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Soils: - PowerPoint PPT Presentation

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Soils:. A Natural Capital or Natural Resource!. Some call it dirt…..But it is Soil !!!. Soil is made of loose, weathered rock and organic material. The rock material in soil contains three noticeable parts: sand, clay, and silt. Soil consists of: 45% mineral 25% water 25% air and

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A Natural Capital or

Natural Resource!

some call it dirt but it is soil
Some call it dirt…..But it is Soil !!!

Soil is made of loose, weathered rock and organic material.

Soil consists of:

45% mineral

25% water

25% air


5% organic matter.

This is just an average!

soil texture
Soil Texture

the way various

soil particles clump


Good soils:

2/3 of intra-soil spaces contain air after excess water has drained.

  • Friable - Crumbles easily.
  • Effects water holding capacity
  • Nutrient retention and supply
  • Drainage
  • leeching
soil structure
Soil Structure
  • When individual particles clump or group together – depends on particle types, size, and how many pores are in between.
question break
Question Break!

Soil that has the feel of clay is that soils

A: structure

B. Texture

There are thousands of different soils throughout the world.

Five important factors influence the specific soil that develops.

Parent Material

This refers to the minerals present during the formation of the soil.

Parent Material

Materials from volcanoes, sediment transported by wind, water, or glaciers are some examples.

mineral composition
Mineral Composition
  • Soils are made of: MINERALS
geological processes
Geological Processes
  • Earths processes like volcanic reactions, earth quakes, tsunamis….
weathering processes that bring about fragmentation or chemical change
Weathering:Processes that bring about fragmentation or chemical change
  • Biological (plants and fungi)
  • Chemical (oxidation & water)
  • Physical (frost/thaw actions-erosion)
Our parent material is mainly Marine sediment (ocean in origin), or produced by steam-river action. Also from the Appalachians.

It may be thousands of feet deep!


The climate of a particular region can have a major influence on the rate of soil formation.


Weathering processes like the cycles of freezing and thawing, along with wetting and drying vary with each region.

Living Organisms

Enriched by organic material from plants & animals with microbes and macrobes


Living Organisms

As they die, organic matter incorporates with weathered parent material and becomes part of the soil.

organic component
  • As humus layer decays, nutrients are recycled back to plants
organic component1
  • HUMUS(sticky brown residue from partially decomposed plants and animals)
    • Humus creates “structure”- how particles cling together
    • Humus holds minerals in soil
Living Organisms

The actions of moles, earthworms, bacteria, fungi, and round worms mix and enrich the soil.

other factors influencing soil formation
Other Factors Influencing Soil Formation:
  • Plant Roots
  • Bacteria and Fungi (Decomposers)
  • Position on Slope
  • Climate
  • Time
  • Rainfall
  • Soil pH
  • Topography

The slope or hilliness of a region can have a major influence on the moisture and erosion of soils.


In many regions, moist, poorly drained soils are located in low areas.


Drier, well drained soils are often found in sloping hillsides. Erosion is often a problem here and can lead to lose of topsoil.


It takes hundreds of years to form one inch of soil from parent material.


Only the top few centimeters are productive in the sense of being able to sustain plant growth.


This is why soil conservation is so important!

soil profile from chapter 1
Soil Profile: From Chapter 1
  • Soil Profile - A series of horizontal layers of different chemical composition, physical properties, particle size, and amount of organic matter.
    • Each recognizable layer of the profile is known as a horizon.

Our soil is a Natural Capital

soil profile
Soil Profile

In a cross-section of soil, various zones are formed.

o horizon organic layer
O Horizon: Organic Layer

It consists of leaf litter and other organic material lying on the surface of the soil.

a horizon topsoil
A Horizon: Topsoil

This layer is usually loose and crumbly with varying amounts of decayed organic matter.

a horizon topsoil1
A Horizon: Topsoil

This is generally the most productive layer of the soil.

Conservation efforts are focused here!

b horizon subsoils
B Horizon: Subsoils

Subsoils are usually lighter in color, dense and low in organic matter.

c horizon transition
C Horizon: Transition

This layer of transition is almost completely void of organic mater and is made up of partially weathered parent material.


Below the C horizon the unweathered bedrock will be found.

soil profiles
Soil Profiles
  • Over 15,000 separate soil types have been classified in North America. However, most cultivated land can be classified as either grassland or forest soil.
    • Grassland Soils - Usually have a deep A Horizon - low rainfall limits topsoil leaching.
      • A Horizon supports most root growth.
soil profiles1
Soil Profiles
  • Forest Soils - Topsoil layer is relatively thin, but topsoil leachate forms a subsoil that supports substantial root growth. (High rainfall areas)
    • Tropical Rainforests
      • Two features of great influence:
        • High Temperatures
          • Rapid decomposition, little litter.
        • High Rainfall
          • Excessive leaching of nutrients.
soil factors that effect aquifers
Soil Factors that effect Aquifers
  • Soil Texture:
  • Soil consists of three soil seperates:
  • Sand (course), silt, clay (finest)
why does soil texture matter

Determines soil pore space

Determines aeration



Affects soil workability

Determines soil drainage

Influences nutrient holding capacity (CEC)

Why Does Soil Texture Matter?


soil properties
Soil Properties
  • Texture Classification- Determined by the size of mineral particles within the soil.
    • Too many large particles leads to extreme leaching- drying out.
    • Too many small particles leads to poor drainage.
      • Gravel >2.0 mm
      • Sand 0.05 - 2.0 mm
      • Silt 0.002-0.05 mm
      • Clay < 0.002 mm
using a soil survey general soil map
Using a Soil Survey: General Soil Map

Use it for getting a broad idea of soil conditions in the county

particle size
Particle Size
  • Particle size determines the amount of air & water contained in soil
  • Pore space is the amount of air or void space between particles. Infiltration occurs here. It is an equation representing a ratio of void space to volume held:
  • Porosity = the void/void total x 100 (5)
  • A mixture of large with small particles results in : more or lower porosity?
  • LOWER!
  • The measure of soils ability to transmit water or groundwater. The larger the pore space the morw permeable.
  • When smaller grains are added is permeability greater or less?
  • LESS!
  • Sand: greater or less?
  • Clay: greater or less? Low permeability due to large surface area but lots of interconnectedness between grains = friction!
pollution and porosity and permeability
Pollution and porosity and permeability

Soil acts as a natural filter to screen out many substances that mix with the water.

But water will transport some contaminants into the groundwater.

The amount of groundwater recharge, storage, discharge, as well as the extent of groundwater contamination, all depend on the soil properties:

soil and pollution
Soil and Pollution

The soil acts as a natural filter. In this context filtering means more than capturing solid particles. Filtering also means retaining chemicals or dissolved substances on the soil particle surface, transforming chemicals through microbial biological processing, and retarding movement of substances.

The soil's ability to lessen the amount of or reduce the severity of groundwater contamination is called soil attenuation. "During attenuation, the soil holds essential plant nutrients for uptake by agronomic crops, immobilizes metals that might be contained in municipal sewage sludge, or removes bacteria contained in animal or human wastes. 18"