Soil quality response to long-term wastewater irrigation in Inceptisols from a semi-arid environment

Thirty-nine paired soil samples belonging to Inceptisols, irrigated with wastewater and well water, were examined to monitor the combination of clay mineralogy, physicochemical properties, and trace metals (Zn, Cu, Cd, and Pb) following long-term wastewater irrigation. Results of XRD analysis indicated that the quantity of clay minerals did not change by long-term wastewater irrigation although some modifications in smectite were occurred in Fluvaquentic Endoaquepts compared to control (well water-irrigated soil). Irrigation with wastewater was resulted in an increase in clay content from 3 to 17%, EC from 90 to 160%, organic carbon from 13 to 44%, and CEC from 10 to 13%. In this context, improvement in total N was as 80–110%, available P as 270–330%, and available K as 5–50% as compared to the control soil. Irrigation with wastewater was led to a significant enrichment in both EDTA-extractable and total metals of Zn, Cu, Cd, Pb, mainly as result of the combination of their addition through wastewater along with interaction between the used wastewater and its receiving soils. In the light of this, wastewater irrigation system showed the relative enrichment (RE) for total-Zn, Cu, Cd, and Pb as 3.6–6.8, 2.8–4.9, 4.4–5.7, and 1.8–2.3, respectively. Fine particle-size fraction (<0.002 mm), organic matter, and calcium carbonates were appeared as the main agents in retaining the total trace metals as reflected in significant positive correlation among the physicochemical properties and the examined metals. Degree of contamination (C_d) for the four analyzed metals was in the range of 3–5. Based on C_d values, the wastewater-irrigated soils were classified as moderate degree of contamination (2 ≤ C_d < 4) to high degree of contamination (4 ≤ C_d < 8). Fluvaquentic Endoaquepts highlighted to be a major contributor of the load and contamination rate of trace metals regarding to geoaccumulation index, contamination factor, and Degree of contamination.     

Vertical distribution of heavy metals in wastewater-irrigated vegetable garden soils of three West African cities

Application of untreated wastewater to irrigate urban vegetable gardens is raising serious concern about possible health risks associated with the consumption of these vegetables particularly with regard to the concentrations of heavy metals (HM) in their edible portions. The soil concentrations of cadmium (Cd), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn), were investigated in seven vegetable gardens from the three West African cities of Kano (Nigeria), Bobo Dioulasso (Burkina Faso) and Sikasso (Mali). Also determined were input–output balances of Cd and Zn from five vegetable gardens under 30 years of wastewater irrigation in Kano. In these gardens Cd (2.3–4.8 mg kg⁻¹) and Zn (13–285 mg kg⁻¹) concentrations throughout the profile attained unsafe levels. The concentrations of Cu (0.8–18 mg kg⁻¹), Cr (1.8–72 mg kg⁻¹), Ni (0–17 mg kg⁻¹) and Pb (0.6–46 mg kg⁻¹) were below the safety thresholds for arable soils. Overall, concentrations of Zn, Cd, Pb and Ni were higher in Kano than in Bobo-Dioulasso and Sikasso. Input–output analyses in Kano indicated that irrigation wastewater contributed annually 400–3,700 g Cd ha⁻¹ and 7,200–22,300 g Zn ha⁻¹, fertilizer 30–2,100 g Cd ha⁻¹ 50–17,600 g Zn ha⁻¹, harmattan dust 0.02–0.4 g Cd ha⁻¹ and 40–200 g Zn ha⁻¹ while 300–500 g Cd ha⁻¹ and 2,700–4,700 g Zn ha⁻¹ came from rainwater inputs. Input–output calculations subtracting the amounts of HM taken out in vegetable biomass and that lost to leaching from total inputs yielded an annual net positive balance of 700–4,160 g Cd ha⁻¹ and 9,350–39,700 g Zn ha⁻¹. If such balances remain unchanged for another 10–20 years vegetables raised in these garden fields are likely to be unsuitable for human consumption.     

