The main purposes of this investigation was to study the following: (1)The role of different organic materials i.e. straw of bean and the Nile compost applied at different rates on reducing the toxic risks of heavy metals through incubatation for different periods succeeded by leaching, (2) Effect of time of leaching on reducing or removal of the studied heavy metals out of soil within the different incubation periods.
To fulfill there purposes, two soil samples were investigated, the first one was a sandy soil collected from Meet Kenana and the second one was a clayey soil collected from Moshtohor, Qalubia Governorate.
An incupation experiment was conducted using soil columns where the columns were packed with 0.5 kg of each soil Bean straw or compost of El-Obour was added at a rate 0, 2 or 4 %.The soils were incubated with the added organic materials and the concerned heavy metals i.e. Co, Ni and Pb applied at three rates i.e. low, moderate and high at the laboratory temperature (25-30°C) for three periods 30, 60 and 90 days. Soil moisture was kept constant at field capacity through application of distilled water each other day After each incubation period, soil in each plastic pot was exposed to washing with distilled water. The filtrates were collected and analyzed for cobalt, nickel and lead. The obtained results could be summarized in the following:
1) The concentrations of the leached metal ions were, as expected, highest upon application of the highest rates of these metal ions, on the other hand, lowest upon application of the corresponding lowest rates. Application of the moderate concentrations of Co, Ni and Pb caused concentrations of these metals ions to be inbetween.
2) The used organic materials can be arranged according to their effect on leaching (moving) the studied metal ions in the following descending order: The compost of El-Obour at a rate of 4 %> bean straw at a rate of 4%>the compost of El-Obour at a rate of 2 %> bean straw at a rate of 2 %> control.
3) The concentration of heavy metals (Pb, Ni, and Co) in the third incubation period were lower than the corresponding values of concentrations of these metal ions in the leachate of the second period. Whose concentrations were lower than those of the first ieachate .
4) The concentrations of the leached metal ions from the sandy soil were higher than the corresponding ones leached from the clayey one.
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