Glenn Harris, UGA Peanut Fertility Specialist
Gypsum (or landplaster, i.e. calcium sulfate) may be in short supply this year. There is no need to panic but it doesn’t hurt to review your options for dealing with this potential problem.
Why the Shortage? Coal burning powerplants that produce a lot of the “smokestack” gypsum we use on peanuts in Georgia have either switched to natural gas as a cheaper fuel source… or it has something to do with COVID-19 . Either way, or both, there has been a disruption in supply.Are there other gypsum sources ? Yes, there is USG 500, the naturally mined product, that should be available, especially in East Georgia and there may be some old ‘wet bulk” or “phosphogyp” available from Florida and maybe even some recycled wallboard. Freight/trucking cost may be a factor depending where you are located though.
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 need 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 10 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 if I get delayed getting gypsum? Or how late is too late to put out gypsum? 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.
Can I put calcium out through a center pivot? Actually yes. 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.
Does every field of peanuts in Georgia need gypsum ? Probably not, so if supply is short 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. Calcium is extremely important for germination of peanut seeds. Technically other fields should be “pegging zone” tested, i.e. soil sample 4 inches deep taken soon after peanuts emerge. If the soil test calcium (Mehlich 1 Extractant) is 500 or higher and the calcium to potassium ratio is 3:1 or higher – 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.
How important is gypsum for peanut production? This probably should have been the first question answered. And the answer …. 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.