Problem of Applying Sodium Selenate to Increase Selenium Concentration in Grassland Plants in Southern Belgium

In a survey of grasslands, mean selenium (Se) concentration in Holcus lanatus was 83 μg kg^?1 (less than 100 μg kg^?1, the minimal concentration protecting mammals from deficiency disorders). Despite rather high levels of soil extractable Se, plant Se availability was supposed to be low because of high soil humus concentration. A pot experiment with common grassland species showed contrasting responses to selenate addition (9 g Se ha^?1 yr^?1). Lolium perenne leaves reached 470 μg kg^?1, and Trifolium pratense reached 292 μg kg^?1. The controls were less than 100 μg kg^?1. Leaves of others species showed greater values both in control and treated series and no significant difference. In a second pot experiment, Melilotus albus, a supposed secondary accumulator, and Lolium perenne as a control were submitted to moderate increased selenate additions (up to 45 g Se ha^?1 yr^?1). The results confirmed that Melilotus albus was a better accumulator with a leaf concentration that could reach the toxicity level of 2 mg kg^?1.     

Protective Role of Selenium on Garlic Growth under Cadmium Stress

The stimulative action and detoxifying effect of selenium on garlic growth under cadmium stress were investigated. Selenite treatment can promote mitosis of garlic root-tip cells and growth of roots and seedlings. Garlic has a strong ability to accumulate the selenium from soil, and selenium content was greatest in garlic seedlings. Addition of selenite at a concentration of 2.0 μg kg^?1 in soil could decrease cadmium content in garlic and protect the seedling growth. The selenium has been shown to have an effective protective role on garlic growth under cadmium stress.     

Conservation of mineral nitrogen in restored soils at opencast coal mine sites: I. Results from field studies of nitrogen transformations following restoration

One of the characteristics of soils located within the cores of stockpile storage mounds at opencast mine sites is their accumulation of ammonium-nitrogen. Two areas of restored land were constructed from soil stockpiled for 3 years; one consisted of mound-surface (‘aerobic zone’) soil, and the other of deeply buried (‘anaerobic zone’) soil. In that constructed from mound-surface soil, concentrations of both ammonium- and nitrate-nitrogen remained fairly stable throughout the first 6 months of restoration at about 12–20 μg g^?1, but in the site constructed from deeply buried soil, concentrations of ammonium-N decreased from an initial high of 160 to 14 μg N g^?1 soil after 14 weeks, and increased again to 42 μg N g^?1 soil by week 29. In contrast, concentrations of nitrate-nitrogen at the latter site increased from an initial 9 μg to a maximum recorded level of 77 μg N g^?1 soil by week 14, before subsiding to 9 μg N g^?1 soil by week 29. Nitrate was considered to have been lost from the restored soils by a combination of leaching and denitrification, as no vegetation was established at these sites. After a short-term stimulation following restoration, soil microbial biomass levels remained fairly constant, though soils (up to 3 years after restoration) were characterized by a very small ratio of biomass C: organic C.     

Patterns of trace metal concentration and acidity in montane forest soils of the northeastern United States

Forest floor and mineral soil samples were collected from subalpine spruce-fir forests at 1000 m above mean sea level on 19 mountains in the northeastern United States to assess patterns in trace metal concentrations, acidity, and organic matter content. The regional average concentrations of Pb, Cu, and Zn in the forest floor were 72.3 (2.9 s.e.) μg g^?1, 8.5 (0.7) μg g^?1, and 46.9 (2.0) μg g^?1, respectively. The regional average concentrations of Pb, Cu, and Zn in the mineral soil were 13.4 (0.8) μg g^?1, and 18.2 (1.2) μg g^?1, respectively. The regional average pH values of the forest floor and mineral soil were 3.99 (0.03), and 4.35 (0.03), respectively. The Green Mountains had the highest concentrations of Pb (105.7 μg g^?1), and Cu (22.7 μg g^?1), in the forest floor. They also had the highest concentrations of Cu (18.0 μg g^?1), in the mineral soil. Site aspect did not significantly influence any of the values. Concentrations of Pb were lower than concentrations reported earlier in this decade at similar sites while concentrations of Cu and Zn remained the same. We believe that these lower Pb concentrations reflect real changes in forest Pb levels that have occurred in recent years.     

