It’s the time of year that peanut farmers love to hate. Area farmers are spreading gypsum on their fields to meet the large Calcium requirements of the peanut crop.
For many years we have had the standard recommendation of 500 pound-per-acre soil test calcium level in the pegging zone as sufficient for maximum peanut yields. However, the new large seeded runner varieties including GA-06G, which is the dominant cultivar planted, responded to gypsum applications up to 1,000 pounds per acre on an irrigated deep sand at the Stripling Irrigation Park in Camilla, Ga. They found this true even when the pegging zone calcium was 950 pounds per acre. Dr. Glenn Harris, Soil Scientist at UGA tells us there is no doubt that the larger seeded runners have a higher requirement for calcium and are more susceptible to calcium deficiencies.
Based on field research in Georgia and Alabama, it looks like the traditional application of 1,000 pounds per acre of gypsum at bloom still works well for these cultivars. In fact, there seemed to be a slight decrease in peanut yields in a few cases when 1,500 pounds per acre of gypsum was applied, which may be due to the extra calcium causing a hidden potassium deficiency. I still see many farmers who apply up to a ton of gypsum per acre, so for their own economic benefit they should consider the work Dr. Harris has done in their decision-making.
Gypsum, which is calcium sulfate , or landplaster, is usually applied during early bloom to provide calcium to the peanut pegging zone. There are a number of good gypsum materials currently on the market. In our area there are two primary sources of gypsum. “Phosphogypsum” is a byproduct of processing phosphate ore into fertilizer with sulfuric acid. Recently, the use of “smokestack” gypsum has become more common. This material comes from coal-burning power plants where lime (calcium carbonate) is used to “scrub” sulfur out of the smokestack emissions, and the end result is gypsum or calcium sulfate.
I only say farmers “love to hate” this time of year, because of the issues with spreadability of the various products, particularly this time of year when gypsum piled at the edge of the field is getting rained on almost daily. Someone on the farm inevitably gets the assignment of riding in or on the spreader to keep a constant stream of gypsum flowing out of the spreader. Here is some footage from one of our area farmers.