Restoring degraded lands: the role of sewage sludge in modulating soil carbon and nitrogen dynamics

Sewage sludge presents significant amounts of organic matter and nutrients and is frequently considered an alternative input for recovering degraded soils. In this scenario, this study aimed to evaluate the impacts of disposing of increasing doses of sewage sludge on the dynamics of C and N in the soil of a degraded area. After the application of five doses of sewage sludge (0, 50, 100, 200, and 400 t ha-1) were evaluated over time (30, 90, 180, 270, and 360 days), the contents of soil C and N, microbial biomass, light organic matter, and humic fractions of soil organic matter. The results showed that sewage sludge contributed to the quality and recovery of degraded soil by providing increases in soil organic C, total N, nitrate, and ammonia contents, microbial biomass C and N, light organic matter, as well as in the C and N stocks in humic substances, especially in humin. Most of the increases in these variables associated with C and N dynamics remained even one year after the application of sewage sludge. The soil quality improvement demonstrates the potential of using sewage sludge in projects to recover degraded areas as an alternative for its final disposal.