Diagnosis of the trophism of rusty soils on the basis of soil trophic index in selected coniferous stands in the Rupin forestry in the Kurpie Plain, NE Poland

The aim of the study was to compare the trophism determined on the basis of soil trophic index (SIG) of rusty soils in coniferous stands and afforested post agricultural rusty soil in the Rupin forestry. The research was carried out in the mesoregion of Kurpie Plain. The studied soils were classified as podzolic rusty soils and gleyic rusty soil. They were formed from glaciofluvial sands (sand or loamy sand) containing from 0% to 4% of clay (<0.002 mm) and from 2% to 17% of silt (0.05-0.002 mm). The pH (KCl) values of 3.9-4.2 were the lowest in the humus horizons and increased to 4.8-5.0 in the parent material, which may indicate progressive acidification. The highest content of exchangeable hydrogen in surface horizons confirms the occurrence of this process. The organic carbon content in humus horizons amounted to 13.23-16.41 g kg(-1), and total nitrogen to 0.83-1.34 g kg(-1). The organic carbon to total nitrogen ratio was the narrowest in the post-agricultural Gleyic rusty soil (12-13), while in the Podzolic rusty soils it was wider and ranged from 15 to 18. Among the exchangeable cations, hydrogen dominated in the cation exchange capacity, and among the basic exchangeable cations calcium cation prevailed. The base saturation in Podzolic rusty soils ranged from 16.0 to 29.8%, while in the post-agricultural Gleyic rusty soil it was the highest and was increasing down the soil profile from 35.3 to 57.1%. Cation exchange capacity was positively correlated with FP and negatively with pH values. The numerical values of the SIG index in Podzolic rusty soils ranged from 16 to 19, which indicates oligotrophic habitats of mixed coniferous stands. The SIG index in the post-agricultural Gleyic rusty soil reached the value of 27, which indicates mesotrophic habitats of mixed broadleaved forests. The SIG values indicated a higher soil trophism than the diagnosis of the habitat trophism on the basis of the Soil and Habitats Survey - Parciaki Forest District.