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.... posted here for fast access and reposting where needed, for those without a quality soil pH probe,....
...The Pour Thru (run-off) Method for Testing Container Media:
* first, test the pH of your usual water source*
1. water containers to saturation (so that a few drops of water come out of the bottom of the container) with the normal irrigation water they have been receiving... do not use a nutrient solution, it will badly skew the results...
2. after container has drained for one hour, place a saucer under the container -- make sure to use a clean, uncontaminated container- any residuals in dirty one will skew the readings,....
3. pour enough distilled (DI)/RO water on the surface of the container to get about 50 mL (1.5 fluid ounces) or so of leachate to come out of the bottom of the container (Table 1)
4. collect leachate for pH and EC testing;
5. calibrate pH and EC meters, if not done recently
6. measure pH and EC of samples, then do this calculation-->
-- Calculation ->>> If your runoff pH is higher than your starting (water) pH, use this equation to determine your soil pH:*
Soil pH = Runoff pH + Difference
--- If your runoff pH is lower than your starting pH, us this equation:
Soil pH = Runoff pH - Difference.
For example, say your the starting pH of your solution before it goes in is 6.5 and the pH of your runoff is 7.0. The difference is +0.5, so using the above equation:
Soil pH = 7.0 + 0.5*
Soil pH = 7.5
If your starting pH is 6.5 and your runoff is 6.0, your difference is -0.5 and using the above equation:
Soil pH = 6.0 - 0.5
Soil pH = 5.5
...The Pour Thru (run-off) Method for Testing Container Media:* first, test the pH of your usual water source*
1. water containers to saturation (so that a few drops of water come out of the bottom of the container) with the normal irrigation water they have been receiving... do not use a nutrient solution, it will badly skew the results...
2. after container has drained for one hour, place a saucer under the container -- make sure to use a clean, uncontaminated container- any residuals in dirty one will skew the readings,....
3. pour enough distilled (DI)/RO water on the surface of the container to get about 50 mL (1.5 fluid ounces) or so of leachate to come out of the bottom of the container (Table 1)
4. collect leachate for pH and EC testing;
5. calibrate pH and EC meters, if not done recently
6. measure pH and EC of samples, then do this calculation-->
-- Calculation ->>> If your runoff pH is higher than your starting (water) pH, use this equation to determine your soil pH:*Soil pH = Runoff pH + Difference
--- If your runoff pH is lower than your starting pH, us this equation:
Soil pH = Runoff pH - Difference.
For example, say your the starting pH of your solution before it goes in is 6.5 and the pH of your runoff is 7.0. The difference is +0.5, so using the above equation:
Soil pH = 7.0 + 0.5*
Soil pH = 7.5
If your starting pH is 6.5 and your runoff is 6.0, your difference is -0.5 and using the above equation:
Soil pH = 6.0 - 0.5
Soil pH = 5.5
Last edited:
...well, 8.3, but yeah close enough,...alkaline soil is fairly uncommon, so one thing I always ask is if your meter is recently calibrated, has reasonably fresh batteries (weak power makes them do wonky things), and are the electrodes clean (residues tend to build up after a while),... if it's all good, then we need to figure out the source of the alkalinity,... under alkaline conditions, a few of the nutrient metals and P, become locked out and unavailable,... So, your water source, hardness (ppm's), soil brand, any amendments put in, your nutrients,...
Thanks GR! I can't take total credit for it all, this is a combo of other sources I've found here and elsewhere,... I still am of a mind that the r-o method is faulted in general, too many sources of potential error, but this modified method helps address some of them... The idea is to get the best possible representative pH, which is why it calls for saturating with the usual water source and whatever native buffering capacity it has, then using pure water (low to no ppm, therefore no buffering capacity) for the final pour to collect leachate, without it adding more buffering action to it, and skewing the results... plus, saturating at first with RO/DI would force more than normal dissolution of solubles into solution, further skewing final collected leachate... it's just an estimate in the end, and done wrong, it's a crappy one! Most folks don't realize, the pH scale is a logarithmic one, like the Richter scale for earthquakes; going from, say, 7.0 to 6.0, is in fact a 10-fold increase in [H+] concentration! In other words, even decimal increments are big changes, despite what appears to be a small numerical increase/decrease,... So, accuracy really matters! It's the reason I keep harping on about peep's getting a quality pH probe, like the Accurate 8, because nothing beats direct in-soil measurements- 
