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SOIL –SOIL – The Fundamental The Fundamental

ConceptsConcepts

SOILSOIL

Geologic definition: Loose surface of the Geologic definition: 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.

SOILSOIL

Traditional definition: Material which Traditional definition: Material which nourishes and supports growing plants; nourishes and supports growing plants; includes rocks, water, snow, air.includes rocks, water, snow, air.

SOILSOIL

Component definition: Mixture of mineral Component definition: Mixture of mineral matter, organic matter, water, and air.matter, organic matter, water, and air.

Air 25%

Mineral Matter 45%

Water 25%

Organic Matter 5%

SOILSOIL

Component definition: Mixture of mineral Component definition: Mixture of mineral matter, organic matter, water, and air.matter, organic matter, water, and air.

Example:Example:

SOILSOIL

Soil Taxonomy definition: Soil Taxonomy definition: Collection of natural Collection of natural bodies of the earth’s surface, in places modified or even bodies of the earth’s surface, in places modified or even made by man or earthy materials, containing living made by man or earthy materials, containing living matter and supporting or capable of supporting plants matter and supporting or capable of supporting plants

out of doors.out of doors. Its upper limit is air or shallow water and its lower limit is Its upper limit is air or shallow water and its lower limit is the depth to which soil weathering has been effective.the depth to which soil weathering has been effective.

SOILSOIL

As a portion of the landscape: As a portion of the landscape: Collection of Collection of natural bodies occupying portions of the earth’s surface natural bodies occupying portions of the earth’s surface that support plants and that have properties due to the that support plants and that have properties due to the integrated effect of climate and living matter, acting upon integrated effect of climate and living matter, acting upon parent material, as conditioned by relief, over periods of parent material, as conditioned by relief, over periods of time.time.

Soil Forming ProcessesSoil Forming Processes

TranslocationsTranslocations

TransformationsTransformations

AdditionsAdditions

LossesLosses

Mineral matterMineral matter

Organic matterOrganic matter

AirAir

WaterWater

Major ComponentsMajor Components

Physical Properties Physical Properties of Soilof Soil

Soil textureSoil texture

Soil structureSoil structure

Soil colorSoil color

Bulk densityBulk density

Three Fractions of Mineral Three Fractions of Mineral MatterMatter

SandSand

SiltSilt

ClayClay

USDA Textural TriangleUSDA Textural Triangle

Granular

Platy

Blocky

(Angular)(Subangular)

Wedge

ColumnarPrismatic

Examples of Soil StructureExamples of Soil Structure

Aspects of Soil StructureAspects of Soil Structure

The arrangement into aggregates of The arrangement into aggregates of desirable shape and sizedesirable shape and size

The stability of the aggregateThe stability of the aggregate

The configuration of the poresThe configuration of the pores

Factors that Affect Aggregate Factors that Affect Aggregate StabilityStability

Kind of clayKind of clay

Chemical elements associated with the Chemical elements associated with the clayclay

Nature of the products of decomposition Nature of the products of decomposition or organic matteror organic matter

Nature of the microbial populationNature of the microbial population

Factors that Affect Factors that Affect Soil StructureSoil Structure

Kind of clayKind of clay

Amount of organic matterAmount of organic matter

Freezing and thawingFreezing and thawing

Wetting and dryingWetting and drying

Action of burrowing organismsAction of burrowing organisms

Growth of root systems of plantsGrowth of root systems of plants

Important NoteImportant Note

All of these have a loosening effect on All of these have a loosening effect on the soil, but they have no effect on the soil, but they have no effect on aggregate stabilityaggregate stability

Bulk DensityBulk Density

Determined by dividing the weight of Determined by dividing the weight of oven-dry soil in grams by its volume in oven-dry soil in grams by its volume in cubic centimeterscubic centimeters

The variation in bulk density is due The variation in bulk density is due largely to the difference in total pore largely to the difference in total pore spacespace

Effects of Bulk DensityEffects of Bulk Density

Engineering propertiesEngineering properties

Water movementWater movement

Rooting depth of plantsRooting depth of plants

Soil ColorSoil Color

Indicator of different soil typesIndicator of different soil types

Indicator of certain physical and Indicator of certain physical and chemical characteristicschemical characteristics

Due to humus content and chemical Due to humus content and chemical nature of the iron compounds present in nature of the iron compounds present in the soilthe soil

Major Forms of Iron and Effect Major Forms of Iron and Effect on Soil Coloron Soil Color

Form Chemical Formula Color

Ferrous oxide FeO Gray

Ferric oxide (Hematite) Fe2O3 Red

Hydrated ferric oxide (Limonite) 2Fe2O3 3H2O Yellow

Want to learn more Want to learn more about soil?about soil?

Visit NRCS’ website at the National Soil Visit NRCS’ website at the National Soil Survey Center at www.soils.usda.govSurvey Center at www.soils.usda.gov

Prepared by Earl D. LockridgePrepared by Earl D. LockridgeNational Soil Survey CenterNational Soil Survey CenterLincoln, NELincoln, NEUSDA NRCS ~ An equal opportunity provider and employerUSDA NRCS ~ An equal opportunity provider and employer

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