Nitrogen

Toxic Elements: The micronutrients are always needed in smaller amounts, and any small reduction in their amount might cause deficiency symptoms, while an increase in their amount can cause toxicity. Toxicity can result from any reduction in mineral ion concentration that results in tissues losing 10% of their dry weight. Although the degree of toxicity differs amongst plants, it is also difficult to identify. The majority of mineral toxicity prevents other minerals from being absorbed. Example: Chlorosis is brought on by a nitrogen deficiency.
Essential Elements: The substance that must be consumed since the body cannot produce enough of it to meet all of its demands.
They are used
(a) as parts of chemical compounds in plants that relate to energy, such as magnesium and phosphorus.
(b) Enzyme activators or inhibitors, such as magnesium and zinc.
(c) For controlling osmotic potential, such as potassium.