Bhumika Kansal

A greenhouse experiment was conducted to evaluate the effect of fly-ash application on dry-matter yield and nutrient composition of 60 day-old rice and wheat plants and on pH and available nutrient status of soils. Fly-ash was collected from an old deposit of a thermal power plant and was mixed with seven soils (varying in texture and CaCO3) each at 0, 2, 4 and 8% (w/w) levels. Moderate rates of fly-ash application (2–4% w/w) had a beneficial effect on the dry-matter yield of paddy, but a higher level (8% w/w) had a significant depressing effect. Addition of fly ash resulted in a significant increase in the contents of N, S, Ca, Na and Fe and a significant decrease in P and Zn contents of rice. The residual effect of fly ash on dry-matter yield and nutrient composition of a subsequent wheat crop was non-significant, except for the Fe content of the wheat plants which increased significantly from 138 ppm in the control to 161 ppm at 8% level of fly-ash addition. The pH and available nutrient status of soils after harvest of the rice and wheat crops were not affected by the application of fly-ash. However, the mean DTPA-extractable Fe content in soils increased significantly from 12 ppm in the control to 18·1 ppm in soils amended with 8% fly-ash.

Ash samples were collected from a dumping site (fly ash) and an electrostatic precipitator (ESP ash) of a 440 MW thermal power plant for characterization. Analysis of ash samples showed that the major matrix elements in fly ash were Si and Al, together with significant percentages of K, Fe, Ca and Mg. Some of the biologically-toxic elements, Ni, Cr, Pb, B and Mo, were also present in substantial amounts. Ash collected directly from electrostatic precipitator (ESP ash) was finer in texture, lower in pH and generally richer in nutrients than the ash collected from dumping sites (fly ash). The saturation moisture percentages of both the ashes were higher, but the bulk density was lower, than the normal cultivated soils. Calcium was the dominant cation of the exchange complex, followed by Mg2+, Na+ and K+. Contents of available sulphur were quite high. Among DTPA extractable micronutrients, only iron was present in significant amounts, but the contents of hazardous constituents were very low. Compositions of watersoluble constituents of both the ashes were substantially affected by water: fly ash ratio and decreased with dilution. The rate of release of sodium was found to be much less than calcium and magnesium.

Cadmium is a potentially toxic heavy metal that enters food chain from the soil through various anthropogenic sources. Availability of metal ions in contaminated soils can be reduced by the addition of organic amendments. In this study, effect of organic matter -farm yard manure (FYM) amendment on fractionation and availability of Cd to maize was evaluated. A green house experiment was conducted to determine the toxicity and uptake of Cd by maize in sandy loam soil with and without organic matter. Four levels of Cd (0, 10, 20 and 40 mg kg(-1) soil) and two levels of FYM (0 and 20 tonnes ha(-1)) with three replication in a completely randomized factorial design. Concentration of Cd in maize increased with increasing rate of Cd application. Application of organic matter increased the dry matter yield of maize while reduced the uptake of metal. All the fractions exhibited increase with Cd rates. The addition of organic amendment declined significantly the concentration of water soluble and exchangeable Cd, but increased the amounts of these metals into less mobile fractions (Fe/Mn oxide, organic matter and residual). Dominance of insoluble forms of Cd after the application of organic amendments may be ascribed to the increases of soil OM, pH, EC and available P contents which caused transformation or redistribution of the sorbed phases. This resulted in increasing Cd retention in the more persistent fractions with application of FYM at the expense of reductions in the loosely bound fractions. Thus FYM appears to be agronomically feasible way to off set the adverse effect of Cd toxicity.

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.

Studies on sorption of cadmium were carried out in some sewage irrigated soils. The data followed Langmuir and Freundlich adsorption isotherms. The value of adsorption maxima b was significantly higher if soils of high pH, organic matter, calcium carbonate, cation exchange capacity and clay content. The bonding energy constant K, however, was dependent only on the CaCO3 and total iron content of soils. The constants of Freundlich isotherms followed the same trend as those of Langmuir constants. Release of adsorbed Cd by 1N neutral ammonium acetate decreased with increase in pH, organic matter, CaCO3, cation exchange capacity and clay. Soils with high bonding energy constant and adsorption maxima released lesser amount of cadmium.

The nutrient indexing survey of 33 grape orchards in Bhatinda district of Punjab has indicated medium (23%) to high (71%) available P and high (100%) available K in the soils. The petiole analysis also showed high amounts of both P (36%) as wen as K (67%). The concentratioos of Zn, Sand N in the petioles were below their critical limits in 58, 27 and 9% of the samples. The categorisation of the petiole analyses on the basis of yield data confirmed the inadequacy of Zn. Comparison of the data of the present study with those of the 1979 survey in the same area has revealed that the concentrations of P, Zn, Fe and Mn have increased but those of K and eu have decreased over a period of ten years.