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Old 26-04-2003, 01:26 PM
David D.
 
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Default How to visually distinguish Potassium and Mag deficiencies?

Where a leaf or soil analysis is not helpful (e.g. the lab has no
reference for a particular plant's NPK etc. requirements due to the
plant's being uncommon), and one has to fall back on visual cues to
find out what is missing from a plant's nutritional intake (assuming
otherwise balanced nutrition), how does one visually distinguish
Magnesium from Potassium deficiencies?

Both affect older leaves. Both cause marked interveinal chloriosis
with reduced new growth. I know that in some cases, Potassium
deficiencies cause corrugation deformities in new growth as well (e.g.
passionfruit), but not always. I also read that Potassium shows marked
scorching on the leaf edges, but again, not always, and indeed,
pictures of Magnesium deficiencies in some crops also show necroses in
affected leaves. The one symptom (and its a judgement call rather than
an absolute, which isn't really helpful) that Potassium has in
contrast to Magnesium deficiency, is that affected leaves are dropped
more reluctantly with the former than in the latter.

Can the readers of this forum chime in on what can be used as
distinguishing criteria between the two deficiencies? I'm fairly sure
that Nitrogen deficiency isn't a factor, because there with that
deficiency there is an overall yellowing, and interveinal chloriosis
is not generally noted.

Thanks in advance.
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Old 26-04-2003, 01:26 PM
Oz
 
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Default How to visually distinguish Potassium and Mag deficiencies?

David D. writes
Where a leaf or soil analysis is not helpful (e.g. the lab has no
reference for a particular plant's NPK etc. requirements due to the
plant's being uncommon), and one has to fall back on visual cues to
find out what is missing from a plant's nutritional intake (assuming
otherwise balanced nutrition), how does one visually distinguish
Magnesium from Potassium deficiencies?


Apply a foliar feed of Mg, K and K+Mg and observe the effects.
I would suggest leaving some controls, and adding a multi-element foliar
feed to your little trial.

--
Oz
This post is worth absolutely nothing and is probably fallacious.
Note: soon (maybe already) only posts via despammed.com will be accepted.

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Old 26-04-2003, 01:26 PM
Torsten Brinch
 
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Default How to visually distinguish Potassium and Mag deficiencies?

On 16 Dec 2002 19:45:29 -0800, (David D.)
wrote:

Where a leaf or soil analysis is not helpful (e.g. the lab has no
reference for a particular plant's NPK etc. requirements due to the
plant's being uncommon), and one has to fall back on visual cues to
find out what is missing from a plant's nutritional intake (assuming
otherwise balanced nutrition), how does one visually distinguish
Magnesium from Potassium deficiencies?

Both affect older leaves. Both cause marked interveinal chloriosis
with reduced new growth. I know that in some cases, Potassium
deficiencies cause corrugation deformities in new growth as well (e.g.
passionfruit), but not always. I also read that Potassium shows marked
scorching on the leaf edges, but again, not always, and indeed,
pictures of Magnesium deficiencies in some crops also show necroses in
affected leaves. The one symptom (and its a judgement call rather than
an absolute, which isn't really helpful) that Potassium has in
contrast to Magnesium deficiency, is that affected leaves are dropped
more reluctantly with the former than in the latter.

Can the readers of this forum chime in on what can be used as
distinguishing criteria between the two deficiencies? I'm fairly sure
that Nitrogen deficiency isn't a factor, because there with that
deficiency there is an overall yellowing, and interveinal chloriosis
is not generally noted.


As you set it up, it is an almost impossible situation , if not
downright impossible. K deficiency would be more likely than Mg
deficiency to make the plant appear weakly built, but basically you
would seem to me to need to know the plant better before this or other
visual cues really could mean anything to you. This could be from
observation in and of its natural habitat, or from experiment.
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Old 26-04-2003, 01:26 PM
Dennis G.
 
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Default How to visually distinguish Potassium and Mag deficiencies?

(David D.) wrote:

(...)
Both affect older leaves. Both cause marked interveinal chloriosis
with reduced new growth. I know that in some cases, Potassium
deficiencies cause corrugation deformities in new growth as well (e.g.
passionfruit), but not always. I also read that Potassium shows marked
scorching on the leaf edges, but again, not always, and indeed,
pictures of Magnesium deficiencies in some crops also show necroses in
affected leaves. The one symptom (and its a judgement call rather than
an absolute, which isn't really helpful) that Potassium has in
contrast to Magnesium deficiency, is that affected leaves are dropped
more reluctantly with the former than in the latter.

(...)

If you weren't certain it was a deficiency of one of those nutrients,
I would suspect nutrient leaching from excess flow through irrigation.
General chlorosis is one easily recognizable symptom of poor nutrition
that can occur in some substrates even when feeding regularly.

If you are monitoring tissue analysis for hydroponic growth,
adjusting pH to match known natural substrates of the plant would be a
first step, IMO. After that I would check the tissue analysis for
possible interference with take-up of one of the major nutrients(and
availability of sulphur and possibly calcium depending on the native
substrate information). After that I would adjust minor elements based
on information from the tissue burns.

If it is a field crop, I know nothing.....except that organic
fertilizers and ground rock have often been highly recommended in this
newsgroup g

Dennis

Dennis
 
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