Most people believe N-P-K to stand for the
nitrogen, phophorous, and potassium, but that
is somewhat incorrect. These are commonly
referred to as the major elements along with
calcium, magnesium, and sulphur. They are the
major contributing compounds in plant growth.
N: nitrogen, used to stimulate new vegetative growth and overall health.
P2O5: phosphorus oxide, used to stimulate flower development and rooting.
K2O: potassium oxide, used to stimulate stem growth and overall health
N-P-K ratings on the labels of fertilizers are misleading at best. They
represent N: nitrogen, P2O5: phosphorus oxide,
and K2O: potassium oxide. These molecular
compound ratios are not the same as the
elemental ppm of the associated primary
element, except in the case of N. They are
only the guaranteed minimum amount of the
A fertilizer labeled 30-10-10 can have up to a
total of 80% N, along with 10% P2O5, and 10%
K20 and still be "accurate". It could have any
combination of N, P2O5 and K2O adding up to
100%, as long as it has at least the MINIMUM
listed of any of the three. You could have 50%
nitrogen in 10-30-20. These types of labels
are misrepresentative. Anyone using them to
establish a controlled nutrient balance is not
doing their plants any service.
As a general guidline, the N-P-K numbers can be roughly converted to
elemental ppm. N, nitrogen is the only element
to convert from the label at the ratio of 1 to
1. P2O5, phosphorus oxide, converts to
elemental P, phosphorous at a ratio of 1 to
.4. K2O, potassium oxide, converts to elemntal
K, potassium at a ratio 1 to .8. This
demonstrates the radical difference between an
N-P-K of 1-1-1 and an actual elemental ratio
I have only found Botanicare and Green Air Products Genesis nutrients to
give the actual ELEMENTAL ppm after dilution.
I used to mix my own solutions from ammonium
nitrate, calcium nitrate, magnesium nitrate,
potassium nitrate, potassium phosphate and
other reagents and know from nutrient analysis
of the misleading nature of N-P-K labels.