Cumulative Effects of Sewage Sludge on Soil Physical and Chemical Characteristics

Wastewater sludge has relatively high amounts of organic matter and salts which favorably affect the physical and chemical characteristics of the receiving soil. Hence, it can be used as a cheap fertilizer if properly utilized. A number of studies have been reported in Iran on the effects of sludge on soil chemical properties but few studies have been conducted to investigate its effects on soil physical characteristics. In order to study the cumulative effects of sludge on hydraulic conductivity, bulk density, MWD, soil infiltration, EC, and soil pH, an experiment was conducted in a complete randomized design with 7 treatments (1 × 22.5, 2 × 22.5, 3 × 22.5, 1 × 45, 2 × 45 and 3 × 45 ton/ha wastewater sludge) in three replications over three years. The above mentioned traits were measured after the third year of the experiment period. Results showed that increasing amounts of sludge enhanced saturated hydraulic conductivity, soil infiltration, MWD, and EC but decreased bulk density. A significant correlation was observed between the amount of sludge and soil physical characteristics. Factor analysis showed that the amount of sludge and all soil physical characteristics were in first order (physical characteristic factor) which explained 71% of the total variance, indicating the high impact of sludge on soil physical characteristics. The second factor was pH (a chemical characteristic) that explained only 17% of the total variance. Finally, no relationship was found between pH and soil physical characteristics.