Testing Soil pH

[mrbong73]

Hi folks,
There seems to be a common misconception among cannabis growers regarding how to test the pH of your soil.
Now I know there are the "testers" and the "non testers" in soil gardens so I don't want to go into that here.
Most soils have a buffering capability so small adjustments in water pH will usually not have an immediate effect on the soil pH. (As I understand it)

Also, I have never seen a scientific study or heard of a testing lab that uses container runoff to test for soil pH. (I would love to hear otherwise)
Study

Just an FYI kinda thing.

http://www.eutechinst.com/tips/ph/15_soil_ph.pdf

An excerpt from a USDA article:

Measuring Soil pH in the Field
Pocket pH meters, standard dyes, and paper pH indicator strips are commonly used when pH is measured in the field. Pocket pH meters can be used in 1:1 H2O or any soil:salt solution. The meters must be well maintained and calibrated to be reliable. They are sensitive and can become faulty. Clean them as specified, keep them well calibrated, and do not leave them where they will be subject to excessively hot or cold temperatures.

Although they continue to improve, pH meters are less dependable than standard dyes, which are quite accurate. Soil pH measured with pH meters in a laboratory setting and then measured with dye differs by a pH unit of no more than 0.3 when the dye is used carefully. Temperature extremes and prolonged exposure to sunlight can affect the reliability and longevity of dyes. Several kits are in use. Some of them include a neutral salt. As a result, the pH measured from different kits may vary. The same indicator dyes that are applied to 1:1 H2O can be applied to 1:2 0.01 M CaCl2 and 1:1 1 N KCl soil:water suspensions.

Paper pH indicator strips are bonded with dyes. They can be used in 1:1 H2O or any soil:salt solution. They are as accurate as standard liquid dyes and are not so sensitive to temperature and sunlight. Unlike pocket pH meters, these strips are not subject to breakage and do not need to be calibrated and maintained. Indicator colors are easily distinguishable.

Cite

 

[mrbong73]

Here's one way outlined in the above study:

Procedure:
1. Calibrate the pH meter over the appropriate range using the standard buffers.
2. 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.
3. Add 5 mL distilled or deionized water to the sample.
4. Stir vigorously for 15 seconds and let stand for 30 minutes.
5. 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.

 

[waayne]

Excellent thread mrbong
The protocol you are suggesting works very well and is accurate.
I have tested my soil this way for a couple of decades.With excellent results.
I always let my slurry soak 24 hours before testing though......:pimp:

 

[Udyana Peace]

mrbong73

In the 'real world' of agriculture the test and analysis conducted in conjunction with testing pH as it relates to Base Saturation and CeC is the real indicator of viability and fertility. [cite from Clemson University]

pH is certainly 'an indicator' of a soil's fertility but it is not the holy grail as viewed by most cannabis growers.

A holdover from the original hydroponic days perhaps? i.e. not much basis in soil science in the whole scheme of things.

UP

 

[mrbong73]

Thank you wayne and UP for stopping by.

I do wonder how the alkalinity of tap water (mine is 450ppm and 7.8pH) affects the soil pH over time.

Any thought on using citric acid(via fresh lemons) to neutralize carbonates etc in the water.

Only fuzzy understanding on how this works.

 

[Shredder]

Yup, good idea to add citric acid to high ph water. Look in the canning dept of the grocery store to find it powdered and ready to use. I put a tea spoon of it in a squirt top water bottle, fill with water, shake and your good to go. Just give your water bucket a squirt or two and check the ph until you get it where you want it. Once you get a feel for how much to use, you don't have to measure each time.