Home pH Testing of Soil

[moray-eel-bite]

Originally Posted by drew51

Ha! Now that is funny. Current co2 is .04% Only one other time in earth's history has co2 been this low. Don't buy into the political stuff which is not allowed here.
Besides the fact that PH is a measurement of hydrogen ions. How many hydrogen ions in co2?
BTW I live surrounded by automotive factories. My rainwater is 7.0. A side effect of clean air. I grow blueberries and have to add acid even to my rainwater.
I use rainwater to test soil PH as it is neutral.

Yes, pH is a measure of hydronium ions. CO2 becomes carbonic acid in water. CO2 is higher in the atmosphere such that the ocean is 30-40% more acidic than it was 100 years ago. Rainwater is not neutral, it's almost always acidic due to the lack of buffering capacity as stated above.
None of this is political, it's fact. Scientific fact.

Cheers.

[TomNJ]

Wouldn't boiling distilled water remove any dissolved C02 and return it to pH 7? Of course it should be cooled before using. That said, I agree the pH of the distilled water makes little difference due to its lack of buffering capacity.

TomNJ/VA

[feldon30]

I thought I knew how to measure pH. Then I read this thread.

I have one similar to this:

[moray-eel-bite]

Originally Posted by TomNJ

Wouldn't boiling distilled water remove any dissolved C02 and return it to pH 7? Of course it should be cooled before using. That said, I agree the pH of the distilled water makes little difference due to its lack of buffering capacity.

TomNJ/VA

Yes, boiling the water removes the dissolved CO2, and will bring it back closer to 7, but both distilled and RO water still contain some measureable ions (Calcium etc). If you want a pH 7 exactly you'll need a buffer either bought or created. However, the small amount of ions really won't change the pH enough to matter in a soil sample.
pH is a logarithmic scale. ie. pH of 7 means a hydronium ion concentration of 0.0000001 mol/L. every step is a ten-fold increase ie. pH 6 is 0.000001 mol/L. (I think someone said 100 above, but it's actually a ten-fold increase). The soil will most probably create a buffer itself due to the presence of clays etc., so the small amount of hydronium ions present in the water will be buffered (ie. will change the pH only a very small amount). In some very sandy or other rare types of soil there is almost no buffering capacity and the water you start with will make a minor difference.

[Worth1]

Originally Posted by moray-eel-bite

Yes, boiling the water removes the dissolved CO2, and will bring it back closer to 7, but both distilled and RO water still contain some measureable ions (Calcium etc). If you want a pH 7 exactly you'll need a buffer either bought or created. However, the small amount of ions really won't change the pH enough to matter in a soil sample.
pH is a logarithmic scale. ie. pH of 7 means a hydronium ion concentration of 0.0000001 mol/L. every step is a ten-fold increase ie. pH 6 is 0.000001 mol/L. (I think someone said 100 above, but it's actually a ten-fold increase). The soil will most probably create a buffer itself due to the presence of clays etc., so the small amount of hydronium ions present in the water will be buffered (ie. will change the pH only a very small amount). In some very sandy or other rare types of soil there is almost no buffering capacity and the water you start with will make a minor difference.

Yeah I added an extra 0 to see if you would catch it.

No really we aren't making the atomic bomb here the poor feller just wants to measure PH in a soil sample.

Tomatoes like an acid soil below 7.
PH is important but there is little difference to a tomato if it is 6.5 or 6.6.

Worth

[4season]

I have a meter like Feldon posted, it shows my soil with a PH around 7.5 to 8. A bit less where well amended. The tomatoes still produce OK in soil that will foam if you pour vinegar on it.

[FLRedHeart]

Good question earlier about whether it matters if you test with a 1:1 or 1:2 dilution of DW. If you flip the question around, you can just ask, what is the worst the pH can be off from these dilutions, using 50% 100% and 200% the volume of water:

1:0.5 ... 0.18 units towards neutral
1:1 ... 0.30 units towards neutral
1:2 ... 0.47 units towards neutral

The soil is a reservoir (as mentioned, "buffers") and the DW contributes essentially nothing measureable relative to it. The most important thing is to allow the mix to come to equilibrium and not be too hasty in making your measure, and to remove any pebbles, especially limestone or coral, etc. That will allow the soil ample opportunity to release its readily available ions as happens with a rain or irrigation and likely come within measurement error for all three dilutions above.

If you have any doubt about your particular soil, all you need to do is check at 1:1 and 1:2 for yourself and if you observe any difference on any of these meters, which is unlikely, you can have your own rule of thumb. The picture of the Chinese green 3 in 1 meter is not a genuine pH meter even though it is sold that way. It may or may not be accurate for a game of pH horseshoes. Measurements with it are heavily affected by soil conductivity and water content, which is not a simple deal, so you really need a pH electrode based meter which is probably around $50 or so to have confidence in the result.

