[APD] Re: more water and electrolytes

[Roger Miller <roger at spinn_net>]

In an earlier post I neglected to mention the role of sodium.  Sodium is not 
an essential nutrient, but like chloride tends to appear in plant analyses at 
significant levels anyway.

Potassium is used by plants to activate some enzymes and to regulate osmotic 
pressure.  When potassium is in short supply some plants -- perhaps all -- 
can use sodium to regulate osmotic pressure in the place of potassium.  That 
role probably accounts for the relatively high concentrations of sodium that 
sometimes appear in plant analyses.


Roger Miller
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