Selenium Behavior in Open Bulk Precipitation, Soil Solution and Groundwater in Alluvial Fan Area in Tsukui, Central Japan

A monitoring study was carried out in an alluvial fan area in Tsukui, Central Japan during the study period of 1999–2003, in order to explain selenium (Se) behaviors in ecosystem combined with air, soil and groundwater. Monthly Se concentrations in open bulk precipitation (rainfall+aerosol, gaseous deposition and etc.), soil solution (collected by porous ceramic-cup) and groundwater ranged from 0.1 to 1.4 μg L^?1 (volume-weighted average: 0.34 μg L^?1), 0.21 to 1.0 μg L^?1 (0.48 μg L^?1) and 1.6 to 2.4 μg L^?1 (2.2 μg L^?1), respectively. Se concentration in open bulk precipitation was negatively correlated with the rainfall amount. Se concentration in soil solution significantly increased with DOC concentration in soil solution. Besides, despite atmospheric Se input and rainfall to the grassland study area, Se concentration in soil solution and groundwater received no significant effect from the rainfall amount, pH, Se, DOC, SO₄ ^2?, NO₃ ^? and EC in rainfall. Even though Se concentrations in groundwater were significantly correlated with soil solution volume, Se, DOC and NO₃ ^? and groundwater level, the result of multiple regression analyses (MRA) indicated that the groundwater Se was negatively influenced by groundwater level, which depended on groundwater recharge. Se was transported into the groundwater through the groundwater recharge that largely increased in this alluvial fan study area after heavy rain.     

Estimation of the adenylate energy charge in unamended and amended agricultural soils

To determine relatively low concentrations of adenine nucleotides in agricultural soils a NaHCO₃-based extradant was developed and compared with the trichloroacetic acid-paraquat-phosphate extradant. The new medium, consisting of chloroform, sodium bicarbonate, phosphate and adenosine (pH 8.0) gave soil extracts which could be investigated without further neutralization and dilution. ATP was measured directly in the soil extracts by the luciferin-luciferase system. ADP and AMP were estimated after their enzymatic conversion to ATP by standard methods. The quantities of nucleotides corrected for recovery of standards were used to calculate the adenylate energy charge (AEC) from the formula AEC = [ATP] + 1/2[ADP]/[ATP] + [ADP] + [AMP], The AEC was estimated in six unplanted soils from agricultural fields. A very similar energy charge of 0.3-0.4 was found in all soils sampled which indicates a low metabolic activity of the soil population. Two other soils with a pronounced difference in biomass-C content were used to investigate the influence of different amendments on the AEC. In an experiment with low glucose supplements up to 500 μg C g^?1 soil, the soil with the low biomass-C (a cambisol) showed a distinct increase of the AEC from 0.34 to 0.50, whereas the soil with the high biomass-C content (a phaeozem) increased its AEC only slightly from 0.32 to 0.37. In another experiment with high glucose supplements the phaeozem reached its maximum AEC value of 0.56 after the addition of 4000 μg Cg^?1 soil. An amendment with 8000 μg C g^?1 soil gave no further increase. In the combisol the addition of 1000 μg C g^?1 soil increased the AEC to 0.61. Higher supplements gave only a slight further increase to a maximum value of 0.67 after the addition of 8000 μg C g^?1 soil. The same AEC value was reached when the cambisol was amended with a mixture of organic substrates at a concentration of 10,000 μg C g^?1 soil.     

