I agree with those who have said measuring water, nutrient solutions and/or runoff pH are not accurate methods of testing soil pH.
Here are some links to studies testing the (un)reliability of different soil pH probes:
http://ipcm.wisc.edu/wcm/pdfs/2004/PetersJune2.pdf
"Even though this was not a highly scientific study, is clear that the accuracy and resultant value of pH measurements taken in the field are subject to a tremendous amount of potential variability. It can not even be stated with much confidence that an in-field test can give a reliable assessment of whether a field has a relatively high vs. low soil pH."
http://www.joe.org/joe/2001august/tt3.html
"Despite careful attention to moistening the soil and shining the tip of pH test probes, all four probes read 6 in limed and non-limed soils."
"All in-field pH test methods, except the test probe, produced satisfactory measurements of soil pH as compared to results from 82 laboratories testing the same soils"
"A soil probe that was inserted into moist soil in plots provided poor response to soil pH and is not suitable for diagnosis of soil pH problems."
Here is the soil pH testing method I use (used to be online at
http://ag.udel.edu/extension/informa...c/chap3-95.htm but not anymore):
Soil pH Procedures
Equipment:
pH meter with appropriate electrode(s).
Electronic balance or standard, 5 cm3 stainless steel scoop.
Pipettes or automatic dispensers.
1-oz. paper cups or equivalent.
Reagents:
Distilled or deionized water.
Standard buffer solutions for calibrating pH meter, usually pH 4.0 and pH 7.0.
Procedure:
Calibrate the pH meter over the appropriate range using the standard buffers.
Scoop 5 cm3 (or weigh 5 g) of sieved, air-dried soil into a paper cup. See Chapter 2 for details on soil sample preparation and scooping technique.
Add 5 mL distilled or deionized water to the sample.
Stir vigorously for 15 seconds and let stand for 30 minutes.
Place electrodes in the slurry, swirl carefully, and read the pH immediately. Ensure that the electrode tips are in the slurry and not in the overlying solution.