Soil Characteristics
Soil
• a layer of natural materials on
the earth’s surface containign
both organic and inorganic
materials and capable of
supporting plant life.
Soil
• The material covers the earth’s
surface in a thin layer.
• It may be covered by water, or
it may be exposed to the
atmosphere.
Soil
• Soil contains four main
components: inorganic material,
organic matter, water, and air.
Soil
• Ideal soil should contain about
50% solid material and 50%
pore space.
• About half of the pore space
should contain water and half of
the space should contain air.
Soil
• Inorganic material consists of
rock slowly broken down into
small particles.
• The organic material is made up
of dead plants and animals
varying in stages of decay.
Soil
• The percentages of the four
main soil components varies
depending on the kind of
vegetation, amount of
mechanical compaction, and the
amount of soil water present.
Soil
• Soil is formed very slowly.
• It results from natural forces
acting on the mineral and rock
portions of the earth’s surface.
• The rock is slowly broken down
to small particles resulting in
Parent Material
• Soil parent materials are those
materials underlying the soil and
from which the soil was formed.
• There are five major categories of
parent material: minerals and
rocks, glacial deposits, loess
deposits, alluvial and marine
deposits and organic deposits.
Parent Material
• Minerals are solid, inorganic,
chemically uniform substance
occurring naturally in the earth.
• Some common minerals for soil
formation are feldspar, micas,
silica, iron oxides, and calcium
carbonates.
Parent Material
• Rocks are different from
minerals because they are not
uniform.
• There are three types of rocks,
igneous, sedimentary, and
metamorphic.
Parent Material
• Igneous rocks are those formed
by the cooling of molten rock.
• Sedimentary rocks are those
formed by the solidification of
sediment.
Parent Material
• Metamorphic rocks are simply
igneous or sedimentary rocks
which have been reformed
because of great heat or
pressure.
Parent Material
• During the ice age, glaciers moved
across areas of the northern
hemisphere.
• They ground, pushed, piled,
gouged, and eventually deposited
great amounts of rocks, parent
material, and already formed soil
material.
Parent Material
• Loess deposits are generally
thought of as windblown silt.
• Alluvial and marine deposits are
water borne sediments.
• Alluvial deposits are left by
moving fresh water.
• Marine deposits are formed on
ancient ocean floors.
Parent Material
• Organic deposits are partially
decayed plants that live plants
are able to root and grow in.
• These are found in swamps and
marshes.
Weathering
• When minerals are exposed to
weather, they begin to break
down into smaller pieces.
• This is mostly done by heating
and cooling of the minerals and
rock.
Weathering
• Some minerals are water
soluble which means they
dissolve when exposed to water.
• Some rocks may contain some
minerals that are water soluble
and only that part of the rock
will dissolve. Ex: some caves.
Weathering
• When a tree or other types of
plants begin growing in the
cracks of rocks, this may speed
up the break down of the rock
because of the pressure the
roots may exert.
Weathering
• Ice can also speed up the
weathering process on rocks.
• If a rock has a crack that can fill
up with water, when the water
freezes, it can literally crumble
the rock into small pieces.
Weathering
• Rocks can also be broken down
by mechanical grinding such as
wind blowing sand at high
speeds or glaciers causing rocks
to grind each other.
Weathering
• New soil is continually being
made, but it takes a long time to
create new soil and if it isn’t
managed properly, soil can be
eroded away quicker than it can
be made.
Organic Matter
• In most soils, the proportion of
organic matter is relatively
small (2-5%).
• Its importance in formation and
production is much higher than
the small % would suggest.
Organic Matter
• Soil organic matter decaying
plant and animals.
• As they die, they are attacked
by microorganisms: fungi,
bacteria, and others.
Organic Matter
• There are two types of organic
matter.
• Original tissue is that portion of
the organic matter that can still
be recognized.
• Twigs and leaves covering a
Organic Matter
• Humus is organic matter that is
decomposed to the point where
it is unrecognizable.
• The brown color you sometimes
see in soil is a good example.
Organic Matter
• Purposes of organic matter: affects
the soil structure by serving as a
cementing agent, returns plant
nutrients to soil (P, S, N), helps
store soil moisture, makes soil
more tillable for farming, provides
food (energy) for soil
microorganisms, which makes the
Characterizing Soils
• The Soil Profile
• Most soils have three distinct
layers called horizons.
• The horizons are called A
Horizon (topsoil), B horizon
(subsoil), and C horizon (parent
Characterizing Soils
• The top soil is the most
productive because that is
where all the nutrients are.
Soil Physical Properties
• Slope is defined as the angle of
the soil surface from horizontal.
• It is expressed as the % of rise
over run.
Soil Physical Properties
• Slope effects the productive
potential in numerous ways:
Rain runoff, soil erosion, the
use of farm machinery, and
contour farming.
Soil Physical Properties
• Texture refers to the proportions of
sand silt and clay in the soil.
• Course-textured soils are and
sandy and do not hold water well,
while fine-textured soils contain
clay and tend to hold more surface
moisture.
Soil Physical Properties
• Flood hazard refers to the
likelihood that the soil will
flood.
• This may occur in flood plains
near rivers and greatly reduce
plant production.
Soil Physical Properties
• Erosion as a soil property, refers
to the degree that the soil has
already been damaged.
• May range from none to severe.
Soil Physical Properties
• A field used for crop production
that has little or no erosion can
continue to be used for crops.
• But a severely eroded field may
need to be turned into pasture
where it is always covered.
Soil Physical Properties
• Topsoil and subsoil thickness
refer to the depth of those layers
that are available for plant
production.
• Thin topsoil and/or thin subsoil
can greatly limit crop
production
Land Capability
Classification
• Land capability class categorize
the productive potential of the
soil.
• The classes generally range
from class 1, the best land for
agricultural production, to class
VIII, the least productive.
Land Capability
• In general, class 1 through class
IV are for row crop production,
and V through VIII are not
suitable for row crop production
for various reasons.
Land Capability
• Class I is the best land for row
crop farming.
• It is level, well drained, deep,
medium textured, not subject to
erosion or flooding, and easily
cultivated.
Land Capability
• Class II is just as good, but it
may have some limitations such
as sloping land or slight
erosion.
Land Capability
• Class III can still be cultivated,
but it has some severe
limitations.
• The land may have moderate
slope, erosion or a shallow root
zone.
Land Capability
• Class IV has severe limitations,
but can still be cultivated with
good management practices.
Land Capability
• Class V is nearly level, but has
some property which makes it
unsuitable for farming.
• It may be very dry, very rocky, or
most often very wet.
• This class is quite suitable for
pasture, wildlife habitat, or forest
production.
Land Capability
• Class VI is just a more serious
version of V.
• It has severe limitations, but can
be used for the same things.
Land Capability
• Class VII has some severe
limiting properties.
• It may be very steep or be
severely eroded and have deep
gullies
Land Capability
• Class VII may be very course.
• This can be turned into pasture
but grazing must be controlled.
• It can also be used as forest or
recreation.
Land Capability
• Class VIII has one or more
extreme limitations.
• It should be left in its natural
state for recreation and wild
life.
• It has little agriculture value.
Soil Classification
• The first unit of classification is
the order.
• All soils fit into one of ten orders.
• Each order is broken down into a
suborder, which is broken down
into great groups, then subgroups,
and then families.
Soil Survey
• Soil survey is the process of
classifying soil.
• The results of the surveys in
certain areas is published in
what is known as the Soil
Survey Report.
Soil Survey
• Then they develop a map from
the survey.
• Scientists then use this as tool
for figuring out the land
capability.