What is soil structure? (with photos)

Soil structure helps determine whether a piece of land can support animal or plant life.

Soil structure is the shape that soil takes based on its physical and chemical properties. Each individual unit of soil in the overall structure is called a ped. Soil structure is most easily determined by taking a sample of undisturbed soil and looking closely at its shape. Soil shape will fall into one of the following categories: granular, crumb, block, platinum, prismatic, columnar, plain or solid granulate.

Some plants respond well to sandy soil, and some do not.

Granular soil looks like crumbs. This soil is found where the roots have penetrated the soil. Not to be confused with grated soil, which is very porous. Each individual fragmented soil particle does not fit each surrounding ped because the shape of each individual ped is approximately spherical.

Blocky soil looks like irregularly shaped blocks. The shape of each individual ped is caused by the peds that surround it. Each ped block can be divided into smaller ped blocks.

Platy Solo Peds are thin, flat, and plate-like. They are oriented in the horizontal direction. This structure is commonly found in compacted soil.

Prismatic peds are vertical columns that can be several centimeters long and are found in lower horizons. Columnar Peds are also vertically oriented columns, but they are covered by a “lid” of salt. Columnar soil is found in arid regions of the world.

Soil structure is easily determined by sampling.

Single-grain soils are broken down into individual soil grains that do not clump together and generally remain loosely compacted. This structure is found in sandy soils. The massive soil structure, on the other hand, appears in solid masses and does not have the propensity to break easily under light pressure. This structure is associated with very fine textured soils, such as clay.

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Soils that contain 90% minerals and about 10% organic matter, also called humus, are able to support plant growth well.

Soil structure is determined by many factors, including climate, physico-chemical processes and biological processes. Climatic cycles have a significant effect on soil structure. Freezing and thawing, wet and dry, clay translocation and other various pedogenic – soil-forming – processes affect the entire soil structure to varying degrees throughout the structure. The effects are greatest on the top layer, where the exposure is direct.

Soil structure plays an important role in building a solid foundation.

The phase changes of water – solid, liquid and gas – have a dramatic effect on soil structure. These phases are influenced by soil temperature. Running water causes soil in one location to erode and be deposited in another location. The freeze-thaw and shrink-swell process that the water phase changes determine changes the volume of the soil.

Biological processes include the influences of organisms of various sizes in the soil. The amount of organic matter in the soil is a factor in how the soil aggregates and separates into peds. Animals that live in the soil help to compact the soil in different ways. The secretions of these animals also influence the structure of the soil.

Another consideration when discussing soil structure is the soil’s ability to support plant life. Soils are made up of four different components: minerals, organic matter, air and water. Soils that contain 90% minerals and about 10% organic matter, also called humus, are able to support plant growth well. Soils that contain small amounts of organic materials have a hard time supporting plant life.

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