It controls the processes used to make proteins vital to new protoplasm in the cells. Nitrogen is essential to the production of chlorophyll and is responsible for leaf growth, as well as, overall size and vigor. Phosphorus is necessary for photosynthesis and provides a mechanism for energy transfer within the plant. Phosphorus is associated with overall vigor and is used at it's highest levels during germination, seedling and the fruiting or flowering stages of growth. It also increases chlorophyll levels in the foliage and helps regulate the stomata openings so plants make better use of light and air.
Potassium is important in all stages of plant growth.
Magnesium is the central atom in every chlorophyll molecule and is essential to the absorbtion of light. It aids in the utilization of nutrients and also neutralizes soil acids and toxic compounds produced by the plant. The other secondary nutrient, calcium, is for the manufacturing of cells and overall growth. Trace elements are vital to chlorophyll formation and must be present in minute amounts. Little is known about the exact amounts needed.