Agro-industry sludge as a potential organic fertilizer for a prompt nitrogen release

The aim of this study was to evaluate the sustainability of an agro-industry sludge as a nitrogen (N) fertilizer in perennial crops by assessing its dynamics of release of: 1) N as ammonium (NH4+)- and nitrate (NO3−)-N, and 2) carbon as soil respiration. In incubation assay, application of agro-industry sludge promoted the maximum NH4+-N concentration (50 mg kg−1) 2 h after application, then it decreased with time until day 26. NO3−-N increased, reaching the maximum between day 60 and day 100, according to a second degree function. Agro-industry sludge showed a slower release of NO3−-N compared with urea. Soil basal respiration and cumulative amount of carbon dioxide were higher in sludge from day 71 on. In field, soil NO3−-N increased after fertilization treatments and was higher in Calcari Stagnic Cambisols soil. Sludge showed a potential lower environment impact in terms of mineral N release, than urea