SOILSFORMATION, EROSION, AND

CONSERVATION

Miller Chapter 10

I. Soil: Formation Erosion, and Conservation

A. What is Soil?complex mixture of eroded rock,

minerals, decaying organic matter, water, air, and living organisms.

Ratios Differ among various soil types…

Average Ratios:45% Minerals25% Water25% Air5% Humus

B. How Soil is Produced

-Weathering of rock -Depositing of sediment -Decomposition of matter

C. Soil Zones (MATURE)-Soil is arranged into

zones called… SOIL HORIZONS-A cross-section of soil

horizons is called… SOIL PROFILE-Most mature soils have

at least three of the possible horizons

LAYERS/HORIZONS

O Horizon – Top layer/Surface Liter Layer

-Characterized by debris and animal waste

-Brown/black in color

A Horizon – • Top Soil Layer -Consists of porous mixture of

partially decomposed organic matter called…

• HUMUS • Inorganic minerals -Most plant roots and organic

matter found here.

B Horizon – Subsoil Layer andC Horizon – Parent Material

• Contain most of soil’s inorganic matter and varying mixtures of sand, silt,clay, and gravel

• C Horizon lies on BEDROCK

Soils: zones

O horizonLeaf litterA horizonTopsoil

B horizonSubsoilC horizonParent

material

Mature soil

Young soil

Regolith

Immature soil

Bedrock

D. Soil Properties*Soils vary in content of … Clay Silt Sand Gravel-Relative amounts of different size and types determines SOIL TEXTURE-LOAMS – soils of equal mixture

100%clay

Increasingpercentage silt

Increasingpercentage clay

0

20

40

60

80

80

60

40

20

0100%sand 80 60 40 20 100%silt

Increasing percentage sand

CLAY

SILTSAND

1. Infiltration: Water moving through

the soil layers

2. Leaching: Soil components from upper layers being carried to lower layers

3. Porosity:

the measure of the volume of pores and distance of pores per volume of soil

4. Permeability:the rate at which water and air can move through soilWater Water

High permeability Low permeability

5. Soil Structure: The way in which soil particles

are organized and clumped together Texture Nutrient Infiltration Water-Holding Aeration Tilth

Capacity Capacity

Clay Good Poor Good Poor Poor

Silt Medium Medium Medium Medium Medium

Sand Poor Good Poor Good Good

Loam Medium Medium Medium Medium Medium

6. Soil pHA measure

of the acidity of the soil

II. Soil Erosion1. The movement of soil components, especially surface litter and topsoil, from one place to another*Two main agents are…

-Flowing water -Wind

2. Types Of Water ErosionA. Sheet – Moving of water in wide flow

B. Rill – Fast moving water that cuts small channels

C. Gully – • Ditches and gulley’s are

caused by fast moving water over steep, exposed soil

Areas of serious concern

Areas of some concern

Stable or nonvegetative areas

Global Soil Erosion

3. U.S. Soil Erosion -1/3 of the original top soil has been washed or blown away.

-USDA states that soil is eroding 16x faster than it can form.

-USDA estimated loss of $30 billion dollars from erosion in 1997

The Dust Bowl

A.Desertification- The productive potential of

arid or semiarid land falls by 10% or more due to…

Human activities Climate changesMUST REDUCE…Overgrazing & deforestation

4. Other Problems Associated With Soil

Moderate Severe Very Severe

B. Salinization-• The accumulation of salts in soil

• Often associated with irrigation

• Effects:• Stunts crop growth• Lowers crop yields• Kills plants

Severe Salinization

C. Water logging- An over abundance of

water within the soilEvaporation

TranspirationEvaporation

Waterlogging

Less permeableclay layer

III. Soil Conservation1. Reducing soil erosion and restoring soil fertility.

2. Farming Techniques A. Conventional-tillage

farming*Tilling in the fall

B. Conservation-tillage farming

1. Minimum Tillage Farming

2. No Till Farming

3. Terracing – • Creation of broad, nearly level terraces that run across the contour of the lands

-Mostly used on very steep gradients.

4. Contour Farming- • Plowing/planting crops in rows across the sloped contour of the land.

5. Strip Cropping- • Alternating rows of crops with low, ground hugging vegetation.

6. Alley Cropping/Agroforestry-

• several crops planted together in strips or alleys between trees or shrubs

7. Windbreaks/Shelterbelts- Rows of trees to reduce wind erosion.

Conservation During Urban Development

IV. Soil Restoration-Fertility can be returned by using one of two major types of fertilizer… A. Organic B. Inorganic

-Animal manure-Green manure

Organic fertilizer

-Compost

Commercial inorganic fertilizer

Extreme Erosion