The nitrogen is a chlorophyll component and it directly influences the photosynthesis. Its role on the vegetative growth is well known. It’s also a major component of the proteins.
The phosphorus interferes directly in all energy transfers within the plants. It promotes the rooting and the growth. A red coloration of the stem or the leaves is often a visible symptom of phosphorus deficiency. The quality of fruit, vegetables and grain depends on that element. Phosphorus improves the fertility and the fructification.
The potassium acts on the ions assimilationand the water balance. It improves the glucoses and sugar molecules accumulation in the fruit or the roots at maturity.