Good soil PH meter

420harvest · 10-25-2009, 02:33 PM

Can anyone recommend a good accurate soil ph meter?

Healer · 10-25-2009, 07:41 PM

Meters made to test soil are notoriously inaccurate. Back when I grew in soil I tried and tried to find an accurate soil pH meter to no avail, found this study concluding that they are inaccurate too.

Quote:

Extension agronomists are often asked by farmers to determine why crop plants are stunted or have abnormally colored leaves. Soil acidity and alkalinity are common fertility problems that can cause these symptoms. In a study to measure the accuracy of in-field pH test kits, hand-held pH meters and pH color indicator kits provided fast and reliable results. Soil pH probes gave poor measurements of soil acidity and should not be used by Extension agents. Results by untrained personnel with hand-held pH meters varied by individual. Agents using pH test kits should read instructions carefully before using these instruments.

Then I found these instructions for using a hydro meter to test soil pH, which I used many times with distilled water. It came from a major university .edu site; the page has since been taken down but I saved it.

Quote:

Soil pH Determination

Soil pH is usually determined potentiometrically in a slurry system using an electronic pH meter (McLean, 1982). The proliferation of pH meters in recent years precludes an in-depth discussion of meter operation; specific instructions are provided with individual units. However, several precautions are presented as general considerations for all labs. First, electrodes should be checked and maintained frequently to prevent residue buildup which may affect operation. Rinsing between each soil sample, however, is not usually necessary. Electrodes should be protected in a way which prevents insertion to the very bottom of a slurry vessel which will cause abrasion of the sensing surface, decreasing electrode life and causing inaccurate readings. All meters should be calibrated routinely at two points before operation. One point of calibration should be at pH 7, while the other should be chosen based on the range of soil pH normally encountered by the lab. A lab dealing mainly with acid soils should calibrate across the acid range (second point at pH 4, for example) while a lab dealing with mainly alkaline soils should calibrate across the alkaline range (use second pH buffer at pH 9 or 10).

Reference and/or combination electrodes for measuring soil pH should be chosen carefully because flow rates at the liquid junction can affect the accuracy of soil pH readings. Labs may wish to use a set of reference soil samples of known pH to evaluate the performance of electrodes. Such samples should be stored and handled under carefully controlled conditions to prevent changes in soil properties over time. The reference soil pH of these samples should be determined using the average reading of several meters. Electrodes which fail to produce pH readings consistent with established values when calibrated with clear buffers can be calibrated successfully using the reference soils themselves, but only if soil storage and handling are well controlled.

Soil pH is normally measured in a soil-water slurry. The presence of soluble salts in a soil sample may affect pH, and for that reason, some analysts prefer to measure it in a mixture of soil and 0.01 M CaCl2 (Graham, 1959; Schofield and Taylor, 1955). The excess salt in this solution masks the effects of differential soluble salt concentrations in individual samples. Procedures for each method are given below.

Soil pH Procedures

Equipment:

1. pH meter with appropriate electrode(s).
2. Electronic balance or standard, 5 cm3 stainless steel scoop.
3. Pipettes or automatic dispensers.
4. 1-oz. paper cups or equivalent.

Reagents:

1. Distilled or deionized water.
2. 0.01 M CaCl2: Completely dissolve 1.47g CaCl2.2H2O in 1 L of distilled or deionized water.
3. 1.0 M CaCl2: Completely dissolve 14.7g CaCl2.2H2O in 100 mL of distilled or deionized water.
4. Standard buffer solutions for calibrating pH meter, usually pH 4.0 and pH 7.0.

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.
6. For the CaCl2 pH measurement, add 1 drop of 1.0 M CaCl2 solution to the previous sample. Alternatively, prepare a sample as was done in steps 2 and 3, using 0.01 M CaCl2 instead of water. Stir vigorously and let stand for 30 minutes, stirring occasionally. Read the pH as in step 5.
7. Save the water pH soil sample for use in the lime requirement determination procedures described below.

Shorter version:

The amounts of soil and water can be reduced or increased as long as both are by the same factor.

Soil pH Procedures

Equipment:

1. pH meter
2. scale
3. small container to hold soil sample and water
4. Distilled water

Procedure:

1. Weigh 5 grams of air-dried soil in container
2. Add 5 mL distilled water to the soil sample.
3. Stir vigorously for 15 seconds and let stand for 30 minutes.
4. Place pH meter sensor in the slurry, swirl carefully, and read the pH immediately. Ensure that the sensor tip is in the slurry and not in the overlying solution.

420harvest · 10-25-2009, 09:19 PM

What about testing the runoff with a hydro meter?

**Lou Cypher** · 10-25-2009, 09:50 PM

Quote:

Originally Posted by 420harvest

Can anyone recommend a good accurate soil ph meter?

Hanna Soil pH/Temp Waterproof Meter |

Healer · 10-25-2009, 10:47 PM

Quote:

Originally Posted by 420harvest

What about testing the runoff with a hydro meter?

Testing the pH of runoff is not an accurate method of measuring soil pH. I wish it were that easy.

surfnsailor · 10-25-2009, 11:54 PM

What if we got the top 10 cultivators in here to say how they keep their soil in spec?

From Booty to Buzz to Blue and right on down the list.

420harvest · 10-26-2009, 12:12 AM

very good idea

PiGMaN · 10-26-2009, 04:07 PM

As long as the soil you are usin is desent quality,( store bought not recycled potting mix or the crap you dug up out of the garden )
Add lime to your soil and aways ph test the water you wont have to check or even think about your soil ph.

420harvest · 10-26-2009, 07:17 PM

Whats a good cheap water ph tester?

Healer · 10-28-2009, 08:57 PM

I've been using this one for the last year or so, and another Oakton previously that worked great until I dropped it, probably just needs a new sensor. You might be able to find a better price, just grabbed the first link to it I found.

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