in general, GA, UA, APA and ASA in sludge-amended soils decrease dramatically of 30 days of incubation at all C:N ratios and doses of sludge.
taking into account the evolution of the enzyme activities during the incubation period, two different stages can be distinguished: a first stage lasting 30 days during which a great activation of the enzymes as a result of adding the different doses and C:N ratios of sewage sludge was recorded, and a second stage lasting until the end of the incubation in which a major decrease in the enzyme activities in soils treated with the sludge was recorded.
the first stage depends on microbial growth and available substrate for enzymes stimulated by addition of sewage sludge to soil
thus, increase microbial activity may have synthesized enzymes in the soil.
the second stage depends on contents and availability of sludge borne metals