Soils Introduction

Soils Introduction

1. What is soil?

   • Mostly mineral, but it can also be organic
   • At least 10cm deep
   • Capable of supporting plant growth
   • Is affected by soil forming processes
     • Soils do not occur randomly; they do occur in a predictable fashion across a land surface and they change throughout time.
   • An ideal soil is 45% mineral, 5% OM, and 25-25% air and water
   • Key Soil Characteristics
     • Colour
       • Standard notation: HUE Value/Chroma 10 YR 9/10 = white10YR 5/6 = Brown 10YR 1/2 = BlackDark = OrganicRed = IronWhite = Loss of IronBrown = Organic matter, less than blackValue: 0 (Black) - 10 (White)Chroma: 0 (Pastel) -  10 (Bright)
     • Texture
       • Aeration and drainage: textural discontinuities between layers can lead to reduced drainage Rooting depth: heavy clay soils and compaction can reduce the ability of plants to root adequately Fertility: clay retains nutrients better Erosion control: wind or water can transport sand and silt, because clay readily aggregates. 
     • Structure
       • Structural units develop as a result of adhesive substances ("glue," clay and organic matter) and external forces (compaction, swelling/wetting, freezing, bioturbation).
       • Texture: a property that is inherited from soil parent material Structure: forms in response to pedogenetic processes
         • Both structure and texture have influence on soil performance. Susceptibility to erosion: increased in structureless soils, especially those high in sand and silt (lacking "glue") Susceptibility to compaction: increased with blocky or massive structure; high clay content Aeration: structure creates porosity. When soil aggregates (clay + OM), empty space is left behind as pores. Drainage: Water can move through the profile to lower horizons. This is impacted largely by clay. Impeded by blocky structure. Root growth: Lower bulk density makes this easier for plants Microbial activity: Granular, loamy soil is best for a microbial habitat.
   • Classification System

2. Soil Formation

   • 1. The accumulation of parent material
     • Parent materials may be
       • Parent materials are a large determining factor is soil TYPE, but they are not the only factor.
       • Organic vs Mineral
       • Residual vs transported
         • Sorted or unsorted
           • Mode of transportation alters texture, making it sorted or unsorted. Mode of transportation also provides some common patterns of surface expressions across a landscape.
         • Modes of deposition for transported PM
           • Alluvial: moving water
             • Fluvial deposits will be sorted, but vary - larger rocks will be deposited higher up the river channel, where there was more energy, and smaller and smaller sized rocks will be desposited further down. 
           • Lacustrine: standing water
             • These materials will be VERY fine and very well sorted. 
           • Marine: tides
           • Eolian: wind
             • Highly sorted, fine material
           • Glacial: ice, moraines
             • Morainally deposited materials are angular in shape, but have SOME rounding. They are highly unsorted materials
           • Colluvial: gravity
             • VERY unsorted and VERY angular. (Note that while ice is also angular, this is MORE ANGULAR)
   • 2. The effects of soil forming factors at large
     • Factors of Soil Formation
       • Soil = f(Cl, O, R, P, T)
       • Climate
       • Organisms
       • Parent material
       • Relief'
       • Time
   • 3. Differentiation of horizons w/in soil by soil forming processes
     • Soil forming processes
       • Additions
         • Additions of organic matter, water, etc. Organic matter comes from dead organisms and water usually comes from precipitation and then percolates throughout the profile.
       • Losses
         • Water percolation can cause losses through horizons, or can cause the loss of organic matter from the surface. Clay, iron oxides, and organic matter can also be "pulled" through the soil profile
       • Translocation
         • A horizon to other horizons. Predominately clay moving, and Fe oxides. Clay is translocated as a solid, and Fe Oxides are translocation as dissolved substances in soil soultion.
       • Transformation
         • OM, minerals... transformation occurs when something completely becomes something else (X -> Y). The molecular makeup of the object changes