Soil chemical properties and corn production in a sewage sludge-amended soil

The application of sewage sludge into agricultural soils, as organic fertilizer or soil conditioner, is becoming an increasingly more attractive alternative. It is occurring because of the high costs and environmental impacts caused by other sludge disposal methods, besides the presence of plant nutrients and organic matter in the sludge and the need to reduce costs in agriculture. However, sewage sludge can contain heavy metals, pathogenic microorganisms, and toxic organic compounds. In order to study the impact of sewage sludge application in agricultural areas, a two-year experiment was implemented to determine the changes in soil chemical properties, mainly in the P, Cu, Ni and Zn contents, in an eutroferric clayey Red Latosol (Rhodic Eutrustox) cropped with corn. The experiment consisted of two application rates of sewage sludge and a control with chemical fertilization. Soil samples were collected at the 0-0.05; 0.05-0.10, and 0.10-0.20 m depths after the corn harvest in both years for a routine chemical analysis and the Ni content. Additionally, a sequential P extraction for samples of the 0 to 0.05 m, layer was carried out in the following order: CaCl2 (P biologically most available); NaHCO3 (available P); NaOH (P adsorbed to the Fe and Al oxides); HCl (P adsorbed to Ca) and nitric-perchloric digestion (residual P). Corn yield was higher in the treatments with sludge application. The available P content in soils that received sludge application was similar to those of the treatment without sludge and with chemical fertilizer. However, sludge application increased the labile and moderately labile P fractions in the surface soil layer. The data suggested, however, increased Cu, Ni, and Zn concentration in soil and Zn concentration in plants. Thus, a constant monitoring of soils that receive application of sewage sludge is required for an adequate control of the metal levels.