"Michi Henning" wrote in message
...
At 100 ppm NO3 there is some evidence that plants themselves shut down
at
normal (0.05 - 0.1 ppm) Fe and trace levels.

Ah, I didn't know that, thanks! Do you have any links?

I knew someone would ask for references :-)

Sorry Michi, I read it somewhere and it seems to agree with my
observations/experimentation, but for the life of me I can't find the
reference. From memory it was in relation to commercial cultivation of
aquatic plants. It may have been on a hydroponic site, but like I said I
can't find it at the moment.

Regards
Graham.