Zinc, copper and manganese availability in soils treated with alkaline sewage sludge from Paraná state (Brazil)

Abstract

ABSTRACT In Paraná, most of the sludge generated in sewage treatment plants is subjected to the prolonged alkaline stabilization process. Although it is known that the alkaline sewage sludge contains micronutrients such as Zn, Cu and Mn, little is known about the availability of these elements in soils treated with this type of sewage sludge. Thus, the objective of the study was to evaluate the influence of alkaline sewage sludge from Paraná on Zn, Cu and Mn availability in soils. Twenty sewage treatment plants were selected throughout Paraná, where alkaline sewage sludge and the most representative agricultural soil of the each region were collected. Each soil was incubated for 60 days with alkaline sewage sludge rates (0, 10, 20, 40, and 80 Mg ha-1) from their region. Subsequently, Zn, Cu and Mn availability was determined using the Mehlich-1 extractant. The alkaline sewage sludge increased Zn availability and decreased Mn availability in most soils. Cu showed intermediate results, with increased availability, primarily in medium texture soils and decrease in most of the clayey soils. In soils with pH close to ideal for the plant growth, the alkaline sewage sludge rate should be carefully calculated so that there is no excessive increase in the pH and Zn, Cu and Mn imbalance.