Decomposition of Sewage Sludge Compost in Soil: I. Carbon and Nitrogen Transformation

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Abstract
Laboratory incubation studies were conducted to determine the rate and extent of decomposition of sewage sludge compost in soil. Freeze‐dried compost made from undigested sewage sludge was mixed with three soils (a loamy sand, a silt loam, and a silty clay) and a sand at rates of 0, 2, 4, and 6% of the dry weight. The mixtures were incubated at 22C in a constant atmosphere of CO2‐ and NH3‐free air. Rates of mineralization and decomposition were determined by monitoring CO2 and NH3 evolution and changes in the organic and inorganic fractions of C and N with time. Cumulative CO2 evolution was linearly related to the rate of sludge compost applied. Approximately 16% of the compost C evolved in 54 days of incubation. Nitrogen mineralization was lowest in the silt loam‐compost treatment. In the sand‐compost mixture, mineral N was immobilized during incubation. Ammonia volatilization from all of the treatments was minimal. Approximately 6% of the compost N in the loamy sand‐compost treatment had mineralized after 54 days incubation. Interlattice fixation of NH4+ may have occurred in the silt loam and silty clay soils.
Funding Information
  • Maryland Environ. Serv., Annapolis, Md.