Soil Science Simplified Ppt 1 - Intro

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Soil Science SimplifiedPpt 1 - Intro

• BHS Envirothon Competition Team

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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

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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.

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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.

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• 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.

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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
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• 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.

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• 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.

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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.

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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.

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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!)

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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
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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.

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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.

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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.

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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.

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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.