Soils

Soils Products of weathering

Soil Characteristics Regolith Loose material covering solid rock Dust, sediment, broken rock Soil is the only part that supports the growth of plants

Soil Characteristics Composition Texture Structure

Soil Composition Mineral matter Organic matter (humus) Broken rocks Remains of dead organisms Source of nutrients Increases ability to retain water Percentage varies Bogs are almost all humus, deserts have very little

Soil Composition Water Air Provides moisture for chemical reactions Provides nutrients in a form that plants can use Air Source of CO2

Soil Texture The proportions of particle sizes Influences ability to support plant life Based on % of clay, sand and silt

Soils SAND: Drains quickly; dries out

Soils LOAMY SAND: falls apart when handled.

Soils LOAM: feels spongy Drains well without drying out Contains more nutrients

Soils SANDY LOAM:

Soils SANDY CLAY:

Soils SILT LOAM:

Soils CLAY: Drains slowly Hard for plant roots to grow

Soils SILTY CLAY:

Soils SILTY CLAY LOAM:

Soils CLAY LOAM:

Good Quality Soils Typically consist of 50 % organic and mineral matter Other 50 % consists of pore spaces Air and water circulation

Soil Structure Soil particles form clumps that give soils a particular structure Determines: How easily it will erode How easily it can be cultivated Water infiltration

Soil Formation

Parent Material Source of the mineral matter Bedrock Residual soil Unconsolidated material Transported soil

Parent Material Affects: Rate of weathering and soil formation Unconsolidated material forms soils more quickly than residual Plant fertility Determines types of plants that can grow

Soil Formation Climate: Time: Temperature, humidity, precipitation Most important factor Time: Older soils are thicker

Soil Formation Organisms When living things die, decomposers break them down They become part of the soil Add nutrients to soils Plant acids speed up weathering Burrowing leaves holes for air and water circulation

Soil Formation Topography/Slope Steeper slopes have more erosion, less water

Soil Profiles Soil forms top down At different depths, soil varies in: Composition, texture, structure and color

Soil Profiles Mature soils tend to have 3 distinct horizons

Soil Horizons O A B C Humus, typically considered part of A Topsoil, mostly organic matter B Subsoil, lower limit of roots and burrowing, Hardpan – clay that forms a compact layer C Partially weathered parent material

Pedalfer Forms in temperate areas with more than 63 cm of rain each year Much of the eastern US B horizon Large amts. of iron oxides (reddish brown)

Pedocal Forms in drier western US Less clay (b/c weathering is slower) Contain calcium carbonate – light brown

Laterite Hot, humid, tropical areas Lots of water Distinctive orange-red Almost no organic material (quickly used)