Soil Sodium Testing

1. The amount of sodium (Na) in the soil is another important factor in determining its suitability for supporting trees and shrubs because sodium strongly influences water infiltration and soil aeration.

a. Soil Sodium Adsorption Ratio - Soil sodium hazard is best described by the Sodium Adsorption Ratio (SAR), an indication of the likelihood of reduced soil permeability (water infiltration) and aeration, especially on heavy-textured (clay) soils. A soil SAR >13 suggests a likelihood of reduced soil permeability and decreased plant survival and growth.

b. Exchangeable Sodium Percentage - Another useful indicator of potential soil sodium hazards is Exchangeable Sodium Percentage (ESP). ESP measures the amount of soil exchange capacity occupied by sodium and expressed as a percentage. As the ESP goes up, more exchangeable sodium is available, and the greater the potential for negative plant and soil impacts. An ESP >15% indicates that soil sodium will probably limit permeability.

2. Soil Sodium Management Options. What corrective actions, if any, can be taken if your soil sodium level indicates that there is likely to be a problem growing trees and shrubs? Attempting to use leaching to remove excess sodium can actually result in higher exchangeable sodium and soil pH, two undesirable side-effects. To prevent this, sodium must first be displaced from soil exchange sites by adding calcium to the soil in the form of gypsum. After application of the gypsum, the profile can then be leached of sodium salt by-products to prevent an increase in overall soil salinity. It is recommended that landowners consult agriculturists, their local county extension agent, or their local USDA Natural Resources Conservation Service office for specific recommendations on gypsum application.

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Last Modified: 10/10/2007