ec/pH meters

[Jim Barrett <jeb@gnv.ifas.ufl.edu>]

The differences you are seeing are due to the different techniques used and
would be expected.  You are doing a 2:1 test and most labs do a saturated
media extract (SME) procedure that is closer to a 1:1.  I am not familiar
with Ohio's procedures, but probably at the time of measurement the salts
are about twice as concentrated in their procedure as in yours.  This does
not mean that one is correct and the other is wrong.  It does cause a
problems if you have a recommended Ec of say 1.5 and do not know if it is
based on a 2:1 or SME test.  It also means that one can not directly
compare their own results with a labs.  However, with time and good records
for a given crop, one should generally know the desired Ec levels for their
test and the lab's.

Jim Barrett


>Return-path: <owner-florinet@agvax2.ag.ohio-state.edu>
>Date: Thu, 29 Jan 1998 16:56:55 -0600
>From: Marty Reichenberger <mreich@terraworld.net>
>Subject: ec/pH meters
>Sender: owner-florinet@agvax2.ag.ohio-state.edu
>To: Florinet <FLORINET@agvax2.ag.ohio-state.edu>
>Errors-to: owner-florinet@agvax2.ag.ohio-state.edu
>Warnings-to: <>
>Reply-to: Marty Reichenberger <mreich@terraworld.net>
>X-Listname: Floriculture Faculty Discussion Group
> <FLORINET@agvax2.ag.ohio-state.edu>
>
>Since we are discussing soil testing meters, I have a question for those
>who use the Myron AG-5 EC/pH meters.  We use a 2:1 distilled water to
>soil ratio, let the solution stand for 12 hours, decant off the solution
>and test it.  The results of the EC are, let's say 1.3.  If we send the
>same sample to a lab, Ohio State, the reading they are getting is
>approximately 2.5.  Is anyone else noticing that much difference in the
>EC readings?  The pH agrees with Ohio State 100%.  I have calibrated the
>meter with the solution supplied, and the meter is nearly new.  I also
>spoke with the company and they told me that if the calibration solution
>was reading correctly, then the meter was working.  Any ideas of the
>problem we are having?  We have let the solution stand for 15 minutes to
>24 hours and the EC reading increases, but never near laboratory
>values.  I am also extremely careful in the prep of the solution being
>tested.  Any ideas to help would be appreciated!!!!!
>
>Thank you,
>Marty Reichenberger
>Green Thumb Greenhouse
>Independence, KS
>
>