Topic 1. The Soils Around Us

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Topic 1. The Soils Around Us
Environmental Soil Chemistry 12 January 2005
(900-1015 a.m.)

• Professor Kyoung-Woong Kim
• Soil Environment Laboratory
• Department of Environmental Science and
  Engineering

Gwangju Institute of Science and Technology
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Concepts of Soil

• What is soil ?
• The natural bodies in which plants grow
• The foundations of houses and factories
• Beds for roads and highways
• Used to absorb waste from sewage systems
• A reason for studying soils
• What they are and how they can be used
• Determining how best to conserve soils for
  future generations

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Concepts of Soil

• Definition of Soil (Alloway, 1995)
• A complex heterogeneous medium comprising
  mineral and organic solids, aqueous and gaseous
  components
• - Mineral
• Weathering rock fragments and secondary
  minerals
• - Organic matter
• Living organisms, dead plant material, and
  colloidal humus
• - Solid components
• Interconnected voids (pores) of various size

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Two Approaches Pedological and Edaphological

• Pedology
• From the Greek word Pedon, which means soil or
  earth
• The origin of the soil, its classification, and
  its description
• Treat soil as a natural entity
• - a biochemically weathered and synthesized
  product of nature
• Highway and construction engineers
• Edaphology
• From the Greek word Edaphos, which also means
  soil or ground
• Soil from the standpoint of higher plants
• Soil as a natural habitat for plants
• Improving productivity

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A Field View of Soil

• Soil vs Regolith
• Regolith unconsolidated material overlying rock
• Horizon characteristic layering
• Soil
• - upper and biochemically weathered portion of
  the regolith
• - the product of both destructive and synthetic
  forces

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The Soil Profile and Layers (Horizons)
Profile vertical section of a soil

• A horizon
• - Darker than the lower horizon
• - Due to the accumulation of organic matter
• - Some products of weathering
• B horizon
• An accumulation of varying accounts Si-clays,
  iron and aluminum oxides, gypsum, an calcium
  carbonate

• A depth of 1-2 (m) representative of temperate
  region soils
• Gradual transition

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Topsoil and Subsoil

• Topsoil
• The upper 12-18 (cm)
• Plowed and cultivated
• Major zone of root development for crop
• Profile
• Not commonly disturbed by soil tillage
• Crop production affected by root penetration,
  moisture nutrient
• Land-use decision nature of the subsoil

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Mineral (Inorganic) and Organic Soils

• Mineral (Inorganic) soil
• Comparatively low in organic matter which
  generally ranges 1-6
• Organic Soil
• Dominated by organic material contain more than
  50 organic matter by volume (at least 20 by
  weight)

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Major Components of Mineral Soils
Major components Inorganic or mineral materials,
organic matter, water, and air

• Loam surface soil
• - 45 soil volume
• - 5 organic matter
• - 25 water space
• - 25 air
• Subsoil
• - lower in organic matter
• - lower in total pore space
• - higher percentage of small pores

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Mineral (Inorganic) Constituents in Soils

• Size and composition stone, gravel ( gt 2mm ),
  sand (0.05 2 mm), silt (0.002-0.05 mm), clay (
  lt 0.0002 mm), colloid ( lt 1 um)
• Soil texture sandy loam, silty caly and clay
  loam

Table 1.1 General Properties of Tree Major
Inorganic Soil Particles.
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Mineral (Inorganic) Constituents in Soils

• Primary and Secondary Minerals

• Inorganic fraction the original source of the
  mineral elements
• Soil Structure
• The arrangement of the sand, silt, and clay
  particles

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Soil Organic Matter

• Organic Matter
• An accumulation of potentially disintegrated and
  decomposed plant and animal residues and other
  organic compounds
• Binding mineral particles into granules
• Major soil source of phosphorus, sulfur, and
  nitrogen
• Humus
• Complex compounds that are relatively resistant
  to decay

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Soil Water A Dynamic Solution

• Water - held in the soil pores
• Soluble constituents Soil water ? Soil
  Solution
• The movement of soil water
• Downward in response to gravity
• Upward to replace that lost by evaporation
• The water in the large and intermediate size
  pores
• ? The water in the tiny pores and in thin films
• Not all soil water is available to plants

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Soil Water A Dynamic Solution

• Soil Solution
• Containing small but significant quantities of
  soluble inorganic and organic compounds
• Critical property of the soil solution

• pH
• Influence the solubility, and the availability
  to plants of several elements

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Soil Air Another Changeable Constituent

• Soil air
• The composition dynamic and varies from place
  to place
• Higher moisture content and CO2 and lower O2 than
  in the atmosphere
• The content and composition
• Determined by the water content of the soil
• After a heavy rain or irrigation large ? medium
  ? small pores
• Drainage sequence
• Soils with a high proportion of tiny pores to be
  poorly aerated

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The soil A Rich and Varied Biological Laboratory

• Quantity of living organisms
• Influence the physical, chemical, and biological
  properties of soils
• Processes of decay
• Release from organic forms of essential plant
  nutrient (N, P, S)

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Clay and Humus The Seat of Soil Activity

• Clay and humus
• A large surface area and surface charge
• Cation exchange capacity
• - Determining the suitability of soils
• - Humus greater nutrient and water holding
  capacities
• - Clay larger amount

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Interaction of Components - Supplying Plant
Nutrients

• Four major soil components minerals, organic
  matter, water, and air
• The bulk of most nutrient elements
• Molecular or structural framework of primary and
  secondary minerals, organic matter, and soil
  solution
• Essential element availability

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Soil and Plant Relations

• Use of essential elements for crop production

• Absorb the essential nutrients
• Chemical carrier in plant cells
• Microorganisms in the vicinity of roots

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• Thank you for your attention !!