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.
Re-evaluation of dryland trials with pegging zone soil calcium levels greater than 500 pounds per acre demonstrated there was no additional increase in yield due to applied gypsum, suggesting that this critical value is more appropriate for dryland peanut production.
“We analyzed each study individually,” says Howe.
“We didn’t see a lot of differences using statistics, but we did see a lot of substantive trends. I didn’t really want to know about one site at one time; I wanted to know what was going on in general. We did an overall study that takes out the site-specific variables and looks at gypsum as a whole.”
Seed calcium, she says, was highly influenced by gypsum treatment, irrigation and peanut cultivar, and it was a good indicator of soil calcium availability.
“Adsorption of calcium was detected throughout the development phase of the peanut indicating that calcium should be present throughout the entire growing season for maximum uptake. The data also suggest that loss of calcium from the pegging zone through high rainfall events could affect late season calcium acquisition.”
Overall, production of peanuts without irrigation, especially in drier years, can benefit most from gypsum applications, says Howe.
Yield was increased by 30 percent with gypsum applications without irrigation. This translates to 500 to 1,000 pound per acre of additional peanut yield and a 3.5 to 5 percent increase in peanut grade.
“It was no surprise that irrigation outperformed dryland, and that Georgia 06G outperformed Georgia Green, she says.
“When we looked at the non-irrigated, we saw a nice response to different rates of gypsum. The yield increased by 280 pounds per acre per every 500 pounds of gypsum applied. However, when we looked at the irrigated sites, there was no difference. I think this is one reason we see a lot of inconsistencies in results from studies.”
Previous research has indicated that calcium probably was taken up during the first bloom period for peanuts, according to Howe.
“But our research showed that calcium was taken up throughout the growing period. So if we had a tropical storm during the growing season, there might be some benefits to some of these solution products applied through the pivot.
“Maybe you could get some calcium in there to help you out through the late-season if you think you’re running low.”
Howe says she thinks the large-seeded varieties do require a little more calcium, but she doesn’t think there’s a reason to adjust current recommendations.
“But if you’re in a borderline situation, you’ll probably want to go with more calcium rather than against applying more. If you’re in that critical zone, err on the side of adding it for the larger-seeded varieties.”
Researchers also looked at the economic benefits of gypsum, she says. Improvement of yield and grade directly translated into higher peanut prices.
Using 2011 peanut prices with the yield and grade of dryland Georgia-06G peanuts from these studies, the price increased by $103, $127 and $199 per acre with the addition of 500, 1,000 and 1,500 pounds of gypsum per acre, respectively, compared to the no gypsum treatment.
These returns are more than four times larger than for the irrigated Georgia-06G trials and sufficiently high to recoup the $12 to $32 per-acre cost of gypsum (assuming $50 per ton).
“Obviously, it’s important to look at what the soil test indicates for the pegging zone for calcium. It’s also important to look at irrigation. If you’re farming non-irrigated land, then in a wet year, you’ll probably see the same effects as you do from irrigation.”
As far as soil type, she adds, sandy soils will enhance drought conditions, and it’ll cause the calcium to leach.