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Re: Phosphate Nutrition



Andrew Bennett wrote:
> I put on a great deal, mostly that nasty superphosphate
> stuff that smells like stale blast furnaces. No sign of
> harm (weeds grow better than ever - looks 100% organic!)
> But - the analysis comes back showing an increase only a
> small fraction of what I put on, or at least paid for.
> 
> Don't bother to tell me to stop using that nasty stuff as
> I already have.


Okay, the damage is done. Triple phosphate just stays on the top of the
soil. Unlike nitrogen, it will not leach down into the soil. If your
province is hilly at all, it's more likely that your SuperP is washing
down slope into local bodies of water with any other loose silt. Shallow
weed roots take advantage of the wealth of superphosphate. Your grapes
are also somewhat shallow rooted, but probably not getting the full
benefit of what you put applied. Also, like many other salts whether or
not they leach readily, high concentrations tend to feel nasty to
beneficials like earthworms, so they eschew the top of the soil where
concentrations are highest. They won't help bring it down to the lower
soil strata. Like any other salt-type fertilizer, you also kill the
beneficial bacteria in the upper soil strata. Colloidal clay phosphate,
although harder to find, is more friendly to the environment -
earthworms don't mind so much, bringing it readily down to the lower
strata. But if you use roundup, which kills the earthworms and other
beneficials in the upper strata, I fear the colloidal phosphate still
may be to little or no avail.

snip...
>They mutter about
>absorption on the clays. (I thought that was cations?)

Cation exchange capacity (CEC) is higher in clay than in loamy or sandy
soil due to the higher surface area available to the cations - ergo -
they bind more readily to clay than sand. This greatly affects the
availability of your phosphorus. All your "P" cations are bound to the
clay in the very edge of the soil surface. I don't have the scientific
explanation for why colloidal clay gets around this, but I understand
that colloids in general are suspendable in water - perhaps allowing
them travel below the soil surface.

If you put on a lot of phosphate, start watching your nearby ponds: if
they start algae-loading you'll know why.
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