Muriate of Potash

Rodger Whitlock
Tue, 08 Nov 2005 08:21:03 PST
On  8 Nov 05 at 11:10, Stephen Putman wrote:

> Second, it is true that chloride is not good for plants at
> some level, but not much information on exactly what that
> level might be for individual species in specific cultural
> situations.

Actually, the question of which plant requires which nutrient 
in what quantity was studied to death long ago. The only issue 
is that ornamental bulbs simply aren't economically important, 
so you won't find much, if anything, on the requirement of 
Crocus oreocreticus for potassium, say.

> Third - this leaves us wanting to know more about Potassium
> Sulphate which may not have the same problems, but there is
> less information.  I regularly top dress bulbs in my garden
> with Muriate of Potash, and I have added some of it, dissolved
> in water along with other chemical fertilizer to potted bulbs,
> but not in any sort of controlled experiments.

Sulfur is an essential nutrient for plants. We always think of 
nitrogen, potassium, and phosphorous being the three 
most important plant nutrients, but several others are required 
in considerable quantities: sulfur, calcium, and magnesium are 
the ones that come to mind.  

> Who has specific information on Potassium Sulphate and its
> use?

From "Western Fertilizer Handbook", fifth edition, 1975, pp. 
22 et seq:

> The anions indirectly affect the physical properties of soil
> by altering the ratio of calcium and sodium attached to the
> clays. The important anions are bicarbonate, carbonate,
> chloride, and sulfate.
> Chloride (Cl) is found in all natural waters. In high
> concentrations it is toxic to some plants. All common
> chlorides are soluble and contribute to the total salt
> content (salinity) of soils.
> Sulfate (SO4) is abundant in nature. Sodium, magnesium, and
> potassium sulfates are readily soluble. Calcium sulfate
> (gypsum) has a limited solubility. Sulfate has no
> characteristic action on the soil except to contribute to the
> total salt content. The presence of soluble calcium will
> limit its solubility. 

p. 60, under "Primary Plant Nutrients":

> Potassium is taken up by plants in the form of potassium
> ions (K+). It is not synthesized into compounds such as
> occurs with nitrogen and phosphorus, but tends to remain in
> ionic form within cells and tissues. Potassium is essential
> for translocation of sugars and for starch formation. It is
> required in the opening and closing of stomata by guard
> cells. Potassium encourages root growth and increase crop
> resistance to disease. It produces larger, more uniformly
> distributed xylem vessels throughout the root system. (etc) 

p. 63, under "Secondary Plant Nutrients":

> Uptake of sulfur by plants is in the form of sulfate ions
> (SO4--). Sulfur may also be absorbed from the air through
> leaves in areas where the atmosphere has been enriched [sic]
> with sulfur compounds from industrial sources.

> Sulfur is a constituent of three amino acids (cystine,
> methionine, and cysteine) and is therefore essential for
> protein synthesis... Sulfur is present in oil compounds
> responsible for the characteristic odors of plants such as
> garlic and onion.

> Sulfur is generally deficient in Oregon, Washington, and
> Idaho. In these states, the sulfur-supplying power of the
> soil is frequently so low that even grain crops require
> sulfur fertilization. 

p. 74 under "Micronutrients":

> Chlorine is required in photosynthetic reactions in plants.
> Deficiency is not seen in the field due to its universal
> presence in nature. 

Myself, I've always made a point of avoiding chloride-based
fertilizers, also sodium based ones such as sodium nitrate.

Rodger Whitlock
Victoria, British Columbia, Canada
Maritime Zone 8, a cool Mediterranean climate

on beautiful Vancouver Island

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