Why is sodium (Na) included in my soil report?

When you send out your yearly soil sample for testing, SoilKit sends back your analysis results with the levels of many elements such as potassium and phosphorus that are essential nutrients for healthy plant growth. These insights let you know which nutrients are deficient, what fertilizers are needed for the year, and how much should be applied. However, one element included in soil testing is not normally required for plant growth: sodium (Na). This element is never deficient in the soil and is never applied as a soil amendment. So why do we test for it?

There are two main reasons why it's helpful to test soil for sodium levels. One reason is to check for excessively high sodium, and the other is for calculations related to your soil's overall health.

Soils with excessive sodium levels relative to calcium and magnesium (i.e. >15% CEC saturation) are officially termed sodic soils and are also known as black alkali soils or slick spots. These soils are quite challenging for plant growth due to the detrimental impacts of sodium on soil health. Sodium dramatically disrupts soil structure by dispersing soil particles and preventing aggregate formation, creating soils that water cannot penetrate. Further, sodium can interfere with nutrient and water uptake by plant roots and cause salt stress. Sodic soils usually cause obvious symptoms such as crusty soils, ponding water, and distressed plants, but soil testing is important for diagnosis and treatment. You can read more about sodic soil managment in this article from the University of California Agriculture and Natural Resources.

In more typical soils with low sodium levels, it's still important to include sodium in soil testing because it's needed for the calculation of cation exchange capacity (CEC). Total CEC is determined based on the amounts of all exchangable (easily available) cations in the soil, including calcium, magnesium, potassium, and sodium. Click here for an article from Ohio State University explaining the details of how this calculation works. The important thing to know is that higher CEC is associated with improved soil health since it indicates a greater potential for absorbing, retaining, and providing essential plant nutrients.

With SoilKit, you can gain insights into the health of your soil through lab test results and by discussing any questions about your soil report with our team of experts. If you're concerned about your soil's sodium levels or any other issue, reach out to us today through your SoilKit365 dashboard.