august 2008 soil characteristics modified by georgia agricultural education curriculum office june,...
TRANSCRIPT
August 2008
Soil Characteristics
Modified by Georgia Agricultural Education Curriculum Office
June, 2002
August 2008
Soil• a layer of natural materials on
the earth’s surface containing both organic and inorganic materials and capable of supporting plant life.
August 2008
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.
August 2008
Soil• Soil contains four main
components: inorganic material, organic matter, water, and air.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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 soil.
August 2008
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.
August 2008
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.
August 2008
Parent Material• Rocks are different from
minerals because they are not uniform.
• There are three types of rocks, igneous, sedimentary, and metamorphic.
August 2008
Parent Material• Igneous rocks are those
formed by the cooling of molten rock.
• Sedimentary rocks are those formed by the solidification of sediment.
August 2008
Parent Material• Metamorphic rocks are simply
igneous or sedimentary rocks which have been reformed because of great heat or pressure.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
Organic Matter• Soil organic matter decaying
plant and animals.
• As they die, they are attacked by microorganisms: fungi, bacteria, and others.
August 2008
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 forest floor are good examples.
August 2008
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.
August 2008
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 soil capable of plant production
August 2008
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 material).
August 2008
Characterizing Soils• The top soil is the most
productive because that is where all the nutrients are.
August 2008
Soil Physical Properties• Slope is defined as the angle
of the soil surface from horizontal.
• It is expressed as the % of rise over run.
August 2008
Soil Physical Properties• Slope effects the productive
potential in numerous ways: Rain runoff, soil erosion, the use of farm machinery, and contour farming.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
Land Capability• Class II is just as good, but it
may have some limitations such as sloping land or slight erosion.
August 2008
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.
August 2008
Land Capability• Class IV has severe
limitations, but can still be cultivated with good management practices.
August 2008
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.
August 2008
Land Capability• Class VI is just a more serious
version of V.
• It has severe limitations, but can be used for the same things.
August 2008
Land Capability• Class VII has some severe
limiting properties.
• It may be very steep or be severely eroded and have deep gullies
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
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.
August 2008
Soil Survey• Then they develop a map from
the survey.
• Scientists then use this as tool for figuring out the land capability.