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 study presents the results of research on the effect of long-term use of phosphorus fertilizers on permanent sugar beet crops for more than 50 years and on the transformation of phosphate forms on light chestnut soil and its yield. Our work aims to establish the main factors of quantitative and qualitative changes in various phosphates in light chestnut soil. Despite the large amount of practical material, the influence duration of phosphorus fertilizer application has not been sufficiently studied on the irrigated soils of Kazakhstan. It should be noted that the current study was carried out in long-term stationary experimental sites for the production of sugar beet with permanent sowing. The introduction of phosphate fertilizers primarily on the permanent crops of sugar beets in the same norms contributes to a more significant increase in gross phosphorus reserves. The soil content of gross phosphorus for 58 years on the control and nitrogen-potassium variants show practically no changes. Furthermore, when phosphorus fertilizers are applied on the variant with the annual application of a single norm of phosphorus and its amount for 58 years (4400 kg∙ha–1 of application doses) its content increased by 2660 mg∙kg–1, and with the introduction of its one and a half norms (6600 kg of application doses) by 2860 mg∙kg–1 of soil.