Nitrogen Transformations and Availability of an Anaerobically Digested Sewage Sludge in Soil
1973
Ryan, J. A. | Keeney, D. R. | Walsh, L. M.
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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