The study analysed the relationship between the granulometric composition of grassland soils as determined by laser diffraction and their content of mineral forms of nitrogen and organic carbon. The content of mineral forms of nitrogen (NO _3-N and NH _4-N) in soil samples – after their extraction with 1% solution K ₂SO ₄, was determined by flow colourimetry. Soil organic carbon content was determined using the Tyurin method. The study examined soil samples collected from 169 control and measurement sites located in different regions of Poland in terms of conditions for agricultural production. Statistical analyses of the research results showed that the grain size of grassland soils had a significant effect on their ammonium nitrogen content but not on their nitrate nitrogen and organic carbon content. In this respect, it was found that there was a positive correlation between the share of the sand fraction and the content of ammonium nitrogen in soils and an opposite relation between the share of coarse silt, fine silt and clay and the content of the aforementioned component. Results of the analyses differ considerably from the results of studies by other authors on the influence of soil grain size distribution on the content of mineral nitrogen and organic carbon in soils based on classical methods of measurements of soil particle size distribution. There is a need to develop solutions to convert and compare results obtained by laser diffraction and standard methods.

This paper presents the results of a study on the level of nitrate leaching from the 0–30 cm layer of grassland (GL) soil in the Lublin Voivodship during the winters of 2018/2019, 2019/2020 and 2020/2021. The amounts of leached nitrates were determined using the Burns model. For the calculations based on this model – directly and indirectly, the results determination of residual nitrate nitrogen, texture and organic matter in GL soils, obtained within the framework of agricultural monitoring of soils by the National Chemical and Agricultural Station (KSChR), and results of system meteorological measurements conducted by the Institute of Meteorology and Water Management – National Research Institute (IMGW-PIB) were used.
The analysed soil samples were taken from 39 permanent control and measurement grassland sites. The research discovered in particular that:
– the average leaching of nitrate nitrogen from GL mineral soil in the three analysed periods was 16.2 and 5.1 kg N∙ha–1 from organic soil;
– on average, in autumn during the entire study period, 55.3% of NO3-N leached from the 0–30 cm layer of GL mineral soil, and 27.3% from organic soil;
– among different agronomic categories of mineral soil, the highest leaching of NO3-N was recorded from medium soil (17.4 kg N∙ha–1) and the lowest from heavy soil (11.5 kg N∙ha–1);
– individually determined values of NO3-N leaching from soil varied significantly from 0 to 68.5 kg N∙ha–1 for mineral soil and from 0.1 to 23.65 kg N∙ha–1 for organic soil.