Soil

Soil in Our Environment

What is soil? Or is it Dirt?

“Gold’s father is dirt, yet it regards itself as noble.” Yiddish Proverb

Is it alive?

Is it fragile?

Formations of SoilsHow much time does it take to form

about 1” of topsoil?

About 1,000 years!

Destruction of SoilsHow long does it take to deplete

about 1” of topsoil?

In a few short years – less than 5 years in some areas

Destruction of SoilsWhat forces of nature do you

suppose cause the largest amounts of erosion?

A hint . . .

Uh Huh . . .

Wind!

What Else?Another hint?

That’s Right . . .

Water!

Destruction of SoilsSo what do you suppose causes soil,

on a large scale, to be so susceptible to wind and/or water erosion?

Destruction of SoilsMismanagement . . .

poor agricultural practicesCarelessnessNeglectLeads to . . . (and the magic word

is?)Erosion – wind and water

Soil loss through plowing

The Outcome?How about the failure of the local

civilization?

What about from a landscape perspective?

Do we still see erosion?What about soil fertility?And plant health and vigor?

Chapter 1Soil Composition and ImportancePages 1 – 24

What is soil?The uppermost layer of the Earth’s

surface – the tectonic plates . . .

The tectonic plates?

Tectonic Plates

?

What is soil . . . . . . A product of? Geologic processes

weathered rock – parent materials

Weathering?Physical and chemical process Physical process . . .

freeze-thawtumbling down hills and streams

Weathering?Chemical process . . .

chemical reactions between rocks and water

Decomposition of parent materials/rocks

End product are soils

What is soil composed of?Minerals . . .

altered physically and chemicallyfrom original bedrock

Organic chemicalsBiomassGasses – air, waterDissolved materials

Soil Composition . . . Made up of three fractions . . .

mineral fractionorganic fractiongasses and water

Mineral fractionSand – 2mm to 0.05mm

Silt – 0.05mm to 0.002mm

Clay - <0.002mmAnalogy – compare a basketball

to a baseball to a BB

Organic fraction . . .Living organisms including:

plants and plant rootsbacteria & fungiworms, insects, etc.dead/decomposing organisms

Organic fraction . . .Organic materials provide a

reservoir of plant nutrients Nutrients are continually recycled as

organic materials

Gasses and water . . . Oxygen (O)Carbon dioxide (CO2)Nitrogen (N), etc.H2O

Gasses and water . . .Fills in pore spaces between the soil

particlesLarger pore spaces contain more

gassesSmaller pore spaces contain more waterSoil pore spaces can take up to 50% of

the volume of a given soil sample

Soil textureWhat did we say made up the

mineral fraction?

Sand . . . Silt and . . . Clay

So soil texture is . . .The percentage (%) of . . .

Sand . . . Silt and . . . Clay . . . By volume We’ll come back to that later. . . .

Name 2 reasons soils are studied?

Agricultural reasons . . . ability to support plant lifesoil fertility

Structural reasons . . . building constructionability to support foundations, footings, etc.

Some definitionsActually, a whole bunch of

definitions . . .

Rocks . . .What are rocks?

consolidated mass of minerals

Minerals . . .And minerals?

unique, repeatable combination of elements stableconsistent hardness, melting point, etc.

Elements . . . What about elements?

found on the periodic table . . .unique combination of protons and neutrons in a nucleus . . . surrounded by electrons

The nucleus . . .Nucleus of an atom contains . . .

protons (+)neutrons (-)and electrons

Three types of rocks . . Rocks are found in three forms . . .

igneous - divided into two groupsmetamorphicsedimentary

Igneous rocksExtrusive igneous rock - lava

volcanic in nature formed by being pushed out of the Earth’s crustsmall to no crystals caused by rapid solidification when exposed to air or waterex. basalt

Igneous rocksIntrusive igneous rock

forms as magma cools within the crust

can form large, distinct crystals caused by slow cooling under ground

ex. granite (Sierra Nevada mountains, Southern California batholiths)

Sedimentary rockMade from sediments

eroded igneous, metamorphic or sedimentary materials deposited horizontally by wind or water solidifies over time and as sediments continue to build over time

Sedimentary rocktypically softer than igneous or metamorphic rockex. sandstone (western Rocky Mountains, Utah, Grand Canyon)

Metamorphic rockThe name implies change . . .

igneous, sedimentary or other metamorphic rock changed by being subjected to heat and or pressurehard, strong and resistant to weathering

Tropical region soils . . .Often subjected to much leaching Basalts – minerals leached out settle

out as clays

Tropical region soils . . .Clay soils in tropical areas start out

fairly fertile leaching from rainfall . . .high temperatures . . . extensive plant growth . . . they loose fertility

Tropical region soils . . .Tropical clay soils tend to be shallow

erode quickly when disturbed . . . by clearing of vegetation and agriculture

Temperate region soilsOften granitic, sandy soils

fertility variessoil depth vary

Parent materialsIt’s all about the rock! Rocks weather How?

Physical and chemical weatheringDecomposition of rocks creates soils

Geography & local weather

Affect:soil formationdevelopment of plant species and varieties

Organic soilsFormed exclusively from organic

matterformed as peat bogs dry outpeat soilsmuck soils

Ex. areas of the Sacramento River Delta

Soil horizons . . . Separate and distinct layers of soil

down to parent materialsand basement rock

Examples:O-Horizon A-HorizonB-HorizonC-Horizon

Soil horizons . . .Soil horizon layers and content . . .very much based on their

surroundingsex. topographydeposition history local weather, etc.

Hatch Act of 1887 Set aside land around the country

for agricultural studiesCreated series of agricultural

experimental stationsProvides funds for Land Grant

schools founded under the Morrill Act 1862

USNRCS US Natural Resource Conservation

Service formerly: US Soil Conservation Service under the United States Department of Agriculture (USDA)part of the Executive Branch of the US Government

USNRCS Provides an interactive website with

regional soil mapshttp://www.nrcs.usda.gov/

Topography . . .Study and graphic representation of

changes of relief features . . .in surface configurations of a given area

Indicates changes in elevations and positions on a map

Alluvial fans . . .Distinct fan-

shaped formation of soil deposition . . .

Found at base of hills or down-stream ends of rivers