Influence of sewage sludge application on physical and chemical propertiesof Gypsisols

The abundant gypsiferous soils of the semi-arid central Ebro valley are ver y sensitive to environmental change. Poor land management practices have ca used severe degradation of the soils near the city of Zaragoza, leading to loss of productivity and of ecological function and badland formation on th e slopes. The use of sewage sludge for land rehabilitation is increasingly being considered as a technical solution to reverse this environmental degr adation and to promote the re-establishment of vegetation cover. This paper describes changes in selected properties of a Gypsisol following the addit ion of sewage sludge. Experiments investigating the influence of a range of application rates were conducted on 60 x 100 cm plots. The magnitudes of i ncrease in salinity and decrease in pH were found to be dependent on the sl udge application rate. Several beneficial changes were observed including i ncreases in organic matter, organic carbon and nitrogen content as well as in soil moisture and porosity. On the other hand, concentrations of major c ations and heavy metals also increase after sewage sludge addition, althoug h, their levels are below the standard limits fixed by the European Union. In order to avoid undesirable side-effects-salinity and toxic concentration s of metals-resulting from the application of sewage sludge to gypsiferous soils in semi-arid environments, it is necessary to characterize the sewage sludge and to determine the most suitable doses. This work highlights the potential of using sewage sludge for land reclamation of degraded soils in semi-arid environments. Nevertheless, the complexity of the processes invol ved requires further research to ensure the safety of sludge application. ( C) 1998 Elsevier Science B.V. All rights reserved.