Classification of soils developed from bottom lake deposits in north-eastern Poland

The aim of the study was to test the suiility of the 6th edition of Polish Soil Classification (PSC6, 2019) for reflecting the typical features of gyttja soils in comparison with the previous editions of PSC, namely PSC4 (1989) and PSC5 (2011), and the newest version of Word Reference Base for Soil Resources (IUSS, 2015). On the basis of described morphology and determined properties, soils were classified according to different soil classifications. In total, 25 soil profiles were investigated, of which 18 developed from bottom lake deposits and 7 from lakeshore deposits. Based on the presence of three main components of lake deposits: organic matter (determined as loss-on-ignition), calcium carbonate, and mineral non-carbonate fraction, several kinds of limnic materials were identified according to PSC6. Soils developed from deep lake deposits unaffected by the murshing process were classified (PSC6) as gyttja soils, and as murshic gyttja soils when the upper layer was composed of gyttja mursh. Some classification problems arose when soils developed from shallow gyttja deposits located on the former lake shore, and their top layer was affected by deposition of colluvial materials from adjacent slopes. In several soil profiles, the top layer developed from the admixture of sand deliberately deposited by man on the gyttja surface in order to improve soil properties. In Laki Dymerskie gyttja land, this sandy top layer is 31-39 cm thick and there are written reports on amelioration of this site by sand cover cultivation (Rimpau method, Sanddeckkultur) carried out since 1885. At present, this layer contains 3-20% SOM and fulfils the requirements of the arenimurszik horizon specified in PSC (2019). The newest edition of PSC enables the user to achieve detailed classification of such soils by using a soil variety, namely the heaped soil (in Polish - nasypowe). According to WRB (2015), such soils are classified mostly as Hypereutric Rheic Drainic Histosols (Limnic, Nechic, Areninovic) ones and Eutric Gleysols (Endoarenic, Drainic, Humic, Limnic, Nechic). Generally, the taxonomic position of soils studied was more detailed according to PSC6 in relation to the occurrence of various soil strata and different soil materials when compared to the previous versions of PSCs. It should be stated that the precision achieved when using PSC6 to classify gyttja soils was similar to that obtained with WRB (2015).