

Re: Name that deficiency

    * From: "Wayne Jones" <waj at mnsi_net>

I reply:

I wonder if for some reason iron would not stay chelated in solution and
therefore could not be measured, the other nutrients in TMG could poison
the plants. There is no reasonable way to measure this but excess
manganese is readily absorbed by plants and can produce toxic symptoms
such as black spots. Manganese might still remain in solution even if it
were not chelated. I keep thinking on how some people have reported that
when they switched to triphosphor lamps that plants did not do so well.
If the those lamps are capable of undoing the trace element chelation
then maybe there is an explaination there. UV light seems to be able to
do this. Maybe the high energy peaks of a triphosphor lamp can do this
as well. It does not seem reasonable that plants alone could account
that amount of trace elements. Where is the stuff going?


If the chelator in TMG is EDTA, the brighter light from triphosphor lamps
could cause more rapid breakdown of the chelator.  I have seen that light
does cause breakdown of iron EDTA and precipitation of the iron.  I had two
identical flasks of 1/5 Hoaglands nutrient soulution plus iron EDTA, one in
the dark and the other in about 1000 foot candles of fluorescent light
(regular fluorescents---triphosphors weren't invented then), and I saw
precipitate develop in the flask in the light, but no precipitate in the
dark flask.

I think that DPTA is a much more light resistant chelator, although it
might not be resistant to UV light.  CIBA-GEIGY  sells iron DPTA.  It might
be worth your while to get some of that so that you can try out your theory
that you are raising other micronutrients to toxic levels in the effort to
get measurable iron.  If you can't find any source of iron DPTA, I can send
you some.

I think that the likely reason that plants didn't do so well for some
people who switched to tri-phosphor lamps is that the brighter light caused
more rapid growth and greater demands on nutrients and something ran out,
causing deficiency and allowing algae to get started, etc.  You have to
work harder to keep everything supplied when the light is more intense.

Iron can be hard to supply in adequate amounts, and low-level iron
deficiency does not look like the classic iron deficiency where the new
growth is very pale.  Low level iron deficiency can mimic nitrogen
deficiency or potassium deficiency or both.  The reason may be that the
plants are actually unable to get enough nitrogen or potassium because of
the iron deficiency.  I have seen examples of both apparent N and K
deficiencies that didn't make any sense because I knew how much nitrate and
how much potassium was in the water.  Pushing iron DPTA cleared up the

Paul K.