Date: Mon, 8 Sep 1997 13:23:48 +0000 From: Guy.VanDerKinderen@rug.ac.be To: cp@opus.hpl.hp.com Message-Id: <aabcdefg3427$foo@default> Subject: The great baking soda story
Hi Randy and everyone interested,
Have been following the amazing debate on baking soda and CP's a
little bit the past few weeks, sometimes with delight. Randy, I hope
you did'nt ran to the North Pole in the meanwhile, to escape that
famous 'panel of judges'. I must admit you have a strange way of
introducing your ideas, but the item stimulated my curiosity, rather
than discarding it. And although I'm still struggling with the 'oily'
part of this matter, the idea of adding baking soda, or
sodiumbicarbonate as we should know by now, may not be that stupid as
it seems to be to certain people. We've already met some chemistry in
the discussion, but the proposed acid/base reactions and resulting
salt formation, as would occur in an aquous solution, are not really
representative with regard to the substrate in which CP grow. For
instance, in these matrices one is dealing with positive or negative
correlated interactions between ions, which are investigated - after
extended soil analyses - by computer (clustering and PCA). From
studies made by plant-ecologists (which I have been able to
assist closely) at two Belgian nature reserves, with peatbogs,
heathlands, and CP's (about 4 species, which is great news in CP-poor
Belgium), I have been collecting some data which may illustrate that
in a certain situation, addition of bicarbonate could be beneficial
to our plants. Especially with regard to 'watering by the tray'
system, pots standing in a stagnant layer of water, as used by many
CP lovers. Here's some facts (from the studies), thoughts and
tentative comparisons and conclusions, which of course may be
discussed.
First, as Steve already suggested, bicarbonate indeed is an
important ion in the buffering capacity of peat soils, and Ca and Mg
ion levels are closely related with this acidity/alkalinity. Within
certain limits, pH changes will be compensated by HCO3-, and this is
function of its concentration (!). Moreover, temporary hardness of
(soil)water is bicarbonate compensated, that is at normal pH levels
(i.e. 5-7 at the site where the CP grow). Another important fact is
the strength at which kations are adsorbed to soil particles:
H+>Al+++>Ca++>Mg++>K+>Na+.
What will happen if the situation becomes acidified, mostly due to
external influences such as acid rain, agricultural activities or
even by natural causes? In certain limits the buffering capacity
will compensate, but with increasing acidifacation a sesuence of
physical and chemical events will occur, which eventually will alter
whole plant communities if the influence persits. First CO2 is set
free from the bicarbonate with increasing H+, as already indicated
by earlier commentors. At pH 4.2, HCO3- is no longer found in the
soil. The bicarbonate compensated temporary hardness will shift to a
persisting hardness, which may be compensated by e.g. sulfate. With
decreasing pH, adsorbed kations will be leached out, starting with
sodium. Later, also Ca and Mg ions, which were originally associated
with bicarbonate, start leaching (if Alumina ions ever start
leaching, then the area has a severe problem). The CP's of the
studied areas typically do not grow under these conditions.
Another phenomenon in nature which is worth noting with regard to
the above mentioned cultivation technique, is peat formation. This
proces will start under waterlogged, anaerobic conditions, in which
sulfur compounds from organic debris, will be transformed to
hydrogensulfide with its characteristic rotting-egg odor. The gas may
in its turn be transformed to sulfuric acid by oxidizing bacteria,
with the resulting acidifying result.
Now, lets turn back to the 'water in tray' cultivation method.
Although we all try to give our plants the best care, the situation
of a plant potted in peat and other additives, and standing in a
layer of water, is certainly not comparable with a natural and
healthy dynamic system. For instance, to compensate for this, we
(should) repot regularly. However the basic physical and chemical
events will take place according to the circumstances, even in our
pots, and this situation is much more sensitive to external changes,
and internal as well. The substrate will already become acidified,
only by the plants' respiratory products. The process may only be
speeded up by using acid (rain)water. The effects of the results of
acidification, together with those of waterlogging by the tray
system, may be dramatic. Acidification disturbes the bicarbonate
buffering system (which is lost through CO2 release), and eventually
kations are leached in the sequence as described above. In addition,
anaerobic processes in the waterlogged lower part of the substrate
may also result in increased acidification. Many CP-lovers are
familiar with this process because of the stinking H2S it produces.
Several CP's do not tolerate these circulmstances for a prolonged
period. In this case, victims might be helped by applying
bicarbonate, as it restores pH, buffering and ion-interactions,
although maybe not for another long period. The additional sodium may
not be that problem, since it replaces part of the leached ions and
becomes retained by soil particles. In the studied areas, sodium was
even more prominently (in much higher concentrations) present than
potassium.
Now, the exact situation in which Randy uses his baking soda receipe
is still not very clear to me (again, especially the oil part), but
this may be one explanation why the treatment could be beneficial to
(his) plants. So, before we start raising red flaggs, lets first use
our brains (and I don't underestimate the newcomers) and take idea's
into consideration, even - or especially - if they derive from old
popular uses. The painkilling effect of willow bark was long known
before science 'discovered' it, and later the aspirin.
Indeed, some simple experiments may be carried out to experience the
effect of baking soda on peatsoil or plants planted in it, as certain
commentors already suggested.
Stay allert,
Guy VdK
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