Effects of Inorganic and Organic Fractions of Enriched Cow Manure and Sewage Sludge on Distribution of Lead Chemical Fractionation in Soil

Cow manure and sewage sludge add heavy metals to soil. Organic and inorganic fractions in these compounds can immobilize heavy metals such as lead (Pb) and affect their bio-availability. This investigation was conducted to compare the effects of organic and inorganic fractions of sewage sludge and cow manure on distribution of lead chemical forms in soil as a completely randomized design. Treatments consisted of application of 10% (w/w) enriched sewage sludge and cow manure (6 g Pb kg-1 organic amendments). Another treatment was also used in which soil Pb concentration was increased to 600 mg kg-1 soil using Pb (NO3) 2 salt. To compare the effects of organic and inorganic fractions، organic carbon، iron oxide and easily reducible iron and manganese were removed from cow manure and sewage sludge، and were added to the soil by 10% (w/w). The samples were incubated at 23-25ºC for 111 days and their moisture was maintained at 80% water field capacity. More than 50% Pb in Pb (NO3) 2 treatment was in exchangeable fraction، while for cow manure and sewage sludge treatments more than 40% Pb was found to be in oxide fraction. Application of cow manure and sewage sludge increased the Pb in oxide fraction by 14. 8 and 17. 5%، respectively. Removing organic carbon fraction of cow manure and sewage sludge increased the Pb bound to residual fraction by 12% and 14% respectively. Removing iron oxide fraction of sewage sludge and cow manure decreased the Pb bound to oxide fraction by 8% and 13%، respectively. Removing easily reducible iron and manganese decreased the oxide fraction of Pb by 16% and 14%، respectively. It is concluded that، despite relatively high amounts of organic carbon in the sludge and manure، inorganic fractions of these materials have more significant effects on availability of Pb in soil.