Ammonium and nitrate concentration in the soil were determined at 0-30, 30-60, and 60-90 cm after using two sources of nitrogen fertilizers: Cote N (4) and stabilized ammonium nitrate (SAN). Cote N (4) is a controlled release fertilizer that releases N within four months. Both fertilizers Cote N (4) and SAN were applied in an asparagus plantation with furrow irrigation. Nitrogen rate for the Cote N (4) treatment was 105.3 kg ha-1 and for the SAN treatment was 230 kg ha-1. Cote N (4) was applied at the beginning of the crop, before the first irrigation, and SAN was split in five fractions, each fraction coinciding with one furrow irrigation. Results of soil nitrate concentration showed that nitrate from SAN might pose a pollution threat for subsurface water or at least it might be lost by runoff to places where N application is not intended. Tissue N concentration was determined in phylloclades showing that there should be found other ways to assess whether proper nitrogen (N) nutrition has been achieved in asparagus. The yields of the experiment suggest that to assess the efficiency of a N fertilizer it should be applied a minimum N requirement to target the expected yield and the soil N supply should be also considered.