Sewage sludge effects on gas fluxes at the soil–atmosphere interface, on soil δ13C and on total soil carbon and nitrogen

The objective of this work was to study the effect of long-term and continued application of sewage sludge on total carbon and nitrogen, soil δ13C and on the gas fluxes at the soil–atmosphere interface under field conditions in the tropical region. To that effect, four applications of sewage sludge from an industrialized region were performed on a Dark Red Dystroferric Latosol. Sludge was incorporated to the soil at concentrations of 0, 1, 2, 4 and 8 times the recommended rate based on their nitrogen content in four consecutive corn cultivations. All sludge rates increased the concentration of soil C and N as compared to the control. The soil C contents at the highest sewage sludge rate increased by 55% and 48% at the layers from 0 to 10 cm and from 10 to 20 cm, respectively, as compared to the control. In the case of soil N, the increase was in the order of 59% and 66% at the highest sludge rate at the layers from 0 to 10 cm and from 10 to 20 cm, respectively, relative to the control. The increase in soil C content was derived from the sewage sludge, as demonstrated by δ13C analyses and, since the soilʹs δ13C contents were negative, it is suggested that the soil is sequestering carbon contained in the sewage sludge. The application of sewage sludge increased the flux of CO2, N2O and CH4 to the atmosphere, by 220%, 320% and 165% respectively, for the highest sewage sludge rate, when compared to the control. Even though greater emission of gases was observed as compared to the control and to the treatment corresponding to the cropʹs recommended mineral fertilization, it is important to note that part of the C added via sewage sludge is becoming sequestered in the soil.