稻米和土壤微量元素的空间变异

Consumption of rice is the main source of micronutrients to human in Asia. A paddy field with unknown anthropogenic contamination in Deqing County, Zhejiang Province, China was selected to characterize the spatial variability and distribution of micronutrients in rice grain and soil. A total of 96 paired soil and rice grain samples were collected at harvest. The micronutrients in the soil samples were extracted by diethylenetriamine pentaacetic acid (DTPA). The mean micronutrient concentrations in rice grain were 3.85 μg Cu g-1, 11.6 μg Fe g-1, 39.7 μg Mn g-1, and 26.0 μg Zn g-1. The mean concentrations were 2.54 μg g-1 for DTPA-Cu, 133.5 μg g-1 for DTPA-Fe, 30.6 μg g-1 for DTPA-Mn, and 0.84 μg g-1 for DTPA-Zn. Semivariograms showed that measured micronutrients in rice grain were moderately dependent, with a range distance of about 110 m. The concentrations of the DTPA-extractable micronutrients all displayed strong spatial dependency, with a range distance of about 60 m. There was some resemblance of spatial structure between soil pH and the grain Cu, Fe, Mn, and Zn. By analogy, similar spatial variation was observed between soil organic matter (SOM) and DTPA-extractable micronutrients in the soil. Kriging estimated maps of the attributes showed the spatial distributions of the variables in the field, which is beneficial for better understanding the spatial variation of micronutrients and for potentially refining agricultural management practices at a field scale.     

Forms of trace metals from inorganic sources in soils and amounts found in spring barley

Barley (Hordeum vulgare L.) was grown on a sandy soil given different doses of cadmium carbonate (salt), copper carbonate (malachite), lead carbonate (cerussite), and zinc carbonate (smithsonite) in a pot experiment conducted in a greenhouse. The element compounds were added to the soil in amounts equivalent to the following levels of the metals: Cd 5, 10, 50 μq ^?1; Cu and Pb 50, 100, 500 μg g^?1; Zn 150, 300, 1500 μg g^?1. Sequential extraction was used for partition these metals into five operationally-defined fractions: exchangeable, bound to carbonates, bound to Fe-Mn oxides, bound to organic matter and residual. The residue was the most abundant fraction in the untreated soil for all the metals studied (43 to 61% of the total contents). The concentration of exchangeable Cd (0.2 μg g^?1), Cu (0.01 μg g^?1), Pb (0.1 μg g^?1), and Zn (1.4 μg g^?1) were relatively low in the untreated soil but increased markedly in the treated soils for Cd (up to 31 μg g^?1) and Zn (up to 83 μg g^?1), whereas only small changes were observed for Cu and Pb. The pot experiment showed a significant increase in the Cd and Zn contents of barley grown on the treated soils, but only small changes in Cu and Pb concentrations.     

Effect of sodium chloride on CO2 evolution,ammonification, and nitrification in a Sassafras sandy loam

Sodium chloride, at rates up to 100 mg g^?1, was added to a Sassafras sandy loam amended with finely-ground alfalfa to determine the effect of NaCl on CO₂ evolution, ammonification, and nitrification in a 14-week study. A NaCl concentration of 0.25 mg g^?1 significantly reduced CO₂ evolution by 16% in unamended soil and 5% in alfalfa-amended soil. Increasing NaCl progressively reduced CO₂ evolution, with no CO₂ evolved from the soil receiving 100 mg NaCl g^?1. A 0.50 mg NaCl g^?1 rate was required before a significant reduction in decomposition of the alfalfa occurred. The NO^?₂-N + NO^?₃-N content of the soil was significantly reduced from 40 to 37 μg g^?1 at 0 and 0.25 mg NaCl g^?1, respectively in the unamended soil. In the alfalfa amended soil, nitrification was significantly reduced at 5 mg NaCl g^?1. At 10 mg NaCl g^?1, nitrification was completely inhibited, there being only 6 and 2 μg NO^?₂-N + NO^?₃-N g^?1 in the alfalfa amended and unamended soil, respectively. In the alfalfa amended soil NH⁺₄-N accumulated from 6 μg g^?1 at the 0 NaCl rate to a maximum of 54 μg g^?1 with 25 mg NaCl g^?1. These higher NH⁺₄-N values resulted in a 0.5 unit increase in the pHw over that of the 0 NaCl rate in the alfalfa amended soil. At NaCl concentrations above 25 mg g^?1 there was a reduction in NH⁺₄-N. The addition of alfalfa to the soil helped to alleviate the adverse affects of NaCl on CO₂ evolution and nitrification.     

