(COMPLETE) LEC 2: Soil Basics/Physical Properties

What is SOIL?

the unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants

Soil is often metaphorically referred to as the “___of the earth.”

skin

Enumerate the four primary components that compose soil

1. minerals

2. air

3. water

4. organic matter (living or dead material)

In a balanced soil system, what percentage of the total volume is typically occupied by solids?

approximately 50%

In the three-phase soil system, what two components each typically comprise 25% of the volume?

liquid (water) and gases (air)

What specific material constitute the “solids” phase of soil?

soil mineral particles and organic matter

what does the “liquid” phase (soil solution) contain besides water?

dissolved nutrients, chemicals, and gases

List three common gases found in the “gases” phase of soil

(N2) Nitrogen, (O2) Oxygen, (CO2) Carbon dioxide

In soil science, what is the fundamental difference between soil and dirt?

soil is a functional ecosystem for growth, whereas dirt is displaced material found on clothes or under fingernails

How does soil contribute to atmospheric modification?

it modifies the atmosphere by emitting and absorbing various gases

List six reasons why soil is considered important to life and society?

1. Plant growth media

2. atmospheric modification

3. animal habitat

4. construction media

5. water filtration

6. carbon capture

What is the acronym used to remember the five factors of soil formation?

CLORPT

Enumerate the five factors represented b the acronym CLORPT

CLimate

Organisms

Relief

Parent Material

Time

(CLIMATE) Which two major climatic forces directly influence the weathering of soil materials?

Temperature and precipitation

(ORGANISMS) What are the four categories of organisms involved in soil formation?

plants, animals, micro-organisms, and meso-organisms

List three examples of micro- or meso-organisms found in soil

bacteria, fungi, and worms (or insects)

(RELIEF) what is another term used to describe the ”relief” factor in soil formation?

Topography

Enumerate four specific aspects of Relief (topography) that affects soil

shape, slope, elevation, and aspect

In the context of relief, what does the term “aspect” refer to?

the direction a slope faces?

(PARENT MATERIAL) What is meant by the statement that soil “inherents” traits from its parent material?

The chemical and physical properties of the soil are determined by the original rock or deposit from which it formed

(TIME) How does the complexity of soil horizons typically change as a soil ages?

older soils generally develop more distinct and numerous horizons compared to younger soils

What is a “soil profile”?

a vertical section of soil showing its various layers or horizons

Which soil horizon is characterized primarily by organic matter such as decaying leaves?

O Horizon

The A Horizon is commonly known by what name?

Topsoil

Which horizon is described as the “eluviated horizon,” appearing light-colored due to the leaching of minerals?

E Horizon

What characterizes the B Horizon, also known as subsoil?

it is rich in minerals that have moved down from the A or E horizons

The C Horizon represents the ___from which soil developed

parent material

What does the R Horizon in soil profile represent?

Bedrock (a mass of rock that weathers to form parent material).

What are the 4 key physical properties of soil

1. soil color

2. soil texture

3. water-holding capacity

4. permeability

What is determined by how soil mineral and organic particles combine to form the matrix and pore spaces?

water-holding capacity and permeability

Which soil order is typically associated with red or orange colors in a soil profile?

Oxisols

Which soil order is characterized by very dark, organic-rich colors?

Histosols

Soil texture is determined by the relative proportions of which three particle sizes?

1. sand

2. silt

3. clay

Of the three soil separates, which particles are the largest?

sand particles

Of the three soil separates, which particles are the smallest?

clay particles

Clay particles are defined as being less than___mm

0.002

What is the diameter range for silt particles?

0.05 to 0.002 mm

What is the diameter range for sand particles?

2.0 to 0.05 mm

How many distinct soil texture classes are indentified on the Soil Texture Triangle?

12

What organization developed the “Soil Texture by Feel Method” for field estimation?

Natural Resources Conservation Service (NRCS)

What are the 3 materials needed to perform a soil texture by feel method?

1. soil sample

2. water

3. flow chart

If the sample will not stay together to form a ball, which soil textural classes does it belong?

sand, loamy sand

If a soil ball falls apart when tossed or bounced, which soil textural classes does it belong?

sandy loam

If a soil is slick and shiny with a soapy feel, which soil textural classes does it belong?

high clay content: sandy clay, clay, silty clay

A soil that feels floury and smooth is most likely classified as which texture?

silt loam or silt

If it stays together, place it between your thumb and index finger. Apply pressure and rub the sample smoothing it out on your thumb. If the sample is ruffled or broken the soil is

sandy clay loam, clay loam, silt clay loam

If it stays together place it between both palms and rub them together vigorously. If the ball comes apart the soil is

loam, silt loam, silt

In the Jar Method of determining texture, which layer settles first at the bottom?

The sand layer

In a settled jar of soil and water, where is the clay layer located?

at the top of the sediment, appearing only after the water is clear

Approximately how long does it take for the silt layer to form in the Jar Method?

about 2 hrs

What is the definition of soil “pore space”?

The open area between soil particles that is filled with either air or water

3 examples of “living” organic matter in soil

1. bacteria

2. worms

3. fungi

3 examples of “dead” organic matter in soil

1. leaf litter

2. dead roots

3. decomposing critters

How does slope steepness (relief) affect soil formation?

It influences water runoff, erosion rates, and the amount of water that infiltrates the soil

Why is time considered a critical factor in soil formation?

Soil processes occur slowly, and time allows for the development of distinct horizons from the parent material

The inorganic component of soil’s solid material is primarily composed of___

minerals

What physical property describes the ease with which water and air move through soil?

permeability

What is “water-holding capacity”?

the ability of a soil to retain water for use by plants

How is the A horizon typically distinguised from the E horizon?

The A horizon contains more organic matter, while the E horizon is leached and lighter in color

What role does soil play in the global carbon cycle?

it acts as a reservoir to capture and store carbon

How does precipitation (climate) influence soil weathering?

water provides the medium for chemical reactions and physical transport of materials within the soil profile

Which soil component serves as a “living filter” to clean water?

the soil matrix itself

What specific gas, essential for plant roots, make up a significant portion of the 25% gas phase in healthy soil?

Oxygen

Why is parent material considered the “starting point” for soil?

it provides the raw mineral base that climate and organisms act upon over time

What do we call the three-dimensional diagram used to classify soil based on sand, silt, and clay content?

The Soil Texture Triangle

In the soil profile diagram, which horizon is found deepest and consists of unweathered material?

R Horizon (Bedrock)

According to the Jar Method, which particles settles within minutes?

Sand particles

In the context of relief, how do flat/low-lying areas compare to hills/mountains in soil formation?

flat areas often accumulate materials and moisture, while hills are more prone to erosion and faster runoff

What is the primary function of the “soil solution”?

to provide water and dissolved nutrients to plants

How does temperature (climate) affect the rate of soil formation?

higher temperatures generally increase the rate of chemical weathering and organic matter decomposition

What determines whether a soil pore is filled with air or water at any given time?

the amount of moisture present and the size of the pore space

3 examples of “larger critters” that contribute to licving soil organic matter

1. insects

2. burrowing mammals

3. reptiles

Why is the O horizon often absent in some soil profiles, especially incultivated fields?

decaying organic matter may be removed, decomposed rapidly, or mixed into the A horizon by plowing

What is the result of adding water to a soil sample during the texture by feel method?

it allows the user to test the soil’s plasticity, stickiness, and ability to form shapes