abstract: The aim of the present work was to investigate the mineral forms of nitrogen transformation in soil irrigated with communal wastewaters and estimation of a possibility of using organic soil and different plants for wastewater cleaning. The field experiments were performed on peat-moorsh and mineral-moorsh soils under willow, rape and grass-mixture crops, irrigated with 2nd stage purified wastewaters from “Hajdow” treatment plant in Lublin. The results showed marked effects of wastewater irrigation on the concentration of mineral forms of nitrogen in soil solution taken from various depths (10, 30, 50, 70, 100 cm) of the soil profile. Limiting values of selected contamination indexes and of soil aeration status were established. The soil was proved to behave as a biological filter for the introduced contaminants. Nitrogen concentration in drainage waters increased with increasing wastewaters dose. Higher concentration of N-NO3- and lower concentration of N-NH4+ were observed in the spring season (intensification of the process of nitrification). Therefore, in spring, the dosage of wastewater should be limited to prevent nitrates (V) against entering ground waters. In terms of suitability for N-NH4+ wastewaters purification, plants can be arranged in the following order: grasses, willow, and rape; in the case of the N- NO3- ion concentration, the corresponding plant order will be as follows: grasses, rape, and willow. In each of the cases under discussion, the concentration of N-NO3- in the drainage waters did not exceed 15 g N m-3, which meets the requirements of the European Union. Application of wastewater in single irrigation dose may constitute a valuable source of nitrogen in the cultivation of plants for industrial purposes. Part of this work was performed under the Grant PBZ 31-03.