WEATHERING & EROSIONWEATHERING & EROSION weatheringweathering = change in physical form or chemical = change in physical form or chemical composition of rock materials exposed at earth’s surfacecomposition of rock materials exposed at earth’s surface

TWO MAIN TYPESTWO MAIN TYPESmechanical weatheringmechanical weathering = physical processes break down = physical processes break down

rock into smaller piecesrock into smaller pieces1. does not change chemical compositions of rocks and 1. does not change chemical compositions of rocks and mineralsminerals2. also called 2. also called disintegration or disintegration or physical weatheringphysical weathering3. common agents include ice, 3. common agents include ice, plants, animals, gravity, plants, animals, gravity, running water, windrunning water, wind

4. main factors that cause processes are temperature and 4. main factors that cause processes are temperature and pressurepressure5. processes:5. processes: a. a. exfoliationexfoliation = curved sheets peel = curved sheets peel

away from exposed bedrockaway from exposed bedrock 1) 1) jointsjoints = long, curved cracks = long, curved cracks

parallel to surface parallel to surface 2) overlying rock gradually erodes2) overlying rock gradually erodes 3) also called 3) also called pressure release fracturingpressure release fracturing b. b. ice wedgingice wedging = water freezes in cracks, = water freezes in cracks,

expands, and forces rock apartexpands, and forces rock apart 1) also called 1) also called frost wedgingfrost wedging 2) volume of water expands by 10% 2) volume of water expands by 10%

when frozenwhen frozen 3) each time ice thaws and refreezes it goes further into 3) each time ice thaws and refreezes it goes further into

rock widening crackrock widening crack 4) common at high elevations and climates where 4) common at high elevations and climates where

temperature varies above and below freezingtemperature varies above and below freezing

c. c. salt crackingsalt cracking = salts that are dissolved in water found in = salts that are dissolved in water found in pores of rock will crystallize when water evaporates pores of rock will crystallize when water evaporates causing widening of cracks and pushes grains apartcausing widening of cracks and pushes grains apart

d. d. abrasionabrasion = wearing and grinding = wearing and grinding of rock surfaces by of rock surfaces by

friction & impactfriction & impact- produces rocks with smooth, - produces rocks with smooth, rounded appearancerounded appearance

e. e. root pryroot pry = seed germinates in = seed germinates in

rock crack, pressure from rock crack, pressure from developing root enlarges crackdeveloping root enlarges crack

f. digging activities of burrowing animals expose new rockf. digging activities of burrowing animals expose new rock surfacesurface

g. thermal expansion and contractiong. thermal expansion and contraction 1) at surface rocks warm and cool as air temperature 1) at surface rocks warm and cool as air temperature changeschanges 2) rock expands when heated and contracts when it is 2) rock expands when heated and contracts when it is cooledcooled 3) if heated rapidly surface will expand faster than interior 3) if heated rapidly surface will expand faster than interior which may cause fracturewhich may cause fracture 4) hot object will crack when cooled too rapidly4) hot object will crack when cooled too rapidly

chemical weatheringchemical weathering = processes break down rock by = processes break down rock by changing its chemical compositionchanging its chemical composition

1. also called 1. also called decompositiondecomposition2. caused by water, acids, bases, 2. caused by water, acids, bases, oxygen, and other substancesoxygen, and other substances3. all other factors being equal, rate of reaction doubles with 3. all other factors being equal, rate of reaction doubles with each 10each 10ooC increase in temperatureC increase in temperature4. processes:4. processes: a. a. hydrolysishydrolysis = chemical reaction of water with other = chemical reaction of water with other

substancessubstances 1) water can dissolve minerals as 1) water can dissolve minerals as

it passes through rock and then it passes through rock and then deposit different substances in deposit different substances in their placetheir place

2) 2) leachingleaching = when water carries = when water carries dissolved minerals to dissolved minerals to

lower layers of rock or soillower layers of rock or soil

b. b. carbonationcarbonation = minerals react with carbonic acid = minerals react with carbonic acid 1) carbon dioxide from air dissolves in 1) carbon dioxide from air dissolves in

water to create a weak carbonic acidwater to create a weak carbonic acid 2) speeds up hydrolysis2) speeds up hydrolysis 3) can produce underground caverns3) can produce underground caverns 4) results in formation of clay minerals4) results in formation of clay minerals

c. c. oxidationoxidation = chemical reaction of oxygen with other = chemical reaction of oxygen with other substancessubstances

