This work was conducted to evaluate the influence of the irrigation system on the accumulation of nitrate in potato tubers. Over a 5-year period (1987–1993), nitrate contents were monitored in reference fields in different Agricultural Enterprises of La Havana province, in which  traditional irrigation systems were used (Fregat, DDA and Volschanka) These are different types of machines for irrigation by aspersion, that were used in Cuba before the fertigation system was established. During this period the rates of application of N per ha were higher than 450kg/ha (applied at sowing), and the yields were less than 20t/ha. Similarly, a study work was conducted in 1999 in potato fields with a localized fertigation system, which allows the joint application of both N fertilizer and water. The rates of application of nitrogen per ha were averaging 237kg/ha. The water (4333m3/ha – 4710m3/ha each 3–4 days) was distributed directly in the furrows, to very low pressure, through tubes located to the height of 20–45cm on the furrow; this technology, improved (until 10%) the efficiency of the irrigation by aspersion. The results obtained showed that the highest tuber yield of 36.42t/ha and lowest nitrate in potato tubers (40ppm) was produced by fertigation and the lowest tuber yield of 15t/ha and highest nitrate in potato tubers (724ppm) was produced by traditional irrigation systems. The field results on N use efficiency were further confirmed by those obtained from lysimeters (lisimetric tanks with an area of 0.2375m² and 60cm deep, with potato [Desiree Variety] as indicative crop), which were installed at the same field site and ¹⁵N-labelled urea fertilizer (20% ¹⁵N). The fertilization rate used for the potato was 180kg of N per ha, two methods of application of the fertilizer were compared: one at sowing and another as split applications  (50% at sowing and 50% at 30 days later). The results obtained by means of the isotopic method proved that the efficiency of N fertilizer rises to 35% when was applied at times when the crop is in the most need for nitrate (30 days after the germination of the crop). In the case of fertigation the dose can be divided into several applications and be applied in the moments of maximum demand. In the management conditions established up to 1993, the nitrate contents in tuber exceeded the permissible limit of 250 mg/kg. Though the introduction of fertigation in potato fields matches with a period of diminishing urea applications, it can be asserted that the low nitrate content (less than 100 ppm) in potato obtained under this condition is due to the combination of two characteristics of this irrigation system, more efficient use of the fertilizer and high harvesting yields.  

Key words: ¹⁵N–labelled fertilizer, stable isotope, N use efficiency, irrigation, fertigation, potato, nitrate content, lysimeters, field trial.