Re: Chelated iron and rusty nails

>George wrote:
>> We need to provide a source of iron in a form easily usable by plants
>> (Fe++, not Fe+++) by root uptake AND leaf uptake.

This is true. 

>>  It should be clear
>> to everyone here that a lot of plants (especially fast growing stem
>> plants like Rotala and Alternanthera sp.) don't really use their roots
>> for much nutrient uptake.  

In general stem plants are fast growing and do not depend on their roots for
nutrient uptake.  but I never thought of Rotala and Alternantera as falling
into this growth category.

>>Plants that get nutrients through their
>> roots need the nurients to be bound to organic substances (chelated)

This is not true!!  Plants that get their nutrients through their roots CAN
get the nutrients (like iron) that are bound to organic substances, but do
not NEED to get them that way.  Chelation is one way to keep the nutrients
soluble and accessible.
Iron oxide will precipitate when added in solution to an aquarium.

>> Let's keep in mind that there are complex chemical processes taking
>> place in the substrate that go far beyond what we understand.

>>  A rusty ten-penny nail is not going to get you there. 

I would not be so quick to draw that conclusion!  
Another effective way to provide iron to plant roots is through reduction of
Fe+++ to Fe++.  This takes place in an oxygen limited environment, like a
substrate without much circulation. Maybe chelated iron is needed to
suplement the initial iron provided by laterite in a system with undergravel
circulation, but other strategies can be used in other systems. Although I
have not tried to use a rusty nail, I have talked to successful plant
growers that use such small pieces of metallic objects in the substrate.
Others on the net use soil (which contains iron) and some have even
suggested the use of steel wool. Small pieces sounds like it could be very
beneficial. The precipitates from iron oxide solutions will also become
available to plants through chemical changes in a reduced environment. IMHO
(i.e. I am not a chemist), the problem with these latter methods is the
possiblity of providing TOO MUCH iron and other micronutrients.