1) usually turns useful material to waste1) usually turns useful material to waste 2) attacks iron-bearing minerals 2) attacks iron-bearing minerals 3) causes mineral to rust or turn 3) causes mineral to rust or turn

reddish in colorreddish in color

d. d. acid precipitationacid precipitation = nitrogen and sulfur oxides in air = nitrogen and sulfur oxides in air combine with watercombine with water

1) more corrosive than pure water1) more corrosive than pure water 2) dissolves minerals faster2) dissolves minerals faster

e. plant acidse. plant acids 1) 1) humic acidhumic acid = produced by plant roots = produced by plant roots

and decaying plants and decaying plants 2) usually lichens and mosses that 2) usually lichens and mosses that

grow on rocksgrow on rocks

spheroidal weatheringspheroidal weathering = occurs more = occurs more quickly at corners and edges of rock quickly at corners and edges of rock outcrops and boulders causing them outcrops and boulders causing them to become roundedto become rounded

RATES OF WEATHERING depends on:RATES OF WEATHERING depends on:1. composition of rock: determines resistant to being broken 1. composition of rock: determines resistant to being broken downdown a. determined by materials that holds fragments of a. determined by materials that holds fragments of sediments togethersediments together b. sedimentary rocks are generally more easily weathered b. sedimentary rocks are generally more easily weathered than igneous or metamorphic rocksthan igneous or metamorphic rocks c. quartz least affected by chemical and mechanical c. quartz least affected by chemical and mechanical weatheringweathering

2. amount of exposure2. amount of exposure a. amount of time exposed: longer exposure results in a. amount of time exposed: longer exposure results in more weatheringmore weathering b. amount of surface area: more are exposed, more b. amount of surface area: more are exposed, more weatheringweathering 1) increased by fractures and joints1) increased by fractures and joints 2) weather more rapidly2) weather more rapidly3. climate: variables include precipitation, temperature, and 3. climate: variables include precipitation, temperature, and evaporationevaporation a. greatest effect due to rainfall and freezing and thawing a. greatest effect due to rainfall and freezing and thawing produced by alternating hot and cold weatherproduced by alternating hot and cold weather b. rate of chemical reactions increase as temperature b. rate of chemical reactions increase as temperature increasesincreases c. very rapid in warm, humid areasc. very rapid in warm, humid areas d. slower in hot, dry areas and very cold climatesd. slower in hot, dry areas and very cold climates

4. 4. topographytopography = elevation and slope of surface = elevation and slope of surface a. colder at higher elevations so ice wedging often a. colder at higher elevations so ice wedging often increasesincreases b. steep slopes allow fragments to be pulled downhill by b. steep slopes allow fragments to be pulled downhill by gravity and washed awaygravity and washed away c. as materials move down slope exposes new surfaces for c. as materials move down slope exposes new surfaces for weathering to occurweathering to occur

EROSIONEROSIONerosionerosion = process that removes and transports weathered = process that removes and transports weathered

sediments from one location to another sediments from one location to another1. four main agents: gravity, running water, glaciers, wind1. four main agents: gravity, running water, glaciers, wind2. have several things in common:2. have several things in common: a. carry sediments only when have enough energy of a. carry sediments only when have enough energy of motionmotion b. all drop load of sediments when b. all drop load of sediments when energy of motion decreases = energy of motion decreases =

depositiondeposition3. gravity causes rock fragments/materials 3. gravity causes rock fragments/materials to move down slopesto move down slopes

4. water has more power to move large particles of 4. water has more power to move large particles of weathered material than normal windsweathered material than normal winds a. greatest when water is moving rapidlya. greatest when water is moving rapidly b. can carry more material over longer distances before b. can carry more material over longer distances before depositingdepositing5. 5. watershedwatershed = network of streams that drain an area as = network of streams that drain an area as

water works its way to oceanwater works its way to ocean a. a. rill erosionrill erosion = caused by running water in small channels = caused by running water in small channels on the side of slopeson the side of slopes b. b. gully erosiongully erosion = forms a deep and = forms a deep and

wide channelwide channel c. streams and rivers carry billions of c. streams and rivers carry billions of

metric tons of sediments and metric tons of sediments and weathered materials to coastal weathered materials to coastal areas every yearareas every year

