Chapter 15Chapter 15Soil ResourcesSoil Resources

Overview of Chapter 15Overview of Chapter 15

o What is soil?What is soil?o Soil PropertiesSoil Propertieso Major Soil OrdersMajor Soil Orderso Soil ProblemsSoil Problemso Soil Conservation Soil Conservation o Soil ReclamationSoil Reclamation

SoilSoil

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

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

Soil CompositionSoil Composition

o Mineral Particles (45%)Mineral Particles (45%)• Weathered rockWeathered rock• Provides essential nutrients for plantsProvides essential nutrients for plants

o Organic Material (5%)Organic Material (5%)• Litter, animal dung, dead remains of plants Litter, animal dung, dead remains of plants

and animals, humus (picture)and animals, humus (picture)

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

Soil CompositionSoil Composition

o Pore space Pore space • 50% of soil50% of soil• Soil air- good for Soil air- good for

aerationaeration• Soil water- Soil water-

provides water to provides water to rootsroots

Soil HorizonsSoil Horizons

o O-horizonO-horizon• Rich in organic Rich in organic

materialmaterial

o A-horizonA-horizon• TopsoilTopsoil

o B-horizonB-horizon• Lighter colored Lighter colored

subsoilsubsoil

o C-horizonC-horizon• Weathered parent Weathered parent

materialmaterial

Soil OrganismsSoil Organismso There are millions of microorganisms in There are millions of microorganisms in

1 tsp of fertile agricultural soil1 tsp of fertile agricultural soil

Soil OrganismsSoil Organisms

o Soil organisms provide Soil organisms provide ecosystem ecosystem servicesservices• Def: Important environmental benefits that Def: Important environmental benefits that

ecosystems provide ecosystems provide

o ExamplesExamples• Decaying and cycling organic materialDecaying and cycling organic material• Breaking down toxic materialsBreaking down toxic materials• Cleansing waterCleansing water• Soil aeration (especially done by Soil aeration (especially done by

earthworms)earthworms)

Nutrient Nutrient CyclingCycling

o Nutrients are cycled Nutrients are cycled between plants, between plants, organisms and soilorganisms and soil

o ExampleExample• Bacteria and fungi Bacteria and fungi

decompose plant decompose plant and animal wastesand animal wastes

• They are They are transformed into transformed into COCO22, soil nutrients , soil nutrients and waterand water

Soil PropertiesSoil Propertieso Soil TextureSoil Texture

• Relative proportion of sand, silt and clayRelative proportion of sand, silt and clay• Sand: 2mm-0.05mmSand: 2mm-0.05mm• Silt: 0.05mm-0.002mmSilt: 0.05mm-0.002mm• Clay: >0.002mmClay: >0.002mm

Soil PropertiesSoil Properties

o Soil texture affects soil propertiesSoil texture affects soil propertieso Coarse textured soil (sandy)Coarse textured soil (sandy)

• Will not hold water well- flows through Will not hold water well- flows through easilyeasily

o 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 to Due to negatively charged surface, able to

hold onto important plant nutrients (Khold onto important plant nutrients (K++, , CaCa2+2+, NO, NO22

--))

Soil PropertiesSoil Properties

Soil PropertiesSoil Properties

o Soil AciditySoil Acidity• Measured using pH scaleMeasured using pH scale

• 0-7 = acidic0-7 = acidic• 7 = neutral7 = neutral• 7-14 = basic7-14 = basic

• 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 6-7Optimum soil pH is 6-7

• This is the pH where plant nutrients are most This is the pH where plant nutrients are most available to plantsavailable to plants

• Soil amendments (ex: lime) can be used to Soil amendments (ex: lime) can be used to achieve this pHachieve this pH

Soil ProblemsSoil Problems

o Soil ErosionSoil Erosion• Def: wearing away or removal of soil from Def: wearing away or removal of soil from

the land the land • Caused primarily by water and windCaused primarily by water and wind

o 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 erosiono Accelerated by poor soil management Accelerated by poor soil management

practicespractices

Case in Point: American Case in Point: American Dust BowlDust Bowl

o Great Plains have low Great Plains have low precipitation and subject precipitation and subject to droughtto drought• 1930-1937 severe drought1930-1937 severe drought• 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 east Winds blew soil as far east as NYC and DC.as NYC and DC.

