Environmental Science: Toward a Sustainable Future Richard T. Wright

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Environmental Science Toward a Sustainable
Future Richard T. Wright
Chapter 8

• Soil Foundation for Land Ecosystems
• PPT by Clark E. Adams

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Global Trend Where Did All the Farms Go?

• Poor farming practices loss of soils and
  farmland
• Erosion
• Salinization
• Development in United States loss of 1.4
  million acres of farmland per year

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Why a Study of Soil Is Important

• 90 of the worlds food comes from land-based
  agriculture.
• Maintenance of soil is the cornerstone of
  sustainable civilizations.
• Simply stated, it is the foundation of
  terrestrial life.

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Soil Foundation for Land Ecosystems

• Soil and plants
• Soil degradation
• Conserving the soil

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Soil and Plants

• Soil characteristics
• Soil and plant growth
• The soil community

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Topsoil Formation
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Soil Profile
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Soil Texture

• Soil texture refers to the percentage of each
  type of particle found in the soil.
• Loam soil is approximately 40 sand, 40 silt,
  and 20 clay.

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Soil Texture

• Sand
• Silt
• Clay

Large
Small
Smaller
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Soil Texture
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Soil Texture and Properties (see Table 8-2)
Texture Water Infiltration Water-holding Capacity Nutrient-holding Capacity Aeration
Sand Good Poor Poor Good
Silt Medium Medium Medium Medium
Clay Poor Good Good Poor
Loam Medium Medium Medium Medium
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Soil Classes

• Mollisols fertile soils with deep A horizon
  best agriculture soils
• Oxisols iron and aluminum oxides in B horizon
  little O horizon poor agriculture soils

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Soil Classes

• Alfisols well-developed O, A, E, and B horizons
  suitable for agriculture if supplemented
• Aridisols little vertical structure thin and
  unsuitable for sustainable agriculture

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Water Transport by Transpiration
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PlantSoilWater Relationships
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Productive Soil

• Good supply of nutrients and nutrient-holding
  capacity
• Infiltration, good water-holding capacity,
  resists evaporative water loss
• Porous structure for aeration
• Near-neutral pH
• Low salt content

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The Soil Community
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Humus

• Partly decomposed organic matter
• High capacity for holding water and nutrients
• Typically found in O horizon

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Formation of Humus
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Humus and Development of Soil Structure
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Soil Degradation

• Erosion
• Drylands and desertification
• Irrigation and salinization

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The Results of Removal of Topsoil Sand and Gravel
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The Importance of Humus to Topsoil
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Erosion Wind or Water

• Splash erosion impact of falling raindrops
  breaks up the clumpy structure of topsoil
• Sheet erosion running water carries off the fine
  particles on the soil surface
• Gully erosion water volume and velocity carries
  away large quantities of soil, causing gullies
  (see Fig. 8-14)

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Desertification

• Formation and expansion of degraded areas of soil
  and vegetation cover in arid, semiarid, and
  seasonally dry areas, caused by climatic
  variations and human activities.

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Dryland Areas

• Cover one-third of Earths land area
• Defined by precipitation, not temperature
• United Nations Convention to Combat
  Desertification (UNCCD)
• Fund projects to reverse land degradation
• In 2003, 500 million available in grants to fund
  projects

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Dry lands and Desertification Formation of
Desert Pavement
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Causes of Soil Degradation
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Contour Farming and Shelterbelts
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A Global View of Soil Degradation
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Irrigation

• Flood irrigation (see Fig. 8-21)
• Center-pivot irrigation (see Fig. 7-16)
• Can extract as much as 10,000 gallons/minute
• Irrigated lands
• 67 million acres or one-fifth of all cultivated
  cropland in the United States
• 667 million acres worldwide, a 35 increase over
  the past 30 years

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Salinization What It Looks Like
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Salinization

• A process of distilling out dissolved salts in
  irrigated water and leaving it on the land
• A form of desertification, since land is rendered
  useless
• Worldwide an estimated 3.7 million acres of
  agricultural land is lost annually to
  salinization and waterlogging

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Conserving the Soil

• Cover the soil
• Minimal or zero tillage
• Mulch for nutrients
• Maximize biomass production
• Maximize biodiversity

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End of Chapter 8