Changes in soil structure of light-textured soil after 41-years of fertilization with mineral fertilizers

In the modern agriculture the mineral fertilizers are considered to be a significant intensifying factor, predominantly in sandy soils. The usage of mineral fertilizers results in the changes of the soil properties and therefore the farmers should acquire the knowledge from this area so that they can react flexibly. For this the reason was established long-term experiment (start in 1975) at the sandy soil (in the locality Skierniewice, Poland), where the soil structure, contents of total and available macronutrients and Mn oxides after the application of the mineral fertilizers were studied (Control – no fertilizers, NPK – NPK fertilizers, CaNPK – CaNPK fertilizers). The soil samples were taken from the depth 0–25 cm in the autumn 2017 in all above-mentioned treatments. The results showed that in CaNPK, content of dry-sieved macro-aggregates (DSAma) in size class 1–0.5 mm significantly decreased by 26% and 24% compared to Control and NPK treatment. In comparison to NPK treatment, CaNPK fertilization had statistically significant effect on increase of higher size classes of DSAma on one hand, and it decreased content of dry-sieved micro-aggregates (DSAmi) on the other. In CaNPK, contents of water-stable macro-aggregates (WSAma) in size classes >5 mm and 5–3 mm were higher by 70% and 44%, respectively than in control. Content of available K increased from 28.6 mg.kg-1 in control to 78.7 mg.kg-1 in NPK and to 81.8 mg.kg-1 in CaNPK. The NPK treatment, compared to control showed significant decrease in available Ca and Mg by 31 and 27%, respectively. Ninety-four years continuous inputs of NPK as well as CaNPK significantly increased total content of Mn by 39% and 33%, respectively compared to control. Contents of free Mn oxides varied from 0.013 g.kg-1 to 0.077 g.kg-1 and both NPK and CaNPK mineral fertilization decreased their contents. In comparison to control, the content of amorphous Mn oxides was significantly decreased by mineral fertilization – in case of NPK by 71% and in case of CaNPK by 57%. The same trend (decrease due to mineral fertilization) in crystalline Mn oxides was observed. Our results confirmed positive effects of Ca and Mg on contents of macro-aggregates, however a strong effect of Mg than Ca with DSAma was determined. Free as well as amorphous Mn oxides have positive effects on a higher size classes of DSAma 5–1 mm. Total Mn and all its oxides positive correlated with WSAma in size class 2–1 mm.