pH etc..

[PaphMadMan]

Maybe it's just a matter of semantics, PMM. If the soil holds it and prevents it from being washed away, it seems to me that it is not allowing it to readily dissolve...

A thorough technical explanation of the chemistry is beyond me without consulting references, and I'm an analytical chemist by profession. But the short answer is: Cations held by soil CEC definitely ARE readily available to plants, and that is the relevant point. Clay and humus compounds have net negative charge and hold onto cations to balance charge, but essentially those cations are still in solution even though the anions may not be. Uptake by roots is mostly an active process by swapping cations and the ones held by CEC are largely available for that process just as if they were free in solution.

 

[gego]

Here's an article from the same website about anion-cation balance.
http://www.smart-fertilizer.com/articles/Cation-Anion-Balance

 

[Ray]

Hey, Kirk.

As a ceramic engineer, I studied a lot about clays, but admittedly that was a LONG time ago. However, edges of clay particles - they are plate-shaped - can be positively-, or negatively charged, depending upon the pH. If too acidic, they tend to bond face-to-face, in a "stack" like a deck of cards, but if you raise the pH, you get edge-to-face bonding, like a house of cards. That's why we add lime to clay soils to "open them up".

That's why I believe that the pH can affect the availability of nutrients in soils moree than it does in solutions.

 

[Stone]

But pH adjustment of nutrients solutions for hydroponic systems is fundamental.
The reason for the pH reduction from about 6.5 to 5.5 in soiless media is because the metals become bound to organic particles. This is especially true for Fe. That is why when growing in mainly bark, a increase of between 1/2 and 1 unit back to say 6.7-7 should make Fe less available.
(which is what I am interested in)
At the same time Mo becomes more free.
The link to the Fe paper says that the EDTA is a stable chelate for metals EXCEPT Iron which means that if I use a fertilizer where all the micros are EDTA (which I have) and keep pH above 6.5, I effectively reduce Fe availability to the plant by 50%.
Whether this is a good thing for limestone Paphs or not I don't know but I think it may be some kind of starting point to get figure closer to the mastersianum and emersonii in Roth's post. No doubt hangianum, cahnii, sanderianum etc etc would be the same.
Maybe even 6.7 would be enough (barely acid). I remember many years ago growing big plants of parishii and micranthum very well with a water pH of 9-10 and osmocote which was mainly urea, and that's it! No chelates at all.

 

[Happypaphy7]

I've been wondering about pH quite a bit recently since pretty much all my henryanum seedlings started to grow nice big leaves but all has chlorosis leaving only the veins darker green.

I checked the run through pH on all my plants and there were two groups regardless of the type of mix (I have mostly orchita based mix or coconut husk chips based), and they were 5-5.5 and 6.0 group.

I thought the first group had it a bit too acidic, and now the second table makes me wonder if those seedlings are suffering iron overdose.

I did some search and it says under iron toxicity, manganese deficiency symptoms appear first.
I looked up some images and perfect match!

Now, can someone advise me how to best increase pH??

I'd like to have it around 6.0-6.5 ideally.
I grow at home, so no special equipment.

Thanks!

Oh, and another thing is some of my bulldog hybrids tend to have their tips brown when old, which always bothered me, and while doing the above mentioned search, it may also be related to iron toxicity. hmmm...
I know they definitely do not match any diseases I can think of.

 

[Happypaphy7]

It might be a mistake to assume that plants growing on limestone have their roots receive water with a high pH.
I've measured pH of water trickling over plant roots attached to limestone and the pH was 7.0. In these habitats maybe the majority of water moving to the roots is close to being pure rainwater still.
So first you need to decide what pH is more important to the roots the solid media or the free water.

Adding on to that, many of these plants do have some moss blankets and many other vegetations growing near or over their roots, not to mention some of these plants may excrete enzymes and such that creat acidic root zone for better nutrient uptake.

I remember reading about pH measurement of Paph. armeniacum on their habitat. The pH of the root area was between high 5 to low 6.

 

[Stone]

I've been wondering about pH quite a bit recently since pretty much all my henryanum seedlings started to grow nice big leaves but all has chlorosis leaving only the veins darker green.

I checked the run through pH on all my plants and there were two groups regardless of the type of mix (I have mostly orchita based mix or coconut husk chips based), and they were 5-5.5 and 6.0 group.

I thought the first group had it a bit too acidic, and now the second table makes me wonder if those seedlings are suffering iron overdose.

I did some search and it says under iron toxicity, manganese deficiency symptoms appear first.
I looked up some images and perfect match!

Now, can someone advise me how to best increase pH??

I'd like to have it around 6.0-6.5 ideally.
I grow at home, so no special equipment.

Thanks!