Assessing long-term changes in cadmium availability from Cd-enriched fertilizers at different pH by isotopic dilution

The application of commercial phosphate fertilizers containing Cd as an impurity is an important source of Cd to agricultural soils. The changes in the Cd status and its bioavailability in soils taken from a field trial were investigated after several years of application of fertilizers with a range of Cd contamination levels to soils. Various soil pH regimes were achieved by liming. The isotopic dilution technique was used to determine both the plant available (L-value) and isotopically exchangeable (E-value) Cd pools in soils. Firstly, we found that the L-values after 10 year of application were significantly higher at pH 5.0 than at pH 6.0, and this was reflected in the increased Cd uptake by wheat at the lower pH. There was no significant effect of the rate of soil Cd application on the L-values. Although long-term use of Cd enriched P-fertilizers increased the total concentration of Cd in soil, the impact on wheat production was insignificant. Most cultivated soils in Norway are maintained at soil pH between 5.5 and 6.5 by frequent liming. That brings up the second interesting finding, the possible impurity of lime used in this experiment. The lime was not analysed, as it was unexpected that liming might raise the total content of soil Cd substantially. That seems, however, to have been the case for this experiment since we find increase of total Cd even in the low-Cd input blocks of the trial.     

The effect of fertilizer additions on the solubility and plant-availability of Cd, Ni and Zn in soil

We conducted a pot experiment to investigate the effect of fertilizer additions on the solubility of Cd, Ni and Zn in soil solution and their uptake by plants. Radish (Raphanus sativus cv. Crystal Ball), oat (Avena sativa cv. Thule) and water spinach (Ipomoea aquatica cv. Kangkon) were grown in a naturally metal-rich soil. From day 7 after planting, fertilizers were added daily to each pot. Additions of fertilizer nutrients affected the pH of soil and soil solution, soluble and tissue concentrations of Ca, Mg, K, Cd, Ni and Zn differently in three plant species. The trend of soil and solution pH was in the order: water spinach < radish < oats, that resulted highest soluble and plant tissue concentrations of Cd and Zn in the water spinach followed by radish and then oats. However, Ni concentration in the soil solution increased in all pots and was not affected by pH changes. Soil solution pH increased by more than 1unit in the pots with radish and oats, indicating that mechanisms other than acidification, such as ion exchange and root exudation, may be responsible for the increased heavy metal uptake in these two plant species. Paired t-test showed significantly higher uptake of Cd and Zn in the radish plants resulting in lower concentrations of these elements in the solution. The contribution of mass flow to the supply of major cations and heavy metals varied among elements and plant species. Cadmium, Zn and K were taken up rapidly by all plant species in response to the amount supplied by mass flow. In contrast, the supply of Ni was in excess of its uptake by radish and water spinach. The uptake of all elements was positively correlated (p<0.0001) with mass flow and the transpiration rate in individual plant species. The study suggests that fertilizer cations increased the uptake of metals by improving growth conditions, but the magnitude of increase depended on plant species. This revised version was published online in November 2006 with corrections to the Cover Date.     

Liming impacts barley yield over a wide concentration range of soil exchangeable cations

Liming has widespread and significant impacts on soil processes and crop responses. The aim of this study was to describe the relationships between exchangeable cation concentrations in soil and the relative yield of spring barley. The hypothesis was that yield is restricted by the concentration of a single exchangeable cation in the soil. For simplicity, we focused on spring barley which was grown in nine years of a long-term experiment at two sites (Rothamsted and Woburn). Four liming rates were applied and in each year the relative yield (RY) and the concentrations of exchangeable cations were assessed. Liming had highly significant effects on the concentrations of most exchangeable cations, except for Cu and K. There were significant negative relationships (either linear or exponential) between the exchangeable concentrations of Mn, Cd, Cr, Al, Fe, Cu, Co, Zn and Ni in soil and soil pH. The relationships between RY and the concentrations of selected exchangeable cations (Mn, Ca and Al) were described well using log-logistic relationships. For these cations a significant site effect was probably due to fundamental differences in soil properties. At both sites the concentrations of exchangeable soil Al were excessive (>?7.5 mg kg^?1) and were most likely responsible for reduced barley yields (where RY?≤?0.5) with soil acidification. At Rothamsted barley yield was non-limited (where RY?≥?1) at soil exchangeable Mn concentrations (up to 417 mg kg^?1) greater than previously considered toxic, which requires further evaluation of critical Mn concentrations.

