An Introduction to SoilAn Introduction to Soil

Bryan McElvanyBryan McElvanyResearch CoordinatorResearch Coordinator

Warnell School of Forest ResourcesWarnell School of Forest Resources

Patrick DaviesPatrick Davies

DIRTDIRTThis is the stuff under your This is the stuff under your

fingernailsfingernails

Why is soil science intimidating?Why is soil science intimidating?

Whole new vocabularyWhole new vocabulary Hard to visualizeHard to visualize Somewhat complex topics like chemistry and Somewhat complex topics like chemistry and

physicsphysics

What is soil?What is soil?

Several different ways to define soilSeveral different ways to define soil

1) 1) Geologic definitionGeologic definition:: Loose surface of the Loose surface of the earth as distinguished from solid bedrock earth as distinguished from solid bedrock (support of plant life not required).(support of plant life not required).

2) 2) Traditional definitionTraditional definition:: Material which Material which nourishes and supports growing plants nourishes and supports growing plants (includes rocks, water, organic material, air).(includes rocks, water, organic material, air).

What is soil made of?What is soil made of?

Mineral MatterMineral Matter Organic MatterOrganic Matter AirAir WaterWater

What is the function of soil?What is the function of soil? Plant mediumPlant medium Recycling system for Recycling system for

nutrientsnutrients Animal homeAnimal home Engineering mediumEngineering medium System for water System for water

supply and purificationsupply and purification

The ability of soil to perform those The ability of soil to perform those functions is dependant upon:functions is dependant upon:

Soil TextureSoil Texture Soil StructureSoil Structure Soil ChemistrySoil Chemistry Soil AgeSoil Age Site Factors (topography, water, etc)Site Factors (topography, water, etc) Etc.Etc.

Soil Formation FactorsSoil Formation Factors

There are five main factors that influence There are five main factors that influence soil formation processes.soil formation processes.

1)1) Type of Parent MaterialType of Parent Material

2)2) ClimateClimate

3)3) TopographyTopography

4)4) Biotic Components Biotic Components

5)5) TimeTime

Parent MaterialParent Material

Two major divisions in type of parent materialTwo major divisions in type of parent material1)1) Residual-Formed in place (Residuum)Residual-Formed in place (Residuum)2)2) Transported-Parent material was moved by:Transported-Parent material was moved by:

- wind (Eolian)- wind (Eolian)- ice (Glacial)- ice (Glacial)- gravity (Colluvial)- gravity (Colluvial)- water:- water:

rivers (Alluvial)rivers (Alluvial) oceans (Marine)oceans (Marine) lakes (Lacustrine)lakes (Lacustrine)

Soil Formation ProcessesSoil Formation Processes

Transformations – modification of soil constituents. Transformations – modification of soil constituents. Mineral weathering, organic matter breakdown.Mineral weathering, organic matter breakdown.

Translocations – movement up, down, or laterally of Translocations – movement up, down, or laterally of soil constituents.soil constituents.

Additions – movement of soil material in from Additions – movement of soil material in from outside sources. Organic material from leaves, dust outside sources. Organic material from leaves, dust from atmosphere.from atmosphere.

Losses – movement of soil material out of the soil. Losses – movement of soil material out of the soil. Transportation to groundwater, erosion of surface Transportation to groundwater, erosion of surface materials.materials.

Soil Formation ProcessesSoil Formation Processes

Soil Formation in ActionSoil Formation in Action

The soil formation processes, operating under the The soil formation processes, operating under the influence of the soil formation factors, is the driving influence of the soil formation factors, is the driving force in soil genesis.force in soil genesis.

Important questions to remember are:Important questions to remember are: What transformations and translocations took place in the What transformations and translocations took place in the

parent material to form this soil? parent material to form this soil? What materials were removed?What materials were removed? What was added? What was added? How did the climate and topography affect those processes How did the climate and topography affect those processes

over time? over time?

Soil HorizonsSoil Horizons

As soils develop they form layers called Horizons.As soils develop they form layers called Horizons. These horizons have distinct characteristics produced These horizons have distinct characteristics produced

by soil forming processes.by soil forming processes. Master horizons include the O, A, E, B, and C Master horizons include the O, A, E, B, and C

horizons.horizons. Not every soil contains every horizon based on the Not every soil contains every horizon based on the

level of development of the soil.level of development of the soil. Depth of each horizon varies between different soils.Depth of each horizon varies between different soils.

