DYNAMICS OF EXTRACTABLE PHOSPHORUS DURING NONSTERILE AND STERILE INCUBATION OF SLUDGE-AMENDED SOIL

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Abstract
In a laboratory experiment we followed the dynamics of P availability in sludge-amended soil. A clayey soil (Glendale) and a sandy soil (Latene) were amended with three rates (0, 15, and 30 g kg−1) of gamma-irradiated, dried, anaerobically digested sewage sludge. Triplicate 300-g samples of each soil and sludge rate were incubated for 84 d at 35°C and 0.03 MPa moisture tension. Samples were periodically taken to determine NaHCO3- and H2O-extractable P. In subsequent experiments, Glendale soil was sterilized by either gamma irradiation (50 kGY) or autoclaving to study the effects of microbial activity on NaHCO3-P and H2O-P. Sludge amendment significantly increased NaHCO3-P levels in both soils throughout the 84-d incubation period. NaHCO3-P values for both soils were directly related to the amount of sludge added. A rapid rise in NaHCO3-P occurred in the 1st wk of incubation, but values remained fairly constant thereafter. For days 7 to 84, values of NaHCO3-P for the 0-, 15-, and 30-g kg−1 treatments were 16, 35, and 50 mg P kg−1 and 6, 27, and 44 mg P kg−1 for the Glendale and Latene soils, respectively. Sludge amendment significantly increased H2O-P levels in only the Latene soil. However, in both sludge-amended soils, H2O-P significantly increased with time over the 84-d incubation period. Soil sterilization by irradiation had no effect on NaHCO3-P and H2O-P levels, compared to nonsterilized soil. Soil sterilization by autoclaving had a much greater effect on indigenous soil P than irradiation. Although data from the autoclave experiment were highly variable, no consistent differences were observed between the sterile and nonsterile soils. We conclude that NaHCO3-P and H2O-P increases in sludge-amended soil are the result of chemical rather than microbial transformations. © Williams & Wilkins 1985. All Rights Reserved.