In The Zone

Questions and answers about calcium, a critical element needed in the top 4 inches of soil.

As a legume, peanuts use the symbiotic relationship with bacteria added as an inoculant to fix atmospheric nitrogen into a form usable by the plant. The deep tap root is good at scavenging residual soil phosphorus and potassium. The next limiting element becomes calcium, which can lead to “pops” or no kernels and reduced yield. Researchers have also found that calcium is critical for good germination rates of peanuts saved for seed.

University of Georgia soil scientist Glen Harris answers some of the top calcium-related questions.


What is the recommended calcium application rate?

A: The University of Georgia Extension recommends using gypsum when a pegging zone soil sample at 4 inches deep, taken soon after peanut emergence and when the results say you have either 1) less than 500 pounds of calcium per acre or 2) a calcium to potassium ratio of less than 3:1. If either of these criteria are not met, then it is recommended to apply 1,000 pounds per acre of gypsum at early bloom — approximately 30 to 45 days after planting.

Peanuts to be saved for seed should automatically receive 1,000 pounds per acre of gypsum at early bloom even if these levels are met.


Can I base my gypsum or calcium needs on a fall soil sample?

A: This is better than nothing, but it is still better to base your calcium needs on a pegging zone soil sample. Soil samples taken in the fall were likely taken 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.


Is liquid calcium a viable option to meet the crop’s needs?

A: It depends on what liquid calcium product 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 could be the more affordable option but check on price and availability.

Liquid calcium applied through a center-pivot irrigation is considered a soil-applied application because the amount of water per acre is such that it runs off the leaves and into the soil to reach the developing pods.


Is foliar-applied calcium a possible alternative?

A: Foliar products do not provide the rate of calcium needed and, even if they did, calcium does not translocate through the plant from the leaves to the pods. Calcium has to be absorbed with water directly through the walls of the developing pods in the pegging zone (top 4 inches or so of soil) not through the roots or any other part of the peanut plant.

Foliar calcium products with a recommendation of one quart per acre and sprayed at a total spray volume of 10 to 20 gallons per acre do not provide enough calcium.


When is applying lime a better option than gypsum?

A: Lime should be applied before planting since the calcium in lime is not as soluble as the calcium in gypsum. If you are deep turning the soil, do this before applying lime so you don’t bury it. The calcium needs to be in the top 4 inches or the pegging zone. 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 a “liquid lime?” Has it been tested?

A: There is a product currently available called “Topflow” that has been field tested at a 12-gallons per acre rate, surface applied at planting. This may not provide as much calcium to the pegging zone as 1,000 pounds 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.


Which is better on dryland peanuts: lime or gypsum?

A: In most years, gypsum outperforms lime applied at planting for providing calcium to the pegging zone. The calcium in lime is less soluble than the calcium in gypsum under limited water situations. In dryland production, and without significant rains, the calcium in lime may not become available to the developing pods in the pegging zone as it would with the use of irrigation.


How late in the season is too late to put out gypsum?

A: 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 have absorbed what calcium there is in the soil solution. It is either enough for kernels to develop or not. After this, damage to the vines during application would not be desirable. PG

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