Residual effects of urban sewage sludge on corn biological yield and chemical composi-tion
A Gandomkar1, H R Rahmani2
A large volume of sewage sludge is produced in the process of urban sewage treatment. The sludge contains relatively large amounts of organic matter, plant nutrients, soluble salts as well as small amounts of some heavy metals. The residual effects of urban sewage sludge on growth and yield of corn and heavy metals and nutrients concentrations in plant were studied in a field trial conducted in one site(Esfahan Agri Res Ctr in Kabutar-abad farm)in central Iran.The treatments included applications of 0, 25, 50 and 100 metric tons of sludge ha-1 in a randomized complete block design with three replication. Biological yield of corn increased from 8.6 to 12.3,18 and 16.3 t ha-1 for 25, 50 and 100 t ha-1 of sludge applications(as compared to the control field) respectively. Concentrations of N, P, K, Fe, Mn, Zn and Cu in plants tissues increased as a result of sludge application.Concentration of Fe, Mo, Zn, Cu and Cr in plant tissues also increased but no toxic symptoms were observed. Concentration of Pb, Cd, Cr, Co and Ni in aerial tissues of corn did not increase as a result of sludge application. The results showed that the average concentration of above elements in all three treatment plants, not exceeded from EPA standards, however, regarding the accumulative property of these elements, in using these sludges in the agricultural soils, the necessary caution and care should be taken. It is concluded that sewage sludge has the potential to be used as an organic fertilizer and soil amendment to improve soil productivity at least for a limited period of time.