The aim of this study was to determine the possible effects on soil health and crop yield of the application of anaerobically digested sewage sludge (SS) at doses of 10 (SS1), 20 (SS2) and 30 (SS3) t ha(-1) yr(-1) to degraded soils under maize (Zea mays L.) and cotton (Gossypium hirsutum L.) in the semi-arid Mediterranean ecosystem in Turkey. Application of SS at different doses did not show any disruptive effect on microbial biomass and activity in the soil. In the microbiochemical parameters analyzed in the soils under the two plant covers treated with SS, increases were seen of 29-30% compared with control, and of 28-30% in comparison with chemical fertilizer application. Yield increases secured by chemical fertilizers were statistically significantly higher than those from the SS1. In maize grain yield, statistically significant increases were shown in comparison with the control of 90% with SS3 and of 86% with SS2. Similarly, seed cotton showed a statistically significant increase in yield of 72% with SS3. Results obtained from the study show that for degraded soils in Mediterranean biodegradability conditions, application of SS at a rate of 30 t ha(-1) yr(-1) can be used both as a soil improver to maintain the soil and as an organic fertilizer to increase crop yield.