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Re: Nitrogen Feedina A Waste?

On Sat, 14 Oct 2000, Cavan wrote:
> The article also said that aquatic plants bring the ammonia through
> their leaves.  Why the jobes spikes then?  How do they bring the
> potassium in?  Through the roots?  The phosphates?

Root feeding .vs. foliar feeding in aquatic plants is a long-standing
technical dispute.  It appears to me that the plants normally (i.e., in
their natural environment) adsorb most of their nutrients through their
roots.  Even weak-rooted stem plants like Egeria densa have been shown to
feed extensively through their roots.  If there are sufficient dissolved
nutrients present in the water then they will take those nutrients through
their leaves; that saves the plants the energy it takes to transport
nutrients from their roots to their shoots.

Unpolluted natural waters don't typically contain much ammonia, phosphate
or iron.  Also, calcium and magnesium while present in the water are
usually more readily available in the substrate.  Even potassium -- which
has relatively little tendency to concentrate in the substrate -- may be
substantially higher in the soil pore water than in the open water.

Of course, things are usually different in aquariums.  Even without
water-column fertilizers the water contains quite a few nutrients due to
fish feeding.  Also, our common substrates are poor growing media compared
to the usually silty and biologically active stuff that plants often find
in nature.  

I think that plants will take nutrients where they find them. Algae, on
the other hand take them only from the water.  If you want to promote
plant growth over algae growth then one possible approach is to feed your
plants through their roots.

Roger Miller