Repeated sewage sludge application to soils can cause changes in some soil chemical properties. The goal of this paper was to evaluate changes in soil organic carbon content, electric conductivity, pH and CEC after sewage sludge application during two years in a row. The soil used was as a Typic Hapludox and, after the sludge application, was planted with sugarcane. The experiment had five treatments: lime + inorganic fertilization, control and sewage sludge in three levels: 33, 66 and 99 Mg ha-1 (dry weight basis) in the first cultivation year (1996/1997) and 37, 74 and 110 Mg ha-1 in the following year (1997/1998). There was an increase in soil organic carbon content, electric conductivity, pH and CEC values, measured 360 days after the sludge application each year. The decrease in soil organic carbon level in the period was adjusted to a first order model kinetics. Soil organic carbon accumulation was also observed and was due to repeated sludge application. There was no cumulative effect on soil electric conductivity for the second sewage sludge application. This allows to conclude that rainfall played an essential role over ion leaching during that period. Increased electric conductivity could be observed in the lower soil depth. The increase in soil pH, after the second sludge application, was lower than that observed after the first one, what indicated the buffer capacity of the soil and alkalinity of the waste. There was an increase in soil CEC, but it was not related to the sludge level applied or to the second application. The changes in CEC were explained based on changes in pH rather than in organic carbon.
Biosolids; soil; chemical atributes