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Soil Science Simplified Ppt 1 - Intro

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Soil Science Simplified Ppt 1 - Intro BHS Envirothon Competition Team Soils/Land Use Objectives This ppt will cover the following objectives: U. Recognize soil as an ... – PowerPoint PPT presentation

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Title: Soil Science Simplified Ppt 1 - Intro


1
Soil Science Simplified Ppt 1 - Intro
  • BHS Envirothon Competition Team

2
Soils/Land Use Objectives
  • This ppt will cover the following objectives
  • U. Recognize soil as an important resource.
  • V. Describe basic soil properties (and formation
    factors)
  • X. Determine basic soil properties and
    limitations, such as mottling and permeability,
    by observing a soil pit or soil profile

3
Why Study Soil?
  • Great Integrator!
  • Medium of crop production
  • Filter water and waste
  • Producer and absorber of gases
  • Home to organisms
  • Medium for plant growth
  • Waste decomposer
  • Source material for construction, art, medicine,
    etc.
  • Snapshot of geological, climatic, biological, and
    human history
  • Essential natural resource.

4
Nature and Function of Soil
  • Soil the unconsolidated cover of the earth,
    made up of mineral and organic components, water
    and air and capable of supporting plant growth.
    Most important function GROW PLANTS
  • Photosynthesis plant ability to combine CO2 and
    H2O from the ground into sugar (C6H12O6). Light
    furnishes the energy for this reaction.
    Nitrogen, sulfur and phosphorus are required for
    synthesis of plant proteins too.

5
  • As a medium for plant growth, soil performs four
    functions
  • Anchors roots
  • Supplies water
  • Provides air
  • Furnishes minerals for plant nutrition
  • The pore space between the solids is taken up by
    water and air.
  • Air takes up part of the pore space not occupied
    by water. As the water increases, the air
    content decreases. In respiration (opposite of
    photosynthesis), plant roots use oxygen and give
    off carbon dioxide. So, soil usually contains
    less oxygen and more carbon dioxide than
    atmospheric air does.
  • Millions of microbes live in each ounce of
    fertile soil. Without them, soils would become
    inactive and lose their ability to support
    plants.

6
Physical Properties of Soils
  • Soils consist of solid, liquid, gaseous and
    biotic components.
  • Sand and silt are merely broken down rock frags
    (consists of quartz, feldspar, mica, or other
    minerals). Chemically they are essentially inert
    compared with clay and organic matter, which are
    responsible for most of the chemical reactions in
    the soil.

Soil fraction Diameter Description
Gravel Larger than 2 mm Coarse
Sand 0.05 - 2 mm Gritty
Silt 0.002 0.05 mm Floury
Clay Smaller than 0.002 mm Sticky when wet
7
  • Clay particles are plastic and sticky when wet.
    They are highly adsorptive of water, gas, and
    dissolved substances. Clays are minute,
    plate-shaped, aluminosilicate crystals consisting
    of silicon, aluminum, iron, magnesium, oxygen,
    and hydrogen.
  • There are several types of clay. Two of the most
    important ones are kaolinite and smectite.
    Smectite clays have the ability to swell on
    wetting and shrink when dry. Smectite enter chem
    rxns more than kaolinitic clays.

8
  • Clay is a negatively charged colloid. This
    negative charge is the reason that positively
    charged cations surround each clay particle. The
    individual cations can be exchanged for each
    other.
  • If the cations can get close to the surface of
    the clay, the neg charge on the clay is largely
    neutralized and the clay particles will cling
    together or flocculated. Calcium and magnesium
    are dominant in this area. They are small and
    effective in holding clay particles together.

9
Soil Texture
  • Texture relative proportion of the various
    grain sizes in a soil.
  • To describe soil texture, names, such as loamy
    sand, silt loam, clay loam and silty clay are
    used.
  • The best soils are generally those which contain
    10 to 20 clay, with silt and sand in
    approximately equal amounts, and a fair amount of
    organic matter.

10
Soil Texture Triangle
  • The content of sand, silt, and clay for the
    twelve main soil texture classes can be found on
    this triangle. Ex. Point A is in the sandy loam
    texture class with 65 sand, 25 silt, and 10
    clay. Not that soils with relatively small clay
    contents (lt40) are in the clay texture class bc
    the properties of clay readily predominate over
    the coarser fractions.

11
Surface Area
  • In comparing clay with sand and silt, it is
    important to be aware of the relative amount of
    surface area of these particle size groups, bc it
    is on the surface that many chemical and physical
    processes take place.
  • Smaller more surface area (clay is tiny!)

12

Kind of Particle Diameter of Particle of Particles in 1 gram Surface area of 1 gram
Sand 2 mm 90 11 cm2
Silt 0.02 mm 90,000,000 (9x107) 1130 cm2
Clay 0.0002 mm 9x1013 113,000 cm2
13
Soil Structure
  • Structure arrangement of individual particles
    in relation to each other. Soil structure is the
    arrangement of particles into small groups, or
    aggregates.
  • Aggregates may be bound together with other
    aggregates in larger masses called peds.
  • Peds come in different shapes that roughly
    resembel sphere, blocks, columns and plates.
  • If the individual particles are arranged in small
    aggregates with rounded edges, we speak granular
    structure. This is very desirable for plant
    growth bc it provides both large and small pores.
  • Some soils lack structure. Sandy soils the
    individual grains act independently of each
    other. No binding substances hold the particles
    together, so the soil has no peds.

14
Pore Space
  • Large pores are readily drained of water and
    filled by air after a heavy rain. They are
    valuable as an aeration system.
  • Small pores hold water against gravity and pull
    water up from a water table by capillary action.
    They are necessary for the water supply of
    plants.
  • Ideal structure includes large and small pores in
    proportions that corresponds to the water/air
    needs of the crop plants given for that culture
    or climate.

15
Soil Temperature
  • Just as important to plant growth as air temp.
    The temp of the surface soil fluctuates greatly
    both during a 24 hr period and with the seasons.
  • Where soil is covered by a dense growth of plants
    or a thick layer of mulch, temperature variations
    are much less severe and do not penetrate deeply
  • Soil temperature has a direct effect on plant
    growth and also influences microbial activity.
  • Freezing and thawing of the soil water also
    affects soil structure. Slow and occasional
    freezing and thawing (like under mulch) is
    beneficial for soil structure.

16
Soil Color
  • Color of soils tells us much about some of its
    other properties.
  • The color of a surface soil horizon depends
    mainly on its organic matter content the darker
    the soil, the more organic matter it contains.
    This organic matter imparts favorable properties
    to the soil, such as better aggregation and a
    high water-holding capacity. Also, dark soils
    absorb more radiation during the day, and radiate
    more heat during the night.
  • In subsoil horizons, soil color indicates the
    wetness and aeration conditions of the soil.
  • In general, reddish and brownish subsoils
    indicate good aeration and little water logging
    (you see the iron red)
  • Grayish and olive colors indicate much water
    logging and a chemical reduction of iron.
  • A mottled subsoil, one with a splotchy pattern of
    brownish and grayish colors, is indicative of a
    fluctuating ground water table.

17
Munsell Color System
  • Defined color in terms of Hue, Value and Chroma.
  • Hue was defined as the actual color, red, blue,
    green, etc.
  • Value was defined as how light or dark a color
    is.
  • Chroma was defined as how strong or weak a color
    is.
  • Soil scientists use the Munsell Color book to
    determine the color of the soil to help determine
    in what type of soil it is along with using
    texture.
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