Unit 1: Soil Unit 1: Soil Composition & Composition &

ImportanceImportanceChapter 1Chapter 1

ObjectivesObjectives

Reasons to study soilsReasons to study soils Definitions of soilDefinitions of soil Parent materials from which soil Parent materials from which soil

formsforms Roles & functions of soilRoles & functions of soil Characteristics of healthy soils & Characteristics of healthy soils &

soil damage riskssoil damage risks

What is soil?What is soil?

Various definitionsVarious definitions ““natural medium for the growth of land natural medium for the growth of land

plants” (USDA)plants” (USDA) Comprised of solids, liquids, gases Comprised of solids, liquids, gases

occurring on land surface, occupies occurring on land surface, occupies space, characterized by horizons caused space, characterized by horizons caused by additions, losses, transformations, by additions, losses, transformations, transfers, or the ability to support transfers, or the ability to support rooted plants in a natural environmentrooted plants in a natural environment

What is soil?What is soil?

Nonsoil – don’t have horizons & will Nonsoil – don’t have horizons & will not support plant growthnot support plant growth Ice landsIce lands Recent lava flowsRecent lava flows Salt flatsSalt flats Bare rock mountain slopesBare rock mountain slopes Moving dunesMoving dunes

Earth’s CrustEarth’s Crust

Outermost 3 – 19 miles of Earth’s radiusOutermost 3 – 19 miles of Earth’s radius Contains Earth’s least dense materialsContains Earth’s least dense materials Highly dynamic – significant changes can Highly dynamic – significant changes can

occur over time due to variety of factorsoccur over time due to variety of factors What changes can occur & how might they What changes can occur & how might they

affect the soil?affect the soil? Most common to undergo geologic changes – Most common to undergo geologic changes –

SandSand SiltSilt ClayClay

Components of SoilComponents of Soil

Various combinations of solids & liquidsVarious combinations of solids & liquids Fluids, air, water occupy the Fluids, air, water occupy the pore spacepore space

between soil solidsbetween soil solids Typical soil is ~ ½ solid, ½ liquidTypical soil is ~ ½ solid, ½ liquid Potting soil much more porousPotting soil much more porous Amount of air varies with the amount of soil Amount of air varies with the amount of soil

water (inverse relationship)water (inverse relationship) Soil air low in OSoil air low in O22, higher in CO, higher in CO22

Water is soil is referred to as Water is soil is referred to as soil solutionsoil solution Contains dissolved ions, nutrients, and other Contains dissolved ions, nutrients, and other

substancessubstances

Components of SoilComponents of Soil Soil solidsSoil solids

Includes mineral & organic substancesIncludes mineral & organic substances Minerals – Minerals – sand & claysand & clay dominate the concentration dominate the concentration Organic materials – Organic materials – humushumus present in a lesser quantity present in a lesser quantity

Arrangement in horizontal layers – Arrangement in horizontal layers – soil horizonssoil horizons A HorizonA Horizon – upper few inches of soil, usually enriched in – upper few inches of soil, usually enriched in

organic matter, most favorable environment for plant organic matter, most favorable environment for plant growthgrowth

Eluvial horizonEluvial horizon – organic matter, minerals, etc. can – organic matter, minerals, etc. can be washed out and down through the soil profilebe washed out and down through the soil profile

B HorizonB Horizon – below the A, lower in organic matter, higher – below the A, lower in organic matter, higher in soluble materials (salts, clays) because of migration in soluble materials (salts, clays) because of migration from the Afrom the A

Iluvial horizonIluvial horizon – material washed in to the soil profile – material washed in to the soil profile

Components of SoilComponents of Soil C HorizonC Horizon – below the B, no effect from – below the B, no effect from

migration of material in the upper two horizonsmigration of material in the upper two horizons Parent materialParent material – contains the materials – contains the materials

from which A & B horizons were developedfrom which A & B horizons were developed

Components of SoilComponents of Soil

Mineral Composition of SoilsMineral Composition of Soils Minerals - Inorganic (nonliving) Minerals - Inorganic (nonliving)

substances, definite composition, substances, definite composition, characteristic physical propertiescharacteristic physical properties Melting temp, shape, color, hardnessMelting temp, shape, color, hardness Primary mineralsPrimary minerals – formed by the cooling – formed by the cooling

of molten rockof molten rock Secondary mineralsSecondary minerals – precipitated or – precipitated or

recrystallized from solutions that contains recrystallized from solutions that contains elements from dissolutions from other elements from dissolutions from other mineralsminerals

