Soil provides a foundation for all life that is above ground. Geologists study a number of physical and chemical characteristics of soil, including its peds. These peds are a physical aspect of the soil that describe the structure of the soil. Soil consists of the following ped types: granular, blocky, prismatic, columnar, platy, single grained and massive.
Granular
Granular soil is typically less than 0.5 cm in diameter and looks a lot like cookie morsels. Granular structures are spherical and have bowed surfaces that aren’t molds of bordering peds. Granular soil is typically found in areas where there are abundant grasslands as well as in modified garden soils that contain organic matter. Granular is easy to work as its elements are divided and linked by soil biota exudates and organic matter materials.
Blocky
Blocky peds are asymmetrical blocks that are typically between 1.5 and 5.0 cm in diameter. These peds are surrounded by flat surfaces that mold the features of nearby soil structures. Blocky structures are equidimensional and pointed blocky if the surfaces cross at sharp angles. Subangular blocky soil occurs if the surfaces are rounded and plane with curved corners. This type of structure is typical in subsoil and surface soils that contain large amounts of clay.
Prismatic
Prismatic soil is typically found in lower spheres, and there are upright lines of soil that can be varying lengths. Prismatic structures are single elements that are surrounded by flat or rounded perpendicular surfaces. The elements are molds of surrounding elements, but are also unique as prismatic structure is longer perpendicularly.
Columnar
Columnar peds are typically found in soils of dry climates, and consist of upright lines of soil with salt sop. Columnar structures are elements that are surrounded by flat or round perpendicular surfaces and are comparable to prisms. The tops of columnar structures are unique, as they are rounded. Typically columnar peds are found in subsoil containing sodium and soils plentiful in swelling clays. These peds are quite dense, and this makes it challenging for roots to go through.
Platy
Platy peds are typically found in compressed soil and are thin, flat, straight plates of matter. Typically, platy peds are found in subsurface soils that are compressed by animals and/or machinery. Platy structures can be separated easily and have a tendency to delay the descending transfer of water and roots in the soil.
Single Grained and Massive
Single grained peds are generally found in sandy soils, and are very movable so it’s easy to break single grained structures into smaller elements. Typically, these particles don’t stick together. Massive soil is hard to break apart and is found in very large clods. There is no visual structure for this ped type.
Soil ped types provide the building blocks for the foundation that supports structures on dry land. Understanding the characteristics of each ped type is critical to many disciplines, including geology and architecture.
Sources:
NASA: Soil Structure (accessed 12/7/2010)
University of Montana: Getting Down and Dirty with Soils (accessed 12/7/2010)
University of Arizona: Soils Glossary (accessed 12/7/2010)
Purdue University: Soil and Landscape Properties (accessed 12/7/2010)
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