forestry

Soil structure is the way soil particles aggregate together into what are called peds. Peds come in a variety of shapes depending on the texture, composition, and environment.

1. Spheroidal: Granular structure consists of spheroidal peds or granules that are usually separated from each other in a loosely packed arrangement. When the spheroidal peds are especially porous, the term crumb is sometimes used. They typically range from less than to greater than 10mm in diameter.

Granular and crumb structures are characteristics of many surface soils (usually A horizons), particularly those high in organic matter. Consequently, they are the principal types of soil structure affected by management. They are especially prominent in grassland types of soils that have been worked by earthworms.

2. Platy: Platy structure, characterized by relatively thin horizontal peds or plates, may be found in both surface and subsurface horizons. In most instances, the plates have developed as a result of soil-forming processes. However, unlike other structure types, platy structure may also be inherited from soil parent materials, especially those laid down by water or ice. In some cases compaction of clayey soils by heavy machinery can create platy structure.

3.Blocky: Blocky peds are irregular, roughly cube like, and range from about 5 to 5omm across. The individual blocks are not shaped independently, but are moulded by the shapes of the surrounding blocks. When the edges of the blocks are sharp and the rectangular faces distinct, the subtype is designated angular blocky. When some rounding has occurred, the aggregates are referred as sub-angular blocky. These type are usually found in B horizon, where they promote good drainage, aeration, and root penetration.

4.Prismatic: Columnar or prismatic structure are characterized by vertically oriented prisms or pillar like peds that vary in height among different soils and may have a diameter of 15omm or more. Columnar structure, which has pillars with distinct, rounded tops, is especially common in subsoil high in sodium. When the tops of the prisms are relatively angular and flat horizontally, the structure is designated as prismatic. Both prisms like structures are often associated with swelling types of clay. They commonly occur in sub-surface horizons in arid and semiarid regions and, when well developed, is a very striking feature of the profile. In humid regions prismatic structure occurs in poorly drained soils and in frangipanes.


Water logging is when the soil surface area becomes saturated; soil pores are full of water. Excess water can’t drain away.
Reasons:
• Heavy rain
• Poor drainage
• Poor irrigation management
• Rising water table
• Undulated land form

Control measures:
• Drain out water
• Land filling
• Water tolerant
• Wetland management
• Good irrigation facilities