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Re: Iron

On Wed, 8 Mar 2000, Chuck Gadd wrote:

> So, what I THINK I learned from this was that iron deficiency can be
> detected by looking at the condition of new growth.  Is this close to
> correct?

I think this is right.

> I believe I've seen signs of nitrate deficiency too, with old leaves dying
> away from the edges, but the leaf veins still green, while new leaves come
> in nice a green for a while.

The leaves may die away from the edges or the end.  Leaves may be light
green for a while, but usually the plants are pretty sick-looking from the
dying and dropped leaves before interveinal chlorosis sets in.  Nitrate
deficiency is easily distinguished if you look at conditions of new
growth, vs. old growth.  What I don't know is how to distinguish iron
deficiency from some of the other metal deficiencies.

> But I'd guess that some nutrient deficiencies
> just slow/stop the growth.
> I guess my question would be:  What nutrient deficiencies will just
> prevent growth, as opposed to causing visual deformities in the plants?

CO2 shortage is the only one I can think of where many plants will grow
slowly without showing pathologic symptoms.  Even then some plants
will get stunted when low CO2 supplies are maintained for a long time.

For other major nutrients (nitrogen and phosphorus in particular) there
may be a range of nutrient supplies over which plants can commonly
regulate their growth rate to match the supply.  Eventually though, there
are problems.

In the case of mobile nutrients, new growth may continue at a high rate
while older growth dies back so that there is a *net* reduction in growth
rate.  In the case of immobile nutrients (calcium for instance) shortages
can lead to a cessation of growth, but while growth is slowed or stopped
it doesn't happen without symptoms.

Also, plants can accumulate stores of some nutrients and use those stored
supplies to make it through temporary shortages, so they may show no
deficiency symptoms even when the nutrient is absent.

Different plants also respond differently to shortages.  I my tanks, vals
suffer calcium deficiency symptoms only at the tip of emerging new leaves,
while the remainder of the leaves are generally normal.  Echinodorus
bleheri(?) shows a gradation of symptoms from mild distortion and slow
growth to death, but the onset is always gradual.  Ammania senegalensis
shows a rapid transition from normal growth to distorted new growth to
death of the growing tip over a period of days.  Calcium deficiency in my
tanks appears to be brought on by high sodium levels, rather than by the
absence of calcium, but I suspect that the deficiency symptoms I observe
follow the usual pattern.

Roger Miller