SEWAGE-SLUDGE EFFECTS ON CHEMICAL-PROPERTIES OF ACID SOILS

Field experiments were established at two locations (on an Oxisol and an Ultisol) to evaluate the effects of 0, 8, 16, and 24 metric tons ha-1 of aged municipal sewage sludge on soil properties and growth of four crop species. Soil samples taken from each plot, before sludge application and at harvest of the crops, are compared here to determine any effects of the sludge on pH, exchangeable acidity, exchangeable bases, cation and anion exchange capacity, and extractable phosphorus and trace metals. To test effects on soil properties in a more controlled environment, soil from one site was incubated with the sludge over a period of 4 months. No detrimental effects and several beneficial effects were observed. In particular, problems of soil acidity were diminished by an increase in pH and exchangeable calcium accompanied by a decrease in exchangeable acidity. Sludge applications also increased BaCl2-MgS64 CEC, but only in the Oxisol did the sum of cations increase. Dilute acid-fluoride extractable phosphorus also increased with sludge additions accounting for 2 to 19% of added sludge P for the Ultisol and 19 to 52% of P added to the Oxisol. Increases in Mehlich-3 extractable Cu and Zn in the soils were approximately equal to the amounts of these elements added to the soil in the sludge.