effect application of sewage sludge and sewage sludge enriched with chemical fertilizer on the rate of organic carbon, respiration and enzyme activity of soil under basil cultivation

sewage sludge with having the organic matter is considered as a source of micro and macro elements. in order to investigate the effect of different levels and period of application of sewage sludge (ss) on organic matter, respiration, and acid and alkaline phosphatase activity, factorial design were studied, in 3 replications. sewage sludge at five levels, (20 and 40 tons of sewage sludge, 20 and 40 tons of sewage sludge + 50 percent of chemical fertilizers (cf) per hectare, without taking sewage sludge) and period of application three levels (two, three and four years) was considered. the results showed that application of ss at all levels, increased soil organic carbon (o.c) and soil microbial respiration and enzyme activity were compared with the controls (p<0.05), but trend of increasing among the treatments was not similar. in both two levels of treatment enriched with fertilizer, the traits increased. meanwhile, the amount of enzyme activity and respiration in high amounts of using ss has a decreasing trend. the maximum amount of o.c, in, 40 tons ss + 50% cf ha-1 with four years application treatment, soil microbial respiration 20 tons ss + 50% cf ha-1 with four years application treatment were measured. but, maximum amount of acid and alkaline phosphatase were observed in 40 tons ss with two years application. according to results, the 20 ton ss + 50% cf ha-1 in four years application treatments were best.