     

Concentration of trace elements in arable soil after long-term application of organic and inorganic fertilizers

The Ruzyně Fertilizer Experiment (RFE, the Czech Republic) was established on a permanent arable field (illimerized Luvisol) in 1955. The effects of long-term application of several organic fertilizers (dung water, farmyard manure, poultry litter) and mineral N, P and K fertilizers on plant-available (extracted by CaCl₂), easily mobilizable (extracted by EDTA), potentially mobilizable (extracted by HNO₃) and total concentrations of trace elements were investigated in 2008. Concentrations of all analyzed trace elements in the applied fertilizers did not exceed the limits permitted by Czech national legislation. Concentrations of As, Cd and Cr were highest in single superphosphate, those of Cu, Mn and Ni were highest in poultry litter and those of Pb and Zn were highest in dung water. Poultry litter had the second highest concentration of As and Zn. Poultry litter supplied the soils with considerable amounts of Cu, Mn and Zn and increased their concentrations in the soil. There was also a significant increase in plant availability of Mn, Ni and Zn and a decrease in soil pH. Although all fertilizers were applied for five decades, total concentrations of As, Cr, Cu, Ni, Pb and Zn in soil remained far below Czech legislation limits. For Cu and Zn this was probably due to the relatively low mean annual application rates of poultry litter. Total Cd concentrations in soil exceeded the legislative limit even in the control (without any fertilizer inputs) and the effect of treatment was not significant. This indicates that fertilizers were not the main source of Cd in the experimental area. Therefore, common cropping practices do not induce soil contamination by trace elements even if they have been applied for more than 50 years.     

The Rengen Grassland Experiment: soil contamination by trace elements after 65 years of Ca,N, P and K fertiliser application

The Rengen Grassland Experiment (RGE) was established in the Eifel Mts. (Germany) on a low productive Nardetum in 1941. Since then, the following fertiliser treatments have been applied along with a two cut system: unfertilised control, Ca, CaN, CaNP, CaNP–KCl and CaNP–K₂SO₄ with basic slag (syn. Thomas phosphate) as the only P fertiliser. The effect of long-term fertilisation on plant-available (extracted with 0.01 mol l⁻¹ CaCl₂), easily-mobilisable (extracted with 0.05 mol l⁻¹ EDTA), potentially-mobilisable (extracted with 2 mol l⁻¹ HNO₃) and total concentrations of trace elements (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb and Zn) in the top 0–10 and 10–20 cm of soil were investigated in 2006. According to redundancy analysis (RDA), the effect of treatment on the concentrations of risk elements was significant and explained 82.3 and 90.6% of the variability in the data in the 0–10 and 10–20 cm soil layers, respectively. Basic slag supplied the soil with considerable amounts of As, Cr, Cu, Fe, Mn and Zn. Following 65 years of fertiliser application the concentrations of risk elements in the soil profile had increased substantially, especially with basic slag. However, threshold limits for total trace element concentration in soil permitted by Czech national legislation were exceeded only in the case of As. The increase in plant-available As concentrations was most critical as it increased the potential uptake of As by plants in plots fertilised with P. Although P treatments received more than 300 g of Cr ha⁻¹ annually, no effect on plant-available Cr soil content was detected. This contrasted with the accumulation of total Cr in the 0–10 and 10–20 cm soil layers. Furthermore, plant availability of Cd, Fe, Mn and Zn was affected by soil pH and generally decreased with the application of quick lime. Plant availability of these elements was not correlated with amounts supplied by fertilisers.     

Towards understanding factors that govern fertilizer response in cassava: lessons from East Africa

Information on fertilizer response in cassava in Africa is scarce. We conducted a series of on-farm and on-station trials in two consecutive years to quantify yield responses of cassava to mineral fertilizer in Kenya and Uganda and to evaluate factors governing the responses. Average unfertilized yields ranged from 4.2 to 25.7 t ha⁻¹ between sites and years. Mineral fertilizer use increased yields significantly, but response to fertilizer was highly variable (−0.2 to 15.3 t ha⁻¹). Average yield response per kg applied nutrient was 37, 168 and 45 and 106, 482 and 128 kg fresh yield per kg of applied N, P and K, respectively in 2004 and 2005. Fertilizer response was governed by soil fertility, rainfall and weed management, but was not influenced by variety, pest and disease pressure and harvest age. Relative N and K yields were positively correlated to SOC and exchangeable K, while response to fertilizer decreased on more fertile soils. Still, fertilizer response varied widely on low fertility soils (e.g. on soils with <10 g kg⁻¹ SOC, responses ranged from −8.6 to 24.4 t ha⁻¹), indicating strong interactions between factors governing fertilizer response. Response to fertilizer was reduced if total rainfall <1,500 mm or rainfall from 0 to 3 months after planting <400 mm. Fertilizer application promoted plant growth and resulted in a better soil coverage and reduced weed competition. Yields in fertilized fields were independent of weed management, unless growing conditions were unfavourable.     

