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.