Using Simple Calculations and Calcium (Ca++) to Displace Excess Sodium (Na+) in the Soil.
Sodium Displacement Program
April 12, 2024
Calcium has been used for a long time in agricultural soils to manage excess sodium, and for good reason. As a divalent cation (cation which contains a valence of two, i.e., Ca++) and a higher ranking on the ionic replacement series (Al3+ > H+ > Ca2+ > Mg2+ > K+ = NH4+ > Na+), soluble calcium will readily take the place of excess sodium ions occupying the exchange sites of soil colloids. Moreover, calcium is a known plant-essential nutrient and is abundant and economically available as a soil amendment for widespread use in turfgrass management.
The following are steps to determine how much calcium to apply to displace sodium:
- Determine how much excess sodium is present in your soil by subtracting 100 ppm (mg/kg) sodium from the value on your soil report.
For example, if your soil report contains 150 ppm sodium, your soil contains 40 ppm more sodium than is desired. 150 ppm - 110 ppm = 40 ppm excess sodium.
- Multiply the excess sodium ppm value by 0.04 to obtain pounds of calcium per 1000 sq. ft. needed to displace the excess sodium.
For example, 40 ppm excess sodium x 0.04 = 1.66 lbs calcium needed per 1000 sq. ft.
- Determine how much calcium amendment product is needed.
Granular gypsum products such as TruGyp® contain about 21% calcium. Therefore, the requirement for the example above is: 1.66 lbs calcium per 1000 sq. ft. / 0.21 = 7.9 lbs TruGyp® per 1000 ft. sq. (344 lbs/acre) required to displace 40 ppm sodium.
- What about Liquid Calcium Products?
Several liquid calcium sources are available to accomplish the same process as listed above. To correctly account for the amount of calcium per gallon of product, the bulk density (weight per gallon) will need to be considered. For example, a calcium gluconate product containing 10% Ca weighs 11.3 LBS/gallon, contains 1.13 LBS of calcium per gallon. Therefore, to apply 1.66 LBS of calcium to displace 40 ppm of sodium using this product: 1.66 LBS Ca per 1000 sq. ft. required = 1.5 gallons of liquid calcium gluconate per 1000 sq. ft. Consequently, to treat 3 acres of greens, it would require 196 gallons of liquid calcium gluconate to displace 40 ppm excess sodium.
