Rusty soil - gleba rdzawa - Soil of the Year 2021 in Poland. Concepts of genesis, classification and regularities of geographical distribution

Gleba rdzawa (Pol.) - the rusty soil is a soil type distinguished in Polish classification system that has been elected as the soil of the year 2021 in Poland. Rusty soils are mainly coarse textured soils, developed from sandy deposits of various origin (glaciofluvial, fluvial, less often aeolian and of weathering) with A-Bv-C horizon sequence. Pale orange enrichment horizon Bv-siderik is a diagnostic one of these soils. The agricultural quality of rusty soils is low, but they constitute valuable habitats of natural and managed forests, on the territory of Poland occupying over 50% of all the forest area. The article discusses the general concepts of the genesis of rusty soils in the following aspects: (1) 'rustyfication' - formation of Fe-Al coatings on sand grains in the By horizon, (2) 'dry pedoclimate' - as an assumed factor responsible for the lack of Fe-Al-oxides mobility, (3) coniferous forest vs deciduous forest vegetation as a soil-forming factor, (4) Pleistocene vs Holocene age and the possible role of periglacial conditions. In Polish classification system rusty soils are currently located close to brown soils (Cambisols), however, in the past they were located in one taxonomic unit with podzolic soils. In international classifications such soils are not distinguished separately and belong to Brunie Arenosols/Psamments. The largest areas of rusty soils in Poland are located in lowlands and uplands, mainly on sandy surfaces of outwash plains, and terraces of ice-marginal streamways and valleys.