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This article in JEQ

  1. Vol. 2 No. 4, p. 489-492

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Nitrogen Transformations and Availability of an Anaerobically Digested Sewage Sludge in Soil1

  1. J. A. Ryan,
  2. D. R. Keeney and
  3. L. M. Walsh2



Samples (50 g) of Warsaw sandy loam soil (Typic Argiudoll) were incubated under aerobic conditions with varying levels of an anaerobically digested sewage sludge (up to 1,880 ppm N on an oven-dry soil basis). Total N, NH4-N, (NO3+NO2)−N, NH3 volatilization, and hydrolyzable forms of N were determined periodically during 16 weeks of incubation at room temperature (23 ± 3C). At low levels (≤ 235 ppm N), the inorganic N was all converted to (NO3+NO2)-N while at the higher levels (≥ 940 ppm N), a significant amount of NH4-N was not nitrified even after 16 weeks of incubation. Recovery of added N was nearly quantitative at the low levels of sewage sludge addition. However, at the higher levels, there was evidence of concurrent nitrification-denitrification. The hydrolyzable N distribution results indicated that very little of the hydrolyzable N was mineralized at the low rates of application. At the high rates of application, apparent development of anaerobic conditions led to more rapid mineralization of the sewage sludge organic N than was found under aerobic conditions. The data indicate that from 4 to 48% of the organic N in the sewage sludge was mineralized to (NO3+NO2)−N in 16 weeks. Thus, the availability of sewage sludge organic N must be considered when evaluating the potential of the material as a fertilizer or a possible source of NO3-N to ground waters.

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