A field experiment was conducted during two years to determine N availability to corn (Zea Mays L.) and NO3- leaching risk from a peat-based organo-mineral fertilizer (OMF) in comparison to conventional mineral N fertilizers (MF). Randomized blocks with four replicates and an unfertilized control were performed during 2003 and 2004. The rate of N application was set at 300 N, 120 P2O5 and 120 K2O kg ha-1. The two growing seasons differed widely for main climatic parameters (air temperature and rainfall) that produced remarkable effects on soil mineral N dynamics. Generally, the higher temperatures that characterized 2003 reduced the differences between MF and OMF. The MF produced a peak in extractable NH4+-N few days after spreading (6-10 d) whereas this peak shifted for the OMF from 5 to 30 days during 2003 and 2004 respectively. The OMF left an higher amount of mineral N during the whole growing season, especially in 2004. At the end of the growing season, the amount of total soil N and their mineral forms (NO3- plus NH4+) in plots fertilized with the OMF were similar to the plots manured with MF and only slightly higher than unfertilized control plot, suggesting that the delay in N availability of OMF was of limited duration and that nearly all NO3- not absorbed by plants was lost by leaching.