Soil Structure

 

Soil Structure, Density, and Porosi Porosity ty Laboratory #4

 

 

Objectives 

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Understand the concept of soil structure and how it differs from soil teture! Understand how soil structure influences other soil properties! Learn how soil structure affects other soil properties structure! and why it is important to maintain soil Learn how land use and mana"ement affects soil structure!  

 

Definition 

Soil structure is the arran"ement of the

primary soil particles sand, silt, and clay$ and other soil materials into discrete a""re"ates!

 

 

Peds 

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Structural units are called peds, and have distinct boundaries and well%defined planes of wea&ness between the a""re"ates! Peds consist of primary particles bound to"ether by cementin" a"ents li&e or"anic matter, clay, and hydrous oides of iron and aluminum! Peds can ta&e several shapes!

 

 

Ped Shapes 

'ranular 

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(loc&y Prismatic  )olumnar  

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Platy  Sin"le%"rained  *assive  

 

'ranular Structure 

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+esembles coo&ie crumbs and is usually less than !- cm in diameter! )ommonly found in

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surface hori.ons where roots have been "rowin"! http/00soils!usda!"ov http/00soi ls!usda!"ov0technical0ma 0technical0manual0ima"es0fi" nual0ima"es0fi"1%12lar"e!jp" 1%12lar"e!jp"

 

 

(loc&y Structure 

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3rre"ular bloc&s that are usually !- % -! cm in diameter! )an be suban"ular or an"ular bloc&y!

 

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Prismatic Structure 

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9ertical columns of soil that mi"ht be a number of cm lon"! Usually found in lower hori.ons!

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)olumnar Structure 

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9ertical columns of soil that have a salt ;cap; at the top! 8ound in soils of arid climates!

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0ima"es0fi"1%: soil crust is a thin soil layer that forms at the soil surface followin" heavy rains!  =illa =illa"e "e or hard pans are hi"h bul& density H!6 

1 "0cm $ layers that occur within the > >p p and  hori.ons! )ompaction caused by traffic of eCuipment, vehicles, or even foot traffic often increases soil s oil

stren"th to levels that restrict root penetration and plant "rowth!

   

Penetrometers 

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=he force reCuired to push a rod into the soil is a measure of soil stren"th! Penetrometers are devices used to measure the resistance of a soil to penetration to estimate the effect of compaction on "rowth, and to detect layers of different soil stren"th! http/00a"news!tamu!edu0dailynews0stories

 

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