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The value of photos of deficiencies

> Your database of images of deficiency symptoms in aquatic plants is one of
> those solutions which, in my opinion, won't necessarily work all the time,
> under all conditions. [SNIP] The ONLY way to determine
> this "range" and "optimum level" is by growing a large number of specimens
> and carefully observing them over time as the various mineral nutrients
> either supplied or withdrawn from their environment. Plant tissue analysis
> is needed to see how MUCH of any particular mineral nutrient is actually
> present in the plant as it is growing.

A number of folks have put forth this argument that you can't really tell
from a photo, yet it seems that our resident gurus (blessings on you all!)
are able to use visual information effectively, which means it can't be
completely useless! Clearly, you can get at least an idea of what might be
wrong from what things look like.  (or is it that folks like James and Tom
have learned to do the Vulcan mind meld with crypts?  ;-)

I think such a database would have four different benefits.  First, it would
be helpful in at least helping people get a vague sense of what may be
wrong.  Second, if there is a wide range of photos of different phosphate
deficiencies, for example, which all look quite different it would act as a
cautionary tale.  Third, it may prove a useful adjunct to the descriptions
of their plants they give here.  ("my swords are all filled with holes, kind
of like picture #529 on the database")  Lastly, your point that looking at a
large number of samples suggests that such a database would be a place for
people to go to look at a much wider range than they are likely to get in
their tanks alone.  As a training tool it may be useful.  There's no need to
make the perfect the enemy of the good here, I think.

Your suggestion that you only know that about limitation by altering it does
suggest a criterion for allowing a photo into the database.  I'd humbly
suggest that submissions try to include a before photo, a description of
what the putative limitation is, and an after photo taken after the putative
limiting nutrient was added and the symptoms were relieved with a
description of anything else that may have changed.

on a somewhat unrelated note, I'd suggest that plant tissue analyses
wouldn't tell you much in many instances.  Even if a plant is limited by a
particular nutrient, it may not be reflected in the tissues. .  If the plant
needs that particular concentration to grow, when it is limited by that
element often the uptake of other nutrients is reduced to maintain that
concentration, so that the tissue concentrations would appear "in balance"
because the uptake of other things is limited by the amount of magnesium in
the tissues.  I'd submit that the real test of limitation is a change in
growth or other symptoms upon increasing the availability of the nutrient.
Note that this can give you a positive result, although negative results are
less informative because the fertilizer you add may or may not be in an
available form.  Thus, the addition of the limiting nutrient may not change
things if the addition doesn't get to the plant, as James points out.

Anyway, just my two cents, which if I understand correctly should come to
under one and a half pence at current exchange rates.... ;-)