6. glacial erosion6. glacial erosion a. effects are large-scale due to ability to a. effects are large-scale due to ability to

scrape and gouge out large sections as scrape and gouge out large sections as movemove

b. able to carry huge rocks and piles of b. able to carry huge rocks and piles of debri over large distancesdebri over large distances

7. wind erosion7. wind erosion a. effects areas of limited precipitation and high temperaturesa. effects areas of limited precipitation and high temperatures mostmost b. usually very little vegetation in place to hold soil in placeb. usually very little vegetation in place to hold soil in place c. wind blown particles can damage natural structures and c. wind blown particles can damage natural structures and human structureshuman structures d. d. windbreakswindbreaks = trees or other plants grown perpendicular = trees or other plants grown perpendicular

to direction of wind as a wind barrierto direction of wind as a wind barrier8. plants, animals, and humans add to erosion by moving soil 8. plants, animals, and humans add to erosion by moving soil location, digging burrows, building highways, etc.location, digging burrows, building highways, etc.

EROSION OF LANDFORMSEROSION OF LANDFORMSgeomorphologygeomorphology = study of earth’s forms or landforms = study of earth’s forms or landforms

geomorphic provincesgeomorphic provinces = areas with distinctive landforms and = areas with distinctive landforms and topographytopography

Ex: Hawaiian Province; Appalachian ProvincesEx: Hawaiian Province; Appalachian Provinces

landscapeslandscapes = physical features of the Earth’s surface found in = physical features of the Earth’s surface found in an areaan area

landformslandforms = features that make up the shapes of the Earth’s = features that make up the shapes of the Earth’s land surfaceland surface

1. result of two opposing processes1. result of two opposing processes a. one bend, breaks, and lifts earth’s crust making elevated a. one bend, breaks, and lifts earth’s crust making elevated landformslandforms b. one is the wearing action of weathering and erosionb. one is the wearing action of weathering and erosion2. three major types:2. three major types: a. a. mountainsmountains = steep landforms of very high elevations = steep landforms of very high elevations

b. b. plainsplains = large, relatively flat areas that do not rise far above = large, relatively flat areas that do not rise far above sea level usuallysea level usually

1) makes up 1/2 of all land in U.S.A.1) makes up 1/2 of all land in U.S.A. 2) very small differences in elevation2) very small differences in elevation 3) areas of low relief3) areas of low relief

c. c. plateausplateaus = high elevation flat surfaces = high elevation flat surfaces 1) rise more than 600 meters up to more than 1500 meters 1) rise more than 600 meters up to more than 1500 meters

above sea levelabove sea level 2) areas of nearly horizontal rocks that 2) areas of nearly horizontal rocks that have been uplifted by forces within Earthhave been uplifted by forces within Earth 3) most are located inland, few near 3) most are located inland, few near

the oceanthe ocean 4) those next to an ocean end in a cliff4) those next to an ocean end in a cliff 5) many are dry, nearly desert areas5) many are dry, nearly desert areas

EROSION OF MOUNTAINSEROSION OF MOUNTAINS

1. 1. youthful mountainsyouthful mountains = those that are being lifted = those that are being lifted a. rugged, have sharp peaks and deep, narrow valleysa. rugged, have sharp peaks and deep, narrow valleys b. usually rises faster than it is erodedb. usually rises faster than it is eroded

2. 2. mature mountainsmature mountains (intermediate) = no longer rising (intermediate) = no longer rising a. rounded peaks and gentle slopesa. rounded peaks and gentle slopes

3. 3. old mountainsold mountains = reduced to a low, almost featureless = reduced to a low, almost featureless surface near sea levelsurface near sea level

a. a. peneplainpeneplain = low, almost level surface usually with low, = low, almost level surface usually with low, rolling hillsrolling hills

1) have been mistaken for plains1) have been mistaken for plains 2) rocks beneath have been tilted 2) rocks beneath have been tilted

and folded by tectonic forcesand folded by tectonic forces b.b. monadnocks monadnocks = knob of rock that = knob of rock that

protrudes above a peneplainprotrudes above a peneplain

4. 4. playaplaya = dry desert lake bed = dry desert lake bed a. in arid regionsa. in arid regions b. could be a low b. could be a low area between area between

mountainsmountains

EROSION OF PLAINS AND PLATEAUSEROSION OF PLAINS AND PLATEAUS1. plains1. plains a. characterized by broad rivers and streamsa. characterized by broad rivers and streams b. plants are mostly grassesb. plants are mostly grasses c. types:c. types: 1) 1) coastal plainscoastal plains = low, flat areas along the coasts = low, flat areas along the coasts

a) called a) called lowlandslowlands due to low elevation due to low elevation b) b) marshmarsh = grassy wetland that is usually flooded with = grassy wetland that is usually flooded with

waterwater 2) 2) interior plainsinterior plains = low flat areas found inland on a = low flat areas found inland on a

continentcontinent a) somewhat higher above sea levela) somewhat higher above sea level b) have good soil for farmingb) have good soil for farming

