Chapter 15Chapter 15Soil ResourcesSoil Resources

Overview of Chapter 15Overview of Chapter 15

What is Soil?What is Soil? Soil HorizonsSoil Horizons Nutrient CyclingNutrient Cycling

Soil Properties and Major Soil TypesSoil Properties and Major Soil Types Soil ProblemsSoil Problems Soil Conservation and RegenerationSoil Conservation and Regeneration

SoilSoil

Uppermost layer of Earth’s crust that Uppermost layer of Earth’s crust that supports plants, animals and microbessupports plants, animals and microbes

Soil Forming FactorsSoil Forming Factors Parent MaterialParent Material TimeTime ClimateClimate OrganismsOrganisms TopographyTopography

Soil CompositionSoil Composition Mineral Particles Mineral Particles

(45%)(45%) Weathered rockWeathered rock

Organic Material Organic Material called humus called humus (5%)(5%) Leaf litter, animal Leaf litter, animal

dung, dead dung, dead remains of plants remains of plants and animalsand animals

Water (25%)Water (25%) Air (25%)Air (25%)

Soil CompositionSoil Composition

Pore space Pore space 50% of soil50% of soil Soil air - good Soil air - good

for aerationfor aeration Soil water - Soil water -

provides provides water to rootswater to roots

Soil Horizons – Soil Horizons – soil separates naturally soil separates naturally over time into distinct layersover time into distinct layers

Soil OrganismsSoil Organisms There are millions of microorganisms There are millions of microorganisms

in 1 tsp of fertile agricultural soilin 1 tsp of fertile agricultural soil

Soil OrganismsSoil Organisms

Soil organisms provide ecosystem Soil organisms provide ecosystem servicesservices Def: Important environmental benefits Def: Important environmental benefits

that ecosystems provide that ecosystems provide ExamplesExamples

Decaying and cycling organic materialDecaying and cycling organic material Breaking down toxic materialsBreaking down toxic materials Cleansing waterCleansing water Soil aeration Soil aeration

Nutrient CyclingNutrient Cycling

Nutrients are Nutrients are cycled between cycled between plants, plants, organisms and organisms and soilsoil

Three major Three major nutrients needed nutrients needed for plant growth for plant growth are Nitrogen, are Nitrogen, Phosphorous, Phosphorous, and Potassiumand Potassium

Soil PropertiesSoil Properties

Soil TextureSoil Texture Relative proportion of sand, silt and clayRelative proportion of sand, silt and clay Sand: 2mm–0.05 mmSand: 2mm–0.05 mm Silt: 0.05mm–0.002 mmSilt: 0.05mm–0.002 mm Clay: >0.002 mmClay: >0.002 mm

What type of soil texture will the following soil compositions produce?2) 80% silt, 10% sand, 10% clay = _________________1) 20% silt, 50% sand, 30% clay = ______________________3) 5% silt, 85% sand, 10% clay = __________________________

4) 40% silt, 40% sand, 20% clay = _________________________LOAM IS THE BEST AGRICULTURAL SOIL! WHY???

Soil PropertiesSoil Properties

Soil texture affects soil propertiesSoil texture affects soil properties Coarse textured soil (sandy)Coarse textured soil (sandy)

Excellent drainageExcellent drainage Fine textured soil (high in clay)Fine textured soil (high in clay)

Poor drainagePoor drainage Low oxygen levels in soilLow oxygen levels in soil Due to negatively charged surface, able Due to negatively charged surface, able

to hold onto important plant nutrients to hold onto important plant nutrients (K(K++, Ca, Ca2+2+, NO, NO2-2-))

This is a close up of a clay particle with a film of water around it. Positive ions are attracted to the negatively charged clay surface.

Soil PropertiesSoil Properties

Soil PropertiesSoil Properties Soil AciditySoil Acidity

Measured using pH scaleMeasured using pH scale pH of most soils range from 4–8pH of most soils range from 4–8 Affects solubility of certain plant nutrientsAffects solubility of certain plant nutrients Optimum soil pH is 6–7, because nutrients Optimum soil pH is 6–7, because nutrients

are most available to plants at this Phare most available to plants at this Ph Since rain is naturally acidic, and since plant Since rain is naturally acidic, and since plant

decomposition produces acids (humic acid), decomposition produces acids (humic acid), and since air pollution with sulfur dioxide and and since air pollution with sulfur dioxide and nitrous oxides leads to acid deposition, LIME nitrous oxides leads to acid deposition, LIME can be added to soils to increase the pH. can be added to soils to increase the pH. LIME IS ESSENTIALLY CALCIUM CARBONATELIME IS ESSENTIALLY CALCIUM CARBONATE

Major Soil GroupsMajor Soil Groups

Variations in soil forming factors Variations in soil forming factors cause variation in soils around globecause variation in soils around globe

Soil TaxonomySoil Taxonomy Separates soils into 12 ordersSeparates soils into 12 orders Subdivided into more than 19,000 soil Subdivided into more than 19,000 soil

series that vary by localityseries that vary by locality Five common soil ordersFive common soil orders

Spodosols, alfisols, mollisols, aridosols, Spodosols, alfisols, mollisols, aridosols, oxisolsoxisols

Major Soil GroupsMajor Soil Groups

SpodosolsSpodosols Form under Form under

coniferous forestsconiferous forests O-horizon O-horizon

composed of composed of decaying needlesdecaying needles

E-horizon is ash -E-horizon is ash -gray under A-gray under A-horizonhorizon

Not good Not good farmland - too farmland - too acidicacidic

Major Soil GroupsMajor Soil Groups

AlfisolsAlfisols Brown to gray-Brown to gray-

brown A-horizonbrown A-horizon Precipitation high Precipitation high

enough to leach enough to leach most organics most organics and nutrients out and nutrients out of O-, A- and B-of O-, A- and B-horizonshorizons

