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What's the most accurate way to measure soil pH

Posted by organic_wonderful (My Page) on
Fri, Mar 4, 11 at 23:11

I have a pH meter and have been told there is a way to use these pH pens to measure soil pH accurately. Is this true? If so, what's the procedure?

I've been lead to believe that those analogue pH meters (the ones with a long pH probe you stick in the soil) are completely inaccurate and are basically useless. I'm not sure if this is right, but I'd love to find out.

I understand you can get chemical tests that use colour changes to give a pH indication, this might be the solution.

What do you guys think?


Follow-Up Postings:

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RE: What's the most accurate way to measure soil pH

  • Posted by jolj 7b/8a-S.C.,USA (My Page) on
    Fri, Mar 4, 11 at 23:59

For a few hundred dollars you can get one that is right every time. My wife went to school four 4 years to learn how to test blood,water & solids.I think the best way is to send a simple to a lab.


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RE: What's the most accurate way to measure soil pH

I have used the inexpensive ($40 to $100) pH meters and have found most of the time they give inaacurate readings reporting soil pH the same as Vinegar and a solution of baking soda, and they will not tell you if your soil has sufficient levels of Calcium and Magnesium. A good reliable soil test from a soil testing lab is much better.


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RE: What's the most accurate way to measure soil pH

  • Posted by ericwi Dane County WI (My Page) on
    Sat, Mar 5, 11 at 9:17

If your pH meter has a calibration feature, and you have a solution of known pH, then you can calibrate the meter, and it should be accurate to +/- 0.1 pH unit. Here in Madison, Wisconsin, our tap water, supplied by the city, has a known pH = 7.6, so I am able to use it for calibrating my pH meter. I use 5% white vinegar, from the grocery store, for the lower point. I have used both a pH meter, and dye indicator solutions, for testing soil pH. The results agree, however, dye indicators are only accurate to +/- 0.2 pH unit. Does your "pH pen" have a battery, and an LCD display?


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RE: What's the most accurate way to measure soil pH

No doubt that the lab is going to give you the best results. I'm using one of the chemical test products that seems to be fairly accurate for what I need it for. Cost me about 20 bucks and used it a dozen times so far.

Here is a link that might be useful: pH test of used coffee grounds


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RE: What's the most accurate way to measure soil pH

  • Posted by ericwi Dane County WI (My Page) on
    Mon, Mar 7, 11 at 13:38

There has to be water present in order to measure pH. The source of the water can affect the test results, and it may dominate the test results. Here in Madison, our tap water has pH = 7.6, so it can't be used for making calibration standards, nor can it be used for hydrating a soil sample. I have used steam distilled water in the past, however the steam distilled water has some lime content, and careful measurement indicated that the pH was around 7.2, so now I am using RO(reverse osmosis) de-ionized water, pH = 7.


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RE: What's the most accurate way to measure soil pH

At the university lab, many decades ago, we would add some water to the soil and shake it up daily for a couple of weeks, ideally a month, testing with the pH meter. This way we could calculate buffer capacity. See bcn.boulder.co.us: buffer capacity. Personally I think that if you don't know about buffer capacity, and don't want to find a lab that will determine buffer capacity for you, then you might as well just shake the soil with some water and use an aquarium test strip.


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RE: What's the most accurate way to measure soil pH

That's actually a rather poor way to measure soil pH, but I've seen a lot of people do it.

For a good soil pH test you first need a representqtive sample of the soil over the area of interest. A hole doesn't provide that. Second, the method is based upn extraction, typically one-part soil to one part water. But if the soil is heavy in clay or organic matter, a 1:2 ratio can be used. Next take an amount of your mixed representative sample - depending on how you're going to measure as little as 2 tablespoons or as much as 1/4 cup will do - and in a very clean container mix it well with the appropriate amount of distilled water (the grocery store or drug store bottled variety will work just fine). A clean glass jar with a tight fitting lid works great for mixing - shake for about 30 seconds, the let it settle for 30 min's to one hour. Then use a suitable method to determine the pH of the soil extraction liquid after settling. Suitable methods can be a good glass electrode or a good colorimetric indicator. The stick-in-the-soil pH probes just don't work.

For more on testing soil pH and other measures of soil health you can do, see the link below.

Here is a link that might be useful: USDA Soil Quality Test Guide


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RE: What's the most accurate way to measure soil pH

What is the source of the water you suggest using Trees?
Unless that water is pH neutral it will affect the reading you get whether using a pH meter or pH strips. Then that test will not give you the information you need to make an intelligent decision about what to do to maybe correct any anomaly.


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