Measuring soil PH

[Corrado & Rina]

Dear all,

Can you measure soil PH using electronic devices? Do you need specialist devices or could you do a good job with a small portable PH meter for fish tanks?

Regards

Corrado

[Steve Garvie]

pH is essentially a measurement of the dissolved hydrogen ion concentration of a solution expressed on a logarithmic scale. It has no direct relevance to a solid.

You would need to dissolve the test soil sample in pure water of pH7 (distilled water; rainwater is generally acidic due to dissolved CO2 & atmospheric pollutants such as sulphides) to assess the "acidity/alkalinity" of the soil.

[Corrado & Rina]

pH is essentially a measurement of the dissolved hydrogen ion concentration of a solution expressed on a logarithmic scale. It has no direct relevance to a solid.

You would need to dissolve the test soil sample in pure water of pH7 (distilled water; rainwater is generally acidic due to dissolved CO2 & atmospheric pollutants such as sulphides) to assess the "acidity/alkalinity" of the soil.

Thanks Steve! I am aware of how PH works, but my point is very, very practical:  can I water a jar full of soil, shake it, leave it there for a couple of hours, and then stick a fish tank PH meter in it to test the PH? Or do I need a different type of PH meter?

Best,

Corrado

[Steve Garvie]

If using a neutral water source to "dissolve" the soil then yes you can use a fish tank pH meter. But the acid/base buffering capacity of the soil is more important than a one-off pH reading.

Check Ebay for hydroponics pH meters as they are not that expensive. It is also worthwhile getting a water hardness/dissolved salts meter as this can be a useful guide when fertilising orchids.

[Robert Pavlis]

A fish tank pH meter and a hydroponic pH meter are probably the same thing. The importance is the accuracy.

For gardens and potted plants a good quality electronic meter should work fine since you only need an approximate reading. In reality you can't change the pH of your soil very much anyways -- not like you can in a fish tank.

Dissolve some soil on distilled water, let sit a couple of minutes, and measure.

pH kits and electronic meters sold for gardeners are useless. http://www.gardenmyths.com/accuracy-of-ph-test-kits/#more-1070

[Corrado & Rina]

It is also worthwhile getting a water hardness/dissolved salts meter as this can be a useful guide when fertilising orchids.

Thanks Steve! Would that be a conductivity meter, or something different?

Additional questions:

1)PH meter, do you have good brands / models in mind?
2)water hardness/dissolved salts meter, do you have good brands / models in mind?

What do you use?

Regards

Corrado

[Steve Garvie]

I'm at work at the moment so I can't check the exact models I use but I bought them on Ebay as a package. Something like this:

http://www.ebay.co.uk/itm/Quality-Digital-PH-EC-TDS-Temperature-Tester-Conductivity-Meter-Hydroponics-/321483386564?pt=UK_Swimming_Pools_Hot_Tubs&hash=item4ad9e72ec4#ht_4036wt_959

You will need to purchase some buffer solutions for calibration.

[Corrado & Rina]

A fish tank pH meter and a hydroponic pH meter are probably the same thing. The importance is the accuracy.

For gardens and potted plants a good quality electronic meter should work fine since you only need an approximate reading. In reality you can't change the pH of your soil very much anyways -- not like you can in a fish tank.

Dissolve some soil on distilled water, let sit a couple of minutes, and measure.

pH kits and electronic meters sold for gardeners are useless. http://www.gardenmyths.com/accuracy-of-ph-test-kits/#more-1070

Thanks a lot. Also for the very instructive link .... I have used the link in the page to read also the other tests, amazing work.

Regards

Corrado

[ian mcdonald]

There are many devices for measuring the pH of soil. They range from the "amateur gardener" to the professional scientist, with prices to match. If you search the internet you should see a wide range.

[Natalia]

Friends,
We can discuss  how device is better, but for accurate measurement in the first place should be the method of calculation. For example: take 50 g of soil of 10 cm depth, add 100 ml of distilled water, mix, allow to stand (or filtered) and then measure the pH. This is an example ...
In fact, all sold garden tools produce large deviations in the measurement. Similar results can be obtained using the paper indicator strip  If you need more precision - it is easier to give a sample to a specialized laboratory.
In garden  is easier to use the test strips.
I am a chemist by profession and I know this topic.

[Jupiter]

Natalia is spot on. My wife is a soil scientist and I've done soil pH recently on hundreds of samples in my work. 50g of soil and 100ml of distilled water (or rain water), shake it up well for a few hours then allow to stand overnight to settle. Measure the pH of the clear water on top. Regarding the pH of your starting water, it hardly matters at all. Rain water or distilled water may measure lower pH than 7, but this is not a measure of the actual titratable acidity. The actual acid forming ions in rainwater are in tiny concentrations and will vanish into insignificance once in the soil.

The pH indicator strips with three pads on the one strip are quite accurate and probably good enough for gardeners applications.

Search for Merck pH indicator strips and look for the ones with three tabs of different indicators. I won't post links to ebay or amazon, but those are the sites you'll find them on.