If the amount of water added to test were a big deal, we'd be in trouble, because soil samples already contain anything from 10% to 60% water by volume (Did you check it ), so precise measurements are really a waste of time and that's why the amount of water added isn't that big of a deal.

[drew51]

Originally Posted by moray-eel-bite

Yes, pH is a measure of hydronium ions. CO2 becomes carbonic acid in water. CO2 is higher in the atmosphere such that the ocean is 30-40% more acidic than it was 100 years ago. Rainwater is not neutral, it's almost always acidic due to the lack of buffering capacity as stated above.
None of this is political, it's fact. Scientific fact.

Cheers.

Still sounds political to me. The CO2 is so low my rainwater is neutral.
Stating it is somehow high, goes against the historical record, and can only be seen as a political statement.
Also the fact that carbonic acid is rarely created when CO2 is dissolved in water, as it needs a catalyst for the reaction. Most CO2 stays as CO2 when dissolved in water. BTW Carbonic acid is used to put CO2 (The fizz) in your soft drinks. The reaction tends to go the other way, but hey nice try!

[FLRedHeart]

Carbon dioxide dissolves in pure rain, and when in solution (not gas), it spontaneously reaches equilibrium in a few minutes with the acid form without any additional catalysts.

If you solve the chemical equilibrium for 360 ppm CO2 which is the average in the atmosphere, you will find that pure rain falling through the atmosphere will have a pH of 5.6 due to the CO2 it picks up.

If you add a small amount of tap water to the rainwater the effect will be wiped out by the alkalinity of the tap. Utilities sometimes have to increase alkalinity after heavy rains, if they source surface waters, since lower pH's will corrode metal plumbing.

[RayR]

Originally Posted by drew51

Still sounds political to me. The CO2 is so low my rainwater is neutral.
Stating it is somehow high, goes against the historical record, and can only be seen as a political statement.
Also the fact that carbonic acid is rarely created when CO2 is dissolved in water, as it needs a catalyst for the reaction. Most CO2 stays as CO2 when dissolved in water. BTW Carbonic acid is used to put CO2 (The fizz) in your soft drinks. The reaction tends to go the other way, but hey nice try!

Carbonic Acid is a weak acid that can go through a few reversible reactions, it can turn back into H20 and CO2 or disassociate into an H+ ion and HCO3- (bicarbonate)

CO2 + H2O ↔ H2CO3 ↔ H+ + HCO3-

Rain water will vary in PH (usually 5.5-6.2) partly because of the amount of carbonic acid formed, temperature and atmospheric pressure would have an effect, also rainfall from lighting storms is more acidic. Catalyst's for the reactions I suppose you could say. Also rain drops can pick up other contaminants on the way down like Sulfur Dioxide among other things that will change the PH.

[Worth1]

Never in my years at tomatoville have I seen such debate over rainwater and a ph test.
Now I really am scared to go out in the rain.
Worth

[moray-eel-bite]

Originally Posted by drew51

Still sounds political to me. The CO2 is so low my rainwater is neutral.
Stating it is somehow high, goes against the historical record, and can only be seen as a political statement.
Also the fact that carbonic acid is rarely created when CO2 is dissolved in water, as it needs a catalyst for the reaction. Most CO2 stays as CO2 when dissolved in water. BTW Carbonic acid is used to put CO2 (The fizz) in your soft drinks. The reaction tends to go the other way, but hey nice try!

I have no interest is discussing this further, this is my last post in this discussion. CO2 levels before the industrial revolution average 180-280 ppm for approx. a thousand years. They are currently 360-400 ppm. This is very well documented. Even Wikipedia will probably document this. Carbon dioxide once in the atmosphere finds it's way into the ocean due to equilibrium chemistry. Also very well documented.
Put carbon dioxide into water where no (or lower than the equilibrium state) carbonic acid exists and it will form carbonic acid. This is simple chemistry. If you understood equilibrium chemistry you would also know that if you stuff enough of anything into an enclosed container you can reverse any reaction. This is why soda fizzes when you change the pressurization upon opening. Change in pressure equals change in equilibrium state. Either way, making soda pop with carbonic acid is not relevant to this discussion.
The earth's oceans have been repeatedly and repeatably measured to have increased in acid content. Again simply a fact.
Rain water in not neutral for the well reasoned and scientifically sound statements made by others in the couple posts above this. There are also some sulphur compounds and nitrogen compounds that contribute in small ways to the pH of rain water, but the main reason is certainly carbon dioxide and hence carbonic acid.
To the person who measured their rainwater and it's exactly 7: The instrument you used to measure it should be thrown away because it doesn't work. Invest in a quality instrument if you want to measure pH reliably. If the instrument you have can't tell the difference between 5.5 and 7 it's not worth using even for a home measurement.


And I'm officially done with the part of the discussion regarding carbon dioxide and carbonic acid and anything 'political'.

