower roots and shoots at concentrations equal to metal uptake. The different metal uptake in the various soils can be related to a linear relationship between Cu and Zn in soil solution in the presence of EDDS and plant uptake, indicating the great importance of measuring and reporting soil solution metal concentrations in phytoextraction studies.     

Modeling kinetics of Cu and Zn release from soils

Kinetics of Cu and Zn release from soil particles was studied using two surface soils with a stirred-flow method. Different solution pH, dissolved organic matter (DOM) concentrations, and flow rates were tested in this study. A model for kinetics controlled sorption/desorption reactions between soils and solutions was globally fit to all experimental data simultaneously. Results were compared to a model that assumes local instantaneous equilibrium. We obtained one unique set of model parameters applicable to different pH, dissolved organic carbon (DOC), and flow conditions. We included DOM complexation of copper ions, which decreased their sorption. The effect of pH was included by assuming proton competition with metal ions for binding sites on soil particles. These results provide the basis for developing predictive models for metal release from soil particles to surface waters and soil solution.     

Use of diffusive gradients in thin films (DGT) in undisturbed field soils

The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal bioavailability in soils under laboratory conditions. In this study we used DGT to investigate the resupply kinetics of Cu and Zn under in-situ conditions in a polluted lysimeter soil and compared the results with laboratory measurements using undisturbed soil cores at defined water contents as well as homogenized soil samples. Results differed considerably between these treatments, although the same soil material was used in all experiments. A small pool of rapidly available Zn was found in the field but not in the homogenized soil. Soil solution pH and dissolved metal concentrations also varied significantly between the soil treatments. In addition, we compared the DGT-measured effective concentration with the uptake of Cu and Zn into the shoots of Lolium perenne (Ryegrass) under the same three types of conditions, i.e., field, soil cores, and homogenized soil. A close relationship was found which was not linear but could be described by a saturation-type behavior. L. perenne is a metal excluder plant, and thus, metal accumulation is limited by translocation of metals from roots to shoots. DGT predicted plant metal uptake much better than the soil solution concentration or pH. The results of this study suggest that DGT may be successfully used under field conditions to study the kinetics of metal resupply. Plant metal concentrations were not well predicted in all cases by the effective concentration CE under field conditions. Some plants took up considerably more metals than estimated by CE. Variations in metal uptake independent of their bioavailability can be caused by local variations in microsite conditions, e.g. light, temperature, water, and nutrients. To some degree, such indetermination has to be expected as an inherent feature of the system and the concept of bioavailability.     

Complexation of copper(ll) in organic soils and in dissolved organic matter--EXAFS evidence for chelate ring structures

Associations with functional groups of natural organic matter (NOM) are of great importance for bioavailability, toxicity, and mobility of trace metals in soils and waters. In this study, the coordination chemistry of copper, Cu(ll), in organic soils and dissolved organic matter (DOM) from soils and streams was investigated by extended X-ray absorption fine structure (EXAFS) spectroscopy. In both soil organic matter (SOM) and DOM (990-11 000 microg Cu g(-1) dryweight, pH 2.8-6.3), Cu(ll) was coordinated by 4 oxygen/ nitrogen (O/N) atoms at a distance of 1.92-1.95 angstroms in the first coordination shell. These four atoms are positioned in the equatorial plane of a Jahn-Teller distorted octahedron. In samples with a pH of 4.8-6.3, a second coordination shell with 2.0-3.8 C atoms was located at a distance of 2.76-2.86 angstroms. A significant improvement (19-39%) of the fit was obtained by including a third coordination shell with 2.0-3.8 O/C atoms involved in single scattering at an average distance of 3.69 angstroms and multiple scattering at an average distance of 4.19 angstroms. Our results provide evidence for inner-sphere complexation of Cu(ll) in NOM and suggest that Cu(ll) is complexed by either one or two five-membered chelate rings involving possible combinations of amino, carboxyl, or carbonyl functional groups. Ion activity measurements showed that less than 0.2% of total Cu was in the form of free Cu2+ in our samples at pH 4.8-6.3.     

Interactions between soil and fertiliser in the supply of nitrogen to ryegrass grown on 21 soils

Perennial ryegrass (Lolium perenne L.) was grown in pots on 21 UK soils, both with and without fertiliser N. The fertiliser N was applied in six equal applications of ¹⁵N-labelled ammonium nitrate, each at the rate of 120 mg N per pot. The first application was mixed thoroughly with the soil, while subsequent applications were made in solution to the soil surface, after each of the first five of the six harvests of herbage. In the absence of fertiliser N, the proportion of the total soil N taken up by the plants, including stubble and roots at the sixth harvest, varied between 1.5 and 4.0%. In the presence of fertiliser N, the proportion varied between 2.1 and 4.7%. The apparent recovery of the fertiliser N was calculated from the difference between the amounts of N in the plants that received fertiliser N and in those that did not, expressed as a percentage of the amount applied. The actual recovery of the applied fertiliser N was determined by analysis of the plant material for ¹⁵N. With all soils at the first harvest, the apparent recovery was greater than the actual recovery. When calculated over all six harvests, apparent recovery of the total amount of fertiliser N was generally close to the actual recovery. This difference from the first harvest probably reflected (i) a reduction in the extent of turnover between fertiliser N and soil N when the fertiliser N was applied to the surface and (ii) a virtually complete uptake of available soil N by the end of the experiment, in both the absence and presence of fertiliser N. Differences between the 21 soils in actual recovery were not closely related, either positively or negatively, to a range of measured soil properties. A mean of 17.2% of the labelled fertiliser N was retained in the soil (excluding visible roots) at the end of the experiment. The lowest retention (6.2%) occurred with the soil which had the lowest contents of organic matter and silt plus clay but, with the other soils, the extent of retention varied only between 14.7 and 22.0% of that applied, and was not closely related to contents of total organic matter or macro-organic matter, or to the C:N ratio of the whole soil or the macro-organic matter.     

