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Samples of Hungarian and Indian soils (heavy and light) from different agro-ecological zones were taken in 1998 and 2002, respectively, and the periodic extractability of DTPA-extractable (plant available form) of Cd was determined after incubation at field capacity with different loads of Cd (10, 20, 40 and 80 mg Cd kg −1 soil) and correlated with some important soil properties. DTPA-Cd was found to be most highly correlated with cation exchange capacity (CEC), followed by organic matter (O.M.) and pH of the soils. A lower amount of added Cd was recovered in the form of DTPA-Cd with an increase in the time interval.

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Agrokémia és Talajtan
Authors:
Krisztina Végh
,
J. Csillag
,
A. Lukács
,
B Panwar
, and
Gy. Füleky

Potassium uptake is the result of numerous simultaneous processes influencing the potassium dynamics in the rhizosphere.The presented research has focused on plant-soil interactions in the potassium supply of soil in the root environment of maize. It was assumed that: 1. roots promote the mobilization of K by the acidification of the rhizosphere soil, 2. roots increase wetting-drying cycles in their environment, and 3. soil total K content affects K release and fixation in the bulk of soil and the root environment.The promoting effect of root activity was detected on K release from soil when feldspar was added as K source to the root environment. A 2-unit reduction of soil pH multiplied K concentration in the soil solution, depending on the feldspar rate. Feldspar application significantly increased the solubility and release of potassium into the soil solution.The effect of pH reduction on the K concentration of soil solution was several magnitudes higher than that of the wetting-drying cycles both in the untreated and feldspar treated soils.Potassium uptake by maize over two generations greatly exceeded the exchangeable pool in the growing media. As a consequence of the exhaustive K uptake K release slowed down to the soil solution, as reflected in the H2O extractable K and ExK contents.Significant K fixation was detected after the K removal of maize in feldspar treated soils. On the contrary, in the treatments without plants increasing feldspar rates increased both H2O extractable K and ExK contents.One-term Langmuir equation, corrected with the originally sorbed amount of K, was fitted to measured data. The maximum amount of potassium adsorption (Kmax, mg∙kg−1) and the equilibrium constant (k) were calculated. The potassium buffering capacity was estimated at zero equilibrium concentration. Both K buffering capacity and the energy of K fixation were high for the rhizosphere soil. In rhizosphere soil samples the energy of K fixation was one magnitude higher as compared to the bulk soil and decreased substantially with feldspar addition. In soils without plants the k equilibrium constant did not change as the result of drying-wetting process only in the case of the 50% soil/feldspar mixture.In the liquid phase of the soil without feldspar application potassium concentration decreased in the one-year drying-wetting cycle, presumably it got into more strongly bounded forms in the low K status soil. In 50% feldspar enriched soil samples potassium concentration in the soil solution increased, likely as a consequence of a slow dissolution of the K content of feldspar.

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Phytoremediation is a green technology for the sustainable remediation of surface soils contaminated with toxic heavy metals. When added to soils the chelating agent ethylenediamine tetraacetic acid (EDTA) increased the solubility of heavy elements for plant uptake during phytoremediation. A greenhouse experiment was carried out with two Brassica species (Brassica juncea and Brassica carinata) grown on artificially contaminated soil (20 and 40 mg Cd kg-1) with EDTA added at a rate of 1 g kg-1 soil. With increasing Cd (0, 20 and 40 mg Cd kg-1 soil) contamination the biomass of both the Brassica species decreased. However, Brassica juncea was more tolerant of high levels of Cd in the soil in comparison to B. carinata. The results indicated that EDTA made the cadmium more available to the plants and lowered the Cd content of the soil. The magnitude of the increase in tissue (stem, leaf and root) Cd concentration was higher in B. juncea than in B. carinata and after the application of chelating agent (EDTA). The Brassica juncea species of Indian mustard has better potential for the phytoremediation of soil heavily contaminated with Cd (40 mg Cd kg-1 soil).

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Phytoremediation is an approach designed to extract excessive heavy metals from contaminated soils through plant uptake. Cadmium (Cd) is among the elements most toxic to living organisms. Health hazards associated with the lethal intake of Cd include renal (kidney) damage, anaemia, hypertension and liver damage. A greenhouse experiment was carried out with Indian mustard (Brassica juncea) grown on artificially spiked soil (100 μg Cd g−1) with EDTA (2 mmol kg−1 in 5 split doses), FYM, vermicompost (VC) and microbial inoculants (MI) such as Azotobacter sp. and Pseudomonas sp. The growth of Brassica juncea L. was better in soil amended with FYM or VC as compared to unamended Cd-polluted soil. Growth was slightly suppressed in EDTA-treated soil, whereas it was better after treatment with MI. The application of FYM and VC increased the dry matter yield of Indian mustard either alone or in combination with microbial inoculants, while that of EDTA caused a significant decrease in the biomass of Indian mustard. The application of microbial inoculants increased the dry matter yield of both the roots and shoots, but not significantly, because MI shows greater sensitivity towards cadmium. The maximum cadmium concentration was observed in the EDTA +MI treatment, but Cd uptake was maximum in the VC + MI treatment. The Cd concentration in the shoots increased by 120% in CdEDTA over the Cd100 treatment, followed by CdVC (65%) and CdFYM (42%) in the absence of microbial inoculants. The corresponding values in the presence of MI were 107, 51 and 37%, respectively. A similar trend was also observed in the roots in the order CdEDTA+M > CdVC+M > CdFYM+M>Cd100+M.MI caused an increase in Cd content of 5.5% in the roots and 4.1% in the shoots in the CdEDTA+M treatment compared with the CdEDTA treatment. FYM, VC and EDTA also increased Cd uptake significantly both in the shoots and roots with and without microbial inoculants.The results indicated that Vermicompost in combination with microbial inoculants is the best treatment for the phytoremediation of Cd-contaminated soil by Indian mustard, as revealed by the Cd uptake values in the shoots: CdVC+M (2265.7 μg/pot) followed by CdEDTA+M (2251.2 μg/pot), CdFYM+M (1485.7 μg/pot) and Cd100+M (993.1 μg/pot).

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