Metal availability in contaminated soils: I. Effects of floodingand organic matter on changes in Eh, pH and solubility of Cd, Ni andZn

Soil pH and Eh play an important role in reducing heavy metal solubility in paddy soils. To assess the effects of flooding and organic matter application on changes in Eh, pH and solubility of Cd, Ni and Zn in contaminated soils, a growth chamber experiment with rice plants(Oryza sativa L.) was conducted. Eh values decreased with flooding time in all three soils. The changes of Eh values were more negative in the tannery and alum shale contaminated soils and stabilized after 30 days of submergence. The Eh changes were not so large in the city sewage contaminated soil as in the other two soils. Soil pH increased with flooding time. During the 65 days of submergence, pH increase was about 2, 1 and 0.6units in the tannery, city sewage and alum shale soils, respectively. In all three soils, organic matter treated soil showed lower Eh and higher pH values compared to untreated soil. Concentration of Cd, Ni and Zn in soil solution decreased with flooding time. The solution concentration of Cd and Zn in the city sewage soil and of Ni in the tannery soil was higher than in the alum shale soil. The soluble metal concentration in all three soils was lower inorganic matter treated soils. Reduced solubility of metals in the organic matter treated soils was related to larger changes of Eh and pH values in these soils. Correlation coefficient calculations also showed that metal solubility decreased with decreased Eh and increased pH in the soil solution. This revised version was published online in August 2006 with corrections to the Cover Date.     

Soil carbon dynamics as influenced by tillage and crop residue management in loamy sand and sandy loam soils under smallholder farmers’ conditions in Malawi

Conservation agriculture (CA) characterised by minimal soil disturbance, permanent soil surface cover by dead or living plants and crop rotations is one way of achieving higher soil organic carbon (C) in agricultural fields. Sandy loam and loamy soil samples from zero tillage (ZT) and conventional tillage (CT) plots were taken from farmers’ fields during the dry season in August 2006. Soil organic carbon (SOC) and soil organic nitrogen (SON), microbial biomass carbon (MB-C) and microbial biomass nitrogen (MB-N), C mineralization and SOC distribution in particle size fractions in 0–20 cm layer were evaluated. Forty eight farmers’ fields were randomly sampled at four different locations in Central and Northern Malawi, representing ZT plots maintained for a different number of years, and ten fields under CT with similar soil type and crop grown were selected. SOC and SON in ZT fields were 44 and 41 % (4 years ZT) and 75 and 77 % (5 years ZT) higher, respectively, than CT plots. MB-C and MB-N in ZT fields were 16 and 44 % (4 years ZT) and 20 and 38 % (5 years ZT) higher, respectively, than CT plots. However, MB-C and MB-N in ZT fields were 27 and 25 % (2 years ZT) and 17 and 9 % (3 years ZT) lower than in CT plots. The proportion of the total organic C as microbial biomass C was relatively higher under CT than ZT treatments. The higher SOC and MB-C content in the ZT fields resulted in 10, 62, 57 % higher C mineralization rate in ZT plots of 3, 4 and 5 years of loamy sand soils and 35 % higher C mineralization rate in ZT plot of 2 years than CT of sandy loam soils in undisturbed soils in the laboratory. Simulating plough from the undisturbed soils that were used for C mineralization experiment resulted in linear curves indicating that all organic C was already depleted during the first incubation period. The relative distribution of soil organic matter (SOM) in silt and clay size fractions was strongly correlated (r = 0.907 and P ≤ 0.01) with silt percentages. Easily degradable carbon pool (C_A,f) was correlated (r = 0.867 and P ≤ 0.05) with organic carbon in sand size fraction. In developing viable conservation agriculture practices to optimize SOC content and long-term sustainability of maize production systems, priority should be given to the maintenance of C inputs, crop rotations and associations and also to reduced soil disturbance by tillage.     

