LECTURE 4 The soil profile Definitions… Bioturbation (J. Winch) Acidophyte (T. Kinnell) Soil monolith (R.P. Solomons) The soil profile… The soil profile… A particular combination of the 5 soil forming factors will lead to different processes which result in particular sets of layers (horizons). A vertical exposure of these layers is known as a soil profile. Major (master) soil horizons… O – horizon: Organic horizon Forms above mineral soil Dead plant and animal residues Often referred to as “forest floor” – fibric (litter layer) Oe – hemic (fermentation layer) Oa – sapric (humified) Oi A– horizon Topmost mineral horizon Organic material = darker colour Coarser texture (why?) E – horizon Zones of maximim leaching or eluviation High concentration of resistant material (sand & silt) Usually under “A” horizon Lighter than horizons above and below it Common under forest vegetation B – horizon Below O, A or E Changed to a point where parent material is no longer discernable Zone of illuviation Where climate is humid, B horizons accumulate materials such as iron/aluminium oxides, silicate clays Where climate is dry, B horizons accumulate calcium carbonate and calcium sulphate C – horizon Unconsolidated material May or may not be same as parent material from which solum formed Below zones of greatest biological activity Loose enough to be dug with a shovel, but retains some structural features of the parent material Upper layers may become part of the solum as weathering and erosion continue R – horizon Unconsolidated rock, little evidence of weathering Transition horizons… Subordinate distinctions… E.G. Oi, Oa, Oe, Bt, Bk Test your knowledge so far… Test your knowledge so far… Name the 5 main functions of soil in ecosystems Name the 5 main soil forming factors Name the 4 main soil forming processes What is a toposequence?