Effect of some organic amendments on the availability and fractions of certain heavy metals of Abo Rawash soil and growing wheat plants

Abstract

Due to good water shortage, accumulation of heavy metals in soil under irrigation with wastewater can cause serious hygienic and environmental problems. However, the availability of metal ions in contaminated soils can be reduced by addition of organic and inorganic amendments. In this study, columns experiment was conducted during the winter season of 2016/2017 to evaluate the effect of applying some organic amendments such as humic acid, rabbit manure and biochar on the availability and forms of some heavy metals (i.e. Zn, Cu, Pb and Ni) in contaminated soil of Abo Rawash area irrigated with wastewater and their impact on growing wheat plants as a strategic crop. The forms of the concerned heavy metals in soil were determined by the sequential extraction method. Results showed that treating the soil with such amendments decreased heavy metals concentrations in soil. The amount of the studied heavy metals was distributed among the different soil fractions following the descending order: organically bound > residual fraction > Fe-Mn oxides bound > carbonate associated > exchangeable. The dry weight of whole plant, weight of 1000 grains and NPK concentrations in wheat plants were significantly increased due to application of these amendments especially humic acid compared to the control. In addition, heavy metals concentrations were significantly decreased in wheat plants under irrigation with wastewater, with the highest effect for humic acid treatment. These results went hand by hand with the effect of humic acid on increasing heavy metals solubility and leachability in soil, and increasing heavy metals concentrations values in the collected drainage water from soil columns under investigation.