Should I Use Gypsum on my Peanuts This Year? Or Maybe an Alternative Source of Calcium? Dr. Glenn Harris

There doesn’t seem to be as much talk about a gypsum shortage this year, but there are still ‘supply chain” issues and price of input concerns to the point where there is plenty of talk about whether to apply gypsum or maybe use an alternative.
To review, UGA Extension recommends using gypsum when you take a pegging zone soil sample (4 inches deep) soon after peanut emergence and when the results say you have either 1) less than 500 lb Ca/a or 2) a Ca:K ratio of less than 3:1. If either of these criteria are not met then we recommend applying 1000 lb/a gypsum m at early bloom (approximately 30-45 days after planting). All peanuts to be saved for seed get 1000 lb/a gypsum automatically since calcium levels in the nut are critical to good seed germination.
Can I use lime instead of gypsum? Yes, but lime needs to be applied before planting since the calcium in lime is not as soluble as the calcium in gypsum. So timing is important. Also if you deep turn you need to deep turn before applying lime so you don’t bury it. So placement is important. The calcium needs to be in the “pegging zone” (top 4 inches). And technically, lime should only be used when you either need a pH adjustment (below 6.0) or start around 6.0 so the lime will not raise the soil pH too high.
What about “liquid lime” ? There is a product currently available called “Topflow” that has been field tested at a 12 gal per acre rate, surface applied at planting. This may not provide as much calcium to the pegging zone as 1000 pound per acre of gypsum and won’t raise the soil test calcium as much but can be considered an alternative if you cannot get gypsum. Even though it is a liquid, it is still lime so it needs to be applied before or at planting.
What about other “Liquid Calcium’s” ? Well, it depends on which “liquid calcium: you are talking about. For example, recent research has been conducted showing 10 gallons per acre of calcium chloride (or 20 gallons of calcium thiosulfate) through the pivot during peak pod fill (around 75 days after planting) can have some benefit. Again, this is not as good as a timely gypsum application but can be viewed as an ‘emergency” or “insurance” application. The calcium in both of these products is basically 100 % soluble and therefore can be applied during peak pod fill. Also, calcium chloride should be the more affordable option but check on price and availability.
What if I get delayed getting gypsum? Or how late is too late to put out gypsum? Again, gypsum should be applied at “early bloom” or approximately 30-45 days after planting. Since “peak pod fill” is around 60-90 days after planting you can still see benefit from gypsum applications made any time before 60 days after planting. It can also depend on water or irrigation since you need water to dissolve the calcium and get it through the hull into the developing kernels.
Does every field of peanuts in Georgia need gypsum? Probably not, so if supply is short or budgets are tight how do you decide which fields get gypsum? First, any peanut being saved for seed should automatically receive 1000 pound per acre of gypsum, regardless of soil test calcium levels. Second, any field where results from a pegging zone test show you need gypsum should get it. Remember, if the soil test calcium (Mehlich 1 Extractant) is 500 or higher and the calcium to potassium ratio is 3:1 or higher in a pegging zone sample then the soil test calcium will be considered adequate and no gypsum will be recommended. This is based on research field trials looking at yield and grade. Research also shows that
gypsum is even more important in dryland compared to under irrigation since water will be more limiting in dryland and less soil test calcium will be available.
Can I base my gypsum or calcium needs on a Fall soil sample? You can, and this is better than nothing, but it is still better to base your calcium needs on a pegging zone sample. Soil samples taken in the Fall were likely taken at a deeper than the pegging zone. Also, calcium can leach out of the pegging zone between a Fall sample and early bloom and give you a false sense of security. Finally, if you take a fall soil sample and then deep turn before planting peanuts you can very possibly turn up soil into the pegging zone that is low in calcium.
How important is gypsum for peanut production? This probably should have been the first question answered. And the answer …. It is very or extremely important! Since peanuts as a deep tap-rooted legume can fix nitrogen and scavenge residual soil phosphorous and potassium, calcium is the most critical element. Lack of calcium in the pegging zone to be absorbed through the hull can result in “pops” or no kernels which obviously reduces yield. Calcium deficiency on peanut can also lead to pod rot.
And again, calcium is critical to germination for peanuts saved for seed for next year.