Re: [CH] pH testing & challange

Harold Eddleman Ph.D. (indbio@disknet.com)
Sun, 21 Mar 1999 09:32:38 -0800 

Byron.Bromley@Gsd-Co.Com wrote:
> 
> 
> Take a Scotch Bonnet, If you can get 40 pods on that plant with a
> soil pH of 8 or 4, I will supply you with all the chile's you can eat 
> 
> Byron

Dear Bryon
  Perhaps, you misread Cameron's letter. I think he was saying pH close
to 6 is good enough for gardening and pH 4 is safe for canning. If I
understood him correctly, I agree with him. I think many people who
think they are operating closer to the optimums than pH 6 might find
much of their garden is below 6. 
  Until a few months ago I had access to a really good pH meter. I
tested the pH of a soil grab from my garden and got pH over 8.0. I was
shocked! I had earlier checked with the Purdue University soil lab on
procedure and I do not think I made any error. The garden has always
done very well. This old house has always been heated by wood and the
ashes went onto the garden for 80 years that I know about. Wood ash is
much higher in Na2O than K2O. Thus, wood ashes may not be as good for a
garden as generally believed. I regret that I never did get around to
taking 20 soil grabs from the garden and testing them I will do that
some day. I intended to see how much the pH varied. 
  I had a blackberry test in that garden with all the cultivars of
thornless blackberry. Some of those are so sour I have not been able to
eat them at some plantations. In my garden those really sour cultivars
seemed to be pretty acceptable. I have since heard that blackberries are
not as sour when grown on high pH soils. I do not know that my soil was
really above 8.0, some error was possible but seems unlikely because I
used pH 7 and pH 10 buffers to stardardize the meter.
  Cameron was saying that quality, dependable pH meters cost $500 to
$700 or $1000 ready to use and that price is very high for a commercial
grower. When one takes a sample for analysis he is told to take soil at
many places and pool the soil. I seems to me the pH could vary greatly
at those sites. Therefore many people who think their pH is correct
might be quite high in places and low in others. 
  As an example of low priced meters is the Hanna Intruments pHep+ for
$39.50 having automatic temperature correction, claiming accuracy of 0.1
pH unit. But there seems to be no provision for calibration, length of
service, etc. (8oo) 504-2662. It appears it would take a large volume of
buffer to check the accuracy of this meter. 
  Twelve years ago I read a book by American Chemical Society on the
trace elements required by plants. The solubility of these elements is
the main reason we are concerned about pH. The book had a chapter on
each element required by plants. The optimum for the various elements
varies a great deal. Looking at optimums, I was puzzled how the
recommended 6.5 or 6.8 came into being (I may have forgotten this may
not be the optimum, and the optimum varies with the crop).
  I had a greenhouse experience I had trouble believeing. I had
landscape clock lying on wire support. This supported 6 inches of pure
sand. In this I planted sweetpotato microcuttings. I fertilized with
liquid plus phosphoric acid. I mixed that in a barrel and pumped that
onto the sweetpotato beds and caught the water that came through for
analysis. I applied lots of fertilized water so that 1/2 ran thru the
sand to wash out any accumulated salts.  The pH of the water going in
was 2 or below, but the water coming out was nearly 7! Sand is a poor
buffer, how could the pH change so much in a minute or less?
-- 
Harold Eddleman Ph.D. Microbiologist.       mailto:indbio@disknet.com 
Location: Palmyra IN USA; 36 kilometers west of Louisville, Kentucky
http://www.disknet.com/indiana_biolab