Calcium Q & A

Shortages, alternatives and targeted application— these are the key topics in 2021.

Editor’s Note: University of Georgia soil scientist Glen Harris answers gypsum-related questions.Gypsum application in peanuts

Q Will there be a gypsum shortage as we have heard about?

A The same rumors made the rounds last year, but gypsum was always available. According to my sources, there shouldn’t be a problem with the gypsum supply this year either. However, the logistics of moving the gypsum is more likely to be the primary problem. In his words, “You may not get it exactly the day you want it, but you should get it pretty soon thereafter.”

Q Is there an alternative to gypsum that will provide the calcium needed by the crop?

A The short answer is “not really.” Gypsum is the best. Lime is also recommended but needs to be done at or before planting and only when a pH adjustment is called for. Other products have been tried, such as 10 gallons of liquid calcium chloride applied through the pivot, but it does not provide as much soluble calcium as 1,000 pounds per acre of gypsum. Also, alternatives do not leave as much calcium in the soil as gypsum does.

Q What can we do in case of a shortage or simply to reduce the tonnage needed?

A We always need to put calcium where it is needed. One tool that I think is underutilized is the pegging zone calcium test. Sampling around the field directly from the pegging zone and learning how much is present will let you know both how much and where it is needed. In places where you already have the UGA recommended 500 pounds per acre and a calcium to potassium ration of at least 3:1, there will not be a yield or grade increase if you do not apply gypsum.

What I am interested in seeing more of is grid sampling and variable-rate gypsum application. Some farmers are starting to implement this strategy to put product out only where needed. One farmer said he now uses less than half of what he was before. If there is a shortage, grid sampling and variable-rate application will probably get more popular.

Q What about foliar-applied calcium products? Is that a possible alternative to gypsum?

A No. 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 1 quart per acre and sprayed at a total spray volume of 10 to 20 gallons per acre do not provide enough calcium.

However, liquid calcium applied through a center-pivot irrigation system is different. This is considered a soil-applied application because the amount of water per acre is such that it runs off the leaves and onto the soil. For comparison, the foliar-fed system applies 10 gallons per acre, whereas applying 1 acre-inch of water through the pivot puts out approximately 27,000 gallons of water!

Q 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.

Q Should I split my gypsum applications and put some on at planting and some at early bloom?

A Research studies have not found this to be a benefit to providing calcium to the crop. In fact, if you get a big rain early, the calcium can leach or move downward out of the pegging zone. Plus, split applications would add an unnecessary trip across the field.

Q 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.

Q What are the recommended calcium requirements in soil and gypsum application rate?

A The current recommendation from the University of Georgia is you need both 500 pounds per acre and a calcium to potassium ratio of at least 3:1 in the pegging zone. If either of these levels is not met in a pegging zone soil test, then apply 1,000 pounds per acre of gypsum at early bloom to runner-type peanuts.

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.

Virginia-Market Type Calcium Q & A

Editor’s Note: North Carolina State University Extension agronomist David Jordan talks about calcium use in Virginia-type varieties.

Q Last year, I applied normal landplaster but still had a lot of pops. What do you think could have been the problem?

A Excessive rain after gypsum application or dry weather during pegging and fruit set can cause pops. Could one of these examples be the reason? All Virginia market-type peanuts should get adequate calcium in the pegging zone. This equates to 1,500 to 2,000 pounds per acre of gypsum at blooming. Calcium must be available in the pegging zone when the first pods begin to form.

Calcium deficiency versus normal seed in Virginia type peanuts
Calcium deficiency versus normal seed in Virginia-type peanuts

Q What is the proper timing for applying landplaster to meet the crops calcium needs?

A Best results are obtained when gypsum is applied in late June or early July. I think some gypsum is going out earlier than needed. If there’s a lot of rain, particularly an excessive amount, after application, it is possible we are running out of calcium later in the season.

Some moisture is needed to make gypsum soluble and calcium available to the peanut fruit. In unusually dry years, peanuts may show symptoms of calcium deficiency, even when recommended rates of gypsum are applied.

Overall, gypsum application is better early than late. Just not too early.

Q What did you find in the potash application field trial you did on peanuts? I understand it was applied up to and after emergence in fairly high rates with little or no incidence of pops.

A We did a series of studies many years ago applying 250 pounds of potash on the soil surface right after planting and observed no major issue. If soil test calls for it, you should apply it, but don’t cut back on gypsum. Of course, high rates of potash can cause issues with nutrient balance, but the rates we typically apply in fields with good fertility programs are not a major issue. We would recommend that potash be distributed throughout the soil profile to the root zone where it is needed.

Q What is the relationship between soil pH and gypsum for peanuts?

A Many years ago, we did a study with a range of soil pH values and rates of gypsum. What we found was that getting your soil pH close to 6.0 will help get a positive return on your gypsum investment. In fact, when soil pH is too low there are times when you will get a negative response to gypsum. Getting the pH right continues to be critical. PG

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