Influence of 96 years of mineral and organic fertilization on selected soil properties: a case study from long-term field experiments in Skierniewice, central Poland

Long-term agricultural experiments allow for the determination of the influence of agricultural practices on soil properties. The objective of the study was to determine the effect of 96-year-old fertilization (NPK mineral fertilization and farmyard manure (FYM) use) on selected physical and chemical soil properties. The research was carried out in an experimental field in Skierniewice, central Poland, where the experiments have been conducted since 1923. Seven soil profiles (Retisols or Luvisols) were studied. Long-term fertilization caused various changes in the chemical properties of the studied soil (pH, the content of total organic carbon (TOC), total nitrogen (TN) and total sulphur (TS); exchangeable acidity (EA), total potential acidity (hydrolytic acidity) (TPA), cation exchange capacity (CEC), the total exchangeable bases (TEB), base saturation (BS)). The effect of long-term fertilization is most evident in the topsoil (the Ap horizon). The NPK fertilization led to acidification which was expressed by the decrease of soil pH (down to the value of 5.1), as well as the increase of EA, TPA, and exchangeable Al. Long-term high-dose FYM application (40 t and 60 t ha<sup>-1</sup> per year) led to the stabilization of soil pH to a level of 6.2–6.5 throughout the soil profile (down to 120 cm). The use of a combination of NPK fertilization and FYM application led to acidification of the topsoil similar to the soil in which NPK fertilizers were applied alone. Long-term FYM application led to the increase in TOC, TN, and TS concentrations in the Ap horizons of the studied soils. Long-term use of NPK fertilizers had no significant effect on soil CEC, however long-term use of FYM increased the CEC in the Ap horizon of soils. An overall positive effect has been confirmed in the use of high doses of FYM (40 t and 60 t ha<sup>-1</sup> per year), which improves the chemical properties (soil pH, TOC, TN, and TS content, as well as CEC) of the soil compared to the control plot and plots with NPK fertilization alone. These findings were confirmed by PCCA analysis.