Friday, 14 July 2006

The Introduction of the Stagnosol Group in WRB: Classification of Soils with Stagnic Properties in Vestfold County, Norway.

Age Nyborg, Eivind Solbakken, Ragnhild Sperstad, and Kjetil Fadnes. Norwegian Inst.-Land Inventory, PO Box 115, As, N-1430, Norway

Since the mid 80'ties a national program for detailed soil mapping at a scale of 1:5000 on cultivated land has been going on in Norway. When the WRB-system was introduced in 1998, a lot of effort was made to adapt and adjust the mapping system in such a way that WRB could serve as a field classification system. For most Norwegian soils the WRB is functioning well, but for some soils the 1998 edition does not recognize their most important properties on group level. The result is some WRB groups containing very dissimilar soils. A large portion of Norwegian cultivated soils consists of materials with a high content of silt and clay. This texture in combination with relatively high annual precipitation and freezing and thawing, results in stagnic properties. For the farmer this means drainage problems, problems with soil compaction and risk for winter damage on grassland. It also means higher risk of erosion and surface runoff. This poster points out some of the advantages of introducing Stagnosols in the WRB, and takes the soil map of the agricultural land in Vestfold County, Norway, as an example. Vestfold County which is located southwest of Oslo, is one of the most important agricultural areas in Norway covering 4400 ha. The main crops are cereals, oilseeds and vegetables. Annual precipitation varies from 820 to 1150 mm and mean annual temperature varies from 4.8 to 7.4 degrees C. The county can be divided into three distinct regions based on differences in geology, geomorphology and soils. The Lågen Valley in the west consists of alluvial terraces where Cambisols dominate. Silt and clayrich marine sediments dominate the central part where Albeluvisols, Stagnosols and Gleysols are common. Land levelling has been a common practice in this area. Along the coast and on top of an end moraine that runs close to and parallel with the coastline, we find coarser marine sediments where Arenosols and Cambisols are common. This end moraine marks the last advancing stage of the last ice age glacier. Close to 60% of agricultural land in Vestfold County consist of soils that are imperfectly or poorly drained. 90% of these soils have stagnic properties within 50cm depth from the soil surface. Half of them are placed in stagnic units of the Albeluvisol group. The rest used to belong to stagnic units of the Cambisol, Luvisol, Regosol, Umbrisol and Phaeozem groups. Today these soils are grouped together in the proposed Stagnosol group. In Vestfold, the Stagic Albeluvisols are found in older marine landscapes, 6000 to 12000 years old, with undulating topography characterized by deep stream gullies and clay slide pits. The Stagnosols are mainly developed in relatively young marine sediments with a silt loam or silty clay loam texture. They are commonly found in gently sloping to flat areas. Most of these soils have weakly developed argic or cambic horizons overlying a compact C-horizon. It is in the best interest of the farmer that the soils that qualify as Stagnosols are grouped together. The internal drainage is very slow and the soil stays wet for a long time after snowmelt in the spring. Heavy rains may cause ponding in some places and water runoff with resulting soil loss in other places. The need for artificial drainage is high in these soils, but it seems like artificial drainage is more effective in Stagnic Albeluvisols than in Stagnosols due to the higher amount of macropores. In these cases the fact that the soil has stagnic properties is more important than the presence of an argic horizon or a cambic horizon. Introducing Stagnosols in the soil map of Vestfold County has made it easier to visualize areas where drainage problems are the main soil management restraint. At the same time moving the Stagnic Cambisols to the Stagnosol group has resulted in a more homogeneous Cambisol group consisting of moderately well drained soils with loamy texture.

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