Definition for Essential elements
From Biology Forums Dictionary
Over 95 percent of the dry weight of a flowering plant is made up of three elements—carbon, hydrogen, and oxygen—taken from the air and water. The remaining 5 percent of the dry weight comes from chemicals absorbed from the soil. Roots absorb the chemicals present in their surroundings, but only 14 of the elements absorbed are necessary for plant growth. These 14 elements, along with carbon, hydrogen, and oxygen, are called the 17 essential inorganic nutrients, or elements. Some of the essentials are needed in larger amounts than others and are called the macronutrients; those needed in lesser amounts are the micronutrients. All elements are needed in specific amounts. Note that there is a dispute among plant physiologists concerning the role of nickel in plant nutrition. Since many physiologists exclude it as essential, in some textbooks, lists like the following consist of only 16 essential inorganic nutrients. The 17 are:
- Macronutrients absorbed from the air: oxygen, carbon, and hydrogen.
- Macronutrients absorbed from the soil: nitrogen, potassium, magnesium, phosphorus, calcium, and sulfur.
- Micronutrients from the soil: iron, boron, chlorine, manganese, zinc, copper, molybdenum, and nickel.