Components of SoilComponents of Soil RocksRocks – mixtures of minerals – mixtures of minerals

IgneousIgneous – cooled molten rock – cooled molten rock SedimentarySedimentary – sediments deposited in water – sediments deposited in water

& consolidated materials& consolidated materials Form from one time rock, minerals, soil particles, Form from one time rock, minerals, soil particles,

and soluble substances cemented into hard massesand soluble substances cemented into hard masses SandstonesSandstones Shales – consolidated clays & siltsShales – consolidated clays & silts Limestones – clays, silts, and sands cemented Limestones – clays, silts, and sands cemented

in mixtures of calcium carbonates and in mixtures of calcium carbonates and magnesium carbonates (50% mass is magnesium carbonates (50% mass is carbonates)carbonates)

Dolomites – magnesium carbonatesDolomites – magnesium carbonates Quartzites – silica-cemented sandsQuartzites – silica-cemented sands

Components of SoilComponents of Soil MetamorphicMetamorphic – igneous or sedimentary rock – igneous or sedimentary rock

hardened/altered by heat, pressure, reactions hardened/altered by heat, pressure, reactions with other chemical solutionswith other chemical solutions

may be as hard or harder than other forms, weather to may be as hard or harder than other forms, weather to produce similar soilsproduce similar soils

Gneiss – minerals form segregated light/dark bands Gneiss – minerals form segregated light/dark bands (granites)(granites)

Schist – fissile/foliated (flaky/layered), composed of Schist – fissile/foliated (flaky/layered), composed of many mineralsmany minerals

Slate – hardened shale or siltstone, very hard (pool Slate – hardened shale or siltstone, very hard (pool tables, chalkboard)tables, chalkboard)

Quartzite – recrystallized quartzic sandstone, formed Quartzite – recrystallized quartzic sandstone, formed by heat & pressure, slow to weather, produces sandy by heat & pressure, slow to weather, produces sandy & shallow soils& shallow soils

Marble – hardened limestone or dolomite (easily Marble – hardened limestone or dolomite (easily decomposed)decomposed)

Components of SoilComponents of Soil

Mineral soilsMineral soils Develop from minerals and rocksDevelop from minerals and rocks Mostly quartz, feldspars, dark minerals, Mostly quartz, feldspars, dark minerals,

lime, gypsumlime, gypsum Weather to sands, claysWeather to sands, clays Also provide the majority of soil mineral Also provide the majority of soil mineral

nutrientsnutrients

Organic Materials in SoilOrganic Materials in Soil

98% of all soils are mineral soils98% of all soils are mineral soils Organic soils form from plant Organic soils form from plant

residues in ponded or cold, wet residues in ponded or cold, wet areasareas Decomposition is slowDecomposition is slow Referred to as: peat or muckReferred to as: peat or muck Anaerobic decomposition is slowAnaerobic decomposition is slow Organic soils can be deep if allowed to Organic soils can be deep if allowed to

decompose naturallydecompose naturally Florida Everglades, Stockton Delta in CAFlorida Everglades, Stockton Delta in CA

Organic Materials in SoilOrganic Materials in Soil

Common materials: grasses, mosses, leaves, Common materials: grasses, mosses, leaves, cattails, reedscattails, reeds

All soils contain significant organic All soils contain significant organic mattermatter

Organic soils are very rich when Organic soils are very rich when excavatedexcavated

Less sites for organic soils today as Less sites for organic soils today as many marshes, wetlands, etc. have been many marshes, wetlands, etc. have been drained for development or agriculturedrained for development or agriculture

Historical PerspectivesHistorical Perspectives

Beginnings of agriculture date to Beginnings of agriculture date to 3500 B.C. in Mesopotamia (modern-3500 B.C. in Mesopotamia (modern-day Iraq)day Iraq)

Much irrigation used in those daysMuch irrigation used in those days Through water canalsThrough water canals Some agriculture lost in those areas due Some agriculture lost in those areas due

to silting in of their waterways, to silting in of their waterways, therefore, choking off their water supplytherefore, choking off their water supply

Silts in ancient Egypt were a blessing Silts in ancient Egypt were a blessing as it replenished new soil to the as it replenished new soil to the fields each year with the floodsfields each year with the floods

Historical PerspectivesHistorical Perspectives

First century A.D.First century A.D. Northern Africa served as the food-base Northern Africa served as the food-base

for the Roman Empirefor the Roman Empire Depleted the soil of nutrients which Depleted the soil of nutrients which

contributed to northern Africa’s difficulty contributed to northern Africa’s difficulty growing food todaygrowing food today