Oh, and another thing is some of my bulldog hybrids tend to have their tips brown when old, which always bothered me, and while doing the above mentioned search, it may also be related to iron toxicity. hmmm...
I know they definitely do not match any diseases I can think of.

Funny you should say that hp. My henryis are the same. Growing well but the same weird mottling. My charlesworthii seedlings are beautiful dark green. (My flasker told me when he sows limestone Paph seed they won't grow if the pH is much below neutral. (Make of that what you wish)
Anyway, to increase my pH, I put about a teaspoon of finely ground dolomite in 1lt of water, mix and let it sit for a couple of days. When everything has settled, I decant into another container leaving most of the solids behind - apart from those suspended. I use that water to add to my solution (or rain water of pH6) 1 tablespoon at a time until I get to about 7 or a bit under. (or whatever you want) It might pay to set aside some of the solution and re-test it 2 days later to see if it has changed. If it does, most likely it will go up. In that case just add less of the alkaline water next time. You can do it many other ways but I'm keeping it natural
Also I'm going to stop Fe chelate for a while or at least cut down as much as possible.. and perhaps spray Mn sulphate once in a while.
Hey nothing ventured nothing gained!

 

[Happypaphy7]

Thanks, Mike.

The thing is where I could find powered dolomite. lol
I think I have seen a bag of dolomite chips (big like pebble size) Home Depot, but I would think they are too hard to crush without machine?

Anyways, Bjorn reports that his plants green up nicely after spraying mancozeb, which has manganese and zinc.
I'm not sure if it's legal in NY but I know it is rather low toxic ( to humans) spray.

I have heard different like stone or dolomite degrade at different rates.
I wonder where this dolomite sold at garden stores fall under?
Hmmm

 

[Ray]

Mike, the reason pH control is so important in soilless hydroponics systems is not so much about the availability of nutrients in the solution, but because in the recirculation process the plants deplete the solution of nutrients, and dump plants wastes into the solution. Both of those processes can cause significant swings in the solution pH, so it becomes a good way to monitor that, so that it can be adjusted.

One thing that seems to have been missed (or at least, I missed it) is the fact that we should focus on the substrate pH, more than the solution pH. Both the potting medium ingredients and the plant itself affect that. Even in the case of plants in semi-hydroponics, in which (in the case of PrimeAgra, anyway) the medium has no effect, I have seen reservoir solution pH change significantly overnight. It has been a long time since several of us were measuring it, but using MSURO at an adjusted pH=6.0, I have seen the solution pH dip to upper-3's to low-4's (with no plant damage or precipitation).

 

[gonewild]

I don't think the substrate/media pH is as important for orchids as it is for other plants. The reason being the specialized roots orchids have. I dont think orchid roots interface and relate to the substrate as dependently as "normal" plants do.
I don't think orchid roots have the same CEC function as other plants and don't remove nutrients from soil as do other plants. Orchid roots gain the nutrients when the nutrients flow freely on and into the root velum.

This is just what I think, I have not read a published report relating to the subject. Probably the main reason that I think this is true is because of what I see in pots of Phals. The pH of the media becomes very acidic from whatever Phal roots release into the media. Now the reason I am using this as an example of why the pH of the irrigation water is more important than that of the media is because..... I have Phals growing beautifully that have a flow through pH that can read as low as pH3.9. I have my fertilizer mix at pH 6.5 trying to keep the media pH up closer to 5.0. The point is the media pH is 3.9 and if I were to apply fertilizer water with a pH 3.9 it would destroy the roots really fast. So..... In this case it seems media pH is not important but the water pH is.

 

[DarioU]

In the "Soilless Mix." graphic of Naoki the phosphorus behavior is strange .. phosphorus is assorbed better with very low pH? It is the opposite then in the graphic reported by Stone. Isn't it?

 

[Stone]

Mike, the reason pH control is so important in soilless hydroponics systems is not so much about the availability of nutrients in the solution, but because in the recirculation process the plants deplete the solution of nutrients, and dump plants wastes into the solution. Both of those processes can cause significant swings in the solution pH, so it becomes a good way to monitor that, so that it can be adjusted.

