[CoolDool]

Hi guys.
I recently picked up on a prospective farm project and I need some help.  I have been trying to analyze soil pH. I have come up with some data but have some holes due to lack of knowledge of better methods.
I've tested pH of the soil in a distilled water solution, but my distilled water is high CO2 and is on the acidic side at 5.90pH.

So the hole is not knowing the true pH of my soil given the acidity of the distilled water.
I'd like help with knowing how to solve for this.

Here's an example:

Sample 1: 13.41g of Dirt + 50ml of 5.90 pH Distilled Water = Slurry solution with pH of 8.17

How do I solve for the pH of the dirt itself?

Thanks guys.

Also, if there are any farmers/hardcore gardeners out there, I welcome any suggestions. The water I will be watering with is irrigation. It's highly alkaline. I want to farm tomatoes and other more acidic accustomed plants. People apparently are able to get away with this.  .. I've researched that tomatoes like pH around 5.5-6.5(roughly).  How low would I need to bring the pH of the soil to have a decent growing season given the high alkalinity of the water?

[Borek]

1. Technically pH is defined as a property of a water solution, not of a solid nor slurry. Measured "soil pH" is just a proxy of what is present in the soil, not a "real pH".

2. Even if you were asking about just solutions there would be no way to solve for the pH from the information you have - there is not enough data (a lot depends on the composition of the pH changing substances, be it inorganic salts or humic acids, and their buffering properties).

3. As there is no precisely defined "pH of the soil", the number you get as a "soil pH" to some extent depends on the procedure. However, if you follow the same procedure each time, you get a relative number that allows for comparison of different soil samples and lets you classify them as "more acidic" or "less acidic".

4. Water used in the procedure is always saturated with CO₂, so its lowered pH actually doesn't matter - it is always part of the procedure, and numbers from every measurement already account for that. You can still use the result for comparing soil samples.

[CoolDool]

Ah. Ok.

So the pH is a property of the water solution.

Would you suggest using the actual irrigation water I will be using in practice instead of distilled water? Might this give me results I can work with better?

Also. Is there a way to solve what the result pH would have been had the distilled water been pH 7, instead of pH 5.9, from the results I had? That is, without doing any further testing of any sort. Just solving from what we have? 

That is, if the starting pH was 5.9 and changed to  pH 8.17, is there a way to know based off of this information, what the pH would have been had the starting pH been 7?

[CoolDool]

I'm offering compensation. If anyone has a satisfactory solution to my problem as explained in the opening post and my latter reply, I can venmo/paypal/cashapp 25$. ^_^

[Borek]

Which part of

no way to solve for the pH from the information you have

is confusing?

I understand it can sound like a trivial problem, but it is not. In the case of mixing inert solutions of well defined composition finding the final concentration is simple. But that's not the situation here: unknown acids and bases present in the solution in unknown amounts will react, the equilibrium will shift, and the final pH can be anything between 5.9 and 8.17.

Is there a way to solve what the result pH would have been had the distilled water been pH 7, instead of pH 5.9, from the results I had?

The answer is still "no".

[CoolDool]

Which part of

no way to solve for the pH from the information you have

is confusing?

I understand it can sound like a trivial problem, but it is not. In the case of mixing inert solutions of well defined composition finding the final concentration is simple. But that's not the situation here: unknown acids and bases present in the solution in unknown amounts will react, the equilibrium will shift, and the final pH can be anything between 5.9 and 8.17.

Is there a way to solve what the result pH would have been had the distilled water been pH 7, instead of pH 5.9, from the results I had?

The answer is still "no".

Oh. I'm starting to understand this a little better now. Its due to whatever in the soil, which is not well defined, reacting with the water/c02 in ways that would make pH un predictable to know.

... as far as the pH being between 5.9 to 8.17, that caught my eye. So... the pH wouldn't have a possibility to be over 8.17?

Thanks for your feedback thus far!

[Borek]

So... the pH wouldn't have a possibility to be over 8.17?

Yes, no way to get outside of the initial range.

That is... this is chemistry, there is always some exclusions It can be possible to design some exotic cases. But as long as you work with just a soil and typical water (be it tap, well, river, lake, puddle, distilled water - not something specially prepared to confuse both of us ) no way for the pH to get outside of the range bracketed by the initial pHs of things mixed.