Don’t be salty: Testing for soil salinity

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Updated Apr 30, 2019

Gloved hands holding soilWhen maintaining and creating your customer’s ideal landscape, sometimes you can encounter issues with the soil in the area.

One common problem landscapers face is high soil salinity, which means there is a significant amount of soluble salt in the soil. If you work in an area that’s frequently plagued with saline soils, take a look at what you need to do to properly test the salinity, as well as how you can treat it.

Saline soils

Salinity measures the soluble salts in the soil, and salinity is measured by water extracted from the soil. When soil is too saline, it can cause problems for plants because it makes it much more difficult for them to extract and absorb water from the soil.

According to extension.org, plants are able to concentrate solutes in their roots to increase water absorption from the soil, but when planted in highly saline soils, plants aren’t able to compete for water.

There are numerous reasons why soils can test positively saline, such as the naturally occurring presence of salt in the soil’s parent material, or it could be because of watering and irrigation with high-salt water.

Extension.org says that short but frequent irrigation can lead to an accumulation of salts because the water never percolates below the root zone, carrying excess amounts of salt with it.

Applying excessive applications of fertilizers or other salt-containing materials can also attribute to soil becoming saline, and run-off from roads and sidewalks that may contain de-icing materials has also been known to add to soil’s salinity.

Testing and sampling for salinity

Testing soil for salinity levels can be fairly easy and inexpensive, and it can be done in the spring or fall. Testing in the spring will more than likely be the better option, as this will help you determine the needs of the plants before the growing season begins.

“Plan ahead by contacting the laboratory that will analyze the soil to find out how much time it will take to receive the results, and allow time for implementation of fertilizer recommendations and corrective measures,” extension.org says online.

Extension.org also recommends the following tactics for analyzing the soil:

  • Use an auger-like device or soil probe/tube
  • Scrape away surface litter
  • Sample the soil from the surface down to 12 inches (turf areas can be sampled from zero inches to 6 inches)
  • Be sure the sample is representative – in other words, obtain equal amounts of soil from each sampling increment.
  • Multiple soil samples should be collected from any one given area
  • Composite into one sample to minimize the cost of analysis

During the process of compositing multiple samples into one, it’s important to thoroughly homogenized the soil, then from that take a subsample to submit for analysis.

“Soil salinity levels below 1 dS/m (deciSeimens per meter) are normal in the arid west,” extension.org says online. “Salinity values above 2 dS/m will cause difficulties for salt-sensitive plants, such as beans, carrots, corn, lettuce, sugar maples and Scotch pine. Soil salinity levels above 4 dS/m are problematic for a large variety of landscape and garden plants.”

Treatment

If you find that your soil is saline because of the salinity of its parent materials, it may not be possible to change it. This is because minerals found in the soil will be inherently high in salts, and when the minerals are leached with water, they will continue to release more salts back into the soil.

According to extension.org, most reclamation approaches to treating saline soil involve flushing, or leaching, the soil with clean, pure water.

“Sufficient water must be applied to dissolve the excess salts that have accumulated and cause them to percolate/flow out of the soil profile, particularly the root zone,” extension.org says online. “To accomplish this leaching of salts, adequate drainage is requisite. Once good drainage is assured, the soil can be irrigated with clean water. Run-off should be avoided to prevent erosion.”

Extension.org says the rate of infiltration will determine how quickly water can be applied, and this rate will depend on the type of soil. For fine-textured soils, the infiltration rate will be slower than it would for coarse-textured soils.

To begin, extension.org recommends applying 6 inches of water to reduce salinity by 50 percent and 12 inches of water to reduce the salinity by 80 percent. For sloped areas, it’s recommended to use irrigation via sprinklers, but if you see it’s necessary, flood irrigation can be used on areas that are level.

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