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Re: sodium molybdate

"does anyone know if our plants would experience deficiency if molybdenum
omitted from the trace elements we supply? is there enough of it in the
environment? can cobalt also be left out since (i have heard) it is only
utilized by legumes?"

The ONLY "environment" which matters to your aquatic plants is the one that
you provide to them. Whether or not there is sufficient molybdenum there
naturally is something you would have to look into. Is there any in your tap
water? There wouldn't have to be much (like on the order of parts per
billion). There might be some in some fish foods. Depending upon the
substrate in your tank, there might be some available from that.

Might. Small word, big meaning.

The only "numbers" I've ever seen associated with molybdenum are from Philip
Barack's Soil Science website -
http://www.soils.wisc.edu/~barak/soilscience326/macronut.htm . From the
chart, for every 1,000,000 atoms of N in plant tissue, there would be 1 atom
of molybdenum. It is used by plants as a component of certain enzymes,
including nitrate reductase. In plants fed a diet of nitrate, like most
aquarium plants, the absence of the molybdenum necessary for the production
of the enzyme nitrate reductase will mean that they can't use the nitrate.
Physically, molybdenum deficiency exhibits itself as a change of leaf
shape - they become "whip tailed", very reduced and puckered towards the
stem end, due to necrosis of the leaf tissue. You would probably also see
symptoms of nitrogen deficiency, because without the molybdenum, the plant
can't make efficient use of the nitrate as a source of N.

Unless you are growing legumes in your aquarium, you probably don't need to
worry about cobalt.

This ought to point out one very valuable lesson - regardless of whether an
essential nutrient is called a macronutrient or a micronutrient, whether a
plant needs a million of them or only one, they still need them ALL. It is
false economy to try and "make do" with something you picked up at the local
store, or found left over from last summer's tomato crop if it doesn't have
everything that plants need. Most "micronutrient mixes" that you are likely
to come across at a place like Home Depot are designed as supplements for
plants grown on dry land in soil. Soils usually have lots of micronutrients
present in trace amounts and only a few will need to be supplemented. A
farmer would determine what is needed by having his/her soil tested by a lab
and would then select the trace element mix which contains the missing
nutrients. Ones already present in the soil could safely be ignored.

For our purposes, it is our responsibility to provide the "complete diet" -
we aren't really supplementing natural soil (unless of course, you use soil
in your substrate). A trace element mix designed for use in Hydroponics is
probably more likely to have the complete list of "micronutrients" present
in suitable ratios than one designed to be broadcast dry over your lawn or
vegetable garden. But even here, it is rare for a micronutrient mix to have
ALL of the micronutrients (for example, the ones I use don't contain

But the solution to a "complete diet" need not send you scurrying any
further than your local LFS. Seachem's line of Flourish products (Flourish,
Flourish Iron, Flourish Phosphorus, Flourish Nitrogen, Flourish Trace,
Flourish Tabs, Flourish Excel) will supply everything needed except H2O,
although you would probably be better off in most tanks also adding CO2.
According to their published analyses, every essential and beneficial
element is present and accounted for.

What is it with our constant search for alternatives and off-beat sources?
And what do you do with all those empty plastic enema bottles????

James Purchase