EFFECT OF DRAINAGE ON CHARACTERISTICS OF SOME SOILS OF THE ORKNEY ISLANDS

Three soil profiles with different degrees of drainage impedance devel oped on glacial till derived from Middle Old Red Sandstone sediments i n the Orkney Islands were characterized texturally, chemically and min eralogically. Particular features of these soils were the high organic matter contents (9-50%) of the surface horizon soils resulting from h igh rainfall and cool temperatures. The high exchangeable Na+ and K+ c ontents in surface horizons of two of the pedons are a result of salt spray. The clay mineralogy and the nature and amount of aluminosilicat e gel were affected by drainage class. In general, chlorite dominates the clay fraction of the imperfectly drained soil. However, with incre asing impedence it was gradually displaced by mica which ultimately pr edominates in the very poorly drained saline gley. Vermiculitization o ccurred in the better drained soils. The poorly drained soils were dis tinguished by the absence of chlorite. Goethite was present in all soi ls but lepidocrocite occurred only when drainage was strongly impeded. Hematite was never present in these soils.