The elements that are required or necessary for plants to complete their life cycle are called essential plant nutrients. Additional mineral nutrient elements which are beneficial to plants but not necessarily essential include sodium, cobalt, vanadium, nickel, selenium, aluminum and silicon. The nutrient elements differ in the form they are absorbed by the plant, by their functions in the plant, by their mobility in the plant and by the plant deficiency or toxicity symptoms characteristic of the nutrient. Nutrient Deficiency or Toxicity Nutrient deficiency or toxicity symptoms often differ among species and varieties of plants. A nutrient deficiency occurs when the nutrient is not in sufficient quantity to meet the needs of the growing plant.
Nutrient toxicity occurs when a plant nutrient is in excess and decreases plant growth or quality.
One way to understand the differences in nutrient deficiency symptoms among the plants is knowing the function and the relative mobility of the nutrient within the plant. Table 2 describes the general symptoms of nutrient deficiency and excess often observed for those nutrients. Some nutrients, such as nitrogen, phosphorus, potassium, magnesium, chlorine and zinc, can be easily remobilized within the plant from old plant parts to actively growing plant parts such as young leaves. Other nutrients, such as sulfur, iron, copper, manganese, boron and calcium, are not easily remobilized within the plant. Therefore, the deficiency of the mobile elements usually initially occurs with older leaves while that of the immobile nutrients occurs with the young leaves or stem tips.