Soil pH sensor

hello guys! I am really new to this environment. I am trying to find a pH sensor that can be installed to the soil directly and be interfaced with the arduino. But i am not lucky to find it yet. Do you have any idea guys? Thank you so much for the response. It's will help me a lot.

I have seen regular pH probes that had been ruggedised to use in soil. Those should be able to connect to a regular pH probe amplifier, which in turn can be read by an Arduino.

wvmarle: I have seen regular pH probes that had been ruggedised to use in soil. Those should be able to connect to a regular pH probe amplifier, which in turn can be read by an Arduino.

The soil would have to be soaking wet for that to work well. And it would give you the pH of the water in the soil which may be affected by the soil and not really the soil pH as gardeners tend to want it reported.

A I recall, when doing soil analysis, the standard test for soil pH was to mix 1 part soil with 2.5 parts deionised water (can't remember if it was by weight or volume), so it does need quite a lot of water. As wvmarle says, there are reinforced probes available which used to be called spear electrodes. Likely to be pricey

and not really the soil pH as gardeners tend to want it reported

I'm not a gardener, so what would that "gardener's soil pH" be?

The entire concept of pH depends on lots of water being present.

Yeah there's some measure that gardeners use and call pH that is more of a measure of how much hydroxide salts are present in the soil. I don't understand it very well as I'm not a gardener either. But I am a chemist who has been asked about it a few times and figured out that they have something other than solution concentration of hydronium that they all pH.

Gardeners refer to acid or alkaline soil. What they really mean is soil that is largely chalk based (alkaline) , like mine, or clay and humus based (acid). The practical difference is that you can't grow azaleas or hydrangeas on chalk or decent brassicas on clay. Theory has it that an alkaline soil "locks up" iron and magnesium necessary for chlorophyll production. I live on top of about 200-ft of solid chalk, so adding chelated iron has no effect. It stands to reason that you can't measure the pH of a dry-ish soil with a conventional glass membrane electrode, hence the reason for a standardised soil analysis test. Most of my work was with water and sewage, but I seem to remember that for some of the solids analyses, soil would first be dried at about 100 Celsius, then rehydrated to form a slurry. The only things that appreciate a chalk soil are the sodding snails.

Maybe you are trying the wrong crop. At least some wine grapes do really well in chalky soils.

E.g. the Burgundy region: http://www.winegeeks.com/articles/139

Had a nice crop of black grapes (greenhouse) this year and the black currents love it. Did a tour of Burgundy a few years ago and impressed by the top notch vinyards with great big lumps of chalk everywhere, and the lovely Crème de Cassis. But, somehow, the South Downs aren't quite the same. The French have the knack and the food to go with it.

wvmarle: I have seen regular pH probes that had been ruggedised to use in soil. Those should be able to connect to a regular pH probe amplifier, which in turn can be read by an Arduino.

Which is which? i am thinking of a soil pH meter. But is it possible for it to be interface to the arduino? Thank you.

Please do your own homework, find probes that would be suitable for your specific use and budget, and we'll be happy to comment on specific types and help getting them to work with Arduino.

I know the things exist and at least some work like regular pH probes, which are quite straightforward to get working with Arduino. You can buy a pH sensor amplifier or you can build your own (I did just that on a piece of protoboard just for the fun of it - it actually worked the first time), and that in turn can be read easily by an Arduino, usually through the analog port.

Delta_G: Yeah there's some measure that gardeners use and call pH that is more of a measure of how much hydroxide salts are present in the soil. I don't understand it very well as I'm not a gardener either. But I am a chemist who has been asked about it a few times and figured out that they have something other than solution concentration of hydronium that they all pH.

pH is a measure of H+ ion, not the hydroxide ion (which is just one of many bases that will affect the pH by binding H+) Soil chemistry is very complex with a myriad of acid-base reactions, pH only measures H+, not the other species, so its a part of the story only.

H+ ion is measured because its easiest to measure, the proton is the only ion that can diffuse easily through a large variety of solids, including the thin glass of a pH electrode, so its concentration can be measured unaffected by other charged species in the sample.

In water protons hitch a ride on water molecules, the H3O+ ion, but water is a weak base so they can jump off easily.

I know that's what it means in water. I just don't know what it is supposed to mean in soil. You're not going to find much free hydronium in soil you know. To me the pH of a solid must be a contrived value. It certainly can't be the same as it is in water. It either has to have something to do with the pH you get when mixing with water or something. If that's the case then that would be determined almost entirely by basic salts in the soil. Like I said, you aren't going to find a bunch of free hydronium in dry soil.

Hi guys,

What about disassembling one of these to add in a hi-z amp and read the analog value?

https://www.homedepot.com/p/pH-Meter-HpHMeter/204345613

Note: this type of soil pH meter gets its energy to move the analog needle from the bimetal probes and moisture in the soil.

However, I believe the instructions say "do not leave them in the soil too long". I wonder how long is too long???

What about disassembling one of these to add in a hi-z amp and read the analog value?

First figure out if the readings (1) are consistent and (2) mean anything useful.

Moisture readings shouldn't be too hard - pH is a whole different story.