Solid-solution partitioning of Cd, Cu, Ni, Pb, and Zn in the organic horizons of a forest soil

We report the solid-liquid partitioning of Cd, Cu, Ni, Pb, and Zn in 60 organic horizon samples of forest soils from the Hermine Watershed (St-Hippolyte, PQ, Canada). The mean Kd values are respectively 1132, 966, 802, 3337 and 561. Comparison of those Kd coefficients to published compilation values show that the Kd values are lower in acidic organic soil horizons relative to the overall mean Kd values compiled for mineral soils. But, once normalized to a mean pH of 4.4, the Kd values in organic soil horizons demonstrate the high sorption affinity of organic matter, which is either as good as or up to 30 times higher than mineral soil materials for sorbing trace metals. Regression analysis shows that, within our data set, pH and total metal contents are not consistent predictors of metal partitioning. Indeed, metal sorption by the solid phase must be studied in relation to complexation by dissolved organic ligands, and both processes may sometime counteract one another.     

Evaluation of growth activity of microbes in tea field soil using microbial calorimetry

Calorimetry was used to study the heat evolution associated with microbial growth in tea field soils (growth thermograms) during the microbial degradation of added organic matter. From the actual heat evolution curves (f(t) curves) derived from the growth thermograms under various conditions of pH and water content of the tea field soils, the apparent growth rate constant (mu') of soil microbes was determined as an index of their growth activity. In addition, mu' was compared between tea field soils treated with organic versus compound fertilizer. From the results, the following conclusions were made: (i) In acidic tea field soil (pH less than about 6.0), the growth activity of soil microbes declined with decreasing pH, and mu' was twofold higher at pH 6.0 than at pH 4.3. (ii) In tea field soils (Andosol) with a water content less than about 50%maximum water holding capacity (MWHC), the growth activity declined with decreasing water content, and mu' at 52.5%MWHC was double that at 35.2%MWHC. (iii) The growth activity of microbes in tea field soil treated with organic fertilizer was approximately 1.2-fold higher than that treated with compound fertilizer.     

Heavy metal concentrations and enzyme activities in soil from a contaminated Korean shooting range

Soil enzyme activities and heavy metal concentrations (Cd, Zn, Cu and Pb) were measured at a general shooting range in South Korea. Total heavy metal concentrations varied with pH, and were negatively correlated with moisture content and organic matter. Most enzyme activities (dehydrogenase, acid phosphatase and beta-glucosidase) and ATP values (measure of biomass) were lower in polluted soils, especially in bald spots contaminated by heavy metals and TNT (2,4,6-trinitrotoluene). These data indicate that concentrated shooting activity inhibits enzyme activity and microbial growth. Soil enzyme activities in richly vegetated spots around the general shooting range were higher (2- to 3-fold) than in bald spots, but lower in areas of heavy metal contamination. Our results demonstrate that the dominant plant species in richly vegetated spots accumulated heavy metals from soils, and suggest certain plants may be useful for decontaminating polluted soil.     

Extracellular polymeric substances from Bacillus subtilis associated with minerals modify the extent and rate of heavy metal sorption

Extracellular polymeric substances (EPS) are an important source of organic matter in soil. Once released by microorganisms, a portion may be sorbed to mineral surfaces, thereby altering the mineral?s ability to immobilize heavy metals. EPS from Bacillus subtilis were reacted with Ca-saturated bentonite and ferrihydrite in 0.01 M KCl at pH 5.0 to follow the preferential uptake of EPS-C, -N, and -P. The sorption kinetics of Pb(2+), Cu(2+), and Zn(2+) to the resulting EPS-mineral composites was studied in single and binary metal batch experiments ([metal](total) = 50 μM, pH 5.0). Bentonite sorbed much more EPS-C (18.5 mg g(-1)) than ferrihydrite (7.9 mg g(-1)). During sorption, EPS were chemically and size fractionated with bentonite favoring the uptake of low-molecular weight components and EPS-N, and ferrihydrite selectively retaining high-molecular weight and P-rich components. Surface area and pore size measurements by N(2) gas adsorption at 77 K indicated that EPS altered the structure of mineral-EPS associations by inducing partial disaggregation of bentonite and aggregation of ferrihydrite. Whereas mineral-bound EPS increased the extent and rate of Pb(2+), Cu(2+), and Zn(2+) sorption for bentonite, either no effect or a decrease in metal uptake was observed for ferrihydrite. The extent of sorption always followed the order Pb(2+) > Cu(2+) > Zn(2+), which also prevailed in binary Pb(2+)/Cu(2+) systems. In consequence, sorption of EPS to different minerals may have contrasting consequences for the immobilization of heavy metals in natural environments by inducing mineral-specific alterations of the pore size distribution and, thus, of available sorption sites.