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  • Author or Editor: M. Khurana x
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Zinc and cadmium have been found to interact with each other differently under different conditions. The zinc supply may enhance or offset the phytotoxicity of Cd. Therefore, in a pot experiment, a sandy loam soil (Typic Ustipsamments) was treated with cadmium at rates of 0, 10, 20 and 40 mg kg−1 and with zinc at rates of 0 and 20 mg kg−1 soil to assess their effect on dry matter yield and the concentrations of Cd and micronutrients. There was a significant decrease in dry matter yield due to the phytotoxic effect of Cd. The dry matter yield was not affected by the application of zinc at any rate of Cd application. The concentration and uptake of Cd in the crop increased gradually at increasing rates of cadmium application. The increase in cadmium concentration was greater in the presence of zinc than in its absence. This suggests that the effect of soilapplied Zn is reflected in the enhancement of the Cd content in plants. Thus, zinc application cannot offset the toxic effect of Cd. The relationship of Cd with Zn and Fe was synergistic at all rates of Cd application, whereas Mn and Cu exhibited an antagonistic relationship.

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Raya (Brassica juncea) and spinach (Spinacia oleracea), grown as leafy vegetables, are known to accumulate large amounts of heavy metals in their shoots and roots because of their high biomass and root proliferation. In a pot experiment, a sandy loam soil was polluted with cadmium (Cd) at rates of 0, 5, 10, 20, 40 and 80 mg kg−1 soil to assess the accumulation pattern and its effect on the dry matter yield and mineral composition of these vegetables. There was a decrease in dry matter yield due to the phytotoxic effect of Cd. The rate of Cd application at which a significant decline in root and shoot dry matter yield occurred varied depending on the vegetable. It was 20 mg Cd kg−1 soil in the shoots for both crops. However, the roots of raya were found to be more tolerant of Cd toxicity than those of spinach, as is evident from the fact that a significant decline in dry matter yield occurred at 20 and 10 mg Cd kg−1 soil, respectively. Since no visual toxic symptoms were observed on the leaves of raya in any of the treatments, it is clear that the metal may accumulate in this vegetable without visual evidence of its presence. However, at application levels beyond 40 mg kg−1 soil, toxicity symptoms, in the form of interveinal chlorosis of the leaf lamina followed by necrosis and leaf rolling, were clearly evident in the case of spinach. The reduction in root and shoot growth corresponded with the amounts of extractable Cd in the soils. The total content of Cd in the crops increased gradually as the rate of applied Cd rose and the roots accumulated much higher amounts than the shoots. The relationship of Cd with Zn and Fe was synergistic in both roots and shoots at the lower rates, but antagonistic at higher Cd application rates for both the crops, while in the case of Mn and Cu, the relationship was negative and antagonistic.

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Studies on the sulphur requirements of crops have largely been restricted to single crops without considering its residual availability to the following crop. With this objective, a field experiment was carried out to study the direct, residual and cumulative effect of S in a moong-raya rotation on sandy loam soil having 8.2 mg kg −1 soil of 0.15% calcium chloride-extractable S. The treatment consisted of four levels of S (0, 10, 20 and 40 kg ha −1 ) applied as gypsum. A significant increase in the grain yield of moong was observed at and above 20 kg S ha −1 , but the difference between the grain yields at application rates of 20 and 40 kg S ha −1 was found to be non-significant. The direct application of 20 kg S ha −1 resulted in a significant increase in the grain yield of raya. The residual effect emanating from the application of 40 kg S ha −1 to the first crop of moong significantly increased the grain yield of raya. The cumulative application of S at different rates, to both the crops, was not found to be beneficial. It is therefore suggested from this study that the application of 20 kg S ha −1 to each crop or 40 kg S ha −1 to the first crop of moong was sufficient to obtain optimum yields of both the crops in a moong-raya cropping sequence. The critical levels of S in the whole shoot in moong and raya plants were found to be 0.23 and 0.37%, respectively.

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