# pH testing



## reede (May 17, 2010)

Discussions here have led me to looking further into pH testing and their results, and just what to do with them. I originally ended up with questions due to the change through the year(big drop in one year's pH from spring to fall), sampled on field once a month for a year to try to figure it out, and have been helped out considerably through some conversations with Vincent Haby.

Along in there, I learned of the 'salt' pH test.

So, this spring's set of samples, I sent a few off for soil health testing(another topic that I don't want to veer into in this thread), and got both the water based pH and salt based pH done.

Samples were taken April 14th, Piedmont region of SC, Cecil sandy clay loam soil.

Alfalfa/Bermudagrass hay field Water--6.7 Salt--6.0

Perennial mix pasture Water--6.6 Salt--5.8

Annual mix pasture Water--6.5 Salt--5.6

Perennial mix pasture is BarOptima fescue with white/red/crimson/arrowleaf clover, hairy vetch, and chicory.

Annual mix pasture is finishing up wheat/black oat/winter pea/crimson clover/radish/rape/turnip. Planning to go to a summer annual mix in a few weeks.

So, which number to operate off of from a liming pH management scheme? We have had nice bits of rain here recently, so there is plenty of moisture in the ground. Water pH would say I'm in the right range for the alfalfa, but salt would say I still need work on it.

Thoughts?

Thanks.

Reed


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## r82230 (Mar 1, 2016)

Great questions / information - I'm all ears. I don't know if I get water or salt test results, I have to ask. I imagine water, problem might be where I submit the tests, they don't know also. 

The only thing I try to do is soil sample around the same time each year, for the reasons you mentioned (changes from spring to fall).

Larry


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## reede (May 17, 2010)

Larry,

You can probably email or call and they can tell you if they don't have their methods published on the website. Here, the Clemson lab uses water for pH testing. UGA uses salt, but adds 0.6 pH units to the result to "correct" it back to water numbers.

So far, the folks I have asked at the different labs have been very helpful.

The difficult part is interpretation, and figuring out what you need to do in your individual operation, for the soil/crop/animal/etc. that you happen to be playing with.

Reed


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## somedevildawg (Jun 20, 2011)

I don't see where it matters much if the above samples have not already been "adjusted"......why do they do this? One surely has to be more accurate than the other, if that's the case why bother to "adjust" (assuming water is more accurate?) idk, never mentioned it to my lab, however, I will find out which method they use, just for kicks....I usually put 1 ton per year per acre and call it a year  
Probably could stand more but my pocket book has a hard time standing more......


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## reede (May 17, 2010)

Dawg,

If you are using UGA, they use salt to do the determination, but then add 0.6 pH units as a correction back to water.


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## vhaby (Dec 30, 2009)

Many of the soil testing laboratories in the southern hemisphere, such as New Zealand, Australia, and South Africa, use the salt pH. The main reason, as I understand it and from my previous studies, is that the salt pH is relatively unchangeable with season. While the water pH of soil (2 volumes of water to 1 volume of soil or 1 to 1 water to soil) is higher in spring and lower in fall, the salt pH (2 volumes of 0.02 molar calcium chloride to one volume of soil- a very dilute calcium chloride solution) shows a very slow decline from spring to fall and into spring again. The salt pH does not go up and down with season.

Although some state public laboratories make limestone recommendations based upon soil pH, there are better tests that can more accurately determine a soil's limestone needs. Some laboratories determine a soil's limestone needs based on using a buffer pH relative to a water pH. The buffer pH method uses a solution that has a pH above 7 that when added to an acid soil in the laboratory, declines based on the amount of acid in the soil. Apparently, the change in pH of the buffer solution provides an idea of how much limestone to recommend to achieve a certain pH in the field. Still, other laboratories base their limestone recommendations partially on a test for extractable aluminum.

Personally, I am reasonably confident in determining my soils' limestone needs based on water pH because this is the method I am most familiar with. So, *reede* your soil's water pH of 6.7 (if that is the pH in a fall collected soil sample) for alfalfa/grass production is slightly low. I'd like a soil pH of 6.8 to 7.0 or higher for alfalfa (in samples collected in fall.) *Dawg*, if you apply one ton of limestone per acre every year, you likely are over liming your soils. The rule of thumb is that for every pound of nitrogen that you apply as ammonium nitrate, urea, or urea ammonium nitrate, 1.8 lb of limestone is required to overcome the acidity formed by the conversion of the ammonium to nitrite and then to nitrate in the soil. More limestone is required per pound of nitrogen applied if the N source is ammonium sulfate.

