Soil assessment

March 19, 2018 -  By

Did you know different types of dirt impact the effectiveness of an irrigation system? How quickly a soil type can absorb water will help you determine what kind of irrigation to set up, according to Jeffrey Knight, Ewing’s director of learning and development.

Take a look at the different kinds of soil and their maximum precipitation rates, according to the U.S. Department of Agriculture.

Maximum Precipitation Rate (inches per hour)

Soil Type 0-5% slope 5-8% slope 8-12% slope
cover bare cover bare cover bare
Coarse sand 2 2 2 1.5 1.5 1
Uniform light sandy loam 1.75 1 1.25 0.8 1 0.6
Uniform silt loam 1 0.5 0.8 0.4 0.6 0.3
Heavy clay or clay loam 0.2 0.15 0.15 0.1 0.12 0.08


Clay soils have a low infiltration rate, which means they have a higher risk for runoff.

“Clay soils hold lots of water, but it takes a long time for the water to infiltrate into the soil, so runoff is an issue if the water is applied too fast,” says Knight.

To properly irrigate around clay soils, be sure the water is being applied at a slow, steady rate to avoid flooding the area and wasting water. Knight suggests using rotary type heads with low precipitation rates for best results when working with clay.


Sandy soils react exactly the opposite of clay soils in that they have a high infiltration rate, which means a low holding capacity.

“Sandy soils don’t hold much water, but they do allow it to pass through quickly,” says Knight.

Because of this, sandy soils need to be watered more frequently, but not for long periods of time. Visual observation to see how the soil reacts to water plays a key part in helping to determine what kind of irrigation system is best to use.

Drought-tolerant plants thrive in sandy soils, and if possible, Knight suggests working to match these types of plants with this soil.


Silt is the final soil type. Its infiltration rate is not considered high or low, but in between. Knight says the best way to determine what kind of irrigation system is best for this soil type involves visually observing how quickly the soil is absorbing the water.

“Silty soils can often handle runtimes of spray heads up to 10 minutes,” Knight says. “But before making a final selection, be sure to visually observe the soil’s reaction to water.”


The term loam is used to refer to a mix of clay, sand and silt.

“To know exactly what type of soil you have and to determine the amount of nutrients that are available to the plant material you’re working with, request a soil test,” Knight says.


Kayli Hanley is a former writer for Ewing Irrigation & Landscape Supply. This article originally ran on Ewing’s blog at

This article is tagged with and posted in Irrigation+Water Management

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