For wastes that have significant liming potential, agronomic rate is determined by the lime equivalent and the lime requirement of the soil to which the waste will be applied. Regarding nitrogen, sewage sludge and similar biosolids contain nitrogen in both organic and inorganic forms. Most of the nitrogen in sludge is in the organic form which is unavailable to plants until it is converted to inorganic nitrogen. Most of the inorganic nitrogen is in the form of ammonium and ammonia. Ammonia nitrogen is subject to loss by volatilization.
Losses are greater for alkaline material left on the surface.
Injection below the soil surface minimizes losses. Small amounts of nitrate, another inorganic form of nitrogen, are present in sludge. Ammonium and ammonia in soil are converted to nitrate by naturally occurring microorganisms within a few days to a few weeks depending on soil temperature and moisture. A portion of the organic nitrogen is mineralized, converted to an inorganic form as the organic compounds in sludge are decomposed, and thus becomes available during the growing season after sludge is applied to the land. The inorganic ammonium, ammonia, and nitrate produced during decomposition of the organic substances in sludge are identical to the ammonium, ammonia, and nitrate found in commercial fertilizers.