NPK means
A chemist comments: When
they say NPK they refer nominally to the element, but of course it never will
be the element but combined.
It
is common usage to give the ratios rather than a confusing amount of the
actual compounds.
But
the compounds should be ones that occur as waste products not dangerous
products which have no place in a living cycle of life!
N
the element is a gas and unreactive - only the legumes are known to
"fix" nitrogen gas.
K
or potassium is a soft dangerous metal you can cut with a knife and catches
light in water!
P
is also a dangerous element - ironic as it can be poisonous as the element or
in OP toxins! - it also can spontaneously ignite in warm air.
So
NPK ratios tell you of the relative amounts but not in what they are
contained.
N
in urea is fair enough - urea is the waste product of many animals.
But
P is not to be found as an OP toxin and I would question that to include this
as a source of P is like claiming cyanide as a source of nitrogen!
Animals
would never excrete such material unless they were dying.
Looking for information on phosphorus source in inipol EAP
22:*