3) 3) high plainshigh plains = those along the foot of the Rocky = those along the foot of the Rocky MountainsMountains

a) rise over 1500 m above sea levela) rise over 1500 m above sea level

2. plateaus2. plateaus a. a. youngyoung = deep stream valleys separating broad, flat = deep stream valleys separating broad, flat

regionsregions b. b. maturemature = eroded into rugged hills and valleys = eroded into rugged hills and valleys c. landforms created by erosion and weatheringc. landforms created by erosion and weathering 1) 1) mesasmesas = small, table-like areas = small, table-like areas

a) flat topped hillsa) flat topped hills b) covered by layer of resistant rock protecting soft b) covered by layer of resistant rock protecting soft rock beneathrock beneath

2) 2) buttesbuttes = small, narrow = small, narrow topped formations topped formations

a) have steep slopesa) have steep slopes b) smaller than mesasb) smaller than mesas

WEATHERING AND SOILWEATHERING AND SOIL1. 1. regolithregolith = layer of weathered rock fragments mixed with = layer of weathered rock fragments mixed with

clay and sand clay and sand 2. 2. bedrockbedrock = solid, unweathered rock that lies beneath the = solid, unweathered rock that lies beneath the

regolithregolith a. often referred to as a. often referred to as parent rockparent rock3. 3. soilsoil = complex mixture of minerals, organic material, water = complex mixture of minerals, organic material, water

and gasesand gases a. result of chemical and biological activity over long periods a. result of chemical and biological activity over long periods of timeof time b. soil-forming process begins b. soil-forming process begins

when weathering breaks when weathering breaks solid bedrock into smaller solid bedrock into smaller

piecespieces

4. 4. humushumus = dark, organic material = dark, organic material a. made of pieces of decaying plants and animalsa. made of pieces of decaying plants and animals b. light and spongy, readily absorbs waterb. light and spongy, readily absorbs water c. soils rich in this will usually be dark colored c. soils rich in this will usually be dark colored d. holds in soil nutrients and makes them available to d. holds in soil nutrients and makes them available to plantsplants e. part of any fully developed soile. part of any fully developed soil

SOIL EROSIONSOIL EROSION1. occurs worldwide and is normally slow1. occurs worldwide and is normally slow2. deposited elsewhere as transported soil2. deposited elsewhere as transported soil3. accelerated erosion3. accelerated erosion a. a. overgrazingovergrazing = occurs when livestock eat every bit of = occurs when livestock eat every bit of

grass off landgrass off land b. b. desertificationdesertification = desert formation = desert formation 1) damaged by overgrazing in areas that receive little 1) damaged by overgrazing in areas that receive little

rainrain 2) changes wind patterns and drives away moisture 2) changes wind patterns and drives away moisture

laden cloudsladen clouds 3) happening on 3) happening on

every continentevery continent

c. clearing of forests for farmingc. clearing of forests for farming 1) soil in tropical rain forest depends on nutrients 1) soil in tropical rain forest depends on nutrients

provided by forestsprovided by forests 2) when cleared farmers deplete nutrients from soil in a 2) when cleared farmers deplete nutrients from soil in a

few yearsfew yearsd. d. gullyinggullying = furrows plowed up and down slopes allowing = furrows plowed up and down slopes allowing

faster water movement creating larger furrowsfaster water movement creating larger furrowse. e. sheet erosionsheet erosion = strips away parallel layers of topsoil = strips away parallel layers of topsoil

exposing subsoilexposing subsoil 1) continuous rainfall1) continuous rainfall 2) wind during dry periods2) wind during dry periods 3) 3) “dust bowl”“dust bowl” = poor farming practices = poor farming practices

and drought resulted in topsoil and drought resulted in topsoil being carried away by the wind being carried away by the wind creating dust stormscreating dust storms

