What Is the Difference Between Saline & Sodic Soils?
Saline and sodic soils are similar in that each type of soil has too much sodium, which can negatively impact the plants growing in the soil. However, there is a difference between the two, and it is important to correctly identify the issue so that you can take the proper steps to correct the soil.
Saline soils have excessive amounts of soluble salt, while sodic soils have high amounts of exchangeable sodium in the soil itself.
Difference Between Salinity and Sodicity
Although saline and sodic soils have similar problems, they are different conditions with different appearances. High soil salinity levels indicate large amounts of soluble salts, including sodium, potassium, calcium, chloride and magnesium, according to the University of California Davis Global Soil Health Portal. The soil will likely still appear to be of good quality and structure, but you may notice a white crust, and plants will suffer in saline conditions. The excess salt impacts osmotic potential, and soil moisture is held in the soil rather than being absorbed by the plants, advises Oklahoma State University Extension.
Sodic soils, on the other hand, have excessive amounts of sodium on the clay particles of the soil. As a result, the soil degrades, and permeability is reduced, advises University of California Agriculture and Natural Resources. You may notice puddling, dark-colored soil and a crust on the soil surface. In addition to poor soil quality and drainage, the sodium in the soil will compete with calcium, potassium and magnesium and cause nutritional deficiencies in plants.
Saline-sodic soils have both issues. These soils don't tend to have the darker color and poor structure of sodic soil.
Testing for Salinity and Sodicity
Salinity has many potential causes. Natural causes include seawater flooding or a high water level combined with high rates of evaporation and transpiration. Some fertilizers and irrigation water may also contribute to the problem. Although you may suspect that you have saline or sodic soil based on the appearance of the soil and the symptoms of the plants, you should still get a soil test to confirm the diagnosis and determine the severity of the problem.
Contact your local extension office for information on a soil salinity test. Multiple soil samples may be requested from soil depths of 3 to 12 inches, advises Oklahoma State University Extension. A soil sample from a nearby area may be useful for comparison purposes.
The salinity test examines several soil properties, including electrical conductivity, the exchangeable sodium percentage, sodium adsorption ratio and soil pH. Normal soil has an electrical conductivity of less than 4 ds m-1, an exchangeable sodium percentage of less than 15 percent and a sodium adsorption ratio of less than 13 percent, advises University of California Agriculture and Natural Resources. Normal soil also has a good structure and a pH of less than 8.0.
Correcting Soil Salinity
Similar to normal soil, saline soil has an exchangeable sodium percentage of less than 15 percent and a sodium adsorption ratio of less than 13 percent. The readings indicating saline soil include electrical conductivity results that are greater than 4 ds m-1 and a pH level of less than 8.5. Although you may see white salt crusts on the surface, saline soil otherwise has a good structure.
You can reduce soil salinity by using irrigation to reduce the salt concentration in the soil. Make sure to use good-quality water with low salt levels to flush the soil, advises University of California Agriculture and Natural Resources. You can do this by flooding the soil with water and allowing it to continuously pond or by using a sprinkler pond using a smaller amount of water and allowing the soil to dry out between applications. Make sure there is good drainage before beginning this process.
If you consistently have issues with moderate- or high-salinity soils, consider planting salt-tolerant crops and plants. Plants like asparagus and barley are highly tolerant of saline conditions, advises K-State Research and Extension. Other tolerant and moderately tolerant crops include oats, sunflowers, corn and soybeans. Be sure to avoid plants that are sensitive to salt, such as strawberries, peppers, onions and carrots.
Correcting Soil Sodicity
Sodic soil should have an electrical conductivity reading of less than 4 ds m-1, similar to normal soil. However, other results will be abnormal. Results will indicate an exchangeable sodium percentage of greater than 15 percent and a sodium adsorption ratio of greater than 13 percent. The soil will also have poor structure and will be very alkaline with a pH reading of 8.5 or more.
Correct sodic soil by adding soil amendments that will replace the sodium ions with calcium and reduce the soil pH. Use the test results to determine the amount of each element to add to the soil. Gypsum is commonly used to achieve this. Be sure to mix in the gypsum so that all the soil in the plant's root zone is treated.
If the soil already has large amounts of lime or calcium carbonate, use sulfur or sulfuric acid to amend the soil instead. When you add sulfur, soil bacteria oxidize the element to create sulfuric acid, which dissolves the lime so that the calcium is free to replace the sodium. While you can add sulfuric acid directly for quicker results, this is not recommended since it is a dangerous substance to handle.
Saline-Sodic Soil Remediation
If you have saline-sodic soil, the test results will indicate electrical conductivity that is greater than 4 ds m-1 and a soil pH level of less than 8.5, similar to saline soils. The results will also indicate the abnormal results associated with sodic soil – specifically, an exchangeable sodium percentage greater than 15 percent and a sodium adsorption ratio greater than 13 percent. Soil condition and structure for saline-sodic soil varies.
Correct saline-sodic soil using the same methods. First, correct the issue of sodic soil by adding gypsum to the soil. Use sulfur if the soil is high in lime. Once the sodic elements are corrected, flush the soil with low-salt water to correct salinity.
Amending the soil with organic material, such as well-rotted compost, and planting salt-tolerant crops can help improve soil structure and drainage while you work to correct saline-sodic soils. For all of these soil remediation methods, be sure to continue to monitor the soil salinity and sodicity to ensure that you get the desired results.
- University of California Davis Global Soil Health Portal: Salinity
- Oklahoma State University Extension: Interpreting Soil Salinity Analyses
- University of California Agriculture and Natural Resources: Drought Tip - Reclaiming Saline, Sodic and Saline-Sodic Soils
- K-State Research and Extension: Saline and Sodic Soils: Identification and Management
Maureen Malone has been a professional writer since 2010 She is located in Tucson, Arizona where she enjoys hiking, horseback riding and martial arts. She is an outdoor lover who spends her weekends tending her raised garden and small orchard of fruit trees.