Current peanut calcium recommendations can be confusing to growers because they differ by state.

However, cooperative research between Alabama and Georgia is attempting to fine-tune these recommendations, especially considering the planting of large-seeded varieties.

In Alabama, additional calcium is recommended if levels in a pegging zone soil test — the top 3 to 7 inches of soil — are less than 300 pounds per acre. However, Georgia recommends additional calcium when levels are less than 500 pounds per acre, unless the calcium to potassium ratio is less than 3:1.

“In Alabama, if soil calcium is between 175 and 300, and no lime is required, then you would add about 250 pounds per acre,” says Julie Howe, Auburn University agronomist.

“If the soil calcium is less than 175, then you need to add 250 pounds per acre with lime or 500 without lime. It’s all based on pH. If you don’t need the lime to adjust your pH, then that sets the requirement for gypsum.”

Howe presented peanut calcium research data during a recent certified crop advisor training session held in Auburn.

“In Georgia, they say you need to apply 1,000 pounds of gypsum per acre if soil calcium is less than 500. So we have one set of criteria of about 300 and one of about 500, or they say to apply when the calcium to potassium level is low, and I haven’t seen many fields with a calcium to potassium level of less than 3:1,” she says.

Based on these current recommendations, researchers in Alabama and Georgia began conducting studies looking at calcium requirements for peanuts, especially with newer large-seeded varieties.

The tests evaluated the effect of calcium fertilization and irrigation on the yield, grade and germination of runner peanut cultivars.

“Many of the original studies were conducted 30 years ago with varieties that are no longer planted, and seed sizes for some of the newer varieties are considerably larger,” says Howe.

Several trials evaluating the response of two cultivars of runner peanut (Georgia Green and Georgia-06G) to gypsum applications (0, 500, 1000 and 1,500 pounds per acre) and irrigation were conducted between 2008 and 2010 in south Alabama and Georgia.

Trials were conducted in Coastal Plain soils with pegging zone calcium between 356 and 996 pounds per acre.

“Using the Alabama criterion, none of the soils would have had a calcium fertilization recommendation, but using the Georgia criterion, five of the 14 soils would,” says Howe.

Results from the experiments showed an increase in yield, grade and germination in response to gypsum application when peanuts were grown under dryland conditions, she says.

In contrast, peanut yields in irrigated sites did not respond to gypsum applications, but there was a slight increase in grade and germination.

Thus, the recommendation of adding calcium only when the pegging zone soil had levels less than 300 pounds per acre was adequate for irrigated peanut production but inadequate for dryland production, she reports.