Effects of tillage systems on soil organic carbon dynamics, structural stability and crop yields in irrigated wheat (Triticum aestivum L.)–cotton (Gossypium hirsutum L.) rotation in semi-arid Zimbabwe

In southern Africa, tillage research has focused on rainfed smallholder cropping systems, while literature on high-input irrigated cropping systems is limited. We evaluated the effects of conventional (CT), minimum (MT) and no-till (NT) tillage systems on soil organic carbon (SOC), bulk density, water-stable aggregates (WSA), mean weighted diameter (MWD) and crop yields in an irrigated wheat–cotton rotation. Soil data were monitored in the first and final year, while yields were monitored seasonally. Average bulk densities (1.5–1.7 Mg m⁻³) were similar among tillage systems, but often exceeded the critical limit (1.60 Mg m⁻³) for optimum root growth. Conversion from CT to MT and NT failed to ameliorate the high bulk densities associated with the alluvial soil. SOC (g kg⁻¹) at 0–15 cm was higher (P < 0.05) under MT (3.9–5.8) and NT (4.2–5.6) than CT (2.9–3.3). Corresponding horizon SOC stocks (Mg C ha⁻¹) for the tillage treatments were; 9.3–13.9 (MT), 9.3–13.5 (NT) and 7.3–7.7 (CT). In the final year, significant (P < 0.05) tillage effects on SOC stocks were also observed at 15–30 cm. Cumulative SOC stocks (Mg C ha⁻¹) in the 0–60 cm profile were higher (P < 0.05) under MT (32.8–39.9) and NT (32.9–41.6) than CT (27.8–30.9). On average, MT and NT sequestered between 0.55 and 0.78 Mg C ha⁻¹ year⁻¹ at 0–30 cm depth, but a net decline (0.13 Mg C ha⁻¹ year⁻¹) was observed under CT. At 0–30 cm, MT and NT had higher (P < 0.05) MWD (0.19–0.23 mm) and WSA (2.3–3.5%) than CT (MWD: 0.1–0.12 mm, WSA: ≈1.0%). Both MWD and WSA were significantly (P < 0.05) correlated to SOC. Seasonal yields showed significant (P < 0.05) tillage effects, but 6-year mean yields (t ha⁻¹) were similar (CT: 4.49, MT: 4.33, NT: 4.32 for wheat; CT: 3.30, MT: 2.82, NT: 2.83 for cotton). Overall, MT and NT improved soil structural stability and carbon sequestration, while impacts on crop productivity were limited. Therefore, MT and NT are more sustainable tillage systems for the semi-arid regions than conventional tillage. S. Chakanetsa—Deceased.     

Potassium supplying capacity of some tropical alfisols in southwest Nigeria as measured by intensity,quantity and capacity factors

Experiments were conducted in the laboratory, greenhouse and on farmers’ fields to determine, the potassium (K) supplying capacity of some soils in Ogun State, Nigeria, using equilibrium parameters as measured by quantity, intensity and activity indices. The result showed that the potassium status of the soils varied widely. Total K varied from 14.2 to 104 cmol kg⁻¹ in the green house soils and 46.05 to 89.1 cmol kg⁻¹ in the field soils. On the average, exchangeable and solution K constituted 0.39 and 0.09% of the total K, respectively in the greenhouse soils. The potential buffer capacity (PBC), which measures the ability of the soil to maintain the intensity of K in the soil solution, varied from 12.24 to 39.25 (ML^−1/2). About 50% of the soils studied in the green house and in the field have high PBC indicating slow release of K to the soil solution. The specifically bonded K which constituted the bulk of the labile K (K_L) that is immediately available is generally low. It ranged from 0.10 to 0.29 cmol kg⁻¹ with a mean of 0.18 cmol kg⁻¹ in the greenhouse soils, and mean of 0.16 cmol kg⁻¹ in the field soils. These low values accounted for the appreciable responses to K application by soybean in most of the soils studied. The change in Gibb’s free energy (ΔG) values, which measures the intensity of exchangeable K relative to other cations, is moderate in most of the soils. Correlation analysis showed that all the forms of K correlated positively and significantly with soybean dry matter yield at the first cropping harvest. However, soybean K concentration in the first harvest was only positively correlated with available K, exchangeable K, solution K and fixed K (P < 0.01). The clay content of the soil is also positively and significantly correlated with K forms. The prediction equation showed that the soil’s clay content is a major determinant of labile K, equilibrium activity ration (EAR) and the potential buffering capacity. The EAR is also strongly determined by the ECEC and the K saturation (R ² = 0.990, 0.996, P < 0.01). The critical level of soil labile K, available K and specifically bonded K are 0.21, 0.35, and 0.19 cmol kg⁻¹, respectively. Thus, with the use of available K as the index of K fertility, about 50% of the soils are K deficient. Hence potassium fertilization is necessary for enhanced production of soybean in these sites.     

