Sewage sludge from wastewater treatments contains organic matter and plant nutrients that may play an important role in agricultural production and maintenance of soil fertility. The present study aimed to evaluate the effect of increasing sewage sludge rates on soil chemical properties, heavy metal concentration in soils and plants, and the growth of maize and bean plants cultivated in pots under greenhouse conditions. Two soil types with different clay contents were used for application of six sewage sludge rates (equivalent to 0, 10, 20, 30, 40, and 60 Mg ha-1). Sludge application led to a decrease of pH and general increase in organic matter, total nitrogen, phosphorus, potassium, sodium, calcium, and magnesium concemration, with exception of potassium and sodium contents in one of the soils. Furthermore, the sludge doses increased maize and bean plants dry matter production. The concentration of heavy metal (Zn, Cu, Mn, Fe, and Pb) found in the sewage sludge, soils, and in plants were below the limits established for agricultural use; thus it seems safe to allow their utilization without major risks to the environment.
heavy metals; organic waste; biosolid
