SOIL AND PLANT ANALYSIS (1+1)

Types of Structure

There are four principal forms of soil structure
1)Plate-like (Platy)

• In this type, the aggregates are arranged in relatively thin horizontal plates or leaflets.
  
• The horizontal axis or dimensions are larger than the vertical axis.
• When the units/ layers are thick they are called platy
• When they are thin then it is laminar.
• Platy structure is most noticeable in the surface layers of virgin soils but may be present in the subsoil also.
  
• This type is inherited from the parent material, especially by the action of water or ice.
2)Prism-like

• The vertical axis is more developed than horizontal, giving a pillar-like shape.
• Vary in length from 1- 10 cm.
• Commonly occur in sub soil horizons of arid and semi arid regions.
• When the tops are rounded, the structure is termed as columnar and when the tops are
flat / plane and clear cut, it is called as prismatic structure.
3) Block-like

• All three dimensions are of almost the same size.
• Irregularly six faced with their three dimensions more or less equal.
• When the faces are flat and distinct and the edges are sharp angular, the structure is named as angular blocky.
• When the faces and edges are mainly rounded it is called sub angular blocky.
• These types usually are confined to the sub soil and their characteristics have much to do with soil drainage, aeration and root penetration.

4)Spheroidal (Sphere-like)

• All rounded aggregates (peds) may be placed in this category.
• Not exceeding an inch (2.5 inch) in diameter.
• These rounded aggregates are usually loosely arranged and can be readily separated.
• When wetted, the intervening spaces generally are not closed so readily by swelling as may be the case with a blocky structural condition.
• Therefore in sphere-like structure, infiltration, percolation and aeration are not affected by wetting of the soil.
• The aggregates of this group are usually termed as granular when they are relatively less porous.
• When the granules are very porous, they are termed as crumbs.
• This is specific to the surface soil, particularly, high in organic matter/ grass-land soils.
5)Granular

• Resembles biscuit crumbs and is usually less than 0.5 cm in diameter. Commonly found in surface horizons where roots have been growing.
6)Single Grained

• Soil is broken into individual particles that don not stick together. Always accompanies a loose consistency. Commonly found in sandy soils.
7)Massive

• Soil has no visible structure, is hard to break apart and appears in very large clods.



8)Wedge structure

• Elliptical Interlocking lenses that terminate in acute angles, bounded by slickensides. This structure is not limited to Vertic Martials or Vertisols. Also present in soil with high clay content and with expanding clays.