One unintended consequence of nitrogen use in agriculture is an increase in nitrate content in ground waters. Nitrogen content was evaluated in soil samples from specific hydrographic regions of Poland from the 60-90 cm soil layer, in which this nutrient is not readily available to the main root mass of crop plants and may negatively affect the environment. It was revealed that Nmin content in specific hydrographic regions was highly dependent on both the soil type and land use. Notably higher values of Nmin content were observed for organic soils. The highest N contents were found in the grasslands of the north-western area of Poland, while they were slightly lower in several regions of the main Odra River catchment and west of the Vistula River. The area with a high Nmin content in soils under maize was significantly larger compared to the grasslands area and primarily included the hydrographic regions of the Odra River basin in its south-western stretch, and of the Vistula River on its western and south-eastern side. With regard to the arable land under mixed cereals, the soils with the highest Nmin content in the non-root layer were predominantly located in hydrographic regions belonging to the main Odra catchment and to the catchment of the Vistula River in its upper course.