MadSci Network: Earth Sciences

Re: Is there a standard method to measure soil pH (acidity)?

Date: Fri Jun 25 16:44:40 1999
Posted By: Charles McClaugherty, Faculty, Environmental Science (Ecology), Mount Union College
Area of science: Earth Sciences
ID: 929959513.Es

There are two generally accepted methods for measuring soil pH

The official and rarely used method calls for usin a 0.011 Molar soution 
of Calcium chloride.  This creastes an ionic strength similar to what 
might be found in soil water and therefore diplacing a few more protons 
thatn would be found in distilled water.  The other involves using 
distilled water.  The latter approach almost always gives a higher pH valu 
(about 0.5 units in a typical forest soil)

The bigger question might be what proportion of water and soil you should 
have in your mix.  In general the answer is that one should use only as 
much liquid as is necessary to allow you to submerse your probe.  The 
actual proportion varies depending on how much organic matter is in your 

Finally, after mixing the soil and liquid, it is very important to allow 
the suspension to settle as clay particles can migrate pst the electrod 
and cause instability (drift) in the readings.  

The important thing is to report HOW you made the measurements.
Good Luck!

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