Struktura gleb w wybranych lasach miejskich Wrocławia

The objective of the research was to assess the soil structure parameters (the index of cloddiness, of pulverization, of soil structure and the mean weighted diameter of soil aggregates – MWDa), as well as the selected chemical soil properties (pH, the content of organic carbon, total nitrogen and available potassium and phosphorus) in the three urban forests in Wrocław (SW Poland) depending on the occurrence of tree species (Quercus robur, Fagus sylvatica, Carpinus betulus). Soil samples were collected under the crown of each tested tree taxons, from three different sites, in three replications, separately in every forest. The soil was taken from two layers: 0−20 cm and 20−40 cm. The structure and weight of mechanically solid soil aggregates were determined using dry separation method. The content of total nitrogen was determined with Kjeldahl method, while phosphorus and potassium – with Egner−Riehm method. Organic carbon was determined with the use of elementary carbon analyser Behr C−50 IRF. The pH was determined by poten− tiometric method in 1M solution of KCl. The results were statistically analysed using the ANOVA. The correlation coefficient between the mean weighted diameter of soil aggregates and the content of organic carbon in the soil was calculated. The tree species occurring in the urban forests of Wrocław affected the soil structure parameters as well as changed the chemical properties of the soil. In both Mokrzański and Rędziński Forests the significantly higher index of soil cloddiness was observed under hornbeam crowns than in the oak and beech surroundings. In the Osobowicki Forest the highest index of cloddiness was determined on the soil with the oak. In general, higher values of index of soil structure and the mean weighted diameter of soil aggregates were noticed for the hornbeam sites than the oak and the beech ones. There was a significant positive corre− lation between the MWDa and the content of soil organic matter (r=0.711, Y=0.4569·x+1.6523). The differences in the content of organic carbon depending on tree species were observed in the Rędziński Forest, while in content of total nitrogen also in the Mokrzański Forest. The highest content of organic carbon and nitrogen was noticed in the soil under the hornbeam. The species of trees affected the content of phosphorus and potassium in the soil, but there was no unambiguous direction of changes.