Nitrogen Mineralization Of Sewage Sludge And Its Effects On Poplar Growth And Soil Quality

On the basis of the incubationexperiment in Lab and the pot experiment in greenhouse, the nitrogen (N) mineralization of sewage sludge and its effects on soil quality (soil physic-chemical properties, heavy metal content and enzyme activity) and poplar growth were studied in order to find the best sludge input as a fertilizer. The main results were as follows:1 The N mineralization of sweage sludge joined in soils was divided into two phases: the quick mineralization and the slow mineralization, and for all treatments the kinetics models of mineralization were fitted to the one pool kinetic model.2 Over an incubation of 16 weeks,the mineralized N from the soil organic N was increased with the increase of sludge added, while the mineralized N from the sludge organic N and its ratio to total organic in sludge added were dereased.3 Incubation temperatures had a great influence on N mineralization of the sludge. The cumulative percentage of N mineralization was significantly increased with increase of incubation temperature ranged from 10℃to 30℃in this experiment.4 Application of sewage sludge as fertilizer had an obvious effect on the height, diameter at ground and biomass of poplar seedlings, and such effects were also different between in the silty loam soil and the sandy loam soil. The growth of poplar seedlings was the best when the sewage sludge was applied in ratio of 3%, and then with the increase of sweage sludge applied the bimass of poplar seedlings in other treatments was decreased. Meanwhile, Sewage sludge applied significantly increased the N and P absorption of poplar, and the N and P uptaken by poplar in the treatment of 3% was obviously greater than that in the treatment of 6% and 12%.5 Sweage sludge applied in soil not only significantly increased the content of organic matter, N and P in soil, but also increased the content of heavy metal (Cu and Zn) in soil, especially when the sludge was applied over 6%. However, the soil pH value was decreased due to the sludge.6 Application of sludge had also influences on soil enzyme activity to some extent. The activity of soil catalase and urease was increased with the increase of sludge appied in soil, while the changes of activity of sucrase and alkaline phosphatase in soil were not obvious with the increase of sludge applied in soil.