Do Chernozems occur in Poland? Distribution, properties and regional variation of black soils in the loess belt of Poland

Although Chernozems have appeared on Polish soil maps since the late 19th century, their occurrence in Poland is omitted from global and regional soil maps and the reports of foreign authors. This paper aims to verify the occurrence, abundance and properties of soils that meet the criteria for Chernozems as defined by the World Reference Base for Soil Resources (WRB) in five ‘chernozemic’ regions in the loess belt of southern Poland. This analysis identified Chernozems in 15–55 % of the studied soil profiles in four of the five ‘chernozemic’ regions, while the major accompanying soils in all regions were Phaeozems. Most Phaeozems have chernic horizons; therefore, the crucial characteristics allowing classification as a Chernozem or Phaeozem were the presence and depth of secondary carbonates. The spatial variation of Haplic and Calcic Chernozems, which prevail in the (south) central and eastern regions, was strongly affected by erosion, while clay illuviation was relatively poorly indicated in soil profiles. Soils in the fore-mountain regions were extensively leached of carbonates and often had argic horizons, which implies a predominance of Luvic Phaeozems. Gleyic/Stagnic Luvic Chernozems/Phaeozems prevailed in the westernmost region, which is characterised by plain topography and imperfect water drainage. The topsoil pH, soil organic carbon and clay contents of Polish Chernozems and Phaeozems decreased from the easternmost region towards the west and south, where the humid ‘oceanic influences’ or ‘mountain influences’, respectively, are considered responsible for more intense soil leaching during the Holocene period. The soil organic carbon (regional mean values in a range of 1.7–2.8 %), clay (11–21 %) and pH (6.4–7.4) values in Chernozems and Phaeozems developed from loess in southern Poland are lower compared to Chernozems of the steppe zone of southern Russia, Ukraine and Moldova, but comparable with their values reported from neighbouring Central European countries (northwestern Ukraine, Slovakia, Czechia and Germany). The presence of chernic horizons in all studied regions affirms (a) the polygenetic origin of Chernozems and Phaeozems with subsurface argic horizons, and (b) the large potential of regenerative or conservative agriculture in combating erosion and restoring humus-rich and biologically active topsoil layers, which can preserve Chernozems and Phaeozems against further decay in southern Poland.