Summary:

The experiment was conducted was in the years 2005-2007 on the very light soil in Kruszyn Krajeński near Bydgoszcz. The influence of sprinkler irrigation and the differentiated nitrogen fertilization on yields of early potato cv. ‘Dorota' was studied. This experiment was established as a two-factorial trial. The first-row factor was sprinkling irrigation applied in two variants: W0 - without irrigation (control), W1 - sprinkling irrigation. The second row factor - differentiated nitrogen fertilization, was used in the four following variants (doses): N0 = 0 kg N•ha-1, N1 = 40 kg N•ha-1, N2 = 80 kg N•ha-1, N3 = 120 kg N•ha-1. Potatoes were fertilized with the full dose of manure, the fertilization with P and K was uniform on all the plots, and it was applied in relation to the soil fertility. The mean yield harvested on control plots (without irrigation) amounted on average 14,41 t•ha-1. Smaller yields, in range 8,75-11,83 t•ha-1, were noted in the first two years of study which were characterized by lower rainfall (161-230 mm), higher yields (22,66 t•ha-1) - in year 2007 that was characterized by the highest rainfall (323 mm) in the vegetation period of the potatoes. The use of irrigation significantly increased the yields, on average to level 28 t•ha-1. The yield increase, obtained thanks to irrigation, amounted 13,59 t•h-1 (94 %). The higher increases of yields (in the range 15,03-17,99 t•ha-1 - i.e. 127 %) were noted in the first two years of investigation with lower rainfall during the vegetation period, and the lowest productive results (7,78 t•ha-1, i.e. 34,3%) the irrigation caused in the year characterized by the highest rainfall. The nitrogen fertilization was effective on control plots only in case of the last, wet year of investigations. Significant interaction of sprinkler irrigation and nitrogen fertilization in formation of potato marketable yields was observed. The increasing doses of nitrogen caused - in conditions of irrigation - significant yield increase, which amounted, on average for three years 32,17 t•ha-1. The highest yield was noted on plots fertilized with dose 120 kg N•ha-1 (N3). Average from three years, the increase of yield obtained thanks to irrigation amounted 11,61 t•ha-1 with dose 40 kg the N•ha-1, 16,01 t•ha-1 with dose 80 kg N•ha-1, and 16,69 t•ha-1 with dose 120 kg N•ha-1. The higher was nitrogen dose, the higher was productivity of 1 mm of water from irrigation. This productivity, on av-erage or the three years, amounted: 113,4, 127,2 and 126,5 kg•ha-1•mm-1, for the nitrogen doses: 40, 80 and 120 kg N•ha-1, respectively.