De bodemgesteldheid van het gebied tussen Lemmer en Blokzijl in het randgebied van de Noordoost Polder

The cause for research was the complaint of considerable desiccation of the grasslands after the reclaiming of the North-East Polder. Soil conditions were studied, and watertable soil infiltration, and productivity and quality of grassland were assessed.

Originally the area was a peatbog, flooded about 300 A.D. by the Zuyder Zee and covered with clayey sediments ('knip' clay, also sandy sediments of leveelike form). The transition between clay cover and peat was a black layer of peaty clay rich in humus. Dikes were constructed after 1400.

Regional extension and composition of the peat was studied. It was initiated in the Boreal Period, as Phragmites and Carex peat (topogene) and Sphagnum peat (ombrogene) with a rise in watertable, flooding and subsoil topography. Desiccation caused the 'rodoorn' clays, pillar and prismatic structures of the 'knip' clay, grit-layer formation in peaty clays and severe fissuring, especially in Carex peat. Improvement was difficult, because of the properties of the peat (permeability and irreversible drying). Moling and pipe-infiltration sometimes caused improvement, if the watertable reached the grit layer.

Very dangerous was Sphagnum cuspidatum peat, giving rise to very uneven land, deep fissures and withering of grass.