Importance of Soil
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Objectives
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 List the areas of study involved with soil science.
 Explain the components of the ecosystem.
 Produce a list of areas/careers where soil is
important.
 Identify the soil boundaries.
 Recall the importance of soil.
Areas of Study

 Soil Genesis- study of the origin of soil with special
reference to the processes responsible for its development
 Soil Survey and Classification- systematic examination,
description, classification, and mapping of soils in an
area.
 Soil Physics- branch of soil science that deals with the
physical properties of the soil.
 Soil Microbiology- branch concerned with soil-inhabiting
microorganisms, their functions, and activities.
Continued…
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 Soil Fertility- the branch concerned with the quality
of the soil that enables it to provide nutrients and
proper growth for specified plants or crops.
 Soil Chemistry- branch that seals with the chemical
constitution, properties, and reactions of the soil.
 Soil Conservation- branch that deals with the
protection of the soil against physical loss by erosion
or against chemical deterioration.
Soil

 Living dynamic system which forms at the interface
between the atmosphere and lithosphere in response
to forces exerted by climate and living
organisms/biological factors acting on parent
material as conditioned by topography/relief over a
period of time.
Soil

 3-dimensional natural body occupying the earth’s
surface and capable of supporting plant growth.
Components of the
Global Ecosystem

 Lithosphere- upper layer of the solid Earth.
 Biosphere- environment in which living organisms
are found, and which they interact.
 Atmosphere- air surrounding the Earth.
 Hydrosphere- total body of water that exists on or
close to the surface of the Earth,
 Pedosphere- envelope of the Earth where soils occur
and where soil forming processes are active.
Not Just “Dirt”

 Essential factor to our existence
 Foundation for products you use every day
 Ex. Food, clothing, shelter, medicines
Soil is Vital

 Holds water and nutrients that plants need to grow.
 Feeds humans and livestock.
Why Do We Need Soil?

 Acts as a natural filter.
 Provides a foundation for homes.
 Enjoy outdoor activities filled with plants.
 Tiny organisms in the soil are used to develop
antibiotics for humans and animals.
Farmers

 Why would farmers be so dependent on a good
quality soil?
Key Terms

 Fertile- capable of producing or holding a large
amount, as in plants and soil.
 Yield- amount of crop produced.
 Erosion- removal of the top layer of soil by wind and
water.
Soil “What If’s”

 Lacking nutrients or difficulty holding water:
 Crops die, cattle cannot graze.
 Soil is not suitable for agriculture:
 Farmers, producers cannot make a living.
 Soil nutrients lost to erosion:
 Affects the ability to raise crops and livestock.
 Fertile soil:
 Increased yields
Objectives

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Determine how soil is formed.
Compare and contrast organic and inorganic soils.
Distinguish the differences of the soil profile.
List and interpret the five main factors of soil formation.
Assemble a soil profile.
Soil Formation

 Formation of the soil with specific reference to the
process or soil forming factors responsible for the
development of the true soil from parent material.
Soil Development

 The changes in the soil profile brought about by the
natural processes of leaching, translocation of
colloids, accumulation of organic matter, and
continued rock and mineral weathering.
Where does soil come
from?

 Decaying organic matter- Top Layer
 Plants and animals
 Mainly produced from rocks
 Tiny pieces of rock or material
How long to form?

 Hundreds to thousands of years.
Four Components of
Soil

 Inorganic matter (minerals)
 Soil primarily made up of minerals; not living material
 Organic matter
 soil primarily made up of decayed plant and animal
matter; natural
 Air
 Water
Organic Soils

 Productive, nutrient rich soils with a high percentage
of organic matter.
 When plants and animals die, it leads to decay. This
becomes part of the soil, adding nutrients making it
a fertile pace for plants to grow.
Inorganic Soils

 Soils composed of a high percentage of minerals.
 Generally less fertile and less productive than
inorganic soils.
Soil Formation Factors

 Parent Material
 Climate
 Biological Factors/Living Organisms
 Topography
 Time
Parent Material

 Beginning of soil
 Central component of soil but also includes other
sources such as deposits from water, wind, glaciers,
and volcanoes.
 The kind of soil that forms depends on the parent
material.
Climate

 Refers to weather of an area and includes factors of
temperature and moisture
 Climate and weathering forces help break down
parent material
 Wind, precipitation, changes in temperature
Biological Factors/
Living Organisms

 All plants and animals
 Humans, animals, plants, and microorganisms all
affect soil formation
 Churns the soil and promotes air and water flow
 Microorganisms can help decompose plants and
animals and will eventually become part of the soil as
organic matter
Topography

 Physical layout of the land; details such as
mountains, rivers, and valleys.
 Affects soil formation along with climate factors
 Slope affects soil in several ways
 Soils at the bottom will receive more water than on the
slope.
 Soils near the top will be drier and may erode.
 Affects vegetation, erosion, and drainage– all affect
formation.
Time

