Nitrogen (N) is important for optimal crop growth. Basically nitrogen promotes plant growth, especially the leafy, vegetative growth. As it is part of every protein in the plant it plays a part in all processes. It is also important for the creation of chlorophyll, which allows a better photosynthesis.
In an optimal culture, the plant needs to absorb enough nitrogen and can, thereby, grow in the best possible way.
A higher dose of Nitrogen is important in the initial growth phase, as the plant is in its vegetative growth. And in small quantities in the flower phase as at that time it is favourable for the plant to bloom and not grow too much.