South America bears the first real South America bears the first real evidence of soil conservationevidence of soil conservation Incans of Peru built terraces on mountain Incans of Peru built terraces on mountain

sides and filled with soil from the valleyssides and filled with soil from the valleys Cut waterways into the mountain rockCut waterways into the mountain rock

Historical PerspectivesHistorical Perspectives

North American soil historyNorth American soil history European settlers found very different European settlers found very different

problems than they had encountered problems than they had encountered before immigratingbefore immigrating

Violent rains, turbulent wind stormsViolent rains, turbulent wind storms May 1934, dust storm in TX, OK, CO, KA, May 1934, dust storm in TX, OK, CO, KA,

swept 400 b lbs. of soil to the east coast swept 400 b lbs. of soil to the east coast and out to seaand out to sea

Some estimate ½ of the original topsoil Some estimate ½ of the original topsoil has eroded in the past 150 yrs.has eroded in the past 150 yrs.

Historical PerspectivesHistorical Perspectives

History of Soil ScienceHistory of Soil Science Edaphology – investigation into the nature Edaphology – investigation into the nature

of soilsof soils Foresters, agronomists, ecologists, botanistForesters, agronomists, ecologists, botanist

Pedology – study of soil as a geologic Pedology – study of soil as a geologic entity, origin, morphology, geography, entity, origin, morphology, geography, taxonomytaxonomy

History of PedologyHistory of Pedology Russians were first to postulate that soil was Russians were first to postulate that soil was

formed by factors other than underlying rockformed by factors other than underlying rock They included living matter, climate, time, etc.They included living matter, climate, time, etc.

Historical PerspectivesHistorical Perspectives Created the foundation for the American Created the foundation for the American

soil classification system started in the soil classification system started in the 1930’s1930’s

Current system of soil classification & Current system of soil classification & description introduced in 1975description introduced in 1975

Continually updates descriptions & usage Continually updates descriptions & usage recommendationsrecommendations

Soil – A Precious Soil – A Precious ResourceResource

Must appreciate the value of soil and Must appreciate the value of soil and it’s importance in our everyday livesit’s importance in our everyday lives

Engineering & BuildingEngineering & Building Soil is construction materialSoil is construction material

Base of roads, landfills, foundation for Base of roads, landfills, foundation for buildingsbuildings

Engineers must know how much load & Engineers must know how much load & stress a soil can stand without stress a soil can stand without deformingdeforming

Soil – A Precious Soil – A Precious ResourceResource

NRCS – responsible for determining NRCS – responsible for determining degrees of limitations placed on soilsdegrees of limitations placed on soils

Roadbeds, campsites, homes, septic tank fieldsRoadbeds, campsites, homes, septic tank fields Can also be molded into bricks for buildingCan also be molded into bricks for building

Adobe huts build for housing in the American Adobe huts build for housing in the American SouthwestSouthwest

ArchaeologyArchaeology Soil buried with sediment deposits, glacial Soil buried with sediment deposits, glacial

debris is some of the best preservation for debris is some of the best preservation for archaeological materialsarchaeological materials

Soil – A Precious Soil – A Precious ResourceResource

Scientists found pollen from an Scientists found pollen from an ancestor of corn in modern-day eastern ancestor of corn in modern-day eastern Mexico dating to 5100 B.C.Mexico dating to 5100 B.C.

Plants & SoilPlants & Soil Soil provides the 4 basic growth factors Soil provides the 4 basic growth factors

for plantsfor plants Support (Anchorage)Support (Anchorage) OxygenOxygen WaterWater NutrientsNutrients

Soil – A Precious Soil – A Precious ResourceResource

Ability to support (anchorage) depends on depth of Ability to support (anchorage) depends on depth of soilsoil

Oxygen is supplied through pore spaces in the soilOxygen is supplied through pore spaces in the soil Roots must constantly respireRoots must constantly respire Very few plants transport all air internally (rice)Very few plants transport all air internally (rice) Roots only penetrate to a depth at which there is Roots only penetrate to a depth at which there is

sufficient aerationsufficient aeration Water – supplied by soil reservoirWater – supplied by soil reservoir

Most crops needs 12 – 31” of water during the growing Most crops needs 12 – 31” of water during the growing seasonseason