Effects of pentachlorophenol on asymbiotic nitrogen fixation in soil

The effect of 50, 100, 150, and 400 μg sodium pentachlorophenate (Na-PCP) per gram soil was studied in nonsterile soil incubated under aerobic and anaerobic conditions, and in sterilized soil inoculated withAzotobacter sp. isolated from the soil. N₂ fixation was determined by acetylene reduction. Pentachlorophenate at a concentration of 50 μg g^?1 had an inhibitory effect in nonsterile soil incubated aerobically while strong inhibition of dinitrogen fixation in nonsterile soil occurred in the presence of 100 μg g^?1 and above. The EC₅₀ values for the inhibition of nitrogenase activity in nonsterile soil incubated aerobically and anaerobically and in sterilized soil inoculated withAzotobacter sp. suspensions were 49.8±1.4 μg Na-PCP g^?1, 186.8±2.8 μg Na-PCP g^?1, and 660.8±29.3 μg Na-PCP g^?1, respectively.     

土壤含硒量对玉米农艺性状、产量及籽粒硒含量的影响

在2个硒含量的土壤背景下,种植8个不同遗传背景的玉米品种,研究土壤硒含量对玉米品种的农艺性状、产量及硒含量的差异,结果表明:(1)土壤硒含量对玉米的株高、穗位、可见叶片数有增加效应,富硒区玉米的3个指标高于非富硒区,但富硒区的单产未能表现高于非富硒区。(2)供试品种的产量依次为康农玉108(7 822.6 kg/hm2)华玉11号(7 302.11 kg/hm2)双玉919(6940.47 kg/hm2)禾盛玉718(6860.41 kg/hm2)正大999(6 374.98kg/hm2)万玉168(5964.29kg/hm2)恩单804(5889.69kg/hm2)兴农单3号(5692.68kg/hm2)。(3)土壤硒含量对玉米籽粒的硒含量有促进作用,供试品种籽粒硒含量依次为:兴农单3号双玉919万玉168恩单804康农玉108正大999华玉11号禾盛玉718。     

Fluoride in bones of small rodents living in areas with different pollution levels

Bone fluoride concentration was measured in field voles (Microtus agrestis) trapped throughout a year at a moderately polluted site 1 km south of an Al reduction plant at Holyhead, Anglesey. Fluoride values ranged from 300 to 4800 μg g^?1, with a mean of 2074 μg g^?1 and increased with age as judged by dried eye-lens weight and body weight. At a heavily polluted site about 250 m from the pot-room of the reduction plant field voles had bone fluoride concentrations which ranged from 910 to 11000 μg g^?1 with a mean of 7148 μg g^?1. Wood mice (Apodemus sylvaticus) at this same location had a mean bone fluoride concentration of 8430 μg g^?1 and ranged from 1800 to 17 200 μg g^?1. The difference in mean bone fluoride concentration between these two species at this location was not significant (P > 0.1). A sample of field voles from presumed unpolluted sites in other parts of Britain had bone fluoride concentrations which ranged from 23 to 540 μg g^?1 with a mean of 168 jig g^?1. There was a high positive correlation (r > 0.97) between fluoride concentrations in different parts of field vole skeletons. There was no correlation between bone fluoride concentration in field voles and their femur diameters (r < 0.2).     

