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: > In addition to that, there is this. I did a little bit of homework before I > went potassium shopping. I discovered what to me is a bizarre anomaly: > retail gardening products are sold on the basis of potassium oxide > percentage. What makes that bizarre to me is that such products do not > contain potassium oxide (or do they?). Is the idea that you are buying > something which is the equivalent of a raw potassium source which would > yield so much potassium oxide upon burning? Curiously (to my sensibilities > at least) the potassium oxide "content" on the retail products is in big > print; you have to read the fine print to find out what the real source of > the potassium is. > > Help me out here! > > Jim McKenney > > >