ASSESSMENT OF SODIUM AND POTASSIUM CONTENTS AS NATURAL INDICATORS OF SALINITY IN SOILS OF THE KAMPINOSKI AND SŁOWIŃSKI NATIONAL PARKS (POLAND)

Backgrounds.Widłak (2016) has proposed a soil salinity indicator, defined as the ratio of sodium to potassium (Na/K).At sodium concentrations higher than the potassium concentration, the ratio exceeds the value of 1, which indicates a highly adverse effect on the aeration of the root system and the absorption of nutrients by plants.Aim.The aim of the research was to test Widłak's index in dune soils of two Polish national parks: the Słowiński National Park (SNP) and the Kampinoski National Park (KNP).Results.In litter and in all mineral horizons of SNP soils the average salinity index proposed by Widłak was found at values <1.0 (maximum 0.74), which places SNP soils in a group of soils with favourable properties in terms of root aeration and assimilability of nutrients by plants.In KNP soils such favourable conditions were demonstrated for litter and also 5-10 cm and 45-50 cm of soil depth.For the depth of 25-30 cm the Na/K ratio exceeded 1, reaching the value of 1.25.Higher sodium and potassium contents in KNP soils, as compared to SNP, may be a consequence of lower rainfall in the central part of Poland, and thus weaker soil leaching, causing the migration of these elements deeper into the profile.The Na/K ratio may be a measure not only of a better or worse soil status, but also a reflection of climatic conditions.