Fundamentals of Soil Science (1+1)

Types of Soil Structure

Types of Soil Structure:

• Aggregation of soil particles can occur in different patterns, resulting in different soil structures.
• Based on the shape and arrangement of peds or aggregates, soil structure is classified into four principle type –plate like, prism like, block like and spheroidal structure.

1. Plate like:

• 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.Plates often greatly impair water circulation.
• It is commonly found in forest soils, in part of the A- horizon, and in claypan soils. Platy structure if often formed from parent materials and can also results due to compaction of heavy machinery on clayey soils. When the units/ layers are thick they are called “ platy” and when they are thin then it is “ laminar”

2. Prism-like:

• In prism like structure, the vertical axis is more developed than horizontal, giving a pillar like shape. They are commonly found in the subsurface horizons of semiarid and arid regions.
• The prisms having rounded tops are called columnar and mostly occur in subsoils of salt-affected soils. When the tops are flat or level the structure is termed as “ prismatic”.

3. Block like:

• The structure is blocky when soil particles cling together in nearly square or angular blocks having more or less sharp edges.
• The peds have sizes varying from 1 cm to 10 cm. There are two types- angular blocky and sub-angular blocky. In the former, the edges are relatively sharp, whereas in later the edges are rounded.
• They are commonly found in the B-horizon where clay has accumulated.

4. Spheroidal:

• Here the individual particles of sand, silt and clay are grouped together in small, nearly spherical grains. These rounded complexes usually loosely arranged and readily separated.
• When the peds or aggregates are relatively non-porous, they are called granules and porous granules are termed as crumbs. They are commonly found in the A-horizon of the soil profile.

Class of soil structure:

• The class of structure describes the average size of individual aggregates. Usually, five distinct classes may be recognized in relation to the type of soil structure from which they come. They are: Very fine or very thin; Fine or thin; Medium; Coarse or thick; Very coarse or very thick.
• The terms thin and thick are used for platy types, while the terms fine and coarse are used for other structural types.