腐植酸与土壤中重金属离子的作用机理研究概况

在分析我国农田土壤重金属污染状况的基础上,阐述了腐植酸与铬、镉、锌等金属离子在土壤中的作用机理研究现状,认为通过范德华力、氢键、静电吸附、阳离子键桥等形成土壤有机-无机复合体,使腐植质的胶团被吸附在土壤颗粒表面,使带正电的金属离子更牢固地与土壤结合,从而有效防止被农作物吸收。文章指出,腐植物质的结构及其与金属离子作用机理的研究,对于促进腐植酸土壤环境保护领域的应用与相关的技术开发具有重要意义。     

Quantifying soil organic carbon in forage-based cow–calf congregation-grazing zone interface

Recent concerns about global warming due to accumulations of atmospheric CO₂ have encouraged the achievement of better understanding of the roles of animal agriculture in mitigating CO₂ emissions. Grazing can accelerate and alter the timing of nutrient transfers, and increase the amount of nutrients cycled from plant to soil. Our reason for conducting this study is to test whether cattle congregation sites (CCS) typical on most Florida ranches, such as mineral feeders (MF), water troughs (WT), and shaded areas (SA) have higher soil organic carbon (SOC) than in other locations of pasture under foraged-based system. Baseline soil samples around the congregations zones (MF, WT, and SA) and grazing zones in established (>10 year), grazed cow–calf pastures were collected in the spring and fall of 2003, 2004, and 2005, respectively. Soil samples were collected from two soil depths (0–20 and 20–40 cm) at different locations around the CCS following a radial (every 90 degrees: N, S, E, and W) sampling pattern at 0.9, 1.7, 3.3, 6.7, 13.3, 26.7, and 53.3 m away from the approximate center of MF, WT, and SA. The levels of SOC varied significantly with CCS (P ≤ 0.001), distance away from the center of the CCS (P ≤ 0.05), sampling depth (P ≤ 0.001), sampling year (P ≤ 0.001) and the interaction of CCS and soil depth (P ≤ 0.001). Sampling orientations did not significantly affect the levels of SOC. The SA sites had the highest level of SOC of 3.58 g kg⁻¹, followed by WT sites (3.47 g kg⁻¹) and MF sites (2.98 g kg⁻¹). Results of our study did not support our hypothesis that cattle congregation sites typical on most ranches, such as MF, WT and SA, may have higher concentrations of SOC. The levels of SOC (averaged across CCS) within the congregation zone (3.42 g kg⁻¹) were not significantly (P ≤ 0.05) different from the concentrations of SOC at the grazing zone (3.16 g kg⁻¹).     

Uptake and allocation of plant nutrients and Cd in maize,sunflower and tobacco growing on contaminated soil and the effect of soil conditioners under field conditions

Contaminated land may in many cases still be used for agriculture, provided that crops are chosen appropriately, as the accumulation of contaminants varies greatly among cultivars and also plant parts. We aimed to determine whether maize (Zea mays), sunflower (Helianthus annuus) and tobacco (Nicotiana tabaccum) grown on a heavy-metal contaminated soil containing copper (540 mg Cu kg⁻¹), zinc (680 mg Zn kg⁻¹) and cadmium (1.4 mg Cd kg⁻¹) could be used to gradually remediate the soil, while producing valuable biomass. The soil was treated with either a normal fertiliser regime (control), elemental sulphur (S), or the biodegradable chelant NTA (nitrilotriacetic acid), to test how soil acidification or chelating organic compounds would affect the uptake and allocation of selected elements (Ca, Cd, Cu, Fe, K, Mg, Mn, P, S and Zn). The highest concentrations of Cd, Cu and Zn occurred in the leaves and/or roots, while seeds and grains contained much lower concentrations of these elements. All these concentrations, however, were still in the ranges considered normal for the respective plant parts grown on uncontaminated soil. While sunflower and maize could be safely used as food and feed, tobacco would better be used for bioenergy than for cigarette production because of its relatively high foliar Cd concentration. The two treatments (S and NTA) had only slight effects on the uptake and allocation of plant nutrients and Cd. Thus, there was little benefit of these treatments for phytoextraction purposes at this site.     

