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Soil Science Society of America Journal Abstract -

Sewage Sludge Proteins as Labile Carbon and Nitrogen Sources


This article in SSSAJ

  1. Vol. 56 No. 5, p. 1470-1476
    Received: Sept 10, 1991

    * Corresponding author(s):
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  1. R. N. Lerch ,
  2. K. A. Barbarick,
  3. L. E. Sommers and
  4. D. G. Westfall
  1. USDA-ARS Cropping Systems and Water Quality Research Unit, Columbia, MO 65211
    Dep. of Agronomy, Colorado State Univ., Fort. Collins, CO 80523



The study of specific, organic sewage sludge constituents is necessary to augment our knowledge of C and N mineralization in sludge-amended soils. A laboratory incubation study of seven sewage sludges was initiated to test the hypothesis that sewage sludge proteins are labile C and N sources. Sewage sludge proteins were extracted with H2O, 10% (v/v) Triton X-100, and 1.0 M NaOH and determined by the Lowry assay. Sewage sludges were mixed with Bresser sandy loam soil (fine-loamy, mixed, mesic Aridic Argiustoll) at a rate of 10 g dry sludge kg−1 dry soil and incubated at 25 °C and 0.111 kg kg−1 soil water content for 12 wk to determine sludge C and N mineralization. Extractable sludge proteins were highly correlated to C mineralization (r2 = 0.94-0.96), but they were poorly correlated to N mineralization (r2 = 0.40-0.41). This supported the hypothesis that sludge proteins were a labile C source but not a labile N source. However, low molecular weight primary amines (assumed to be predominately protein degradation products) combined with the sludge C/N ratios were highly correlated to sludge N mineralization rates (r2 = 0.91). Nitrogen mineralization of sludge-amended soil followed either zero- or first-order kinetics. Kinetic models of the first-order systems showed that N mineralization was best described as the decomposition of two distinct organic-N pools. Sewage sludge proteins appear to be significant sources of labile C, and their degradation products apparently are critical N sources.

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