NITROGEN MINERALIZATION AND NITRIFICATION IN SOILS TREATED WITH AMMONIUM-SULFATE AND NUTRASWEET SLUDGE

NutraSweet sludge, a by-product of the manufacture of the artificial sweetener aspartame, contains about 40% of its nitrogen (N) in inorganic form and the rest mostly in the form of L-phenylalanine. Although this sludge is often applied to land as fertilizer, the exact management strategy for its optimum use has not been clear. We conducted a laboratory study to compare the evolution of inorganic N contents and nitrification in two soils treated with NutraSweet sludge and ammonium sulfate at rates of 0, 25, 50, 100, and 150 mg N kg-1. Four days after application, the inorganic N recovered from the sludge ranged from 67 to 105%, indicating a fast rate of mineralization. At 25 and 50 mg N kg-1, the overall recovery of inorganic N from NutraSweet sludge was higher than from ammonium sulfate, whereas the converse was true at higher application rates. In Dothan soil with an initial pH of 5.5, nitrate-N as percentage of the N applied was higher in samples with NutraSweet sludge than in those with ammonium sulfate. The opposite effect was observed in Tifton soil, which had an initial pH of 6.8. Due to the fast release of inorganic N from NutraSweet sludge, the material should be managed as an inorganic, ammoniacal N fertilizer.