The range of soils

This illustration shows the size variance of particles from gravel through to clay.

 

Most agriculture applications have soil that ranges between sand (light) and clay (heavy).

Water moves very differently depending on the soil – clay content. As the illustration below shows, water application in soils with high clay content moves slowly and with greater lateral movement, compared to soils with a high sand content.

Note that the sandy soil illustration shows just 24 hours to reach the depth of 183 cm. It takes 48 hours, double the time, for the water to reach this depth with the clayey soil.

Water spread and penetration time and distance in sandy and clay soils. David Whiting (2011)

 

As you want the water to stay around the root zone, more sandy soils require shorter irrigation times, with closer dripper spacing. It is the opposite for more clayey soils, where the challenge is a slower infiltration rate into the soil.

The soil type also impacts on the field capacity, wilting point and available moisture

Percentage of water content by soil type


The available moisture is the difference between field capacity and permanent wilting point.

To recap the information above, we have two major areas of consideration in relation to irrigation.

  • Soil infiltration (intake)

  • The more sandy the soil, the less the water will move laterally (width), so drippers will need to be closer together.
  • The more sandy the soil, the faster the water will move down and risk being lost outside of the active root zone. Irrigation should be shorter and more frequent.
  • As the intake of heavy soils is slower, if the application is too high, the soil does not have enough time to take in the water and run-off will occur. Slower, longer irrigation is required.  

 

  • Soil moisture tension
  • The heavier the soil, the more difficult it is for plants to extract the available water. Therefore, a higher water content is required.
  • As heavier soils retain their water for longer, you irrigate less frequently.  

 

Explore the next module, or search for a specific topic or issue.

Module 2

Overview of drip irrigation systems & components

Module 3

Design, installation and startup

Module 4

Maintenance

Before using these modules, please familiarize yourself with the relevant disclaimers and additional safety and usage information contained within each module.

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