Microbial biomass and biological activity of dark gray forest soils upon application of sewage sludge

The effects of municipal sewage sludge on biological properties (the microb ial biomass, soil respiration rate, and nitrogen fixation activity) and the concentration of heavy metals in the dark gray forest soil were studied. T hree kinds of sewage sludge-untreated sludge, sludge subjected to aerobic f ermentation, and composted sludge-were applied. Judging from data on ecophy siological quotients, the application of sewage sludge causes relatively we ak changes in the microbial activity and microbial biomass of the soil stud ied.