Unit 1: Soil Composition

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Unit 1 Soil Composition Importance

• Chapter 1

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Objectives

• Reasons to study soils
• Definitions of soil
• Parent materials from which soil forms
• Roles functions of soil
• Characteristics of healthy soils soil damage
  risks

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What is soil?

• Various definitions
• natural medium for the growth of land plants
  (USDA)
• Comprised of solids, liquids, gases occurring on
  land surface, occupies space, characterized by
  horizons caused by additions, losses,
  transformations, transfers, or the ability to
  support rooted plants in a natural environment

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What is soil?

• Nonsoil dont have horizons will not support
  plant growth
• Ice lands
• Recent lava flows
• Salt flats
• Bare rock mountain slopes
• Moving dunes

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Earths Crust

• Outermost 3 19 miles of Earths radius
• Contains Earths least dense materials
• Highly dynamic significant changes can occur
  over time due to variety of factors
• What changes can occur how might they affect
  the soil?
• Most common to undergo geologic changes
• Sand
• Silt
• Clay

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Components of Soil

• Various combinations of solids liquids
• Fluids, air, water occupy the pore space between
  soil solids
• Typical soil is ½ solid, ½ liquid
• Potting soil much more porous
• Amount of air varies with the amount of soil
  water (inverse relationship)
• Soil air low in O2, higher in CO2
• Water is soil is referred to as soil solution
• Contains dissolved ions, nutrients, and other
  substances

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Components of Soil

• Soil solids
• Includes mineral organic substances
• Minerals sand clay dominate the concentration
• Organic materials humus present in a lesser
  quantity
• Arrangement in horizontal layers soil horizons
• A Horizon upper few inches of soil, usually
  enriched in organic matter, most favorable
  environment for plant growth
• Eluvial horizon organic matter, minerals, etc.
  can be washed out and down through the soil
  profile
• B Horizon below the A, lower in organic matter,
  higher in soluble materials (salts, clays)
  because of migration from the A
• Iluvial horizon material washed in to the soil
  profile

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Components of Soil

• C Horizon below the B, no effect from migration
  of material in the upper two horizons
• Parent material contains the materials from
  which A B horizons were developed

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Components of Soil

• Mineral Composition of Soils
• Minerals - Inorganic (nonliving) substances,
  definite composition, characteristic physical
  properties
• Melting temp, shape, color, hardness
• Primary minerals formed by the cooling of
  molten rock
• Secondary minerals precipitated or
  recrystallized from solutions that contains
  elements from dissolutions from other minerals

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Components of Soil

• Rocks mixtures of minerals
• Igneous cooled molten rock
• Sedimentary sediments deposited in water
  consolidated materials
• Form from one time rock, minerals, soil
  particles, and soluble substances cemented into
  hard masses
• Sandstones
• Shales consolidated clays silts
• Limestones clays, silts, and sands cemented in
  mixtures of calcium carbonates and magnesium
  carbonates (50 mass is carbonates)
• Dolomites magnesium carbonates
• Quartzites silica-cemented sands

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Components of Soil

• Metamorphic igneous or sedimentary rock
  hardened/altered by heat, pressure, reactions
  with other chemical solutions
• may be as hard or harder than other forms,
  weather to produce similar soils
• Gneiss minerals form segregated light/dark
  bands (granites)
• Schist fissile/foliated (flaky/layered),
  composed of many minerals
• Slate hardened shale or siltstone, very hard
  (pool tables, chalkboard)
• Quartzite recrystallized quartzic sandstone,
  formed by heat pressure, slow to weather,
  produces sandy shallow soils
• Marble hardened limestone or dolomite (easily
  decomposed)

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Components of Soil

• Mineral soils
• Develop from minerals and rocks
• Mostly quartz, feldspars, dark minerals, lime,
  gypsum
• Weather to sands, clays
• Also provide the majority of soil mineral
  nutrients

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Organic Materials in Soil

• 98 of all soils are mineral soils
• Organic soils form from plant residues in ponded
  or cold, wet areas
• Decomposition is slow
• Referred to as peat or muck
• Anaerobic decomposition is slow
• Organic soils can be deep if allowed to decompose
  naturally
• Florida Everglades, Stockton Delta in CA

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Organic Materials in Soil

• Common materials grasses, mosses, leaves,
  cattails, reeds
• All soils contain significant organic matter
• Organic soils are very rich when excavated
• Less sites for organic soils today as many
  marshes, wetlands, etc. have been drained for
  development or agriculture

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Historical Perspectives

• Beginnings of agriculture date to 3500 B.C. in
  Mesopotamia (modern-day Iraq)
• Much irrigation used in those days
• Through water canals
• Some agriculture lost in those areas due to
  silting in of their waterways, therefore, choking
  off their water supply
• Silts in ancient Egypt were a blessing as it
  replenished new soil to the fields each year with
  the floods

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Historical Perspectives

• First century A.D.
• Northern Africa served as the food-base for the
  Roman Empire
• Depleted the soil of nutrients which contributed
  to northern Africas difficulty growing food
  today
• South America bears the first real evidence of
  soil conservation
• Incans of Peru built terraces on mountain sides
  and filled with soil from the valleys
• Cut waterways into the mountain rock

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Historical Perspectives

• North American soil history
• European settlers found very different problems
  than they had encountered before immigrating
• Violent rains, turbulent wind storms
• May 1934, dust storm in TX, OK, CO, KA, swept 400
  b lbs. of soil to the east coast and out to sea
• Some estimate ½ of the original topsoil has
  eroded in the past 150 yrs.

