From: Curtis Johnson
To: Hal White
Date: Aug 1 1998 10:20:18 am
Subject: Salt
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HW> There's a fellow over in "religion" maintaining
HW> that small amounts (unspecified) of salt added to
HW> soil works as a fertilizer for plants..   Any comments?

HW> Is this likely?  For humans we know, for example,
HW> that
HW> A.some elements in small amounts are health-promoting,
HW> though in large doses, toxic--e.g. selenium.

HW> B. Other elements, like mercury, I gather are poisonous
HW> at all levels, though possibly the effect is too
HW> small to matter at the lowest doses.

HW> Could salt, for plants (  or some plants) be like A.
HW> category, in your opinion?  Any refs appreciated.

HW> (For scientists:  yes I realize salt is not an element)

I'll assume for the moment that "table salt" (sodium
chloride) is meant.
I can't think offhand of any plant compound that uses
sodium *or* chlorine.  (Animals, of course, use sodium in nerve
transmission and in the bloodstream to maintain osmolality--i.e.,
the right pressure of fluid within cells and tissues.)  Since
plants can't go around looking for a drink of water whenever
they need it, they have the problem of keeping water in their
cells and tissues--IOW, avoiding wilting.
There are plants, such as kelp and mangroves, that can
grow not only in brackish water but in the sea.  Presumably
kelp and mangrove may be so adapted that they might be in
trouble if reduced to depending on fresh water.
Now to try to verify my reasoning. . . Nothing in my
main book in my library on plants, _Plant and Planet_, Anthony
Huxley (Penguin, 1978) says anything about plants requiring
sodium or chlorine as a nutrient.  In fact:

(p. 251):  "A salinity of over 0.5 per cent is harmful
to most plants:  salt is not only toxic but makes it more
difficult for roots to extract from the soil, because of unsuitable
osmotic pressures . . ."  Tamarisks apparently have glands that
excrete salt.  Many sea coast and salt-marsh plants assimilate
water slowly and store it in their stems.  Mangroves "succeed by
combining a high salt concentration in their sap with a salt-
resistant skin to their roots."

However, p. 385 mentions Israeli experiments in which some
crop plants "have been found, if especially managed, to tolerate
chloride levels up to twenty times higher than previously thought
feasible.  Plants irrigated with saline water seem also to have an
improved capacity for withstanding periods of drought."

Perhaps the individual was confusing drought resistance with
fertility.  Another possibility is that in chemistry, any acid-base
compound is called a salt--ammonium nitrate, a well-known fertilizer,
is such a salt.

Feel free to forward this response.  I'd also be interested
in hearing what Blanche says:  she's a certified Master Gardener.

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