Soil fertility Soil fertility maintained by maintained by leaf litterleaf litter

Major Soil GroupsMajor Soil Groups

MollisolsMollisols Found in Found in

temperate, semi-temperate, semi-arid grasslandarid grassland

Very fertile soilVery fertile soil Thick, dark Thick, dark

brown/ black A-brown/ black A-horizonhorizon

Soluble nutrients Soluble nutrients stay in A-horizon stay in A-horizon due to low due to low leachingleaching

Major Soil GroupsMajor Soil Groups

AridosolsAridosols Found in arid Found in arid

regions of all regions of all continentscontinents

Low precipitation Low precipitation preclude preclude leaching and leaching and growth of lush growth of lush vegetationvegetation

Development of Development of salic horizon salic horizon possiblepossible

Major Soil GroupsMajor Soil Groups

OxisolsOxisols Found in tropical Found in tropical

and subtropical and subtropical areas with high areas with high precipitationprecipitation

Very little organic Very little organic material material accumulation due accumulation due to fast decay rateto fast decay rate

B-horizon is B-horizon is highly leached highly leached and nutrient poorand nutrient poor

Soil ProblemsSoil Problems

Soil ErosionSoil Erosion Caused primarily by water and windCaused primarily by water and wind

Why a problem?Why a problem? Causes a loss in soil fertility as organic Causes a loss in soil fertility as organic

material and nutrients are erodedmaterial and nutrients are eroded More fertilizers must be used to replace More fertilizers must be used to replace

nutrients lost to erosionnutrients lost to erosion Accelerated by poor soil Accelerated by poor soil

management practicesmanagement practices

Soil Erosion by Water and Soil Erosion by Water and WindWind

Case in Point: Case in Point: American Dust BowlAmerican Dust Bowl

Great Plains has low Great Plains has low precipitation and is precipitation and is subject to droughtsubject to drought 1930-1937 severe 1930-1937 severe

droughtdrought No natural vegetation No natural vegetation

roots to hold soil in placeroots to hold soil in place Replaced by annual cropsReplaced by annual crops

Winds blew soil as far Winds blew soil as far east as NYC and DC.east as NYC and DC.

Farmers went bankruptFarmers went bankrupt

Soil ProblemsSoil Problems

Nutrient Mineral DepletionNutrient Mineral Depletion

Often in arid Often in arid and semi-arid and semi-arid areasareas

Salt Salt concentrations concentrations get to levels get to levels toxic to plantstoxic to plants

Soil ProblemsSoil Problems

Soil SalinizationSoil Salinization Gradual accumulation of salt in the soil, Gradual accumulation of salt in the soil,

usually due to improper irrigation usually due to improper irrigation techniquestechniques

Soil ProblemsSoil Problems

DesertificationDesertification Def: degradation of once-fertile Def: degradation of once-fertile

rangeland, agricultural land, or tropical rangeland, agricultural land, or tropical dry forest into nonproductive desertdry forest into nonproductive desert

Crop RotationCrop Rotation Planting a series of different crops in the Planting a series of different crops in the

same field over a period of yearssame field over a period of years

Soil ConservationSoil Conservation

Conservation Conservation TillageTillage Residues from Residues from

previous year’s previous year’s crops are left in crops are left in place to prevent place to prevent soil erosionsoil erosion

Strip Strip CroppingCropping

TerracinTerracingg

Soil ConservationSoil Conservation

Contour PlowingContour Plowing Plowing around hill Plowing around hill

instead of up-downinstead of up-down Strip CroppingStrip Cropping

Alternating strips of Alternating strips of different crops along different crops along natural contoursnatural contours

TerracingTerracing Creating terraces on Creating terraces on

steep slopes to steep slopes to prevent erosionprevent erosion

Preserving Soil FertilityPreserving Soil Fertility

Organic fertilizersOrganic fertilizers Animal manure, crop residue, bone meal Animal manure, crop residue, bone meal

and compostand compost Nutrient available to plants only as material Nutrient available to plants only as material

decomposesdecomposes Inorganic fertilizersInorganic fertilizers

Manufactured from chemical compoundsManufactured from chemical compounds SolubleSoluble

Fast acting, short lastingFast acting, short lasting Mobile- easily leach and pollute groundwaterMobile- easily leach and pollute groundwater

Soil ReclamationSoil Reclamation

Two stepsTwo steps Stabilize land to Stabilize land to

prevent further prevent further erosionerosion

Restoring soil to Restoring soil to former fertilityformer fertility

Best way to do this Best way to do this is shelterbeltsis shelterbelts Row of trees Row of trees

planted to reduce planted to reduce wind erosion of soilwind erosion of soil

Soil Conservation Policies in Soil Conservation Policies in USUS Soil Conservation Act 1935Soil Conservation Act 1935

Authorized formation of Soil Conservation Authorized formation of Soil Conservation Service, now called Natural Resource Service, now called Natural Resource Conservation Service (NRCS)Conservation Service (NRCS)

Assess soil damage and develop policies Assess soil damage and develop policies to improve soilto improve soil

Food Security Act (Farm Bill) 1985Food Security Act (Farm Bill) 1985 Farmers with highly erodible soil had to Farmers with highly erodible soil had to

change their farming practiceschange their farming practices Instituted Conservation Reserve ProgramInstituted Conservation Reserve Program

Pays farmers to stop farming highly erodible Pays farmers to stop farming highly erodible landland