Summary:

The aim of the study was to determine the effect of drip irrigation and ni-trogen fertilization on yields of ‘Kutnowska' onion grown on the very light soil in the region characterized by rainfall deficits during the vegetation period. Field experiments were carried out in 2003-2004 at Kruszyn Krajeński near Bydgoszcz on a soil belonging to the VI class (degraded black earth belonging to the very poor and poor rye complex). Field water capacity in the layer 0-50 cm amounted 57,5 mm, and the effective useful retention was 29,3 mm. Field trial was established and conducted in three replications as two-factorial experiment in split-plot design. Irrigation was the first order factor used in the two variants: without irrigation (control) and drip irrigation at - 30 kPa. The second order factor was nitrogen fertilization: N0 - 0 kg N ha-1(control), N1 -70 kg N ha-1, N2 - 140 kg N ha-1, N3 - 210 kg N ha-1. Drip irrigation was the basic yield-creating factor, securing the cultivation of onion on the loose sandy soil. Marketable yield obtained from ir-rigated plots - average for years and nitrogen doses - amounted 33,2 t•ha-1. Un-der conditions of optimum moisture secured by irrigation, the effectiveness of ni-trogen fertilization was increased. The marketable yield of the irrigated onion was the highest (51,1 t•ha-1) when 210 kg N•ha-1 was applied. Because differences be-tween marketable yields obtained on plots fertilized with 140 and 210 kg N•ha-1 were insignificant, the nitrogen dose of 140 kg N ha-1can be recognized as the op-timum dose for the studied soil-moisture conditions. Drip irrigation - average for years and nitrogen doses - increased the bulb weight from 10,6 g to 61,9 g. The highest single bulb weight (in the range 82,9-88,8g) was obtained on plots fertilized with the highest nitrogen dose under drip irrigation. Onion cultivated under irrigation was characterized by the lower nitrate content as compared to that grown on control plots (without irrigation). This regularity was detected for all the nitrogen fertilization doses.