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Soil Orders. Here we go!. Soil Profiles of the Principal Terrestrial Soil Types . Figure 3-24. Mosaic of closely packed pebbles, boulders. Weak humus-mineral mixture. Alkaline, dark, and rich in humus.

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soil orders

Soil Orders

Here we go!

Mosaic of closely packed pebbles, boulders

Weak humus-mineral mixture



and rich

in humus

Dry, brown to reddish-brown with variable accumulations of clay, calcium and carbonate, and soluble salts

Clay, calcium compounds

Desert Soil

(hot, dry climate)

Grassland Soil

semiarid climate)

Fig. 3-24a, p. 69

Ardosol = Desert Soils
  • Mollisol = Grassland Soils
Tropical Rain Forest Soil

(humid, tropical climate)


light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

oxisol or ultisol
Oxisol or Ultisol
  • Form in hot rainy environments.
  • So what’s the difference Mr. Davis?!
  • Well, ….
  • Ultisols are intensely weathered soils of warm and humid climates. They are typically formed on older geologic locations in parent material that is already extensively weathered.Ultisols have accumulated clay minerals in the B horizon. While generally low in natural fertility (basic cations, Ca2+, Mg2+, and K+) and high in soil acidity (H+, Al3+) the clay content of Ultisols gives them a nutrient retention capacity greater than that of Oxisols, but less than Alfisols or Mollisols. Ultisol soils can be agriculturally productive with inputs of lime and fertilizers. Red Soils of the SE US
  • 10 - Oxisols
  • Oxisols are the most weathered of the 12 soil orders in the USDA soil classification system. (See Lesson 2 -- Processes of Weathering.) They are composed of the most highly weathered tropical and subtropical soils, and are formed in hot, humid climates that receive a lot of rainfall. Oxisols are located primarily in equatorial regions.
  • These soils are extensively leached, and the clay size particles are dominated by oxides of iron and aluminum, which are low in natural fertility (Ca2+, Mg2+, K+) and high in soil acidity (H+, Al3+). While Oxisols are typically physically stable, with low shrink-swell properties and good erosion resistance, these soils require extensive inputs of lime and fertilizers to be agriculturally productive
Tropical Rain Forest Soil

(humid, tropical climate)

What Am I?


light-colored humus

Iron and aluminum compounds mixed with clay

Fig. 3-24b, p. 69

Forest litter leaf mold

Humus-mineral mixture

Light, grayish-brown, silt loam

Dark brown firm clay

Deciduous Forest Soil

(humid, mild climate)

Fig. 3-24b, p. 69

Coniferous Forest Soil

(humid, cold climate)

Acid litter and humus

Light-colored and acidic

Humus and iron and aluminum compounds

Fig. 3-24b, p. 69

Develop from volcanic material.
  • High water holding capability.
  • Fix phosphorus for plant use.
  • Productive forest in the Pacific NW have this soil type.
  • Come from parent material that is rich in clay, like lake beds or shale bedrock.
  • Swell and shrink in response to water.
  • Swell w/water
  • Shrink w/o water; causing engineering problems and crack w/o water.
  • Parent material:
  • incompletely decomposed plant remains, with or without admixtures of sand, silt or clay. Waterlogged areas (bog or peat soils)
  • Environment:
  • Histosols occur extensively in boreal, arctic and subarctic regions. Elsewhere, they are confined to poorly drained basins and depressions, swamp and marshlands with shallow groundwater, and highland areas with a high precipitation/evapotranspirationratio.
  • From
  • Frozen soils, where there is perma frost.
  • Alaska in U.S.
  • Entisols are soils of recent origin. The central concept is soils developed in unconsolidated parent material with usually no genetic horizons except an A horizon. All soils that do not fit into one of the other 11 orders are Entisols. Thus, they are characterized by great diversity, both in environmental setting and land use.
  • (little to no horizon development)
  • Very Diverse: Saudia Arabia deserts, rivers valleys around the world, mined areas.
  • inceptisols(from Latininceptum, "beginning") are soils that exhibit minimal horizon development. They are more developed than Entisols, but still lack the features that are characteristic of other soil orders.

Both inceptisols and entisols have not fully developed, they lack complete horizons, and have formed from fairly new parent material, or areas with low water/precipitation, thus the soil develps slowly.