To those who this thread was actually meant for, who wish to measure pH in soils, there is no reason not to use DI or distilled water when diluting soil for a home pH reading.
If someone else has a question about measuring pH, I will happily answer.

Cheers.

[FLRedHeart]

The OP's original pH meter for $70 seems to be fine, not like the 3 in 1 Chinese one. Morey, 360 to 400 ppmv is the raw data from the National Weather service or maybe an important clean observatory site at the University of Hawaii, which is a little higher than I remembered it being, but you are right.


Drew is right in that there is so little CO2 that at first glance it is difficult to believe.

Here's the way I see it: 390 ppmv CO2 in the air will have the rain pick up as much as 0.6 ppm CO2 (parts per million by weight) in the pure raindrop, a very insignificant amount, and similar to the concentration of chlorine in chlorinated tap water, so little amounts can't be dismissed without thought.


Of that 0.6 ppm CO2, most of it is dissolved CO2 in the same sense as we talk about dissolved oxygen, just bound up in the water and doing nothing much, and if that were all there were to it the pH would be about 7.0.


But the equilibrium Morey is talking about is that perhaps just 0.1 ppm (of the 0.6 ppm) formes "H+" and "HCO3-" spontaneously. If you look at that, the H+ formed by weight is actually only 0.0025 ppm (= 2.5 parts per billion) and this is the active ingredient of what y'all are calling "carbonic acid".


2.5 ppb of hydrogen sounds like nothing, but it happens to be just enough to drop the pH of a raindrop from 7.0 to 5.6. pH is a very sensitive scale around 7.

It is quite possible Drew has measured a pH of 7.0 rain. Maybe he washed his container with tap water that is moderately hard like most of us have and it had a typical bicarbonate content of 100 ppm. I collect rainwater and the best I've ever done is get 3 ppm of total solids. That is cleaner than the distilled water being sold, but whatever the 3 ppm is, whether the rain picked it up in the air, upon collection or from residue, it leaves open the possibility that the pH could be different significantly than what is caused by 0.6 ppm of CO2.


Since the soil is a reservoir of dissolving minerals, the 0.6 ppm, 3 ppm, or 10 ppm, whatever is in the distilled or rain water will be completely overwhelmed by the soil pH and that is why it is of no consequence when diluting by a reasonable amount, as already stated by more than one ;-) But, tap water is a no go for the above reasons of having lots of dissolved crap in it you might not want to drink yourself... I hope I made no mistake in them numbers, but hopefully if there is it can be corrected by Worth who is reading all this stuff

[Worth1]

Yes I am reading everything and I have to say I looked up all the data on sea level acidity and I was shocked.

I found my information on several well respected sites like NOAA.
I spent hours looking and reading.

One thing I would like to mention is rainwater collected at point a wont be the same as rainwater collected at point b.
That should be common sense at least I would think.

As far as soil I did a test on my raised beds with water from my RO source and did a color comparison.
Yes old school but I like it.
My tomatoes wouldn't grow they just sat there.
My indicators said low iron and a ph of around 8.
I spread out an iron supplement and drenched the soil in a high dose of vinegar.
The reaction was wild.
In no time at all the tomatoes almost jumped out of the beds.

No I wont correct anyone I have neither the time nor the inclination to do so.
My practices work fantastic for me and I am willing to help others that is what I am here for.

Worth

[drew51]

People will think what they want to think. Dropping PH from 7.0 to 5.6 is what? Almost 150 times more acidic? The scale is not sensitive, it's just a scale! NOAA and NASA are not highly respected in my book. They are bought and paid for. They must produce results they are told to report, else they will most definitely lose their jobs. This is the most corrupt adminstration at these organizations in their histories. It's super sad to say the least. A friend of mine works for NASA, he can't stand the corruption and is extremly upset about it. His work is with soild rocket fuels.
He told me don't listen to anything NASA says about the weather.
What was ironic when the freedom of information act forced NOAA to release it's raw weather data, the data showed we have been cooling for 18 years, now that was funny!
For me I find ironic that no matter what is happening, we have no way to change it that would actually work. Humans are so egocentric. Mother Nature has the last say, we have no way to change that.

I add acid to my rainwater, I need it at 5.5 and I have to add a lot of acid to bring it in line. I use sulfuric acid. Works great for me, my blueberries are growing like crazy.
I wish my rainwater was acidic one less thing I have to do!
I have also observed that in the winter when I'm not watering the soil PH creeps up to as high as 6.5. The plants are in raised beds with 40% peat 40% pine bark fines and 20% garden soil. You would think this mix would stay low! Yet it creeps up all the same. So i started adding sulfur in the fall. This has worked well, by the spring when plants become active, the PH is right where I want it. I resume the sulfuric acid laced rainwater. Been doing this for three years. Results have been excellent with handful after handful of blueberries.