In a laboratory study, nitrate (NO3−-N) and ammonium (NH4+-N) release from four different plant residues, two manures, and sewage sludge and municipal waste compost were studied for 11 weeks at 25°C, using an incubation method. Cumulative NO3−-N released from residues was in a range of 1808 mg kg−1 (rape) to 15181 mg kg−1 (poultry manure), while Cumulative NH4+-N released was in a range of 497 mg kg− (sheep manure) to 6980 mg kg− (sewage sludge). Total N mineralization ranged from 18207 mg kg−1 for the poultry manure to 2321 mg kg−1 for the rape residues. The simple exponential and power models were found to be suitable to describe N release rates from residues. Nitrogen release rate from power model ranged from 346 (rape residue) to 2174 mg kg−1 week−1 (poultry manure) and was positively related to N content (r = 0.88; P < 0.01) and negatively related to C/N ratios (r =0.67; P < 0.05). The model parameters of N-release are suitable to estimate the N-fertilizer effect of organic residues. Our results suggest that the use of organic residues as a source for short and long-term N supply for crops should be encouraged. Among the various organic residues, poultry manure, potato and sewage sludge had the highest rate constant for N, indicating the high potential availability of N in the early stage of application to soils. This means that there is a great risk of such residues contributing to N losses by leaching.
