Types of Soil Structure

a. Spheroidal:

• All rounded aggregates (peds)
• Not exceeding an inch in diameter.
• Loosely arranged & readily separated; Water/ air circulates very easily through such soils.
• Upon wetting, intervening spaces generally are not closed so readily by swelling- infiltration; percolation & aeration are not affected.
• Relatively less porous spheroidal aggregates-granules; When Very porous spheroidal aggregates- crumb.
• Characteristics of many surface soils (usually a horizon), particularly those high in OM.
• Principal types of soil structures affected by management practices.
• Prominent in grassland soils & soil that have been worked by earthworm.

b. Platy:

• Soil particles arrange in relatively thin horizontal plates.
• Horizontal axis > vertical axis.
• Most notice able in surface layers of virgin soils / forest but may be present in sub soil (E horizon), clay pan soil.
• In most instances, plates develops as a result of soil forming processes, especially by the action of ice or water.
• In some cases, compaction of claley soils by heavy machinery can create plate structures.
• Plates often impair water circulation.

c. Blocklike

• Aggregates are irregular & roughly cube like blocks
• Size range from about 5-50 mm across.
• Individual blocks are not shaped independently, but molded by the shapes of surrounding blocks.
• Blocks are irregularly six faced with their three dimensions more or less equal.
• Angular blocky: faces are flat & edges are sharp angular
• Sub angular blocky: faces & edges are rounded
• Confined to Bt horizon (subsoil); promotes soil drainage, aeration & root penetration.
• Relatively large blocks resist penetration & movement of water.

d. Prismlike:

• Soil structure have prism like / pillar like aggregates (vertical axes > horizontal axes).
• Height of peds varies among different soils & may have a diameter of 150 mm or more.
• Pillars separated by miniature, but definite, vertical cracks.
• Water circulates with greater difficulty & drainage is poor.
• Associated with swelling types clay; commonly occur in sub surface horizons in arid & semi arid regions.
• Columnar structure: pillars with rounded tops, common in sub soils high in Na (natric horizons).
• Prismatic structure: pillars with relatively angular & flat tops; in humid regions, sometimes occurs in poorly drained soils & in fragipans.