It says here that pH control of hydroponic nutrient solutions is mainly use to influence nutrient availability.
If you look at the preferred range for Cabbage and onions (which happen to both be sensitive to iron) the preferred pH is 6.5 - 7.

http://www.simplyhydro.com/ph.htm

 

[myxodex]

These nutrient availability versus pH profiles are necessarily very generalised and are really only a rough guide.
For example the presence of charged soluble organic compounds like amino acids, dicarboxylic acids or humic substances will generally tend to broaden these availability profiles by suppressing precipitation reactions between the components in our fertilisers. Then there is another issue, changes in pH effect different species differently in terms of how efficiently they take up nutrients at different pH's so there is a genetic component. For example; increasing soil pH decreased uptake of NPK in rice, but increased it in wheat and corn. http://www.tandfonline.com/doi/abs/10.1080/00103629809370142

As for the practical issues of controlling pH, I found dolomite lime to be a difficult one to get right, although I know a nursery that uses it routinely without problems. As others have said above, acidification of the medium depends a lot on the NH4 level in your fertiliser more than the pH at which you apply it. I found the Bill Argo article most useful. I use a rule of thumb; I add bicarbonate in ppm, at roughly 4x the NH4 level in my fertiliser. So if I'm feeding at 5 ppm NH4, I add 20 ppm bicarbonate. I simply use my tap water (260 ppm HCO3) because it's easiest. Obviously it depends on other factors, so when I switched from my previous bark to orchiata I noticed that the pH was drifting up a little, so I'm now reducing the amount of tap water I add into my mix.

 

[Happypaphy7]

This is for Aussie Mike.

A couple of pictures, first one is of Doll's Kobold, the second henryanum.

Both had very dark green leaves for a while after deflasking.
Then earlier this year as they started to grow new leaves, they looked terribly light green, some even yellow with only vein left green.

I tried Cal/Mag a few times in a row at first, but nothing changed.
Then I poured some vinegar solutions, which I think helped with color almost immediately, but not very good result still as you can see.

Henry seedlings are slowly recovering, but Doll's Kobold seedlings still look terrible.
In the second picture, all the seedlings had two upper most leaves looking terrible, but as the leaves further develop and mature, green slowly returned.
This has not yet happened, or very little on the DK.

 

[gego]

So it was the vinegar? Cal Mag is base an prob with nitrates which if taken by the roots will make the media attached to the roots go up in pH. So what do you think happened here?

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[gego]

Hh7, what other fertilizer have you applied other than the Cal Mag? What Cal Mag is this?

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[gonewild]

So it was the vinegar? Cal Mag is base an prob with nitrates which if taken by the roots will make the media attached to the roots go up in pH. So what do you think happened here?

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Vinegar is not just a simple acid, it contains a lot of different compounds. So an effect by adding vinegar may not be simply because of the pH change.
Complicated.

 

[gego]

let's go back to Mike's interpretation, he thinks that those cultivated plants that have too much Fe and showed unhealthy were supplied with too much Fe.

Below could be the reasons why:

1. If Fe was supplied in good amount, then for the plants to be able to get a large amount, then we can assume the pH of the solution and around the roots is low enough for that amount to be available.

2. pH was low and Fe was abundant but other micro like Mn and Zinc were in small quantity so that Fe was taken more as an exchangeble ion. No competation with other micros.

3. Fe could be just the right amount but plant was not able to use it efficiently. May need an organic acid like citrate.

1a. The data also showed Mo being low so if pH was that low then Mo could have been unavailable to the plant assuming it was being supplied but was in low quantity. And if pH was low then very likely that urea/ammonium were the main source of N. The accumulated nitrates were probably due to low Mo so the plant was not able to use it efficiently.

Remember the article "Ecology of Paph rothschildianum at the type locality in Kinabalu Park"? The soil chemistry of the rhizosphere of one roth loc 1 has 87mg/g of Fe and 2.4 mg/g of Mn. The foliar concentration showed an Fe of 0.03 mg/g and 0.024 mg/g, almost the same, although Fe is more than 400% more than Mn. Looks likes Fe in this location is way harder to take up than Mn. The pH was 6.7.

The article also showed from the same locality above that the Ca, Mg and K exchangeables were 1339, 2223, and 44 ug/g correspondingly but the foliar concentrations were 6.9, 3.7 and 5.8 ug/g. With such a very low supply of K the plant was able to uptake even higher than Mg. These are all cations but it does show that K are easily absorbed compared to the other two.

I have been talking about charges and the only difference between these three cations are the number of (missing) electrons. It seems it's easier to extract and uptake a K than the two. It is probably true that Na is just as easy as K. And that K,Na and ammonium having only one electron missing, are equally competing each other.

To solve the problem of having too much Fe and low Mn and Z, one option could just be adding more chelated Mn and Z at the same time raise the pH around 6.5 so Mo will be more available and Fe less.

 

[Bjorn]

To solve the problem of having too much Fe and low Mn and Z, one option could just be adding more chelated Mn and Z at the same time raise the pH around 6.5 so Mo will be more available and Fe less.

Spray with some Mancozeb. plus, reduce fertiliser level. Remember, Huntington (Brandon Tam , Lance Birk) fertilises with Ca-nitrate only. And they get good (sometimes fabolous) results.

 

[Ray]

Be careful with vinegar. It's a great herbicide.