Soil formation, microstructure and physical behaviour of Late Weichselian and Holocene Rhine deposits in the Netherlands

Dutch Late Weichselian braided river deposits and Holocene meandering river deposits of the Rhine have been studied and compared. Cross sections demonstrate the lateral and vertical variations of the Late Weichselian sediments. Soil mapping of these deposits, even on a very detailed scale, proves very difficult. Best results have been obtained with a legend based on hydrology enabling the distinction of topo-hydrosequences of well drained brown soils, imperfectly drained mottled soils and poorly drained grey soils.

Advanced soil formation and notably the dramatic processes in the Late Weichselian period (decalcification, clay illuviation, pseudogleying, periglacial formation of a highly reoriented, very dense microstructure) have caused clay mineralogical, chemical and physical changes in the Late Weichselian soils.

The well drained and imperfectly drained Late Weichselian soils have an argillic horizon (Alfisols, Luvisols), occasionally with very low base saturation (Ultisols, Acrisols) and with strong subsequent pseudogleying in the imperfectly drained soils. The Holocene soils demonstrate decalcification and biogenic homogenization as well as some gleying according to their drainage position. These soils are classified as Inceptisols (Cambisols), occasionally as Mollisols (Phaeozems).

Less favourable physical characteristics and behaviour (soil strength, structure stability and tillage behaviour) of the Late Weichselian soils and soil material is quantitatively documented. Differences with the Holocene soils and soil material are statistically highly significant and are caused by differences in texture, content, quality and distribution of organic matter and the highly reoriented, very dense microstructure.

Use as permanent grassland or ley in the crop rotation is recommended to increase levels of biological activity. This seems the only remedy for the imperfectly and poorly drained Late Weichselian soils that are compacted by natural soil forming processes not counteracted by biological activity. Very recently improved drainage of large areas of Late Weichselian imperfectly drained soils has increased the saturated hydraulic conductivity to noncritical levels through increased earthworm activity to some metres depth.