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Soil Types: How Water Is Absorbed

Jule Romans has over 30 years of experience researching and writing on educational topics. She presently works in State Government.

Understanding how soil types affect the amount of water absorbed begins with learning the basics of soil texture. Some soil types can absorb and hold moisture like rich chocolate cake, while others resist water like the surface of a saltine cracker. This analogy helps to explain soil structure.

How Different Soil Types Absorb Water

Take a quick look at any puddle, and it’s a sure bet that you can learn something about the type of soil underneath. Water pools on top of some soil types, but sinks easily into others.

Why does this happen? It happens because of the composition of the soil. To put it more simply, it happens because of the combination of "ingredients" in the soil.

Soil Ingredients Affect Water Absorption

Soils have ingredients in much the same way that baked goods have ingredients. When those ingredients are combined in different ways, the results can be quite different. Some soil types can absorb and hold moisture like rich chocolate cake, while others resist water like the surface of a saltine cracker.

Understanding how soil types affect the amount of water absorbed begins with learning the basics of soil texture.

A good way to understand soil types is to think about baked goods. Chocolate cake and saltine crackers actually do bear some similarity to soil types and soil textures.

Soil Texture

A good way to understand soil types is to think about baked goods. Chocolate cake and saltine crackers actually do bear some similarity to soil types and soil textures.

Think about it this way. When certain ingredients are combined in a recipe, they interact with liquids to create a final product. That final product can be light and fluffy like chocolate cake, or solid and dense like a saltine cracker.

Soil types affect the amount of water absorbed in much the same way that the balance of ingredients affects the overall quality of baked goods. In both cases, it is the way the ingredients fit together that determines the texture of the final product.

Chocolate cake and saltine crackers are very different, but they both involve a combination of somewhat similar ingredients. What makes the difference is the size, shape, and density of the particles (or ingredients) in each.

Soil Ingredients

In baked goods, flour combines with yeast or other ingredients to create small pockets of air that make a light, fluffy confection. If there is not enough air, the resulting product will be dense and thick.

The principle is the same for soil.

The ingredients of soil, however, are particles of crushed rock combined with organic matter or other substances. As the ingredients settle or mix, they incorporate varying amounts of empty space, or air.

Closely compacted soils allow very little room for air and therefore tend to resist taking in water. Soils with plenty of space and air mixed in more readily absorb and hold liquid.

In baked goods, flour combines with yeast or other ingredients to create small pockets of air that make a light, fluffy confection. If there is not enough air, the resulting product will be dense and thick. The principle is the same for soil.

Soil Porosity

As soil particles fit together, they leave small pockets, called pores. These pores, not the particles themselves, fill with water. Particle size and porosity are keys to the texture of soil.

Like chocolate cake, soils with many larger pores will have many places to store moisture. Like a saltine cracker, soils with fewer, smaller pores will have less space for water to stay.

Soil Particles

Soil is composed of millions of small particles of differing sizes. Every soil particle falls into one of three categories, based on its size.

According to Michigan Technical University, clay particles are smallest, measuring under .002 mm. Sand particles are largest, measuring up to 2 mm. Silt particles occupy the middle range. The term “gravel” applies to particles that are from 2 mm to 75 mm in size, but gravel alone is not considered a type of soil.

Loam is the term used to encompass a whole category of soil that is composed of a balance of the three basic types.

Soil Types

Every possible combination of the three main types of particles has its own name, category and identifying features.

Names for soil types include sandy clay, clay silt, silt loam, clay loam, and many other variations. Each type absorbs and holds different amounts of water.

Silty clay soil is closest to the saltine cracker. Rich clay loam would be most similar to the example of chocolate cake.

Soil particle size

Soil particle size

Like chocolate cake, soils with many larger pores will have many places to store moisture. Like a saltine cracker, soils with fewer, smaller pores will have less space for water to stay.

Water Absorption

Soils high in clay tend to be quite dense, so puddles may remain on their surface for a long time.

Soils that contain a balance of clay, silt and sand are lighter and almost fluffy. Puddles do not last long, because the water quickly absorbs into the pores between soil particles.

The balance of ingredients, or texture, determines the amount of water absorbed

References

  • Estimating Soil Texture by Feel. West Texas A & M University. Published by the Texas A&M Agrilife Research Extension at San Angelo. Accessed February 22, 2020.
  • Tech Alive: Soil Particle Size. Michigan Technical University. Published in the Michigan Environmental Education Curriculum Groundwater Supply. Accessed February 22, 2020.
  • Water Holding Capacity by Soil Type. Spectrum Technologies. PDF available. Accessed February 22, 2020.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2020 Jule Romans