IMPROVING THE MICRONUTRIENT AVAILABILITY IN CALCAREOUS SOILS BY SEWAGE SLUDGE AMENDMENT

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Abstract
The pollution associated with non-essential heavy metals in sewage sludge is a hazard usually taken into consideration with land application of such biosolids. The risk of contamination may also be a factor for elements that are essential for plant growth because they are present in sewage sludge in very high concentrations. Calcareous soils, however, are often deficient in elements like Fe and Zn. In this experiment, we attempted to estimate the contribution of sewage sludge application to the input and availability of Fe, Mn, Cu, and Zn in amended soils. In order to study the dynamics of these essential elements, the experimental design was based on the incubation of two calcareous soils having different textures (sandy clay loam and clay loam) amended with composted and non-composted sewage sludge. Sewage sludge application rates to the soils were 30 and 50 g dry sludge kg−1 soil. Also, for each soil, a control treatment with no organic amendment was established. Seven samples were taken from each soil-sludge treatment combination at 0, 15, 30, 60, 90, 120 and 150 days after the start of the incubation. A significant increase in available Fe, Cu, Mn and Zn was observed. The application of increasing rates of sewage sludge slightly increased the available fraction of the micronutrients studied. The influence of soil texture was to increase the available fraction in the clay loamy soil compared to the sandy clay loamy soil. Availability of Fe, Cu, Mn and Zn was continued to increase throughout the incubation period.