I used to have a little battery-operated digital pH meter, glass electrode, buffer solutions, the works, but the electrode got broken, and as I hardly ever used it and we were downsizing furiously at the time, and as pH papers occupy much less drawer space, I use them now. But the narrow range papers with their subtle shades of green are not that easy to read against the colour scale, so are less precise. The trouble is, whenever I do measure soil pH, it always seems to come out at about 6.5, which makes me wonder just what I'm measuring the pH of, the soil or the water.
Soil pH is the result of the interactions between the complex organic acids (mostly fulvic and humic acids of indeterminate structures), simpler organic acids, and the soil mineral particles and their exchangeable cations. In days of yore, I used to know quite a lot about it, but it's all just a distant and uncertain memory now!
10% solids by wt. was the standard for measuring the pH of clays in water, and I imagine it's much the same for soils.
I'll try that. As Mrs Beeton never said 'first get your deionised water'! But plenty of suggestions here as to sources. Thanks everyone. .
Yes. I grow rhodies, azaleas and camellias, so in general the pH is on the acid side, but there are one or two small areas that cause extreme chlorosis, and I want to know if it's simply pH, or something else perhaps poisoning the soil, bearing in mind that the garden was used as a building site a few years ago.
Can only grow those in tubs here on clay over chalk...
Or simply lack of nutrients. Where I covered a cement mixer spoil heap with topsoil the grass has never been that great, but gradual addition of mulched cuttings and weed and feed is improving things
The quick test is to throw nutrientss at that patch - if that fixes it chances are its poor soil, rather than alkalinity
"In the really high-end world, such as the semiconductor industry, 20 megohms is the norm. 20 megohm water is so hungry for ions it will cut through steel."
We used to have a 4 liter glass container of DI in the university lab, and it came complete with an ohmmeter to verify the resistance of the water to electric current flow. That's a measure of ionic purity. I never saw *anyone* draw water from that thing. No lab procedure seemed to need DI.
The article says there are three kinds of water.
Tap water
Distilled water (relatively cheap, automotive store, ionic unknown)
DI water (distilled and deionized, verify with ohmmeter)
The fab at work would use DI water, and the leftovers were put in the waterfowl pond :-) Some of the staff used to joke about what the swans and ducks were swimming in, and "did they know". The reason bird life lived there, is in the winter, all fresh water bodies would freeze up, and any bird seeing water with steam rising off it in the morning sun, would assume they'd died and gone to heaven.
The standing water in a container of distilled, would have the same pH as the wet dirt in the garden (both made that way by CO2), before any buffering agents were present. It would not be an "additional driver", any more than pure rainfall on the dirt would necessarily drive it.
Of course, in modern life, the rain is acidic, as a function of how much industrial activity is nearby. I fondly remember finding printouts at the computer center, in the seventies, where scientists were checking pH in lakes, and some of the lakes were reported as "dead". As the substrate of the lake contained no buffering capability at all, and the water in the lake would simply assume the acidity of the rainfall acting on it. When you see one of those lakes or ponds, it's pretty amazing, because you can "see the bottom", and no fish swim by. The water is crystal clear. This is because nothing wants to grow in the lake, and the water remains "pure-ish" as a result.
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When to use the various waters.
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In Chemistry, you "get your way" by using buffered compounds. You don't want materials which only immediately establish a pH, and then are acted upon by things in the environment (no buffering to prevent shift). You want a compound which disassociates when "pushed" and maintains a pH until the bulk material is "used up". And that's likely to be a garden strategy, is applying a buffered agent to the dirt.
As far as I can remember, the wet pH electrodes in chem lab, were rinsed of "debris" with a nalgene bottle filled with distilled water, then the electrode was stored in its "beaker", with the electrode covered by water. Those electrodes could be damaged by allowing the beaker to dry out. Which means, once you buy a pH electrode, it's like a Chia Pet, and you have to maintain it, or invoke the wrath of the boss when you ruin it.
I don't know if any other electronic instrumentation methods have been developed, since the wet electrode, for measuring pH.
Now, the strangest thing I've seen, is Honda rad coolant, premixed to 50% ethylene glycol, which claims on the side of the container "pH buffered to pH7". Now, I thought that wasn't possible, and I never did discover what they'd used to make that possible. The insanity was the result of using cheap materials for "plumbing" in the car, then using buffered coolant to prevent corrosion. (Heaven help the customer who pours non-Honda shit i their rad...) I cannot recollect the naming of any buffering agents in chem class, where the pH was exactly 7.0. The values are normally "not round numbers", like say 7.4 or 8.2 or whatever.
When a buffering agent has more than one active species in it (A breaks down to B breaks down to C), then you can see the behavior of the buffering agent when you do a titration.
Actually, most don't. Mine grow happily and flower well at pH 6.5 on "clay" soil. Only one small rhodo shows any sign of chlorosis and I think that is more due to deficiency than excess as it under a very large, old berberis which no doubt has its roots removing anything useful before the rhodo gets to them. I regularly water my garden using tap water in this, and previous, prolonged dry spells. The water is at the top level of hardness - just below very hard - at 112 mg Ca/litre (or 281 mg CaCO3/litre). The rhodos /never/ show any sign of chlorosis and grow and flower well. And as for leaf mulch, well, my worms seem to have an aversion to the beech leaves from my neighbour's tree, and leave them on the surface!
As you note (and TNP confirms in his post), trying to grow them on chalkland is a waste of time. But most of the country is /not/ chalkland, and is pretty neutral, especially clay. Even clay over chalk
- if the clay is deep enough - can be a good growth medium for rhodos. Remember that rhodos are shallow-rooted plants, and, in general, nutrients move with rain from the top down - chalk doesn't rise up from lower levels. You can find pockets of soil in your garden which they don't like, but if so, don't try growing them there - go a few metres away and try again.
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