Bioaccumulation of Lead by Indian Mustard in a Loamy Sand Soil Artificially Contaminated with Lead: Impact on Plant Growth and Uptake of Metal

In a screen-house study, the effects of artificially contaminating the soil with lead (Pb) at levels ranging from 0 to 1500 mg kg^?1 soil on the growth and uptake of Pb and micronutrients by Indian mustard [Brassica juncea (L.) Czern.] grown on a loamy sand soil (Typic Ustorthent) were investigated. The crop was grown for 60 days with adequate basal fertilization of nitrogen, phosphorus, and potassium, and dry matter was recorded. The plants were analyzed for total Pb and micronutrients, and the soil was analyzed for diethylenetriaminepentaacetic acid (DTPA)-extractable Pb. The DTPA-extractable Pb measured before sowing of Indian mustard increased consistently and significantly with increase in rates of Pb application to soil. It increased from 0.65 mg kg^?1 in the control to 199.8 mg kg^?1 in soil treated with 1500 mg Pb kg^?1 soil. Significant reduction in the dry-matter yield of Indian mustard occurred with Pb applications of 500 mg kg^?1 soil and greater. The concentration as well as uptake of Pb by Indian mustard increased significantly over control at all rates of its application. It increased from 9.4 μg pot^?1 in the control to 220.6 μg pot^?1 at Pb application of 1500 mg kg^?1 soil. Applications of Pb to the soil decreased the concentration of micronutrients in plants, but a significant reduction occurred only for iron at rates greater than 500 mg Pb kg^?1 soil. However, the uptake of iron, manganese, and copper registered a significant decline at Pb application of 500 mg kg^?1 and greater and that of zinc at 750 mg kg^?1 and greater. In a Typic Ustorthent soil, a DTPA-extractable Pb level of 59.5 mg kg^?1 and plant content of 44.2 μg Pb g^?1 dry matter was found to be the upper threshold levels of Pb for Indian mustard. This study suggests that once the soil is contaminated by Pb, it remains available in the soil for a long time, and such soils, if ingested with food crops, may be a significant source of Pb toxicity to both humans and grazing animals.     

Effect of the herbicide fluazifop-butyl on fungal populations and activity in soil

The side effects of fluazifop-butyl on soil fungal populations and oxygen uptake were studied by incubating soil samples with a range of fluazifop-butyl concentrations (0, 0.6, 3 and 6 μg g^?1) over 8 weeks. Cellulose decomposition in soil was also studied in laboratory experiments with the herbicide which was either incorporated in soil or sprayed onto calico squares which were buried in soil. The mycelial dry weight of six fungal species under the effect of the herbicide was also examined. Fluazifop-butyl had no significant effect on total fungal propagule populations at 0.6 μg g^?1. At 3 and 6 μg g^?1, it caused temporary reduction in fungal populations observed after 1 and 2-wk of incubation. The herbicide had no significant effect on OZ uptake. The decay of calico buried in herbicide-treated soil was generally stimulated, while the decomposition of herbicide-treated calico, buried in untreated soil, was temporary delayed. The mycelial dry weight yields of Aspergillus favus (at 2 and 12 μg mL^?1 of fluazifop-butyl) and Cunninghamella echinulata (at 12 μg mL^?1) were significantly increased. At 24 μg mL^?1 the mycelial dry weight of A. flavus and Alternaria alternata was significantly reduced.     

