Effects of Anaerobically Digested Sewage Sludge Addition on Improvement of a Degraded Nursery Garden Soil

Abstract:

A soil column experiment was conducted to evaluate the effect of 3-year consecutive application of anaerobically digested sewage sludge (ADSS) on a degraded soil from a nursery garden in Hefei City, Anhui Province. Soil physiochemical and microbiological parameters were determined, and accumulation characteristics of heavy metals in the soil were also analyzed. The results showed that 3 years after the ADSS addition, soil texture and physicochemical environment were significantly (P<0.05) improved, and the soil total dissolved salt (TDS) content and electric conductivity (EC) were decreased by 67.6% and 45.3%, respectively, which indicates that the ADSS application showed a improved effects on the degraded soil with secondary salinization due to continuous nursery plantation for several years. The application of ADSS significantly (P<0.05) increased soil organic matter content and nutrients supply. After 3-year ADSS application, soil organic matter was increased by 77.9% and the available nitrogen and phosphorus were increased by 110% and 95.4%, respectively, as compared with the control (no ADSS addition). At the same time, the ADSS application also significantly (P<0.05) enhanced nursery soil microbial biomass and metabolic activities. As compared to the control, soil microbial biomass carbon (MBC) was increased by 207%, and soil urease and alkaline phosphatase activity were increased by 118% and 102%, respectively. The above results showed that the application of ADSS could improve the degraded nursery soil quality. In addition, the nursery soil with 3-year application of ADSS showed an increase in the contents of heavy metals, but the contents of the determined heavy metals were far lower than the secondary level of soil environmental quality standard of China (GB 15618—1995). However the effects of long-term application of ADSS on accumulation of heavy metals in the nursery soil and its ecological risk need further study.