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Historical Perspectives

• History of Soil Science
• Edaphology investigation into the nature of
  soils
• Foresters, agronomists, ecologists, botanist
• Pedology study of soil as a geologic entity,
  origin, morphology, geography, taxonomy
• History of Pedology
• Russians were first to postulate that soil was
  formed by factors other than underlying rock
• They included living matter, climate, time, etc.

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Historical Perspectives

• Created the foundation for the American soil
  classification system started in the 1930s
• Current system of soil classification
  description introduced in 1975
• Continually updates descriptions usage
  recommendations

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Soil A Precious Resource

• Must appreciate the value of soil and its
  importance in our everyday lives
• Engineering Building
• Soil is construction material
• Base of roads, landfills, foundation for
  buildings
• Engineers must know how much load stress a soil
  can stand without deforming

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Soil A Precious Resource

• NRCS responsible for determining degrees of
  limitations placed on soils
• Roadbeds, campsites, homes, septic tank fields
• Can also be molded into bricks for building
• Adobe huts build for housing in the American
  Southwest
• Archaeology
• Soil buried with sediment deposits, glacial
  debris is some of the best preservation for
  archaeological materials

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Soil A Precious Resource

• Scientists found pollen from an ancestor of corn
  in modern-day eastern Mexico dating to 5100 B.C.
• Plants Soil
• Soil provides the 4 basic growth factors for
  plants
• Support (Anchorage)
• Oxygen
• Water
• Nutrients

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Soil A Precious Resource

• Ability to support (anchorage) depends on depth
  of soil
• Oxygen is supplied through pore spaces in the
  soil
• Roots must constantly respire
• Very few plants transport all air internally
  (rice)
• Roots only penetrate to a depth at which there is
  sufficient aeration
• Water supplied by soil reservoir
• Most crops needs 12 31 of water during the
  growing season
• Best soils can only hold 3-4 of water at a time
• Nutrients plants require 17 chemical elements
  for growth
• Others may be required, or help depending on the
  species, but these are true for all plants

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Soil A Precious Resource

• 14 of these essential elements are supplied by
  the soil
• C, H, O are supplied by carbon dioxide from air,
  and water
• Nitrogen is a common component of soil organic
  materials and is only held for a short period,
  often is deficient first
• Other nutrients can be held by electrostatic
  attraction
• Amount of fertility depends on how many nutrients
  are present available
• Soil, Crops, the Human Race
• World population 6.5 b
• Population is ever-increasing
• Expected to raise by 40 by 2050

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Soil A Precious Resource

• Each farmer today feeds 100 people
• Arable (farmable) per person decreasing each year
• Projected to decrease to 1.1 ac/person from 1.45
  ac/person by 2050 in U.S.
• .55 ac/person .375 ac/person worldwide
  respectively
• Disparity between over-nourished nations
  malnourished nations increasing
• Amount of meats grains consumed inversely
  related to income level of the nation
• High meat diets are much more inefficient than
  high grain diets

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Soil A Precious Resource

• Fisheries rangelands currently producing at
  maximum potential
• Responsibility to feed increasing population will
  rest entirely with farmers
• Many acres/yr being converted to
  roads/shopping/dwellings
• Fuel needs also more critical
• Is E85 from corn-based ethanol the answer?
• If not, what are our options?
• What about cellulolytic based ethanol?

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Soil Quality

• Biome interwoven system in which soil, climate,
  living organisms affect each other in a complex
  way
• Soil Pollution
• Soil serves as a depository
• Sewage
• Garbage
• Milling residues
• Wastes can contribute to or destroy cropping
  potential
• Most costly pollution cleanup sites are those w/
  contaminated soils

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Soil Quality

• Hanford Nuclear site in WA - 30b for cleanup of
  contaminated soils
• Soil Misuse
• Many well-intentioned universal soil management
  practices actually degrade the soil
• Some suspect millions/billions acres of soil
  severely degraded
• Ex. Deforestation in Vermont by early American
  settlers caused severe erosion flooding

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Soil Quality

• Common land degrading practices
• Leaving the soil bare (ex.)
• Compacting the soil surfaces (ex.)
• Acidifying the soil (ex.)
• Irrigating without proper drainage (ex.)
• Using chemicals indiscriminately (ex.)
• Sustaining Soils
• Sustainable practices are those that can be
  continued permanently
• Can be difficult, but is vital to the survival
  productivity of our soils

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Soil Quality

• Many soils much healthier today than a generation
  ago, due to conservation practices
• What constitutes a healthy soil?
• Characteristics
• Contents
• Management

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Assignment

• Response to Discussion Question on WebCT
• Due date