Effect of sewage sludge application on cotton yield and contamination of soils and plant leaves

Abstract

In a two‐year field experiment, dry sewage sludge was applied to fields plots at rates of 0,26,42,58, or 77 tons ha^‐1 year^‐1 on a clay loam soil (calcixerrolic xerochrept), well drained with a pH value of 8.15. Cotton was the cultivated plant (Gossypiumhirsutum variety korina). Sequential extraction was used to separate the different forms of the metals (exchangeable, organically bound, carbonates and residual) in the soil‐sludge mixtures. Cotton yield increased in the second year of experimentation compared with the control treatment (without fertilization and no application of sewage sludge). Most of the metals studied cadmium (Cd), zinc (Zn), copper (Cu), and nickel (Ni)] were found in the organically bound, carbonate or residual forms. From the elements in the soil fractions, only Zn in the residual form was correlated with the Zn content of cotton leaves. The diethylenetriaminepentaacetic acid (DTPA) extraction of the plant‐available levels of the elements showed only for Cd a simple linear correlation, between concentration in soils and cotton leaves.