• Farmers went bankruptFarmers went bankrupt

Soil ProblemsSoil Problemso Nutrient Mineral DepletionNutrient Mineral Depletion

Soil ProblemsSoil Problemso Soil SalinizationSoil Salinization

• Def: gradual accumulation Def: gradual accumulation of salt in the soil, usually of salt in the soil, usually due to improper irrigation due to improper irrigation techniquestechniques

o Often in arid and semi-Often in arid and semi-arid areasarid areas• The little precipitation The little precipitation

that falls is quickly that falls is quickly evaporatedevaporated

• Leaves behind saltsLeaves behind saltso Salt concentrations get Salt concentrations get

to levels toxic to plantsto levels toxic to plants

Soil ProblemsSoil Problems

o DesertificationDesertification• Def: degradation of once-Def: degradation of once-

fertile rangeland, fertile rangeland, agricultural land, or tropical agricultural land, or tropical dry forest into dry forest into nonproductive desertnonproductive desert

o Typically a human-induced Typically a human-induced conditioncondition

o Change in vegetation Change in vegetation changes climate, further changes climate, further decreasing precipitation decreasing precipitation levelslevels

Soil ConservationSoil Conservation

o Conservation TillageConservation Tillage• Residues from Residues from

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

• Includes no tillageIncludes no tillage

o 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• Lessens pest and insect diseaseLessens pest and insect disease

Soil ConservationSoil Conservation

o Contour PlowingContour Plowing• Plowing around hill Plowing around hill

instead of up-downinstead of up-down• Decreases soil erosionDecreases soil erosion

o Strip CroppingStrip Cropping• Alternating strips of Alternating strips of

different crops along different crops along natural contoursnatural contours

o TerracingTerracing• Creating terraces on Creating terraces on

steep slopes to steep slopes to prevent erosionprevent erosion

Strip Strip CroppingCropping

TerraciTerracingng

Preserving Soil FertilityPreserving Soil Fertility

o Organic fertilizersOrganic fertilizers• Animal manure, crop residue, bone meal and Animal manure, crop residue, bone meal and

compostcompost• Nutrient available to plants only as material Nutrient available to plants only as material

decomposesdecomposes• Slow acting and long lastingSlow acting and long lasting

o Inorganic fertilizersInorganic fertilizers• Manufactured from chemical compoundsManufactured from chemical compounds• SolubleSoluble

• Fast acting, short lastingFast acting, short lasting• Environmentally sound to limit useEnvironmentally sound to limit use

• Mobile- easily leach and pollute groundwaterMobile- easily leach and pollute groundwater

Soil ReclamationSoil Reclamation

o Two stepsTwo steps1.1. Stabilize land to Stabilize land to

prevent further prevent further erosionerosion

2.2. Restoring soil to Restoring soil to former fertilityformer fertility

o Best way to do this is Best way to do this is shelterbeltsshelterbelts

• Row of trees planted Row of trees planted to reduce wind erosion to reduce wind erosion of soilof soil

Soil Conservation Policies in USSoil Conservation Policies in US

o 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 to Assess soil damage and develop policies to improve soilimprove soil

o Food Security Act (Farm Bill) 1985Food Security Act (Farm Bill) 1985• Required farmers with highly erodible soil Required farmers with highly erodible soil

had to change their farming practiceshad to change their farming practices• Instituted Conservation Reserve ProgramInstituted Conservation Reserve Program

• Pays farmers to stop farming highly erodible landPays farmers to stop farming highly erodible land