Is long-term mineral fertilization a suitable tool for improving the structural state of sandy soils?

In this paper, the impact of the long-term application of mineral fertilizers and manure on the soil structure of a sandy soil is quantified, and the relationships between the soil organic matter, Al and Fe oxides and soil structure of sandy soil with a dependence on the length of fertilizers application are determined. Soil samples were taken from all three long-term field experiments in Poland (sandy Arenic Planosol), which were located at Skierniewice experimental station including a 94-yearold experiment with mineral fertilization, a 41-year-old experiment with mineral fertilization and a 25-year-old experiment with mineral fertilization + farmyard manure. The results showed that in 94-year-old experiment the state of soil structure was the most favourable compared to other experiments (25- and 41-year-old). In 94-year old experiment, NPK rather than CaNPK fertilization had a more pronounced effects on soil structure parameters in comparison to unfertilized control. In NPK treatment the higher content of water-stable macro-aggregates (WSAma) in size classes of: >5, 5–3, 3–2 and 2–1 mm (by 89, 76, 71 and 71%), lower content of SAma 0.5–0.25 mm (by 61%) and higher value of weight mein diameter of waterstable aggregates (MWDm) (by 48%) in comparison to unfertilized control were observed. Especially in 94-year experiment the content of total organic carbon (Corg), labile carbon (CL), humic substances carbon (CHL), fulvic acids carbon (CFK) as well as iron and aluminium amorphous oxides improved soil structure parameters. All in all, the fertilization had different effects on soil structure in the sandy soil with relation to long-term of individual experiments and the highest correlations: SOM, Al, Fe and its forms vs. soil structure were in 94-year >25-year >41-year-old experiment.