In order to base a soil's limestone needs on the salt pH, research comparing both the water pH and salt pH done on a large number of acid soil samples needs to be done and calibrated with soil pH change to limestone addition in the field. For labs running a pH buffer test for limestone recommendations, this test also needs to be done on these samples and related to the salt pH test. Some USA laboratories are working on this, but most are happy with their current method of making limestone recommendations, whatever that method is. My 2c worth.


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## r82230 (Mar 1, 2016)

reede said:


> You can probably email or call and they can tell you if they don't have their methods published on the website. Here, the Clemson lab uses water for pH testing. UGA uses salt, but adds 0.6 pH units to the result to "correct" it back
> 
> Reed


Reed,

Took them awhile to find out, then I got answer - "ah........water based, I think". Based on Vincent's post, I think water based makes sense (different numbers spring/fall decline), in my area anyhow.

Larry


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## FarmerCline (Oct 12, 2011)

It seems like here you can't hardly put out too much lime and it always takes more lime to raise the ph than what the soil test called for. For example I have had soil tests call for 2 tons of lime to raise the ph from 5.3 to get to a target of at least 6.5. In reality I had to have 6-8 tons of lime over a couple years to raise the ph up to that level. Does anyone know why that is? I have been spreading about a ton per year now as maintenance.

Hayden


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## r82230 (Mar 1, 2016)

FarmerCline said:


> In reality I had to have 6-8 tons of lime over a couple years to raise the ph up to that level. Does anyone know why that is? I have been spreading about a ton per year now as maintenance.
> 
> Hayden


What type of fertilizer are you spreading?

I use more lime now and thanks to Vincent's you tube presentation, it finally got in my thick head why I needed to lime more. If I remember correctly it was around the 8 minute mark, where he talks about different fertilizers effect on ph.

If you haven't watch his presentation I would highly recommend, I think it is worth it's weight in gold. I think it is pinned in Soil and Amendments section.

Larry


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## FarmerCline (Oct 12, 2011)

r82230 said:


> What type of fertilizer are you spreading?
> 
> I use more lime now and thanks to Vincent's you tube presentation, it finally got in my thick head why I needed to lime more. If I remember correctly it was around the 8 minute mark, where he talks about different fertilizers effect on ph.
> 
> ...


 I have been spreading mostly a blend of DAP and muriate of potash. Grass crops also get 34-0-0 which is a 50-50 blend of urea and ammonium sulfate. I have used liquid 28% as a form of N in the past also.

Yes, I watched that YouTube presentation.....very informative and worthwhile.

Hayden


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## broadriverhay (Jun 13, 2014)

I was told one can only raise ph by a half point each year as a rule. So with that being said one better not let it get to low or it will take several years to recover. By Clemson recommendations my field requires about 1 1/2 tons every other year. I sample twice every year and this has held true for quite a while.


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## somedevildawg (Jun 20, 2011)

Ya, I have no doubt I over apply lime but most of my fields, edit....all of my fields  we're low when I aquired them and raising Ph is a slow process. And with our humidity, I find myself using more AN than urea due to clumping so I generally err on the side of caution....plus, it's really easy math for them and me when I say "how much is a ton delivered and spread" "$34 per acre" "spin 1 ton per acre on that 35 acre field" I can do that math in my head....as long as I have a couple of scrap pieces of paper and a couple of sharp pencils


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## Hayman1 (Jul 6, 2013)

reede said:


> Discussions here have led me to looking further into pH testing and their results, and just what to do with them. I originally ended up with questions due to the change through the year(big drop in one year's pH from spring to fall), sampled on field once a month for a year to try to figure it out, and have been helped out considerably through some conversations with Vincent Haby.
> 
> Along in there, I learned of the 'salt' pH test.
> 
> ...


Reed, if it is really Cecil SCL, it has a fair abount of the CEC as exchangeable aluminum which is better tested in my recollection with the KCL test . For Fescues, you need lime.


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## reede (May 17, 2010)

Thanks, Hayman1. Most of the farm, and most of the hayfields, are Cecil SCL. Next greatest by percentage is Cecil clay loam, on the steeper areas. Couple of odds and ends otherwise that don't add up to much area. I did not know that about the Cecil, but I don't know much about the qualities of different soil types.


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