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Chapter 15 Soil Resources. Overview of Chapter 15. What is Soil? Soil Horizons Nutrient Cycling Soil Properties and Major Soil Types Soil Problems Soil Conservation and Regeneration. Soil. Uppermost layer of Earth’s crust that supports plants, animals and microbes Soil Forming Factors - PowerPoint PPT Presentation
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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 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
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
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