Editing Soil structure (section)

==Types==

The main types of soil structures are:
* Platy – The units are flat and platelike. They are generally oriented horizontally.<ref name=USDA>{{cite book |editor=C. Ditzler |editor2=K. Scheffe |editor3=H.C. Monger |date=2017 |title=USDA Soil Survey Manual |chapter=Examination and Description of Soil Profiles §Soil structure |chapter-url=https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054253#soil_structure |archive-url=https://web.archive.org/web/20180907145549/https://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/ref/?cid=nrcs142p2_054253#soil_structure |archive-date=2018-09-07 |publisher=Government Printing Office |location=Washington, D.C. |access-date=2 November 2019}}</ref>
* Prismatic – The individual units are bounded by flat to rounded vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct and normally flat.<ref name=USDA/>
* Columnar – The units are similar to prisms and bounded by flat or slightly rounded vertical faces. The tops of columns, in contrast to those of prisms, are very distinct and normally rounded.<ref name=USDA/>
* Blocky – The units are blocklike or polyhedral. They are bounded by flat or slightly rounded surfaces that are casts of the faces of surrounding peds. Typically, blocky structural units are nearly equidimensional but grade to prisms and plates. The structure is described as angular blocky if the faces intersect at relatively sharp angles and as subangular blocky if the faces are a mixture of rounded and plane faces and the corners are mostly rounded.<ref name=USDA/>
* Granular – The units are approximately spherical or polyhedral. They are bounded by curved or very irregular faces that are not casts of adjoining peds.<ref name=USDA/>
* Wedge – The units are approximately elliptical with interlocking lenses that terminate in acute angles. They are commonly bounded by small slickensides.<ref name=USDA/>
* Lenticular —The units are overlapping lenses parallel to the soil surface. They are thickest in the middle and thin towards the edges. Lenticular structure is commonly associated with moist soils, texture classes high in silt or very fine sand (e.g., silt loam), and high potential for frost action.<ref name=USDA/>

===Platy===

In platy structure, the units are flat and platelike. They are generally oriented horizontally. A special form, lenticular platy structure, is recognized for plates that are thickest in the middle and thin toward the edges. Platy structure is usually found in subsurface soils that have been subject to leaching or compaction by animals or machinery. The plates can be separated with a little effort by prying the horizontal layers with a pen knife. Platy structure tends to impede the downward movement of water and plant roots through the soil.

They are found most frequently in the C, E, Bs and K [[soil horizon|horizon]]s as well as in [[sesquioxide]]s (very old soils that are rich in iron and magnesium).

===Prismatic===

In the prismatic structure, the individual units are bounded by flat to rounded vertical faces. Units are distinctly longer vertically, and the faces are typically casts or molds of adjoining units. Vertices are angular or subrounded; the tops of the prisms are somewhat indistinct and normally flat. Prismatic structures are characteristic of the B horizons or subsoils. The vertical cracks result from freezing and thawing and wetting and drying as well as the downward movement of water and roots.

===Columnar===

In the columnar structure, the units are similar to prisms and are bounded by flat or slightly rounded vertical faces. The tops of columns, in contrast to those of prisms, are very distinct and normally rounded. Columnar structure is common in the subsoil of sodium affected soils and soils rich in swelling clays such as the [[smectites]] and the kandite [[Halloysite]]. Columnar structure is very dense and it is very difficult for plant roots to penetrate these layers. Techniques such as deep plowing have helped to restore some degree of fertility to these soils.

===Blocky===

In blocky structure, the structural units are blocklike or polyhedral. They are bounded by flat or slightly rounded surfaces that are casts of the faces of surrounding peds. Typically, blocky structural units are nearly equidimensional but grade to prisms and to plates. The structure is described as angular blocky if the faces intersect at relatively sharp angles; as subangular blocky if the faces are a mixture of rounded and plane faces and the corners are mostly rounded. Blocky structures are common in subsoil but also occur in surface soils that have a high clay content. The strongest blocky structure is formed as a result of swelling and shrinking of the clay minerals which produce cracks. Sometimes the surface of dried-up sloughs and ponds shows characteristic cracking and peeling due to clays.

===Granular===<!-- This section is linked from [[Seedbed]] -->
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In the granular structure, the structural units are approximately spherical or [[Polyhedron|polyhedral]] and are bounded by curved or very irregular faces that are not casts of adjoining peds. In other words, they look like cookie crumbs. Granular structure is common in the surface soils of rich [[grasslands]] and highly amended garden soils with high [[organic matter]] content. Soil mineral particles are both separated and bridged by organic matter breakdown products, and [[soil biota]] exudates, making the soil easy to work. [[Tillage|Cultivation]], [[earthworms]], [[frost action]] and rodents [[bioturbation|mix]] the soil and decrease the size of the peds. This structure allows for good [[porosity]] and easy movement of air and water. This combination of ease in [[tillage]], good moisture and air handling capabilities, and good structure for planting and [[germination]], are definitive of the phrase ''good tilth''.