Do those instant soil testers work?

I've been interested in the instant soil testers, where you can plug it into the ground and it will tell you the pH, TDS, and EC of the soil. I've been looking at Hannah Instrument's equipment. Any suggestions?

I have a Hannah pH/EC meter that works great, but not by just plugging it into the soil. It only works when submerged in a liquid.  To soil EC you need to make a saturated soil extract or use some dilution, often 5:1 water:soil.  It's tricky and I don't use it much for that. 

Some of the inexpensive equipment works well enough for pH and soluble solids/conductivity. To have any confidence, the tool should be checked from time to time with a test solution - could be something as simple as a salt solution of known strength, or a dilute solution of citric acid, vitamin C, or battery acid.  I would not put much stock in the tests for individual minerals or the 'instant fertility kits' from garden centers - much better to send a sample to a lab for that.

Even pH can be misleading in some conditions. Most aggies measure 'soil reaction'  which is the average pH of water from the soil. But if there are large particles of limestone or other alkaline rocks in the soil, this can create alkaline microzones in a soil that measures acid - enough to allow plants to draw what they need from both acid and alkaline environments.

Leucaena wrote:
I have a Hannah pH/EC meter that works great, but not by just plugging it into the soil. It only works when submerged in a liquid.  To soil EC you need to make a saturated soil extract or use some dilution, often 5:1 water:soil.  It's tricky and I don't use it much for that. 

I don't really see how mixing a 5:1 water:soil ratio would be that hard. Could you elaborate a little?

Jonathan_Byron wrote:
Some of the inexpensive equipment works well enough for pH and soluble solids/conductivity. I would not put much stock in the individual minerals or the 'instant fertility kits' from garden centers - much better to send a sample to a lab.

Not if you purchase a real test kit from a lab supply, but those will run you about $600+ dollars. You'd have to a lot of soil tests before it became economical.

HeritageFarm wrote:
I don't really see how mixing a 5:1 water:soil ratio would be that hard. Could you elaborate a little?

From http://ecorestoration.montana.edu/mineland/guide/analytical/chemical/solids/ec.htm

"The saturation paste extract method is the most commonly used laboratory procedure for determining conductivity. The soil sample is saturated with distilled water and mixed to a paste consistency. After standing for one hour, the salts will dissolve and the electrical conductivity of water extracted from the paste is measured using electrodes. A variant of this method involves measuring conductivity from a 1:2 soil-water mixture after 0.5 hours of shaking. The latter method takes less time but often is not as well related to the soil solution as is the saturation paste extract method."

So, a bunch of shaking and waiting, and then hoping that the dilution you used is the same as whatever the author you're reading used.

Also, a lot of info about crop growth and EC is discussed in terms of the EC of the irrigation water, which is what I do measure often.

I have the Horiba B-173, for conductitivy and B-213 for pH.  The are expensive and can
be gotten from Pike Agri in Maine.  Bruce Tainio says plant sap should be 6.4
and if it is higher, you need more or different anions, and if it is lower more cations--usually
Calcium.  There is a lot to read on the Pike Agri site.  Along with a refractometer, you should
be able to grow really good food.

Good Luck,

Dave Rogers in the  Adirondacks