Impact of land use and seasonal freezing on morphological and physical properties of silty Norwegian soils

Land use and seasonal freezing is assumed to influence the transport of water and particles through the soil. The aim of this study was to identify, measure and interpret changes in soil pedality that could influence the transport of water and particles through the soil profile. The morphological, physical and chemical properties of three soils on a plateau in the Vansemb area, south eastern Norway, were compared. The soils have 60 to 90 cm thick silty sediments deposited above a marine clay substratum. One site had always been under natural forest vegetation. The second site had been afforested with spruce for 40 years after centuries of cattle grazing without ploughing. The third site had been under cultivation for about 70 years. Because of winter freezing, the upper horizons display a platy pedality created by the growth of ice segregation blades. This is followed by a desiccation structuration with vertical shrinking fissures lining a prismatic pedality in deeper horizons. As frost penetrates deeper in soils under crop and grassland, the platy structures are deeper in these sites and overlap with the vertical fissure system. As a result of tillage operations, the horizons below the plough layer became denser. This decrease in porosity is to some degree counterbalanced by the active ice segregation and the earthworm activity. Tillage operations are also responsible for the filling of the vertical fissure system with particles from the horizons above. The shift to crop or grassland increased bioturbation, mainly by earthworm populations. This activity remained at least partly preserved, even after 40 years of afforestation. Burrowing animals were absent from the mineral horizons of the forest soil. Comparative studies, as this one, ascertain the orientation of soil evolution; and thus provide essential information for soil management with minimal degradation and particle transport.