Additional index words: irrigation, Kjeldahl-N, drainage water, soil water content. AbstraetLosses of nitrate from an undisturbed sandy loam soil contained in two monolith lysimeters, Lo and L¡, (1 m diameter, 1.5 m deep) under com and irrigation (628 mm) were studied. The crop was fertilized with O (Lo) and 800 (L¡) kg N ha-l. Water draining was collected periodically and analysed for nitrate content during the experimental period (20)(21)(22)(23).Mean values of nitrate concentration in the drainage water were 3.1 and 41.2 mg NOrN 1-1 in Lo and Ll respectively, the latter much higher than the limit imposed by the EC for potable water (11.3 mg N l-I).Three periods were distinguished during the experiment: i) Crop season, in which the total volume of water drained was 310 and 47 mm respectively in the Lo and L l , while the nitrate 10sses were of the same order in both lysimeters ( 21 and 17 kg N ha-l , respectively); ii) Dry season, in which there was no water drainage; and iii) Rainy season, in which the total drained water was 157 and 139 mm, and the nitrate los ses 5 and 91 kg N ha-l in Lo and L¡ respectively.The greater amount of water drained in Lo is due to the lower crop development (grain yield 4.4 and 21.3 t ha-l ; total nitro gen plant uptake 69 and 400 kg N ha-l , in Lo and Ll respectively).Total nitrate losses in Ll account for 13% of the nitro gen fertilizer applied. Most of these losses occur in the rainy season.At the end of the experimental period a decrease of the soil nitrate content was observed in both lysimeters.