 The interaction of the other factors takes hundreds or
thousands of years.
 Why are soils different?
 Soils are different in the world because the factors
involved are different
Soil Horizon

 Layers in the soil created based on level of organic
matter.
 Classified by properties such as color, texture,
structure, thickness, and chemical and mineral
content.
 O, A, E, B, C, R
Horizon “O”

 Top of the soil profile
 Consists of organic matter or humus.
 Decayed organic matter that is part of the soil.
 Ex. Leaves, twigs, branches, dead grass, etc.
 Provides nutrients
 Helps bind soil particles together
 Helps soil retain moisture
 Usually seen in forested soils and wetlands;
generally not in cultivated soils.
Horizon “A”

 Composed of organic and inorganic materials
 Usually dark in color because of higher organic
matter
 Most biological activity occurs here
 Ex. Soil microbes, earthworms, etc.
 If plowed, it extends to the depth of cultivation.
 Also known as the plow layer or zone of eluviation
 Area of clay and chemical loss
Horizon “E”

 Zone of eluviation (removal)
 Generally lighter in color and sandy-- contains little
organic matter due to eluviation
 Downward movement of materials through soil when
it rains
 Maximum clay and chemical loss
Horizon “B”

 Areas where materials leached or washed from the
soil horizons accumulate
 Knows as the zone of illuviation (accumulation)
 The accumulation of materials in one layer of soil that
have been leached out of another layer.
 Clay and chemicals are generally at maximum levels
Horizon “C”

 Consists of soil parent material
 No biological activity here
 Not a zone of eluviation or illuviation
 Little to no rooting in this horizon
 Generally considered to be the lower limit of the soil
 Called the parent material
Horizon “R”

 Bedrock beneath the soil
 Limestone, sandstone, or granite
Affects on Soil

 pH
 Ecosystems
 Erosion
pH

 Soil pH is a measure of the acidity or alkalinity in the
soil.
 Acidity- pH 0-6.9
 Alkaline- pH greater than 7
 Neutral- pH 7
Activity

 Alkalinity
 Acidic
pH in Soil

 Why is it important?
 Affects how nutrients and chemicals are absorbed by
the soil and plants.
 Ex. Nitrogen, Phosphorus, and Potassium
 Too low?
 Plants are more susceptible to take up toxic metals
resulting in death.
 Too high?
 Plants may not be able to use the nutrients like
calcium, phosphorus, and magnesium.
Continued…

 Some plants prefer certain pH ranges.
 If it is above or below their requirements, growth
may be diminished and nutrient deficiencies or
toxicity can result.
 Examples or required pH levels
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Blueberries: pH 5-5.5
Alfalfa: 5.5-6
Soybeans: 6-6.5
Strawberries: 6.5-7.5
Ecosystems

 Community of plants, animals, and microorganisms
that interact with each other and their environment.
 They fertilize the soil by releasing nutrients from
organisms that have died.
 The cycle of life and death that depends on soil is
called the soil food web
 Plants, Burrowing Mammals, Arthropods,
Earthworms, Microorganisms, Protozoa, Nematodes.

Plants

 Soil provides stable support for plant roots, while
providing plants with water and nutrients.
 Can easily be seen, or at least the tops of plants.
Arthropods

 Invertebrates that have no spinal column: insects,
spiders, crustaceans.
 Microscopic or seen with the naked eye.
 Feed on other soil organisms, food source to larger
animals like lizards.
 Help aerate the soil.
 Supply with air
 Improve soil structure through the digestion and
excretion of organic matter into the soil.
Earthworms

 Help decompose organic matter.
 Mix and improve the water-holding capacity of soil.
 Provide channels for roots.
 Increases soil porosity and helps drainage.
Microorganisms

 Bacteria microscopic single-celled organisms found throughout
the soil, especially near plant roots.
 Bacteria in soil have a symbiotic relationship- have a
close, beneficial relationship.
 Helps decompose plant cells that have died.
 Some help bind soil particles, which improves
infiltration, water holding capacity, stability, and
aeration.
Microorganisms

 Fungi Plant-like organisms that lack chlorophyll and
reproduce by spores: molds, mildews, mushrooms.
 Some grow around root cells, which extends beyond
the root system; increases ability of the plant to reach
water and nutrients
 Fungi benefits by receiving sugars from the plant.
Microorganisms

 Protozoa Small single-celled animals that feed mostly on
bacteria and release nitrogen in their waste,
 Help maintain a balance in the ecosystem
 Can be harmful by attacking roots and causing plant
disease
Microorganisms

 Nematodes Very small roundworms abundant in all types of soil.
 Feed on fungi and bacteria, plant roots and tiny
animals.
 Allow moisture around the soil particles to move.
 Can become dormant when weather is too hot or dry.
 Become active when moist
 Decompose organic matter—increases nitrogen and
phosphorus levels.
 Control diseases and recycle nutrients.
Burrowing Mammals

