Check source water used in greenhouse and nursery operations and correct any SAR (sodium adsorption ratio) problems.
Water used in plant production, including greenhouse-grown tobacco transplants, should have an SAR value of 4 or less. For ornamental plants in a nursery setting, SAR values of 10 or greater are cause for concern. High SAR values are most common for water samples from coastal areas.
A high SAR value on a solution analysis report indicates an imbalance among sodium (Na), calcium (Ca) and magnesium (Mg) cations. This imbalance can cause leaf burn due to foliar adsorption of Na. In mineral soils, this imbalance can also lead to poor soil structure, which hinders infiltration of water. In soil-less container media, however, this effect is negligible.
The best way to reduce SAR to the desired level is to add calcium from a source such as gypsum.
To calculate the amount of gypsum needed to reduce SAR to 4, follow these steps.
Calculate the amount of calcium required in parts per million (ppm). Ca needed = 0.004725 Na2 - 1.64 Mg - Ca, where Na, Mg and Ca are the ppm concentrations listed on the Solution Report.
Calculate the appropriate rate of gypsum (22% Ca) to apply by inserting the Ca needed value from step 1 into the following equation. Ca needed × 0.0607 = ounces gypsum per 100 gallons of water
For more information, contact or visit the NCDA&CS Agronomic Division:
Physical Address: 4300 Reedy Creek Road, Raleigh NC 27607-6465
Mailing Address: 1040 Mail Service Center, Raleigh NC 27699-1040
Phone: (919) 733-2655