SOIL COMPOSITIONSOIL COMPOSITION1. three main types of material: include clay, sand and silt1. three main types of material: include clay, sand and silt2. amount of each present determined by composition of 2. amount of each present determined by composition of parent rockparent rock a. clays form from feldsparsa. clays form from feldspars b. sandy soils form from granite and rocks with a lot of b. sandy soils form from granite and rocks with a lot of quartzquartz c. length of time it takes for soil to form also determined by c. length of time it takes for soil to form also determined by parent rockparent rock d. proportion of minerals in soild. proportion of minerals in soil

and in parent rock may not and in parent rock may not be the samebe the same

3. 3. loamloam = most fertile type of soil which is a mixture of = most fertile type of soil which is a mixture of sand, clay, silt, and generous amounts of organic sand, clay, silt, and generous amounts of organic mattermatter

4. 4. residual soilresidual soil = has a bedrock as its parent material = has a bedrock as its parent material a. form in place by gradual weathering of parent rocka. form in place by gradual weathering of parent rock b. layer of different colors and textures formb. layer of different colors and textures form5. 5. transported soiltransported soil = weathered mineral grains carried away = weathered mineral grains carried away

from location of parent rock by water, wind, or from location of parent rock by water, wind, or glaciersglaciers

a. horizons are poorly seen or absenta. horizons are poorly seen or absent b. different composition than the bedrock where it is b. different composition than the bedrock where it is deposited deposited

Loamy soil

soil profilesoil profile = vertical section/sequence of soil layers = vertical section/sequence of soil layers1. commonly present in residual soils1. commonly present in residual soils2. 2. horizonshorizons = several distinct layers seen in undisturbed soil = several distinct layers seen in undisturbed soil3. 3. O horizonO horizon = uppermost layer of mature soil named for its = uppermost layer of mature soil named for its

organic componentorganic component a. contains a. contains litterlitter = organic matter that has fallen to ground = organic matter that has fallen to ground and started to decompose but still retains its original formand started to decompose but still retains its original form b. also has humus with a small proportion of mineralsb. also has humus with a small proportion of minerals

4. 4. A horizonA horizon = second layer = second layer a. generally gray to blacka. generally gray to black b. has humus and organic materialsb. has humus and organic materials c. most fully evolved layerc. most fully evolved layer d. d. topsoiltopsoil = mixture of organic and small rock materials = mixture of organic and small rock materials 1) includes both O and A horizons1) includes both O and A horizons e. zone from which surface water leaches minerals = e. zone from which surface water leaches minerals = zone of leachingzone of leaching

5. 5. B horizonB horizon = third layer = third layer a. also called the a. also called the subsoilsubsoil b. has little or no humus, fewer organismsb. has little or no humus, fewer organisms c. lighter in color (usually red or brown)c. lighter in color (usually red or brown) d. some plant roots reach this layerd. some plant roots reach this layer e. clay gathers heree. clay gathers here f. f. zone of accumulationzone of accumulation = dissolved ions and clay = dissolved ions and clay

accumulate accumulate

6. 6. C horizonC horizon = partially weathered bedrock = partially weathered bedrock a. first stages of mechanical and chemical changea. first stages of mechanical and chemical change b. no humus presentb. no humus present c. very little organic matterc. very little organic matter d. lies directly on unweathered parent rockd. lies directly on unweathered parent rock

7. 7. R horizonR horizon = unweathered bedrock = unweathered bedrock

soil-forming factorssoil-forming factors = control how soil develops as parent = control how soil develops as parent material weathers material weathers

1. parent rock1. parent rock a. whether texture is resistant or easily weathereda. whether texture is resistant or easily weathered b. provides nutrients to soilb. provides nutrients to soil2. time2. time a. young soils - weathering of feldspar and other minerals a. young soils - weathering of feldspar and other minerals may be incompletemay be incomplete b. mature soils have more clay contentb. mature soils have more clay content c. new materials deposited mix and change the c. new materials deposited mix and change the composition and texturecomposition and texture

3. climate3. climate a. determines weathering processesa. determines weathering processes b. 5 basic climate types based on Koppen climatic b. 5 basic climate types based on Koppen climatic classification systemclassification system c. 2 most important factors are temperature and moisturec. 2 most important factors are temperature and moisture d. these affect: d. these affect:

1) physical weathering processes and determine 1) physical weathering processes and determine 2) microenvironmental conditions for soil organisms, 2) microenvironmental conditions for soil organisms, 3) plant growth, 3) plant growth,

4) rates of decomposition, 4) rates of decomposition, 5) soil pH, and 5) soil pH, and 6) chemical reactions occurring 6) chemical reactions occurring

in soilin soil

THE KOPPEN CLIMATIC CLASSIFICATION SYSTEMTHE KOPPEN CLIMATIC CLASSIFICATION SYSTEM

Climate Climate TypeType

DescriptionDescription

AA Tropical moist climates: all months have Tropical moist climates: all months have average temperatures above 18average temperatures above 18ooC(64C(64ooF). F).

