Availability of Nitrogen in Municipal, Industrial, and Animal Wastes

Abstract Nitrogen availability in soil amendments is important from both a crop production and an environmental protection standpoint. Municipal, industrial, and animal wastes were incubated with soil for 16 weeks and then NH 4 + ‐N + NO 3 − ‐N determined. Some of the wastes with high C/N ratios received supplemental inorganic N prior to incubation. Available N was generally greater from aerobically digested municipal sewage sludges than from anaerobically digested ones. However, variation within each sludge type was large and using an average value could lead to large errors in application rates. Availability of N in industrial wastes ranged from immobilization with paper mill sludges to 520 g kg −1 of the organic N in sludge from a poultry processing plant. A regression model, significant at the 0.001% level, predicted availability of N in aerobic and anaerobic municipal sludges within ± 30% of actual values [(g available N)/(kg organic N) = 380 + 135 (g organic N)/(kg waste) − 128(g total N)/(kg waste) + 1020(g C/g organic N) − 1120(g C/g total N), R 2 = 0.89]. The model was not effective with data from other studies with different soils and sludges. The quantity of supplemental inorganic N immobilized by wastes having high C/N ratios increased with inorganic N added.