Soil Soil in Our Environment. What is soil? Or is it Dirt? “Gold’s father is dirt, yet it...
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Transcript of Soil Soil in Our Environment. What is soil? Or is it Dirt? “Gold’s father is dirt, yet it...
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