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re: Clay balls or pellets in an all gravel substrate
Bill Terburg wrote:
> Recently there has been some discussion by Steve
> Pushak and George Booth on the subject of the use
> of clay balls and or pellets.
> In our experience we've found that clay pellets composed
> of one or two parts clay to one part pmdd dry mix works
> extremely well as a general fertilizer and controled substrate
> Interestingly, we've found that the small controlled amounts
> of fertilizers we add via clay pellets do not for the most part
> migrate into the water column. We have performed an experiment
> wherein we added an amount of fertilizer in pellet form to the
> substrate which if added directly to the free water would have
> registered significantly on our test kits. But yet a day later,
> 2,3,4,5,7, still no reading. This is contrary to prevailing wisdom
> which says that substrate fertilizers in gravel migrate quickly into
> the free water.
Interesting. In land crops, a certain amount of clay is valued for its
ability to hold cation nutrients into the soil. The ability is often tested
and quantified in terms of cation exchange capacity (CEC). In your
experiment I would actually expect any cation nutrients (calcium,
magnesium, potassium, etc.) to stay put without leaching _because_
of the clay balls. Plain laterite substrates lack this ability though they
have the ability to sequester the negatively charged phosphate anion.
I have often wondered about the value of a substrate composed of
sufficient amounts of both laterite _and_ clay so that both important
cation nutrients and the phosphate anion can be brought into the soil
from the the water column. To me this methodology provides some of
the benefits of a 'soil' substrate without the potential for leaching
uncertain types and amounts of nutrients. It also provides laterites ability
to help sequestor phosphate.
christopher.coleman at worldnet_att.net