Decomposition of Sewage Sludge Compost in Soil: II. Phosphorus and Sulfur Transformations
1978
Taylor, J. M. | Sikora, L. J. | Tester, C. F. | Parr, J. F.
Laboratory incubation studies were conducted in which sewage sludge compost was mixed with three soils (Evesboro loamy sand, Christiana silty clay loam, and Fauquier silt loam) and a sand at rates of 0, 2, 4, and 6% (0, 44.8, 89.6, and 134.4 metric tons/ha, respectively) of the dry weight. The mixtures were incubated at 22°C under a flow of CO₂- and NH₃- free air. Extractable P in the compost-sand mixtures ranged from 48 to 81% of the total P. The Evesboro-compost-sand mixtures showed an initial net P mineralization trend followed by a slight immobilization trend at 54 days. The Christiana-compost mixtures had less extractable P than the Evesboro-compost mixtures, but did show initial increase in extractable P followed by a decrease during incubation. The iron and aluminum components in the Christiana soil were probably responsible for net immobilization of extractable P. The Fauquier-compost mixtures had the least extractable P and the highest free iron oxide content. Contrary to the other soils, the Fauquier-compost mixture showed initial net immobilization of extractable P followed by mineralization at 54 days. Ammonium acetate extractable S in the sand-compost mixtures was 8 to 11% of the total S. In the Evesboro-compost mixtures extractable S increased after 54 days incubation. The Christiana-compost mixtures immobilized extractable S early in the incubation but net mineralization of S was subsequently evident where the soil was amended with 4 and 6% compost. The Fauquier-compost mixture had the least extractable S and had immobilization-mineralization trends similar to the extractable P data. Both extractable P and S are in sufficient quantities at the 44.8 metric tons/ha application rate to sustain plant growth and, therefore, sewage sludge compost could be used to correct P or S deficiencies in most soils.
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