The Geography of Soils Soil Characteristics

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Chapter 18 The Geography of Soils Geosystems 5e An Introduction to Physical Geography Robert W. Christopherson Charlie Thomsen


The Geography of Soils Soil Characteristics   Color, texture, structure, chemistry Soil Properties   Mineral fraction, organic matter, porosity (gases, soil moisture) Soil Formation Factors Clorpt   Soil Classification   Podzolization, calcification, laterization, salinization Soil orders: Oxisol/Ultisol; mollisol, spodosol, aridisol, histisol Know soil horizons (O, A, B, C, R)


Soil Sampling and Mapping UnitsFigure 18.1


lLaterizationSoil Orders: Oxisols: Amazon region Ultisols: SE USA


Oxisols are deeply weathered. Precipitation >> PET Soluble minerals weathered from A horizon A horizon can be more than 10-m deep A horizon characterized by iron and aluminum oxides, often in high enough concentration to be commercial ores Results in reddish to yellow color Little CEC Low in fertitlity Wet tropical areas Amazon rain forest classic example Ultisols are similar, characteristic of sub- tropical areas such as SE USAOxisols


Oxisols being used for building materials in India


CalcificationPotential ET about the same as precipitation Large amounts of organic matter in O and A horizons, dark color Get carbonate deposition in B horizon Very fertile soils if add water Mollisols characteristic soil order


Mollisol Figure 18.2Dark O horizon above the 1 Dark A horizon between 1 and 2 -these indicate lots of organic matter B horizon below the 2 -the white particles are carbonate nodules Calcification regime -ppt about equal to ET Great plains area


PodzolizationCool climates Precip > PET Forested areas generally Strongly leached Acidic soils Low CEC and low fertility Generally an E or spodic horizon of leached/bleached gray/white Large surface humus layer Iron and Aluminum in B horizon Poor farming areas NE US


SpodosolsCold, forested, moist regimes -NE USA -Boreal forests worldwide Lack humus and clay in the A-horion -A horizon heavily leached -whiteish colorad from 0 to 0.9 Iron and aluminum oxides in B horizon -reddish color above and below 2 Low CEC Infertile soils Acidic soil waters


SalinizationAccumulation of salts in arid areas PET >> precpitation Aridisols dominant soil order


AridisolsPET >> Precipitation Desert soils Pale, light color near surface Long periods of soil moisture deficit Little if any organic matter High CEC Very fertile if add water Salinization is common Here the white color is from salts that have precipitated in the soil


Kesterson ReservoirThe Kesterson Reservoir in the San Joaquin Valley of California is the recipient of water drained from agricultural fields. Studies of the freshwater wetlands at Kesterson have shown that the water entering Kesterson has brought with it boron, selenium and other trace elements. These material have accumulated to toxic levels in plant and animal communities.


Histosols: poorly-drained areas, high OM, wetlands and peat areas


Soil PropertiesSoil Color   Soil Texture   Soil Structure   Soil Chemistry   Soil Acidity and Alkalinity   Soil nutrients


Munsell Soil Color ChartFigure 18.3


Soil Texture TriangleFigure 18.4


Types of Soil StructureFigure 18.5


Soil Colloids and CECFigure 18.6


pH ScaleFigure 18.7


GeophagyPeople around the world eat clay, dirt or other pieces of the lithosphere for a variety of reasons. Commonly, it is a traditional cultural activity which takes place during pregnancy, religious ceremonies, or as a remedy for disease. Most people who eat dirt live in Central Africa and the Southern United States. While it is a cultural practice, it also fills a physiological need for nutrients. And of course, kids all over the world still eat dirt.

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Last Updated: 8th March 2018

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