Best soils can only hold 3-4” of water at a timeBest soils can only hold 3-4” of water at a time Nutrients – plants require 17 chemical elements for Nutrients – plants require 17 chemical elements for

growthgrowth Others may be required, or help depending on the species, Others may be required, or help depending on the species,

but these are true for all plantsbut these are true for all plants

Soil – A Precious Soil – A Precious ResourceResource

14 of these essential elements are supplied by the soil14 of these essential elements are supplied by the soil C, H, O are supplied by carbon dioxide from air, and C, H, O are supplied by carbon dioxide from air, and

waterwater Nitrogen is a common component of soil organic Nitrogen is a common component of soil organic

materials and is only held for a short period, often is materials and is only held for a short period, often is deficient firstdeficient first

Other nutrients can be held by electrostatic attractionOther nutrients can be held by electrostatic attraction Amount of fertility depends on how many nutrients Amount of fertility depends on how many nutrients

are present & availableare present & available

Soil, Crops, & the Human RaceSoil, Crops, & the Human Race World population ~6.5 bWorld population ~6.5 b

Population is ever-increasingPopulation is ever-increasing Expected to raise by 40% by 2050Expected to raise by 40% by 2050

Soil – A Precious Soil – A Precious ResourceResource

Each farmer today feeds ~100 peopleEach farmer today feeds ~100 people ArableArable (farmable) per person decreasing (farmable) per person decreasing

each yeareach year Projected to decrease to 1.1 ac/person from 1.45 Projected to decrease to 1.1 ac/person from 1.45

ac/person by 2050 in U.S.ac/person by 2050 in U.S. .55 ac/person & .375 ac/person worldwide .55 ac/person & .375 ac/person worldwide

respectivelyrespectively Disparity between over-nourished nations & Disparity between over-nourished nations &

malnourished nations increasingmalnourished nations increasing Amount of meats & grains consumed inversely Amount of meats & grains consumed inversely

related to income level of the nationrelated to income level of the nation High meat diets are much more inefficient than High meat diets are much more inefficient than

high grain dietshigh grain diets

Soil – A Precious Soil – A Precious ResourceResource

Fisheries & rangelands currently producing Fisheries & rangelands currently producing at maximum potentialat maximum potential

Responsibility to feed increasing population Responsibility to feed increasing population will rest entirely with farmerswill rest entirely with farmers

Many acres/yr being converted to Many acres/yr being converted to roads/shopping/dwellingsroads/shopping/dwellings

Fuel needs also more criticalFuel needs also more critical Is E85 from corn-based ethanol the answer?Is E85 from corn-based ethanol the answer? If not, what are our options?If not, what are our options? What about cellulolytic based ethanol?What about cellulolytic based ethanol?

Soil QualitySoil Quality

Biome – Biome – interwoven system in which interwoven system in which soil, climate, & living organisms soil, climate, & living organisms affect each other in a complex wayaffect each other in a complex way

Soil PollutionSoil Pollution Soil serves as a depository:Soil serves as a depository:

SewageSewage GarbageGarbage Milling residuesMilling residues

Wastes can contribute to or destroy Wastes can contribute to or destroy cropping potentialcropping potential Most costly pollution cleanup sites are those Most costly pollution cleanup sites are those

w/ contaminated soilsw/ contaminated soils

Soil QualitySoil Quality Hanford Nuclear site in WA - $30b for cleanup of Hanford Nuclear site in WA - $30b for cleanup of

contaminated soilscontaminated soils

Soil MisuseSoil Misuse Many well-intentioned universal soil Many well-intentioned universal soil

management practices actually degrade management practices actually degrade the soilthe soil

Some suspect millions/billions acres of Some suspect millions/billions acres of soil severely degradedsoil severely degraded Ex. Deforestation in Vermont by early Ex. Deforestation in Vermont by early

American settlers caused severe erosion & American settlers caused severe erosion & floodingflooding

Soil QualitySoil Quality Common land degrading practicesCommon land degrading practices

Leaving the soil bare (ex.)Leaving the soil bare (ex.) Compacting the soil surfaces (ex.)Compacting the soil surfaces (ex.) Acidifying the soil (ex.)Acidifying the soil (ex.) Irrigating without proper drainage (ex.)Irrigating without proper drainage (ex.) Using chemicals indiscriminately (ex.)Using chemicals indiscriminately (ex.)

Sustaining SoilsSustaining Soils Sustainable practices are those that can Sustainable practices are those that can

be continued permanentlybe continued permanently Can be difficult, but is vital to the Can be difficult, but is vital to the

survival & productivity of our soilssurvival & productivity of our soils

Soil QualitySoil Quality

Many soils much healthier today than a Many soils much healthier today than a generation ago, due to conservation generation ago, due to conservation practicespractices

What constitutes a healthy soil?What constitutes a healthy soil? CharacteristicsCharacteristics ContentsContents ManagementManagement

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