While peanut production has shifted in recent years from small-seeded to large-seeded runner varieties, calcium recommendations haven’t changed as drastically, says Glen Harris, University of Georgia soil scientist.
“Technically, the calcium recommendations haven’t changed,” says Harris.
“Research from 2008-2010 showed that both the 500 pounds of calcium per acre in the pegging zone requirement and the 1,000 pounds of gypsum per acre overall appears to hold for large-seeded runners, and especially for Georgia-06G.
“Also, when the pegging zone calcium is between 500 and 750 pounds per acre, you are in a ‘grey area,’ and this is where calcium chloride or calcium thisosulfate applied through center pivots may be most beneficial.”
The research — conducted over 11 sites — actually found that yields decreased when the rates were bumped to 1,500 pounds per acre, he says.
The rules for calcium in peanuts remain relatively simple — lime at planting, gypsum at bloom time, says Harris.
“We do it this way because the calcium in lime is not as soluble as the calcium in gypsum, and it needs time to get into the pegging zone and into the nut,” he says.
Original recommendations for providing calcium to the pegging zone called for 1,000 pounds of gypsum or the equivalent (broadcast or banded) at bloom time.
And this was to be applied only if you did not have at least 500 pounds of calcium per acre and a calcium/potassium ration of at least 3:1 in a soil sample taken from the pegging zone soon after the peanuts emerge.
Since calcium is critical to germination, it always has been recommended that any peanut being produced for seed should receive 1,000 pounds of gypsum at early bloom regardless of pegging zone calcium and potassium levels, says Harris.
Research was done about 15 years ago at the University of Georgia using lime at planting to provide calcium to the pegging zone of peanuts.
This method should be used only when lime is recommended according to soil sample results. If lime is used when it isn’t required, it can raise the pH above recommended levels and cause micronutrient deficiencies such as with manganese, he says.
“Also, if you use lime, it should be applied at planting and should not be deep turned. This will allow time for it to break down and be absorbed into the developing nuts.”
Over the past three years, university researchers have tested using liquid calcium chloride or calcium thiosulfate through the pivot during peak pod fill, says Harris.
“This has shown promise for providing calcium to the pegging zone. If gypsum is in short supply, this could be a valuable alternative. Calcium chloride also has been tested in dryland situations by applying in a band behind the presswheel at planting.”
Research showed that calcium chloride and calcium thiosulfate applied through a center pivot improved yield, calcium in the seed, and germination.
However, these products do not increase the soil-test calcium levels after harvest nearly as high as gypsum, so in that regard, they don’t replace gypsum, he says.
Calcium needs to get into the pegging zone because it has to be absorbed directly into the nut, says Harris. “There’s a direct correlation between calcium in the seed and germination, and you probably want to check this on any saved seed. In our rate study, the more calcium we had in the seed, the higher the germination.”
There are multiple sources of lime and gypsum, says Harris, so the selection process can become complicated. But there doesn’t seem to be any difference between the gypsum materials currently available, he says.
Last year, USG 500, PCSA Wetbulk, AgriCal and a new product called Gypsoil were tested and seem to perform equally. Selection can be based on factors such as product availability and how well the material handles, Harris says.
It is better to use gypsum for dryland peanuts, says Harris.
“During the past two years, gypsum at bloomtime has outperformed lime at planting as far as calcium to the pegging zone. This makes sense since the calcium in lime is less soluble than the calcium in gypsum under limited water situations such as in dryland production.”
Also, it has become clear, says Harris, that foliar calcium applications are not recommended on peanuts. “At 1 quart per acre, they do not provide enough calcium, and even if they did, they do not get translocated from the leaves to the developing pods.
“Putting liquid calcium through a center pivot is considered a soil application because you are putting out so much water per acre, that even though the water hits the leaves initially, the majority of it runs off and is basically applied to the soil.”
It is not recommended that growers apply gypsum at planting since there is always a chance that with enough rain or irrigation early on, the calcium in gypsum could leach below the pegging zone, says Harris. This is especially true on sandy soils.
“At this time, it’s not recommended to split gypsum applications and put some on at planting and some at early bloom, but research studies are being conducted to determine if there may be a benefit to this timing of applications.”
Gypsum should be applied at early bloom or approximately 30 to 45 days after planting depending on growing conditions.
“Once you get past 100 days after planting, the majority of pods probably have already absorbed the proper amount of calcium or they aren’t going to. Also, after 100 days after planting, running over lapped vines is not desirable.”