Tomato Fertilizer and NPK ratios

Jim Lykos
Mon, 07 Nov 2005 17:07:57 PST
Hi Mary Sue,

One aspect of NPK ratios that can be overlooked is the difference in calculating fertilizer amounts based on the country of origin, as   NPK ratios are not internationally compatible. I understand that in the USA, the NPK ratios are calculated by comparing  the percentage of N% against Phosphorus oxide% and Potassium oxide%  ie the minerals of N : P2O5 : KO2  in a fertilizer.  However in Australia and presumably other nations we calculate the NPK ratios by the relative amounts of the elements of N, P and K  that the fertilizer contains and not by the oxides of P and K. 

Hence there is a difference in that the NPK ratios used in the USA,  appear to us (in other countries) to have quite inflated P and K ratios and obviously if someone in the USA picks up a recommendation for using a NPK ratio from a member in another country they will  use the wrong  fertilizer unless they make the necessary calculations for a conversion to the USA system.


Jim Lykos
Blue Mountains Australia

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