BB Dry climates: with deficient precipitation during Dry climates: with deficient precipitation during

most of the year. most of the year.

CC Moist midlatitude climates with mild wintersMoist midlatitude climates with mild winters

DD Moist midlatitude climates with cold winters Moist midlatitude climates with cold winters

EE Polar climates: with extremely cold winters and Polar climates: with extremely cold winters and

summers summers

4. topography affects thickness of soil in areas4. topography affects thickness of soil in areas a. on steep slopes rainwater washes away most topsoil a. on steep slopes rainwater washes away most topsoil which will produce thin, coarse, & infertile soilswhich will produce thin, coarse, & infertile soils b. valley floor (lowlands) has deepest and richest soilb. valley floor (lowlands) has deepest and richest soil c. c. aspectaspect = orientation of slope with respect to compass = orientation of slope with respect to compass

directiondirection 1) sun affects side of hill causing water to evaporate 1) sun affects side of hill causing water to evaporate

therefore there are fewer plants and weathering therefore there are fewer plants and weathering occurs more slowly [soil development slowed]occurs more slowly [soil development slowed]

2) south-facing slopes receive more sunlight which 2) south-facing slopes receive more sunlight which allows more vegetation growth & in turn allows for allows more vegetation growth & in turn allows for thicker soils than slopes facing other directionsthicker soils than slopes facing other directions

SOIL TYPES SOIL TYPES 1. polar soils (arctic climates)1. polar soils (arctic climates) a. formed mostly by mechanical processesa. formed mostly by mechanical processes b. form at high elevations and high latitudesb. form at high elevations and high latitudes c. no distinct horizons, soil thin (some only few cm deep) c. no distinct horizons, soil thin (some only few cm deep) and made up of rock fragmentsand made up of rock fragments d. some surface areas poorly drained and boggyd. some surface areas poorly drained and boggy e. bottom layers constantly frozen = e. bottom layers constantly frozen = permafrostpermafrost

2. temperate soils (temperate climates): temperature range 2. temperate soils (temperate climates): temperature range between cool and warm, rainfall not excessivebetween cool and warm, rainfall not excessive a. support forests, grasslands, and prairiesa. support forests, grasslands, and prairies 1) grasslands: rich in humus, rich fertile soils1) grasslands: rich in humus, rich fertile soils 2) forests: less deep, less fertile soil; have aluminum-2) forests: less deep, less fertile soil; have aluminum- rich clays and iron oxidesrich clays and iron oxides 3) prairies: drier, supports only grasses and bushes3) prairies: drier, supports only grasses and bushes b. specific amount of rainfall in area determines type of b. specific amount of rainfall in area determines type of vegetation that will growvegetation that will grow

c. three major horizons can be several meters thickc. three major horizons can be several meters thickd. d. pedalfer soilspedalfer soils = contain clay, quartz, and iron compounds = contain clay, quartz, and iron compounds 1) in areas that receive more than 65 cm of rain a year1) in areas that receive more than 65 cm of rain a yeare. e. pedocal soilspedocal soils = contain large amounts of calcium carbonate = contain large amounts of calcium carbonate 1) in areas that receive less than 65 cm of rain a year1) in areas that receive less than 65 cm of rain a year 2) soil less acidic and very fertile2) soil less acidic and very fertile