<Emphasis Type="Italic">Phytolacca americana</Emphasis> from Contaminated and Noncontaminated Soils of South Korea: Effects of Elevated Temperature,CO<Subscript>2</Subscript> and Simulated Acid Rain on Plant Growth Response

Chemical analyses performed on the invasive weed Phytolacca americana (pokeweed) growing in industrially contaminated (Ulsan) and noncontaminated (Suwon) sites in South Korea indicated that the levels of phenolic compounds and various elements that include some heavy metals (Al, As, B, Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn) were statistically higher in Ulsan soils compared to Suwon soils with Al being the highest (>1,116 mg/l compared to 432 mg/l). Analysis of metals and nutrients (K, Na, Ca, Mg, Cl, NH₄, N, P, S) in plant tissues indicated that accumulation occurred dominantly in plant leaves with Al levels being 33.8 times higher in Ulsan plants (PaU) compared to Suwon plants (PaS). The ability of PaU and PaS to tolerate stress was evaluated under controlled conditions by varying atmospheric CO₂ and temperature and soil pH. When grown in pH 6.4 soils, the highest growth rate of PaU and PaS plants occurred at elevated (30°C) and non-elevated (25°C) temperatures, respectively. Both PaU and PaS plants showed the highest and lowest growth rates when exposed to atmospheric CO₂ levels of 360 and 650 ppm, respectively. The impact of soil pH (2–6.4) on seed germination rates, plant growth, chlorophyll content, and the accumulation of phenolics were measured to assess the effects of industrial pollution and global-warming-related stresses on plants. The highest seed germination rate and chlorophyll content occurred at pH 2.0 for both PaU and PaS plants. Increased pH from 2–5 correlated to increased phenolic compounds and decreased chlorophyll content. However, at pH 6.4, a marked decrease in phenolic compounds, was observed and chlorophyll content increased. These results suggest that although plants from Ulsan and Suwon sites are the same species, they differ in the ability to deal with various stresses.     

Effect of potassic and phosphatic fertilizer type, fertilizer Cd concentration and zinc rate on cadmium uptake by potatoes

In some areas of southern Australia, cadmium (Cd) concentrations in excess of the Australian maximum permitted concentration (0.05 mg kg^–1 fresh weight) have been found in tubers of commercially grown potato (Solanum tuberosum L.) crops. Field experiments were therefore conducted in various regions of Australia to determine if Cd uptake by potatoes could be minimised by changes in either phosphorus (P), potassium (K) or zinc (Zn) fertilizer management.Changing the chemical form in which either P fertilizer (monoammonium phosphate, diammonium phosphate, single superphosphate and reactive rock phosphate) or K fertilizer (potassium chloride and potassium sulfate) were added to crops had little influence on tuber Cd concentrations. Fertilizer Cd concentrations also had little influence on tuber Cd concentrations, suggesting that residual Cd in the soil was a major contributor to Cd uptake by the crops on these soils.Addition of Zn at planting (up to 100 kg Zn ha^–1) significantly reduced tuber Cd concentrations at four of the five sites studied. However, the largest variation was between sites rather than between treatments, with site mean tuber Cd concentrations varying tenfold (from 0.018 to 0.177 mg Cd kg^–1 fresh weight). Factors associated with irrigation water quality at the sites, in particular the chloride concentration, appeared to dominate any effects of changing fertilizer type or Cd concentration.     

Metal availability in contaminated soils: II. Uptake of Cd, Ni and Zn in rice plants grown under flooded culture with organic matter addition

