The aim of the study was to determine the fungal population colonizing the cultivation environment (non-rhizosphere soil and rhizosphere) of three potato cultivars fertilized with varied doses of nitrogen. The study was carried out in 2000–2002 on a strict field experiment in Tomaszkowo on a light, sandy soil representing the 5th soil quality class and belonging to the poor ryepotato complex. The experimental fields were 30.45 m2 and were established randomly. The experiment was completed in 4 replications. The three following potato cultivars were cultivated after winter triticale: Bard – very early, Rybitwa – semi-late and Wawrzyn – late. Manure (25 t/ha) was applied in the fall and polyfoxa 6 (500 kg/ha) was applied in the spring before potato planting. The experiment involved combinations with nitrogen fertilization at 30, 60 and 90 kg/ha as 46% urea applied after potato germination. Non-rhizosphere and rhizosphere fungi were isolated from the examined potato plants in a laboratory at the end of April. The amounts of soil taken from both zones for analyses were equal (1 g). The fungal population was represented by 34 species forming in total 1979 isolates. The largest number of fungal isolates was isolated from the potato cultivation environment in 2001 and the smallest number of isolates was observed in 2002. The largest number of potentially pathogenic and pathogenic isolates: Alternaria alternata, Colletotrichum coccodes and from the genus of Fusarium was obtained in the final, dry and warm experimental year. The soil originating from the cultivation of Bard cultivar was characterized by a larger number of isolates (35.8% of the total number of fungal isolates) than that originating from Rybitwa cultivar (31.0%). The largest number of potential pathogens was isolated from the cultivation of Bard cultivar (19.3% of the total number of colonies). Smaller number of pathogens were isolated from Rybitwa (14.7%) and Wawrzyn (10.4%) cultivars. Potentially antagonist towards pathogens most frequently colonized the soil of Wawrzyn cultivar and very rarely colonized the soil of Bard cultivar. Fungi representing the genus of Penicillium, the remaining species of Mucorales and Trichoderma were rare. The smallest number of potential antagonist towards pathogens was characteristic of the combination with the lowest dose of nitrogen.