O HorizonO Horizon

Layer of accumulated Layer of accumulated organic matter such as organic matter such as leaves, grass, twigsleaves, grass, twigs

Material can be in Material can be in various states of various states of decompositiondecomposition

Generally dark in colorGenerally dark in color

A

E

B

C

R

O

A HorizonA Horizon

Zone of incorporation of Zone of incorporation of organic matter into the organic matter into the mineral soilmineral soil

Generally it’s the most Generally it’s the most productive horizonproductive horizon

High biological activityHigh biological activity Generally dark in colorGenerally dark in color TopsoilTopsoil

AE

B

C

R

O

E HorizonE Horizon Zone of Eluviation or Zone of Eluviation or

leachingleaching Eluviation is the movement Eluviation is the movement

of soil material out of a of soil material out of a layer of soillayer of soil

Soluble minerals and Soluble minerals and organic material move out organic material move out of this horizonof this horizon

Generally a lighter Generally a lighter “washed” appearance in “washed” appearance in colorcolor

A

E

B

C

R

O

B HorizonB Horizon Zone of illuviation or Zone of illuviation or

depositiondeposition Accumulation of materials Accumulation of materials

“washed” from horizons “washed” from horizons aboveabove

This material is commonly This material is commonly clay, humus, sesquioxides, clay, humus, sesquioxides, or a mixture of the threeor a mixture of the three

Variable in color from reds Variable in color from reds and yellows to browns and and yellows to browns and graysgrays

A

E

B

C

R

O

C HorizonC Horizon

Parent materialParent material The unconsolidated The unconsolidated

material that has been material that has been affected little by the soil affected little by the soil forming processesforming processes

A

E

B

C

R

O

Soil TextureSoil Texture

Soil Texture is the relative proportion of the primary Soil Texture is the relative proportion of the primary particles in the soil. particles in the soil.

Sand = 2mm – 0.05mmSand = 2mm – 0.05mm

Silt = 0.05mm – 0.002mmSilt = 0.05mm – 0.002mm

Clay = < 0.002mmClay = < 0.002mm

Soil TextureSoil Texture

This proportion of This proportion of sand, silt, and clay sand, silt, and clay can be grouped into can be grouped into textural classes. textural classes.

Soil texture has a Soil texture has a great deal to do with great deal to do with many other soil many other soil characteristics. characteristics.

Soil TextureSoil Texture

Coarse textured soil – soil that has a higher Coarse textured soil – soil that has a higher proportion of larger particles. Sand, Loamy proportion of larger particles. Sand, Loamy sand, Sandy loam.sand, Sandy loam.

Fine textured soil – soil that has a higher Fine textured soil – soil that has a higher proportion of smaller particles. Clay, Silty proportion of smaller particles. Clay, Silty clay, sandy clay.clay, sandy clay.

Soil StructureSoil Structure

Soil structure is the Soil structure is the arrangement of soil arrangement of soil particles into particles into aggregates.aggregates.

Structureless soils do Structureless soils do occur as either single occur as either single grained or massive.grained or massive.

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

Pore SpacePore Space

The voids between soil particles are called pores. The voids between soil particles are called pores. These can either be filled with water or air.These can either be filled with water or air.

Soil texture plays a major role in total pore space as Soil texture plays a major role in total pore space as well as size of pores. well as size of pores.

Coarse textured soils (sandy) have larger pores, but Coarse textured soils (sandy) have larger pores, but less total pore space.less total pore space.

Fine textured soils (clayey) have smaller pores, but Fine textured soils (clayey) have smaller pores, but more total pore space.more total pore space.

Soil PermeabilitySoil Permeability

Permeability is a measure of how fast air and Permeability is a measure of how fast air and water can move through a soil.water can move through a soil.

Soil texture and soil structure both pay a role Soil texture and soil structure both pay a role in soil permeability.in soil permeability.

Soil Texture and PermeabilitySoil Texture and Permeability

Soil Structure -PermeabilitySoil Structure -Permeability

Granular Blocky PlatyGranular Blocky Platy

Soil WaterSoil Water

Saturated soil is when that soils pores are full of Saturated soil is when that soils pores are full of water.water.

Gravitational water is that water that moves out of the Gravitational water is that water that moves out of the soil due to gravity. This water is generally in the soil due to gravity. This water is generally in the larger Macro-pores.larger Macro-pores.

Capillary water is that water that is held in the soil Capillary water is that water that is held in the soil due to adhesion and cohesion against the pull of due to adhesion and cohesion against the pull of gravity. This water is generally held in the smaller gravity. This water is generally held in the smaller Micro-pores and as a film around soil particles.Micro-pores and as a film around soil particles.

Soil WaterSoil Water

After a major rain event, once the gravitational After a major rain event, once the gravitational water has left the soil, the soil is at Field water has left the soil, the soil is at Field Moisture Capacity. Moisture Capacity.

The wilting point is reached when soil water The wilting point is reached when soil water levels decline to the point that all remaining levels decline to the point that all remaining water is held too tightly by soil particles to be water is held too tightly by soil particles to be removed by the plant.removed by the plant.

Soil WaterSoil Water

Available Water CapacityAvailable Water Capacity

Available water capacity is a measure of the Available water capacity is a measure of the water available to plants. water available to plants.

Commonly defined as the difference between Commonly defined as the difference between the amount of water at field moisture capacity the amount of water at field moisture capacity and the amount at the wilting point.and the amount at the wilting point.

This is the water a plant has a chance of This is the water a plant has a chance of utilizing. utilizing.

Available Water CapacityAvailable Water Capacity

The EndThe End

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