NRES 251 1/22-2/16

Soil Composition

Microbes

Nutrients

Organic Matter

Soil Definition

Natural - livnig being

Complex - varies on depth, time, altitude, and place

Vital - needed for agriculture, plants give us oxygen

Dynamic - changing constantly

Interface - hydrosphere, biosphere, atmosphere, lithosphere

Fragile - easy to damage, just walking over and compacting soil can hurt all plants around the soil (100s of years to fix)

Talented - performs functions that have value

Soil Functions

Water storage and cleaning

Habitat for soil organisms

Engineering medium

• infrastructure

Waste recycling

• soil stores waste in organic compounds

• biogeochemical recycling

Atmospheric Modification

Plant Medium

Plant Medium

• Temperature

  • insulates plants

• Water

• Air

  • soil has an atmosphere in the spaces between the soil

• Support

  • provides an anchor for the roots

• Nutrients

  • required by plants

• Macros

  • cations: Ca2+, Mg2+, K+, H4+

  • anions: SO42-, PO42-

• Micros

  • cations: Cu2+, Zn2+, Mn2+, Ni2+, Fe2+

  • anions: B-, Cl-, Mo-

• Toxins

  • soil can be a buffer (led)

Mineral (Soil Composition)

Sand 2-0.05 mm

Silt 0.05 - 0.002 mm

Clay <0.002 mm

Ideal Soil

45% mineral

50% pores (25% air 25% water)

5% organic matter

Soil Horizons

O - organic matter (>20%)

A - organic matter (<20%)

E - elluviation (leaching and near surface)

B - illuviation (accumulation)

C- parent material (unconsolidated)

R - parent material (bedrock or consolidated)

O Horizon

• very dark in color

• feels greasy or fibery

• is not gritty (sand) or sticky (clay)

• often wet

• Oa - sapric material, highly decomposed

• Oe - hemic material, intermediately decomposed

• Oi - fibric material, least decomposed

A Horizon

• highest quality for plants

• darker in color, high biological activity

• Ap - plow later (abupt boundary)

• Ab - buried horizion

E Horizon

• near surface horizon of leaching or elluviation

• light in color

• could have platy soil structure

B horizon

• subsurface horizon of accumulation or illuviation

• properties are derived from the materials that are accumulating in the horizion

  • Bt - clay accumulation

  • Bh - organic matter

  • Bs - Fe and AI accumulation

  • Bw- weakly developed

C Horizon

• subsurface horizon of parent material

• absent of pedogenic processes such as the formation soil structural aggregates

R Horizon

• Subsurface horizon of consolidated, hard, continuous bedrock

Soil Forming Factors (CLORPT)

• CLimate

  • precipitation

  • temperature

• Organism

  • plants, animals, and people can have differential effects on weathering and soil disturbances

• Relief (topography)

  • hillslope position

  • shoulder is most erodible

    • slope angle getting steeper (convex)

  • backslope is transportations

    • constant slope angle

  • footslope is depositoinal

    • decreasing slope angle (concave)

  • toeslope is most depositional

    • no slope

  • altitude and aspect

    • higher altitude regions are cooler regions

    • in the northern hemisphere, south and west aspects are warmer locations

• Parent Material

  • primary rocks and minerals

    • igneous (basalt, gabbro, granite, rhyolite)

      • formed from hot, molten lava

    • sedimentary (sandstone, limestone)

      • formed from accumulation, deposition, cementation

    • Metamorphic (marble, quartzite, schist, gneiss)

      • changed with heat or pressure

• Time