Sodium Adsorption Ratio, Irrigation, and Soil Health
What Does High SAR Mean For Your Garden?
Are you watering your plants to no avail?
As we see all-to-often in the results of our water quality testing, not all water is created equal. In fact, the chemistry of your irrigation water can be affecting your soil and the plants that depend on that soil for moisture and nutrients.
Because water is a complex mixture of both organic and inorganic chemicals, there can be a large variation in your water’s general properties. One such general property is the “sodium adsorption ratio” (SAR). While high SAR is not ultimately an issue of human health, it does have some other consequences–namely when it comes to your garden.
In this Tips for Taps piece, we ask (and answer) the following questions:
What Is Sodium Adsorption Ratio (SAR)?
Note that the resulting solution to the SAR equation is unitless (because it is a ratio). If you want help understanding this equation, reach out to us and ask firstname.lastname@example.org or search on wikipedia.
How Do I Know If My Water Has A High SAR?
Like most important water parameters, the only way to know your water quality is to test it with Tap Score or any other certified lab.
Along with your water’s SAR evaluation you’ll get a professional water quality analysis including irrigation quality and a detailed health/pipe risk analysis. If necessary, you’ll also be able to filter among unbiased water treatment product recommendations, personalized to your Tap Score report. Our team of water treatment experts, chemists, and engineers can help you identify your SAR levels and better understand your water quality overall along with how to treat it if necessary.
Why is SAR Important?
SAR indicates the suitability of water for use in agricultural irrigation. High levels of sodium ions in water affect the permeability of soil and can lead to water infiltration issues. While the impact severity of high SAR water depends on many specific soil quality factors (such as soil type, texture, drainage capacity, etc), typically the higher the SAR, the less suitable the water is for irrigation.
If your water has a high SAR, that generally means sodium in your water will cause hardening and compaction of your soil. This will reduce infiltration rates of both water and air. Additionally, the increased salinity reduces the availability of water in storage which can be very important for a plant’s growth and resilience (especially if you’re one who forgets to water sometimes).
Aside from decreased water infiltration and availability, high SAR may also lead to temporary over-saturation of surface soil, high pH, soil erosion, inadequate nutrient availability, and increased risk of plant diseases.
Can I Water My Plants If My Water Has A High SAR?
Typically, water with a SAR below 3 is fine for irrigating grass and other common ornamental landscape plants. Alternatively, water that has a SAR greater than 9 may cause significant permeability problems. This is even more true if you have fine-textured soil (like a silty-loam). Want to find out what texture your soil is? This test here can help: Advanced Soil Test.
Coarse-textured (i.e sandy) soils, on the other hand, are typically less susceptible to permeability problems and SAR-related issues. For those types of soils, the irrigation water's SAR can be slightly higher with no major impact.
Crops very sensitive to SAR and typically handle SAR values form 2-8 include:
Crops moderately sensitive to SAR and typically handle SAR values of 8-20 include:
Crops moderately tolerant to SAR and typically handle SAR values of 20-50 include:
Crops tolerant to SAR and typically handle SAR values of 50-100 included:
What To Do About Water With High SAR?
While high SAR water can be used for irrigation purposes, soil may require amendments to prevent long-term damage.
An amendment, such as gypsum, when added to soil or water will increase the calcium concentration in the water. Subsequently, this reduces the SAR as the sodium to calcium ratio is also reduced.
However, it’s important to note that if infiltration is poor due to adverse soil texture, compaction, or a high water table–gypsum won’t lead to any major improvements.
Alternatively, you can also install a whole-home reverse osmosis system–although it is a pricier option. We recommend testing your water first in order to ensure that you make the right choice (and don’t spend money unnecessarily). The Tap Score team of chemists and water quality experts are always ready to her. Reach out here anytime!