3. desert soils (desert climates)3. desert soils (desert climates) a. rainfall less than 25 cm per year, very dry so weathering a. rainfall less than 25 cm per year, very dry so weathering slowslow b. soil thin, often have high levels of accumulated saltsb. soil thin, often have high levels of accumulated salts c. vegetation has to be adapted to surviving long periods of c. vegetation has to be adapted to surviving long periods of droughtdrought d. profiles seldom more than a few centimeters from top to d. profiles seldom more than a few centimeters from top to

bottombottom e. fertile when waterede. fertile when watered

4. tropical soils (humid tropical climates)4. tropical soils (humid tropical climates) a. thick soils develop rapidly due to high temperatures and a. thick soils develop rapidly due to high temperatures and heavy rainfallheavy rainfall b. profile may be 3 meters thick b. profile may be 3 meters thick c. c. lateriteslaterites = soil with iron and aluminum minerals that do = soil with iron and aluminum minerals that do

not dissolves easily in waternot dissolves easily in water d. rain leaches minerals from A horizon, thin humus layer d. rain leaches minerals from A horizon, thin humus layer covers B horizoncovers B horizon e. heavy rains wash away most of e. heavy rains wash away most of

topsoil keeping layer topsoil keeping layer thin and relatively infertilethin and relatively infertile f. characteristic red color due to f. characteristic red color due to

oxidation of iron and aluminumoxidation of iron and aluminum

SOIL TEXTURESSOIL TEXTURES1. classified by size of their particles1. classified by size of their particles2. relative proportions of these particles determine soil texture2. relative proportions of these particles determine soil texture3. affects capacity to retain water and ability to support plant 3. affects capacity to retain water and ability to support plant growthgrowth4. process to determine texture:4. process to determine texture: a. place soil sample along with water in clear jar and shake a. place soil sample along with water in clear jar and shake jar welljar well b. allow particles to settleb. allow particles to settle c. sediments will sort as they settle; c. sediments will sort as they settle;

determine and estimate percentage determine and estimate percentage of settled clay, silt, and sandof settled clay, silt, and sand

d. use this information along with d. use this information along with textural triangle (p.173, Fig. 7-24) to textural triangle (p.173, Fig. 7-24) to determine soil texturedetermine soil texture

5. characteristics: 5. characteristics: a. clays: less than 0.002 mm in diametera. clays: less than 0.002 mm in diameter 1) very fine particles, compact easily, forms large dense 1) very fine particles, compact easily, forms large dense

clumps when wetclumps when wet 2) low permeability to water therefore upper layers 2) low permeability to water therefore upper layers

become waterloggedbecome waterlogged 3) holds positively charged ions3) holds positively charged ions b. gravel (coarse) = unconsolidated mixture of rock b. gravel (coarse) = unconsolidated mixture of rock

fragments or pebblesfragments or pebbles

c. loams: best soils for crops; holds water but does create c. loams: best soils for crops; holds water but does create waterlogging waterlogging

d. sand: 0.06 to 2 mm; water flows through too fast for most d. sand: 0.06 to 2 mm; water flows through too fast for most crops, only good for crops needing low amounts of watercrops, only good for crops needing low amounts of water

e. silt: 0.002 to 0.06 mm; sedimentary material of very fine e. silt: 0.002 to 0.06 mm; sedimentary material of very fine particles intermediate in sizeparticles intermediate in size

soil fertilitysoil fertility = how well can support growth of plants = how well can support growth of plants1. affected by availability of minerals and nutrients, number 1. affected by availability of minerals and nutrients, number

of microorganisms present, amount of rainfall available, of microorganisms present, amount of rainfall available, topography, and level of aciditytopography, and level of acidity2. natural and commercial fertilizers can be used to replace 2. natural and commercial fertilizers can be used to replace mineralsminerals3. legumes can be planted and grown to help replace 3. legumes can be planted and grown to help replace

nitratesnitrates4. limestone can be added to reduce 4. limestone can be added to reduce

acidityacidity5. adding compost, organic mulch, 5. adding compost, organic mulch,

and peat moss help maintain fertilityand peat moss help maintain fertility

SOIL CONSERVATIONSOIL CONSERVATION1. growing cover plants to protect topsoil and hold in place1. growing cover plants to protect topsoil and hold in place2. 2. contour plowingcontour plowing = plow soil in circular bands that follow = plow soil in circular bands that follow

the shape of land the shape of land3. 3. strip-croppingstrip-cropping = crops are planted in alternate bands = crops are planted in alternate bands a. often used with contour plowinga. often used with contour plowing b. together can reduce soil erosion by 75%b. together can reduce soil erosion by 75%4. 4. terracingterracing = constructing step-like ridges that follow shape = constructing step-like ridges that follow shape

of sloped fieldof sloped field5. 5. crop rotationcrop rotation = plant one type of = plant one type of

crop one year and crop one year and different type next yeardifferent type next year