# Soil pH



## cattleman4170 (Jan 26, 2010)

What effect does all this rain have on soil pH? Does the water cause more leaching as it does to fertilizer?


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## vhaby (Dec 30, 2009)

Steve,
Whether the excess rainfall will change soil pH depends on when you normally sample your soils. If you always take samples in the late winter or early spring, you may not notice any change in pH, except that due to small variation in your sampling technique or in lab analytical technique.

However, if you normally sample in fall, especially on sandy, low organic matter, low clay soils, and then you want to compare pH in spring sampled soils, you should notice an increased pH in your spring-collected samples compared to your fall-collected samples. The pH increase in the spring collected samples may be as much as 0.5 pH unit. Why?

Coastal Plain soils, the type mentioned above, normally go toward a more dry condition through summer and into fall. During the same time, fertilizer nutrients (salts) are applied to enhance crop growth. The result of this drying and the slightly increasing salt content causes a salt-effected pH, or a pH that is lower. In a laboratory that tests pH, the procedure normally is done in a 1:1 or 1:2 soil: water suspension in the USA. If a small amount of salt, for example- a few drops of a calcium chloride solution is added to the water suspension, the pH will go lower. The calcium added exchanges additional hydrogen from the clay. Soil pH measures potential hydrogen (pH) in the soil suspension, so if additional hydrogen is removed from the clay into solution, the pH will register this additional hydrogen and the pH value will go down.

For this reason, soil testing labs should analyze pH in a dilute salt suspension such as a 0.01 molar calcium chloride solution (molar is a concentration term- in this case, a very dilute solution of calcium chloride in distilled water). Soil pH measured in this dilute salt solution changes very little from fall to spring, but the measured pH will be lower than that measured in a soil: distilled water suspension. Couldn't we get used to our pH being 0.5 units lower when it gives us a more consistent and accurate measurement that does not change from fall to winter??? This measure of soil pH normally is not used to determine the limestone needed to raise an acid soil pH to a more desirable level for cool-season annuals- limestone needed normally is determined by a lime requirement test.
vhaby


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## cattleman4170 (Jan 26, 2010)

vhaby,
Thanks for the info. I attended a Forage meeting here in Central Alabama on Tuesday night. Dr. Don Ball and Dr. Charles Mitchell from Auburn University were there. I asked the same question during one's discussion on soil pH. I got basically the same answer. You folks are on the same page. 
Thanks for sharing.


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## Barry Bowen (Nov 16, 2009)

Vhaby,

What test are you talking about to measure calcium, are you refering to the CEC numbers or possible the base saturation? I have found at least where I am (silt loam soild in the pedmont of Maryland) that the amount of calcium in the soil is more important than the pH when it comes to growing great hay. It is possible to have a pH in the mid 6 range, but have a calcium only in the 30-40% range. So I guess I am agreeing with you that pH is definately not a test to determine your calcium in the soil.


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## vhaby (Dec 30, 2009)

Mr. Bowen and other HayTalk readers,

First, allow me to apologize for a mistake that I made in my comments regarding soil pH. Please re-read my text; I have gone through it and replaced the word potassium with the word calcium, as it should have been.

The comments that I made regarding soil pH said nothing about testing soils for calcium by using pH as a measure of calcium. I was describing the reason why soil pH changes from late winter/spring to fall, and then why it changes again from fall to late winter/spring.

No one who is knowledgeable about soils and soil testing would use pH to determine the level of calcium in a soil. The test for pH and the concentration of soil calcium are somewhat correlated, but only very poorly so. In a soil testing laboratory, pH is determined in a suspension of soil to water. Calcium is determined in a separate extracting solution such as Mehlich III, 1.0 molar ammonium acetate, or other extractant, but no lab to my knowledge ever analyzes calcium in the filtrate after determining soil pH.

Very few soil scientists these days, if any, pay much attention to soil calcium. It is a rare situation to see a plant growth response to applied calcium because plant growth will be retarded by phytotoxicity of aluminum and/or manganese before soil calcium will become so low that plant growth will respond to added calcium.

If the soil pH indicates that a soil is extremely acidic, limestone is recommended to raise pH. Since limestone is calcium carbonate (calcitic), or calcium magnesium carbonate (dolomitic), the assumption is made that adequate calcium will be available after the limestone has been dissolved by the acidity in the soil. In the case of high pH, above about 7.4, the soil is considered alkaline and alkaline soils contain native calcium carbonate, so the assumption is made that alkaline soils contain adequate plant-available calcium.


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## cattleman4170 (Jan 26, 2010)

The question was " what effect does all the rain have on soil pH" The answer is, NONE.
Thanks


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## hay wilson in TX (Jan 28, 2009)

*You all realize that in theory a soil can be deficient in Calcium and have a high pH? 
There is an idea out there that calcium alone will only push the pH up to 8.0. To go above that requires magnesium or sodium. * There is almost always some magnesium in any soil and that is how a pH with excessive calcium will be in the 8.2 range or higher. To get into the 9.0 pH range requires excessive sodium.

Here I am delving into my area of ignorance. Alfalfa uses 4 or more times the amount of calcium as it does magnesium. Now if the land was limed over time for the alfalfa, with a high Mag Lime, eventually the magnesium levels would become excessive, driving up the pH even when the calcium has been depleted to a deficient level. * Pure conjecture! *


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