Polycyclic Aromatic Hydrocarbons Content in Shoots and Leaves of Willow (Salix viminalis) Cultivated on the Sewage Sludge-Amended Soil

The aim of the present study was to investigate the uptake of 16 PAHs by willow (Salix viminalis) from soil amended with contaminated sewage sludge. Uptake experiments were conducted on field plots using sludge applications of 0, 30, 75, 150, 300, and 600 Mg ha^?1. The total PAH content of control soil and sludge were 49.6 μg kg^?1 and 5713 μ g kg^?1, respectively. The concentrations for the 16 PAHs listed as priority pollutants were measured for soil and plant tissue samples obtained at 0.5, 1.5, 2.5, and 3.5 years. Soil total PAH content decreased significantly within the first half year, followed by minimal changes over the subsequent three years of treatment. PAH analysis was carried out on a HPLC-UV. Total PAH content in control plants was 3.6–7.3 μ g kg^?1 for shoots and 13–27 μ g kg^?1 for leaves. Treated plant tissue content was higher with shoots and leaves containing ～5.5–17.6 and 13.5–33.8 μg kg^?1, respectively. Plant total PAH content did not show a significant trend relative to controls with respect to time. However, uptake did increase in relation to an increased sludge application. Bioconcentration factors (BCF), adjusted by control values, were calculated for total PAH content. BCF values were highest for the initial sampling (6 months) and did not show a significant temporal relationship. BCF values did decrease with increasing sludge application. With respect to individual PAHs, elevated plant tissue concentrations were measured for “light” PAH (e.g. naphthalene, phenanthrene, acenaphthalene) with leaf BCF values correlated with solubility and organic partitioning coefficients.     

The influence of variations in soil copper on the yield and nutrition of spinach grown in microplots on two organic soils

Abstract

Spinach (Spinacia oleracea L. cv. Symphony) was grown in spring 1982 in field microplots of an organic soil (site I a mucky peat) containing 81 to 1063 μg Cu.g^‐1 soil, and cv. America of the same crop taken in summer 1982 on a peaty organic soil (site II) varying in Cu content from 13 to 1659 μg.g^‐1. The variations in soil Cu were mainly due to three rates of Cu applications in 1978 at site II and in 1979 at site I. At site I, the diversity in soil‐Cu had no effect on yield or foliar‐Cu levels in the crop. At site II soil‐Cu was positively correlated with yield and foliar Cu; and negatively with leaf Fe due to a dilution effect. Neither soil Cu nor foliar Cu had any significant effect on Mo in leaves at both sites, except that the increase in yield due to the highest level of Cu at site II was accompanied by an increased plant uptake of Mo. Also, foliar Cu was positively correlated with P, Mg and Mn levels in leaves at site I; and foliar Ca, Mg and Mn at site II.

Residual soil Cu up to 1063 μg.g^‐1 in a mucky peat and 16 59 μg.g^‐1 in a peat showed no signs of causing phytotoxocity or significant nutritional imbalance.     

Effects of nitrogen dioxide on selected soil processes

Nitrogen dioxide gas was rapidly absorbed by soil. After a 15 min incubation at 25°C, soil at a moisture content of 16% absorbed 99% of the NO₂ introduced into the gas-phase volume of a closed system. The presence of microorganisms hatl no influence on the rate of absorption of the gas by soil. The absorption of NO₂ by sandy clay loam soil was not an oxygen- or temperature-dependent process nor did it depend upon the moisture content of the soil. These physical factors acquired significance only in determining the initial rate of absorption of the gas and the rate at which NO₂ diffused through the soil. Exposure of soil to NO₂ resulted in substantial increases in the levels of NO _inf2 ^sup? N in the soil. Chemical oxidation of the NO _inf2 ^sup? N resulted in an increase in NO _inf3 ^sup? N levels. During a 14-day incubation, NO _inf2 ^sup? N concentrations in sterile soil exposed to an atmosphere containing 100 μg ml^?1 of NO₂ decreased from 190 μg g^?1 of soil to 105 μg g^?1 with an accompanying increase in NO _inf3 ^sup? N from 2 μg g^? ₁ to 63 μg g^?1 of soil. Nitrogen dioxide severely inhibited the growth of both aerobic and anaerobic asymbiotic N₂-fixing bacteria in soil. After a 48 h incubation at 25°C, soil aggregates exposed to an atmosphere containing 100 μg ml^?1 of NO₂ contained 88% and 98% fewer aerobic and anaerobic N₂-fixing bacteria, respectively. C₂H₂-reduction measurements showed that nitrogenase synthesis and activity in artificial soil aggregates amended with 2% glucose were inhibited by 20% and 48%, respectively, when exposed to atmospheric concentrations of 35 and 3.5 μg ml^?1 of NO₂, respectively.     

