Effects of repeated applications of sewage‐sludge compost on soil properties have not been sufficiently evaluated with field trials. Field studies were established on an Evesboro loamy sand soil (mesic, coated Typic Quartzipsamment, 97% sand) to compare the effects of sewage‐sludge compost, beef manure, and fertilizer amendments on soil properties. The study site had been fallow for 26 yr and should have provided a positive response to the added organic matter. Compost application rates were based on the assumption that material would be applied either only once or annually. Application rates ranged from those that were too low to supply the total N requirement of a crop (e.g., 33 Mg ha−1) to excessively high rates that would produce maximum soil benefits from the added organic matter (e.g., 268 Mg ha−1). Soil properties such as strength (penetrometer resistance), bulk density, water retention, pH, surface area, total N and P contents, and organic matter were evaluated for 5 yr. Addition of sewage‐sludge compost significantly reduced penetration resistance when compared with the control and fertilizer‐amended soils. Compost significantly reduced bulk density, increased soil water content, and modified pH to greater depths. Specific surface area of the soils increased linearly with the addition of compost and C levels indicated that 24 and 37% of the annually added organic matter decomposed during the 1st yr from the sewage‐sludge compost and beef manure, respectively.

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.

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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.