Higher accumulation of toxic heavy metals in rice grown in contaminated soils may lead to health disorder in humans in tropical countries as rice is a staple diet. A pot experiment was conducted in a growth chamber to investigate the effect of flooding and non-flooding conditions in three soils added with4% organic matter on the concentration and uptake of Cd, Ni and Zn by rice plants (Oryza sativa L.). In flooding condition, the level of standing water was at a height of 2.5 ± 0.5 cm above the soil surface and in non-flooded culture80 ± 5% of water holding capacity was maintained. Flooding condition significantly(p < 0.05) reduced the concentration and uptake of Cd, Ni and Zn in rice grown in all three soils. The overall reduction of metal concentration in shoot at vegetative stage, and straw and polished rice at maturity, under flooding conditions was 84, 89, and 79% for Cd; 21,63and 65% for Ni; and 52, 78 and 16% for Zn, respectively. Organic matter addition significantly reduced the Ni concentration in plant parts but no such reduction was seen for Cd and Zn. Accumulation index of Cd and Zn was 82and 55% higher than that of Ni in the plant and the index of all three metals was higher in the tannery soil than the other two soils. Polished rice contained significantly lower amounts of Cd, Ni and Zn than shoot and straw. Cadmium and Ni uptake in polished rice was > 20% of the total uptake and thus it may be a concern for human health. This revised version was published online in August 2006 with corrections to the Cover Date.     

A three-step metal fractionation scheme for fly ashes collected in an Argentine thermal power plant

A new three-step fractionation scheme was applied to study the distribution of Al, As, Cd, Cr, Cu, Fe, Mn, Mo, Ni, Pb, S, Sb, Ti, V and Zn in fly ashes collected in the electrostatic precipitator of a thermal power plant in the city of San Nicolás (Argentina). Seven samples were collected during one week of operation in 2005. For the fractionation, the scheme applied consisted of extracting the elements in three fractions: (i) soluble and exchangeable elements, (ii) carbonates, oxides and reducible elements and (iii) residual elements. Metals and metalloids at μg g⁻¹ level were determined in each fraction by plasma based techniques namely, inductively coupled plasma optical emission spectrometry (ICP OES) and inductively coupled plasma mass spectrometry (ICP-MS). For validation, a certified reference materials NIST SRM 2711 (Montana soil) was subject to the same chemical sequential extraction procedure. X-ray diffraction powder (XRD) analysis and scanning electron microscopy (SEM) were used to characterize the major minerals present in the matrix. The predominant phases found in the total samples were mullite, quartz, iron oxides and lime. Total analyte concentration varied (in μg g⁻¹) from 1.54 for Cd to 30 600 for Al. The leachability of the 15 elements under study proved to be different. All the elements (except Cd and Pb) were detected in the soluble fraction in the order: Cu (0.10%) ∼ Mn (0.13%) < Ni (0.17%) ∼ Ti (0.19%) ∼ Fe (0.20%) ∼ As (0.21%) < Zn (0.86%) < Al (1.3%) < Cr (2.9%) < V (3.9%) < Sb (6.9%) < Mo (45.1%) < S (58.0%). Percentages higher than 20% of S (24.1%) < V (27.5%) < Mn (29.0%) were detected in the second fraction. Al, As, Cr, Cd, Cu, Fe, Ni, Pb, Sb and Zn were mostly associated to the residual fraction. Recoveries of the overall procedure varied between 106% (Mo) and 72% (Cr).     

Influence of treated sewage sludge applications on temporal variations of plant nutrients and heavy metals in a Typic Xerofluvent soil

The objective of this study is to determine influence of Treated Sewage Sludge (TSS) rates as organic matter and nutrient resource on temporal variations of some macronutrients and micronutrients and heavy metals concentrations in a Typic Xerofluvent soil. The experiment was conducted in Menemen Plain, in the Western Anatolia Region of Turkey in 2003–2005. Moist TSS was added to the soil at the rates of 0, 30, 60 and 90 Mg ha⁻¹ on May 1, 2003. Peanut (Arachis hypogaea) was planted as the first crop. On the other hand, mixture of green barley (Hordeum vulgare) and common vetch (Vicia sativa L.) was planted as the second crop. During the experiment, soil samples were taken five times. Increasing TSS applications to this soil resulted in significantly increased concentrations of total N, Cu, Pb and Ni, and available P, K, Ca, Fe, Cu, Zn, Mn concentrations in soil. However, concentrations of available Mg and Na, total Fe, Zn, Mn, Cd, Co and Cr in soil did not significantly change. Micronutrients and heavy metals concentrations in soil were found under threshold values in all sampling periods in this study. Available nutrient concentrations in the soil decreased particularly in the last sampling periods because of plant uptake of nutrients from the applied TSS. It is recommended that 90 Mg ha⁻¹ moist TSS can be added once in a 2-year period for improving nutrient concentrations in Typic Xerofluvent soil.