Effects of Different Sewage Sludge Concentrations on Soil and Cultivated Raphanus sativus L

Sewage sludge is a residue rich in organic matter and nutrients important for plant growth and soil fertility, but it may contain in its composition heavy metals that can result in toxicity to the plant, soil and humans when used as fertilizer. The objective was to assess microbial activity and heavy metal residues in soil and radish tubers grown with different concentrations of sewage sludge. Carbon microbial biomass, total organic carbon, soil basal respiration and zinc, copper, chromium and lead levels in soil and radish tubers were analyzed. According to the results, application of 30 Mg ha-1 of sewage sludge promoted higher microbial activity and lower metabolic quotient, and resulted in 490 tili-1 of microbial carbon and 11.12% of soil organic carbon. Heavy metal contents in radish tubers were 266.15, 2.82 and 15.42 mg kg-1 of zinc, chromium and lead, respectively, with the lead content found in the samples were above the maximum extent permitted recommended by the Codex Alimentarius.