soils
DESCRIPTION
SOILS. Excerpts of the presentations of: Basic Soil Science &The Soil Resource Web Pages http://www.soils.agri.umn.edu/academics/classes/soil2125/. SOIL i –. - PowerPoint PPT PresentationTRANSCRIPT
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SOILS
Excerpts of the presentations of:
Basic Soil Science &The Soil Resource Web Pages
http://www.soils.agri.umn.edu/academics/classes/soil2125/
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SOIL i –
• SOIL - The unconsolidated mineral or organic material on the immediate surface of the earth that serves as a natural medium for the growth of land plants.
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Soil ii
• The unconsolidated mineral or organic matter on the surface of the earth that has been subjected to and shows effects of genetic and environmental factors of:
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Factors • 1) climate (including
water and temperature effect
• 2) macro- and microorganisms, conditioned by
• 3) relief, acting on • 4) parent material
over a period of • 5) time.
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Soil – A Product
• soil differs from the material from which it is derived (Parent Material) in many :
• a) physical, • b) chemical, • c) biological, and • d) morphological
properties and characteristics.
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Soils are Dynamic
• the % air, % water, % organic matter will change with time and space.
• The Soil Ecosystem = all parts of the soil, including biotic and abiotic.
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Soils and Plant Growth
• Physical support of plants• Provides water and air• Provides essential elements
– Macro-nutrients = N,P,K,Ca,Mg,S– Micro-nutrients =
B,Fe,Mn,Cu,Zn,Mo,Co,Cl
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Soil profile and horizons
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Organic Horizons– O - horizon - organic
material (no mineral materials) 1) forest litter 2) organic soil or peat soils, or muck
• Oi - undecomposed (fibris)• Oe - moderate decomp.
(hemis)• Oa - decomposed (sapric)
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Processes of Mineral Soil Horizon Formation
A. Additions - H2O, organic matter,air, soil particles, salt
B. Losses - H2O, organic matter, CO2 , nutrients by plant removal
C. Transformations - Changes to soil structure, development of clay minerals, weathering of minerals to elements, chemical Rx
D. Translocations - movement from one horizon to another of O.M. Clay, Water, Iron, & Nutrients in colloidal size, (very small particles)
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Mineral Soil Horizons
• A horizon - surface horizons that accumulate O.M.
• Ap = plowed soil
Ap
EB
Bt
BC
C
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E Horizons
• E - (formerly A2) - Translocation out - Zone of Eluviations - Leaching out
• lighter in color than horizons above or below
AE
E/B
Bt
BCC
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B Horizons-two kinds:
• a) Translocation in - below an A, E, or O with an accumulation of clay, iron, humus (O.M. decomposed) or carbonates (CaCO3)
• b) or alteration of the original parent material, development of color or structure
Bt
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C Horizons
• C - little affected by pedogenic processes and lack properties of O-A-B-E- or is the Parent Material
• R = hard rock
C horizon
Solum A + B
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Soil Texture• Soil texture is determined by separating the amount of
sand, silt and clay in a soil and determining the % of each.
• This mineral part of the soil or the Sand, Silt and Clay particles are from the weathering of Rocks and Minerals.
• Soil texture is the single most important physical property of the soil. Knowing the soil texture alone will provide information about:
• 1) water flow potential,
• 2) water holding capacity,
• 3) fertility potential,
• 4) suitability for many urban uses.
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Soil Texture
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Rocks Weather to Soil
• Weathering is the process by which all rocks at the earth's surface get broken down.
• Weathering occurs by both chemical (decomposition) and mechanical processes (disintegration).
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Physical Weathering• Physical weathering - Rocks get broken into pieces but its chemical composition remains unchanged.
• Processes of Phys.Weathering
• 1) Freeze / thaw weathering - occurs when temperature freezes at night and rises during the day. Water expands when frozen which forces rocks open.
• 2) Biological weathering _ Roots of plants grow into cracks and force cracks open.
• 3) Exfoliation - when rock at earth's surface is worn away. • After a rock that has formed deep in the earth is exposed at the
surface it expands and gradually breaks into sheets.
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Chemical Weathering• Chemical weathering -
Rock broken down by chemical change - water always plays a part. For Example:
• Carbon dioxide dissolves in rain water forming carbonic acid which dissolves limestone rock which is carried away in solution as calcium hydrogen carbonate.
• Chemical weathering is faster for limestone than sandstone and is speeded up by heat.
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Chemical Weathering
• Common chemical weathering processes are: hydrolysis, dissolution, and oxidation.
• Chemical weathering produces clays on which vegetation can grow.
• A mixture of dead vegetation, clay, rock fragments of sand and silt size particles produces soil.
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Chemical Weathering
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Chemical Weathering
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Weathering
• Weathering is controlled largely by climate. The more water available, the more likely that chemical processes can proceed.
• Additionally, in warm temperatures chemical weathering can proceed even faster.
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Weathering
• In arid climates, however, weathering processes move very slowly.
• Mechanical weathering will be the dominant process in arid climates;
• however, because physical weathering relies on chemical weathering, it will also be quite slow
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Soil as a Resource
• WHAT DOES SOIL DO? • Healthy soil gives us
clean air and water, bountiful crops and forests, productive rangeland, diverse wildlife, and beautiful landscapes.
• Soil does all this by performing five essential functions:
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Soil as a Resource with 5 essential functions:
1) Regulating water. • Soil helps control
where rain, snowmelt, and irrigation water goes.
• Water and dissolved solutes flow over the land or into and through the soil.
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2) Sustaining plant and animal life.
• The diversity and productivity of living things depends on soil.
• The more productive the soil, the more diversity in both the plant and animal community.
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3) Filtering potential pollutants.
• The minerals and microbes in soil are responsible for :
• filtering, buffering, degrading,immobilizing,and detoxifying organic and inorganic materials, including industrial and municipal by-products and atmospheric deposits.
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4) Cycling Nutrients.
• Carbon, nitrogen, phosphorus, and many other nutrients are stored, transformed, and cycled through soil.
• This is a good thing for it keeps them out of our water systems.
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5) Supporting Structures
Buildings need stable soil for support, the bearing capacity determines the ease of stable construction.
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Deforestation
• The main contributors to land degradation are erosion and soil compaction, as a result of extensive removal of vegetation, exposure of the soils to heavy rainfall, increased evaporation, and later wind action.
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Agriculture
• Agriculture may last for a few hundred of years or it may last for thousands of years.
• Agave production on these fields in Mexico may last for fewer than 50 years due to soil erosion which results in the loss of valuable topsoil.
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Water Erosion
• Water erosion is the wearing away of soil particles.
• Raindrops detach the soil particles.
• As infiltration is reduced, water moving down slope takes the soil with it.
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Wind Erosion
• Wind erosion is the detachment of soil particles by the wind and moving them to another location.
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Chemical Degradatio
n• Chemical spills
can pollute the soil beyond which it can recover naturally.
• Soil remediation can reclaim the soil, making it useful again.