# Tell me about gypsum



## revitup (Sep 19, 2020)

My soil analysis says I need 50# gypsum per 1k sq ft. Centipede. Seems like a lot! My research says gypsum is used primarily to loosen clay soil. My soil is sandy, very sandy. No clay. What is another use for gypsum?


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## revitup (Sep 19, 2020)

My potassium is low and phosphorous is high. Does it do anything to help with those issues?


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## Virginiagal (Apr 24, 2017)

Gypsum will add calcium without raising pH. Centipede likes a pH between 5-6, don't want to go over 6.


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## Greendoc (Mar 24, 2018)

revitup said:


> My soil analysis says I need 50# gypsum per 1k sq ft. Centipede. Seems like a lot! My research says gypsum is used primarily to loosen clay soil. My soil is sandy, very sandy. No clay. What is another use for gypsum?


Centipede also does not like a high Calcium soil. Skip the Gypsum. Who said that you needed Gypsum in spite of the fact that you are trying to cultivate Centipede grass? What is your soil pH, What is the purpose of the Gypsum application besides the numbers on a soil test? Gypsum is a frequently misused product.


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## g-man (Jun 15, 2017)

For centipede, you need low pH, low P and high K. Don't look at the graph low/medium/high levels.

Bag mow to help drive the P lower.


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## revitup (Sep 19, 2020)

The gypsum is a recommendation from my report from a Clemson University Agriculture Service Lab soil test. My PH is 5.9. No change recommended there. 
I have the same question regarding the purpose of the gypsum application hence my original post. See the first note:


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## revitup (Sep 19, 2020)

Greendoc, can you provide a reference for your assertion that centipede does not like high calcium soil? And what is 'high'? I haven't been able to find much on the subject.


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## g-man (Jun 15, 2017)

Maybe give them a call and asked them why the gypsum. I see their recommendations are for centipede, but I don't understand why they will recommend it.


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## Virginiagal (Apr 24, 2017)

Yes, ask them. And also ask about potassium. They are only recommending a little less than a pound per 1000 sq ft a year and I would think it should be more. You could apply SOP to get potassium only. Gypsum can also help displace sodium but 21 lb per acre doesn't seem excessive. Do you ever have saltwater flooding?


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## revitup (Sep 19, 2020)

I was thinking about the sodium displacement property of gypsum also. No salt water flooding at all but we are here in the SC coastal 'low country'. Maybe 21 lbs is higher than desired.


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## Virginiagal (Apr 24, 2017)

According to this, your sodium is not excessive:
https://www.paceturf.org/journal/a_new_look_at_calculating_calcium_requirements

So maybe they're just trying to get the calcium up because it's testing low. But maybe low calcium is ok for centipede. I'm curious what Clemson has to say, so I hope you're going to call them.


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## Greendoc (Mar 24, 2018)

https://edis.ifas.ufl.edu/pdffiles/LH/LH00900.pdf University of Florida. High Calcium and Phosphorus is harmful to Centipede. They have no products to sell, if anything, their usual advice is not to apply anything to lawns.


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## revitup (Sep 19, 2020)

Greendoc said:


> https://edis.ifas.ufl.edu/pdffiles/LH/LH00900.pdf University of Florida. High Calcium and Phosphorus is harmful to Centipede. They have no products to sell, if anything, their usual advice is not to apply anything to lawns.


This is all that I found in that UF article regarding calcium. I might have missed something though:
"one of the common problems of centipedegrass is leaf yellowing called chlorosis, which is usually caused by iron deficiency. This condition is most severe where soil pH is above 6.5 or where the soil contains large quantities of calcium or phosphorus."

Unfortunately I don't have enough info to know if my current calcium level is considered a 'large quantity' (result from the Clemson soil test doesn't seem to indicate that it is), and so I also don't know if the gypsum application Clemson recommends puts it in the 'large quantity' category. 
I did find this statement regarding salt:
"It has poor salt, wear and freeze tolerance." 
Might indicate the gypsum recommendation could be related to sodium displacement.


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## Deadlawn (Sep 8, 2020)

revitup said:


> My soil analysis says I need 50# gypsum per 1k sq ft. Centipede. Seems like a lot! My research says gypsum is used primarily to loosen clay soil. My soil is sandy, very sandy. No clay. What is another use for gypsum?


Gypsum will raise your calcium AND sulfur without changing your pH. If you are low in both of these elements and your pH is OK, gypsum is usually recommended.

There are conflicting reports as to whether gypsum does anything to help soil compaction. But since your soil is sandy, that issue is irrelevant anyway.

Edit: I am now able to see your test results (don't know why the link was broken before). Your sulfur doesn't even register and your calcium is low, so that is why they recommended gypsum. But then others here say centipede doesn't like too much calcium. So how do you raise sulfur without lowering pH?

Well, isn't one of the advantages to growing centipede that it is quite content with low nutrients and water?


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## Greendoc (Mar 24, 2018)

To be honest, I would not worry about increasing Calcium. My Nitrogen source would be Ammonium Sulfate to maintain acidity and raise Sulfur. Potassium source would be Potassium Sulfate or Potassium Nitrate. In other words, there is nothing on that soil test I would be trying to extremely elevate. Centipede is a grass for nutritionally devoid, acidic soils. My experience is that increasing fertility where Centipede is the desired turf causes takeover by weeds and volunteer grasses such as Bermuda or Zoysia.


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## Greyleafspot (Oct 16, 2018)

Not trying to steal the thread but Does st augustine like calcium?


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## Greendoc (Mar 24, 2018)

Greyleafspot said:


> Not trying to steal the thread but Does st augustine like calcium?


Adapted to more alkaline soils than Centipede


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## Greyleafspot (Oct 16, 2018)

Greendoc said:


> Greyleafspot said:
> 
> 
> > Not trying to steal the thread but Does st augustine like calcium?
> ...


Thanks. I ask bc my soil test came back saying I was low in calcium and low In magnesium. The Ph was a 6.3. I put out gypsum for calcium and Epsom salt for magnesium. Really I was low in everything but phosphorus. I put out a 8-12-16 before I got my test back.


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## RichS (Jan 28, 2019)

deleted


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## Ridgerunner (May 16, 2017)

@RichS I don't want to discourage your interest in analyzing soil tests, however; in order to judge nutrient sufficiency levels, you need to know the test method employed. In this case it is M1, and M1 Ca sufficiency levels are 400-700 lbs/acre. 391 lbs/acre may or may not be detrimentally low ( a hair<50/50), but it's not what would be described as "very low".


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