Boron toxicity of strawberry

Abstract

Radlands Crimson strawberries were grown in a glasshouse with 7 rates of applied boron. Wood shavings mulches with different boron concentrations were also applied as separate treatments. Boron toxicity symptoms were produced in leaves by boron rates of 0.32 kg ha^‐1 and greater on a soil containing 1.6 ug B g^‐1 of hot water extractable boron. Concentrations greater than 123 μg B g^‐1 in old leaves were associated with boron toxicity symptoms.

In the B rate experiment, soil boron concentrations greater than 1.9 μg B g^‐1 soil were associated with leaf toxicity symptoms which increased in severity with increasing soil boron concentrations up to 4.1 μg B g^‐1 soil. Wood shavings mulch containing 17 μg B g^‐1 caused boron toxicity symptoms in older leaves whereas mulches containing less than 6 μg B g^‐1 did not produce toxicity symptoms.     

Nitrous oxide emission as affected by alternate anaerobic and aerobic conditions from soil suspensions enriched with ammonium sulfate

The effect of several anaerobic and aerobic cycles of varying duration on N₂O emission and labelled N loss was investigated in (¹⁵NH₄)₂SO₄ amended soil suspensions. No N₂O was evolved from the continuously-anaerobic treatment. The continuously-aerobic treatment produced approximately 0.8 μg N₂O-N g^?1 dry soil in 56 days. Alternate anaerobic-aerobic cycles increased the net N₂O evolution with 7.2 μg N₂O-N g^?1 dry soil produced in 56 days from the 7-day anaerobic, 7-day aerobic treatment. The net N₂O evolution increased further when the duration of the anaerobic and aerobic periods was increased from 7-7 days to 14-14 days (15.7μg N₂O-N g^?1 dry soil in 56 days), although the total ¹⁵N loss from the system was approximately the same for the two treatments. The results of this study show that N₂O evolution from soils is likely to be greater under fluctuating moisture conditions than under either continuously well-aerated conditions, or continuously excess-moisture conditions.     

Effect of elevated concentrations of Cd and Zn in soil on spring wheat yield and the metal contents of the plants

The effect of increasing concentrations of Cd and Zn in a sandy soil on spring wheat (Triticum vulgare L.) yields and the metal contents of the plants was examined in a pot experiment to establish critical levels of these metals in soil. The metals were added (individually and jointly) to the soil as sulfates in the following doses (in μg g^?1, dry wt.): Cd — 2, 3, 5,10, 15, 25, and 50; Zn ?200, 300, 500, 1000, 1500, 2500, and 5000. Cadmium added to soil did not affect yields of wheat. The Zn dose of 1000 μg g^?1 strongly reduced crop yields; at 1500 μg g^? Zn dose wheat did not produce grain. The metal contents of wheat increased with increasing concentrations of Cd and Zn in soil up to 10.3 and 1587 μ g^? of Cd and Zn in straw, respectively. The concentrations of both metals were higher in straw than in grain by factors of 3–7 and 1.5–2 for Zn and Cd, respectively. The relationships between Cd and Zn contents of the plants and soils were best expressed by exponential equations. High concentrations of Zn in soils (1042 and 1542 μg g^?1) enhanced uptake of Cd by plants. The tested threshold concentrations of the metals in soils (3 μg g^?1 for Cd and 200–300 μg g^?1 for Zn) are safe for Zn but are too high for Cd in terms of protecting plants from excessive metal uptake. The critical Cd content of sandy soil should not exceed 1.5 μg g^?.