 Badgers, gophers, mice, prairie dogs, etc. dig
burrows in the soil.
 Helps mix the below-surface material with surface
soil to aerate and fertilize the soil.
 Benefits plants and microorganisms.
 Water runoff soaks into the soil through the burrows
and tunnels and reduces the chance for erosion.
 Mammals help protect new seeds by eating
arthropods that eat the seeds.
Erosion

 Wearing away of the land surface by water, wind,
ice, or other natural agents that detach or remove the
soil from one point to another.
 Removes the topsoil
 Most productive layer—vital to producing healthy
crops.
Types of Erosion
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 Wind
 Saltation
 Soil Creep
 Suspension
 Water
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Splash
Sheet
Rill
Gully
Stream Bank
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Objectives

 Compare and contrast the different types of soil.
 Demonstrate how the soil triangle works.
 Calculate the slope for a given area.

Texture

 The soil texture is described by how much sand, silt,
or clay make up the soil, and can be a combination of
all three.
Sand

 Sand is the largest soil particle ranging from .05 to
2.0 millimeters.
 Only particle to be seen with the naked eye.
 Gritty. Good for making sandpaper, glass blowing,
and adding to concrete before pouring.
 Susceptibility to wind erosion- Moderate
 High if fine sand
 Susceptibility to water erosion- Low
 High if fine sand
Silt

 Smaller than sand and ranges from .002 to .005
millimeters in diameter.
 Smooth and powdery and has a slippery feel when
wet—much like wet baby powder.
 Susceptibility to wind erosion- High
 Susceptibility to water erosion- High
Clay

 Smallest soil particle and is less than .002 millimeters
in diameter.
 Hard and smooth when dry and sticky when wet.
 Can hold nutrients but often holds them too tight
that plants cannot use them.
 Keeps water and air from flowing through the soil.
 Susceptibility to wind erosion- Low
 Susceptibility to water erosion- Low if aggregated
 High if not aggregated
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Slope

 The slope of the land can vary greatly over short
distances, which results in different soil types.
 Man of the differences are related to the amount of
soil erosion and the water content of the soil.
 On steep slopes, erosion is accelerated.
 Little water soaks in, little to no plants, which results
in thin or nonexistent soils.
 In flat areas, there is little erosion and poor drainage.
 Resulting in waterlogged soils that are typically thick
and dark (large amounts of organic matter.)
Terms

 Slope= Rise/Run
 Percent- number or ratio expressed as a fraction of
100
Texas Soil Orders
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Alfisols

 Alfisols have a subsurface accumulation of clay and
have greater than or equal to 35 percent base
saturation.
 Soil samples that fall under this category include
Duval series.
 Duval soils occur in the Northern and Western Rio
Grande Plain on nearly level to gently sloping
uplands.
Aridisols

 Aridisols are the dry soils of the deserts. They have
horizons with accumulations of carbonates, gypsum,
or sodium chloride.
 Soil samples that fall under this category include the
Upton series.
 Upton soils occur in the Trans-Pecos region on nearly
level to moderately sloping uplands.
Entisols

 Entisols are soils with little evidence of soil
formation.
 Soil samples that fall under this category include the
Galveston series.
 Galveston soils occur on nearly level to strongly
sloping coastal terraces, dunes, and offshore barrier
islands along the Texas Gulf Coast.
Inceptisols

 Inceptisols are soils with weakly developed
subsurface horizons. These soils may be shallow to
bedrock, occur on steeply sloping land, or they may
be very deep soils in areas subject to intermittent
flooding.
 Soil samples that fall under this category include the
Weswood series.
 Weswood soils occur along the flood plains of the
Brazos and Colorado Rivers in central Texas.
Mollisols

 Mollisols have a distinctive dark colored surface
horizon that is enriched with organic matter. They
formed under grassland and are naturally fertile.
 Soil samples that fall under this category include the
Pullman series.
 Pullman soils occur in the High Plains on nearly level
and very gently sloping uplands.
Ultisols

 Ultisols are highly weathered soils that have a
subsurface horizon enriched with clay. They have
less than 35 percent base saturation.
 Soil samples that fall under this category include the
Bowie series.
 Bowie soils occur in the East Texas Timberlands on
broad, very gently sloping to moderately sloping
uplands.
Vertisols

 Vertisols are characterized by the presence of a
mineral in the clay fraction called smectite. This
mineral swells markedly when moist and shrinks
when dry.
 Soil samples that fall under this category include the
Houston Black series.
 Houston Black soils occur in the Blackland Prairie in
the central part of the state from Bonham south to San
Antonio.
 Two soil orders not shown on the map are Histosols
and Spodosols, which are mapped in the
southeastern part of the state, are not shown on the
map because they cover relatively small areas.
 Histosols: Histosols are composed almost entirely
of organic matter in all stages of decomposition.
 Spodosals: Spodosols are acid soils with a
subsurface accumulation of iron and organic
matter. These soils generally form under forests.
Babco soils occur in the Flatwoods of southeast
Texas.