The effect of urban sewage sludge on chemical properties, soil basal respiration and microbial biomass carbon in a calcareous silty clay loam soil

The use of organic matter such as urban sewage sludge may help sustainable soil fertility via improving the physical, chemical and biological soil characteristics. The main purpose of this study was to determine the effect of urban sewage sludge on chemical properties, soil basal respiration and microbial biomass carbon in a calcareous soil with silty clay loam texture. Therefore, three levels of water repellency (zero, weak and strong) were artificially created in a silty clay loam soil by adding urban sewage sludge (S0=0:100; S50=50:50 and S80=80:20 sludge weight: soil ratio). Water repellency was determined with water drop penetration time (WDPT) method. Also some chemical properties such as soil acidity (pH) and Electrical conductivity (EC), soil organic carbon (OC), soluble sodium (Na) and soluble potassium (K) were measured. The samples were incubated at 23-25 ºC for 30 days and their moisture was maintained at 70-80 % under field capacity and soil basal respiration and microbial biomass carbon of incubation period was evaluated. The results showed that the effect of urban sewage sludge on chemical properties was significant (P ≤0.0001). The application of urban sewage sludge led to an increased basal respiration (16 and 27 times) and microbial biomass carbon (15.2 and 26.5 times) in the water repellency soils (S50 and S80) than in control soil. The observed positive effect of sewage sludge might due to a high content of organic carbon and nutrients in urban sewage sludge and decrease the labile organic matter and nutrients during incubation period.