How to Test the Porosity of Soils

Written by catherine duffy
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Sandy soil is composed of large, coarse, rapidly-draining particles. Clay soil is made up of fine particles, which when compacted, causes soil to become waterlogged. A grower who knows the porosity of his soil adds drainage systems, compost or a combination of the two in order to improve their soil's structure. A touch test is one way to determine soil's porosity. Clay soil is rolled into a ball and flattened. Sandy soil crumbles and won't hold shape when pressure is released. Soil that doesn't fit into either of these strict categories can also be tested.

Skill level:
Moderately Easy

Things you need

  • Garden spade
  • Water delivery system (bucket, hose)

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  1. 1

    Locate an empty, partially shaded, unpaved area. The spot should be free of roots.

  2. 2

    Conduct the test in the morning to avoid water loss through air evaporation.

  3. 3

    Dig a hole approximately one to two feet deep.

  4. 4

    Fill the hole with water.

  5. 5

    Check the water after several hours. If the water has not been absorbed, then the soil is clay and should be appropriately amended with soil additives, such as compost, to improve the soil's structure. If the hole is empty and the soil is not moist to the touch then the soil is large pored (sandy) and should also be amended.

  6. 6

    Push the garden spade handle into the bottom of the water-filled hole. If the ground does not give, then a layer of hardpan is beneath the topsoil. A drainage system or soakaway should be put in place.

Tips and warnings

  • Soil that does not drain well should be amended with wood chips, bark, or other organic compost material. This material absorbs moisture and is a good breeding ground for earthworms which help aerate compacted soil.
  • Sandy soil benefits from organic compost as well. Wood, bark and other materials help retain water.

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