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  • From: "Suzanne Pierot" <suzanne@hvi.net>
  • To: "gardenwriters-on-gardening" <gwl-g@lists.ibiblio.org>
  • Subject: Re: [gwl-g] soil pH
  • Date: Wed, 14 Apr 2004 19:30:08 -0400

If that's simplistic, I'd hate to read the complicated version.
Suzanne
----- Original Message -----
From: "Jeff Lowenfels" <jeff@gardener.com>
To: "gardenwriters-on-gardening" <gwl-g@lists.ibiblio.org>
Sent: Wednesday, April 14, 2004 6:07 PM
Subject: Re: [gwl-g] soil pH


> Jeff, there are a few different ways to answer this question, but let's
> start with what happens when a plant absorbs nutrients. These are
> electrically charged cations and anions.
> There is a balance or equilibrium between electric charges in the soil.
> Then along comes a root hair with its own surface electrical charges and
> exchanges or absorbs one of the cations (a positively charged nutrient)
from
> one of the clay or humus particles.
>
> Two things of significance happen. First, the plant exchanges or releases
a
> hydrogen cation in return for every nutrient cation it adsorbs. This keeps
> the balance of charges equal but increases the amount of H+ in the soil
> solution, a factor that increases the pH, which is, in fact, just a
measure
> of the H+ in solution. Similarly, if it adsorbs an anion, it releases
(OH)-.
>
> Compost contains lots of humus and clay which have large surface areas
> full of Cation Exchange Sites. When these materials come into contact with
> the root, bingo. So you get a change in pH in the rizoshpere.Go beyond the
> root and you don't get as much exchange if any. Hence the pH stays the
same.
>
> This is an extremely simplistic explanation, never a good idea on a
list
> like this one, as I am sure I am about to find out!
>
>
>
> Cheers,
>
> Jeff L
>
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