Effect of drainage on characteristics of some soils of the Orkney Islands

Abstract

Three soil profiles with different degrees of drainage impedance developed on glacial till derived from Middle Old Red Sandstone sediments in the Orkney Islands were characterized texturally, chemically and mineralogically. Particular features of these soils were the high organic matter contents (9-50%) of the surface horizon soils resulting from high rainfall and cool temperatures. The high exchangeable Na+ and K+ contents in surface horizons of two of the pedons are a result of salt spray. The clay mineralogy and the nature and amount of aluminosilicate gel were affected by drainage class. In general, chlorite dominates the clay fraction of the imperfectly drained soil. However, with increasing impedence it was gradually displaced by mica which ultimately predominates in the very poorly drained saline gley. Vermiculitization occurred in the better drained soils. The poorly drained soils were distinguished by the absence of chlorite. Goethite was present in all soils but lepidocrocite occurred only when drainage was strongly impeded. Hematite was never present in these soils.