What is Soil?

“a living, dynamic system with organic and inorganic components. Soil is a product of its environment and parent material”.

componentsBy volume:

– 45% mineral– 5% organic material– 50% space (air/water)

By mass?– 0% air– 18% water– 80% mineral– 2% organic material

1. The mineral component• inorganic• “mineral”: definition?

– Primary: original components of earth crust

– Secondary: new minerals made by weathering of earth’s crust

• divided by particle size:– Sand, silt, clay

• mineral make-up due to:

a. Parent Materialb. How resistant minerals arec. Climated. “Age”

a. parent materialmaterial on and in which soil

develops

Examples of soil developing IN rather than ON parent material: 1. Apostle Islands

2. Boundary Waters

• 11 different parent materials …..

Regolith/bedrock:weathered rock

Alluvium:deposits on a flood plain from a river

Marine deposits:shell, reef and other “bits” formerly at

bottom of ocean that have been uplifted

Lacustrine deposits: clay deposits originally laid down at the bottom of a lake; lake is no longer there

Example: glacial lakes in MN

Till:unconsolidated material deposited by

glacial ice

Outwash:unconsolidated, sorted material deposited

by meltwater from a glacier

Organic sediments: peat

Volcanic ash

Loess:deep deposits of silt that have been

deposited by wind

Sand:beach sand, dune sand

Colluvium;material that moved downslope, as in a

landslide

• mineral make-up due to:

a. Parent Materialb. How resistant minerals arec. Climated. Age

b. resistance of minerals• Soluble minerals are readily

LEACHED from soil profile (Ca,Mg,Na)

• Certain minerals tend to accumulate in soil– (oxides of Fe, Al, Si)

• mineral make-up due to:

a. Parent Materialb. How resistant minerals arec. Climated. Age

c. Climate• Amount of leaching

• Rate of weathering

• mineral make-up due to:

a. Parent Materialb. How resistant minerals arec. Climated. Age

d. Age• Parent material is (usually) less

influential in “older” (more highly developed) soil

2. Organic Component• Living (primarily

decomposers)

• Non-living (dead and all in-between stages of decomposition)

…about decomposers:• Nutrient recycling

• Respiration

decomposer activity depends on:

climatesoil moisture conditionsMicro-environmental factors (relief,

drainage)

decomposers and climate:1) climate vegetation, litter

(amount, type)

2) rate of decompositionhot,wet >> cold, dry

soil moisture conditions

• Hot, wet preference of decomposers

micro-environmental factors (relief, drainage)

• Slope aspect affects temperature

• Drainage affects anaerobic/aerobic decomposition

3. The Space component• Soil pores

– filled with air and/or water

A. soil air

O2 CO2 N2 H 2O vapor (per cents by volume)

(rh) Above-ground atm. 20.97 0.03 79.0

<100%

Soil (grassland) atm. 18.4 1.6 79.2 100 %

B. soil water• Functions?• Polar molecule