Nitrogen is part of the complex compounds of which protein is built - the foundation of living matter. Nitrogen is also part of chlorophyll, which plays an important role in the photosynthesis of plants. Nitrogen is especially necessary leaves, with a lack of nitrogen the leaves become pale green, plant growth is delayed, the leaves are shrinking. Excess nitrogen - the leaves are dark green, flowering (and fruit in lemon, orange, etc.) is delayed. To supply the plant with nitrogen applied nitrogen fertilizer (ammonium nitrate, ammonium sulphate) and organic fertilizers (manure or slurry).