What symptoms appear in flowering plants when they are deficient in nitrogen?

Nitrogen-deficient plants are thin and weak, with slender, elongated, hardened branches, and small leaves and small flowers. The leaf color gradually changes from dark green to pale from the old leaves to the new leaves, then develops a red-purple hue, until the leaves turn yellow and drop off; in severe cases the whole plant loses its green color. Control methods: apply more decomposed human manure and urine, cake fertilizer, barnyard manure, or fertilizers such as ammonium sulfate, urea, and ammonium nitrate.