Plant nutrient requirements

Does anyone know what concentrations (in water) of N, P, K and trace
elements are optimal in a freshwater planted tank?  I realize that
this depends somewhat on the substrate and possibly other criteria,
but what is the general range of values one should try to maintain?

George Booth once posted an analysis of the Dupla drops, but that does
not tell the whole story, because the effective concentration of the
nutrients will depend not only on how much you add and how often, but
also on how quickly the plants take them up, and how quickly the
chemicals precipitate.

This question was asked by someone in *.aquaria, but as far as I know,
nobody answered.