Potash
Lee Poulsen (Wed, 07 May 2008 16:01:21 PDT)

I think we had this discussion once before quite a while ago. Once
again, the U.S. seems to be sticking to a standard that is completely
different from (and less logical than) what the rest of the world uses.
The Australians clued me into this by pointing out that our 3-number
description of common fertilizer strengths seemed oddly out of
proportion to what they were accustomed to. Then I recalled that the
label on my bag of Apex time-release fertilizer always had a split
label, kind of like a bilingual label, only both sides were in English.
One side is the typical American style numbers, for example: 12-6-12.
The other side is subtitled "Elemental and Metric" and the three numbers
are: 12-2.5-9.9.

Down near the bottom in the "Guaranteed Analysis" sections, on the
American side it says,
quote:
Total Nitrogen (N)...........12.00%
Available Phosphate (P2O5)....6.00%
Soluble Potash (K2O).........12.00%
unquote.

On the "metric" side it says,
quote:
Total Nitrogen (N)...........12.00%
Total Phosphorus (P)..........2.50%
Total Potassium (K)...........9.90%
unquote.

And as you noted, the sources of these three are:
Urea, Ammonium phosphate, and Potassium nitrate, and there is no K2O.

I don't know any reasons other than historical for the U.S. way of doing
this. And I can't see any reason why we continue using it when no one
else does, and we, even in the U.S., want to know what the N-P-K
analysis is, not the N-P2O5-K2O analysis (which is what we get in this
country).

--Lee Poulsen
Pasadena, California, USDA Zone 10a

Jim McKenney wrote: