Nutrition refers to the need (and use) of the 18 basic chemical elements essential to normal plant growth

18 Basic Chemical Elements:
Carbon, hydrogen, and oxygen are found in the air and water

Nitrogen, phosphorus, potassium, magnesium, calcium, and sulfur (found in the soil) are called macronutrients

Iron, zinc, molybdenum, nickel, manganese, boron, copper, cobalt, and chlorine (found in the soil in much smaller amounts) are called micronutrients

Nutrient Levels
Nutrient levels are usually expressed as Total Dissolved Solids (TDS) in parts-per-million (ppm) and are derived from the basic measure of Electrical Conductivity (EC)

Fertilization
Fertilization is the term used when these nutrients are artificially supplied to the plants for uptake through the roots or leaves (root or foliar uptake)

Foliar Absorption
Under normal growing conditions plants take-in most nutrients (except carbon, hydrogen, and oxygen) through the roots

However, the leaves can also absorb some nutrients if they are sprayed on in a diluted solution or supplied by a fog generator

Care must be taken that the nutrient concentration is not too high or leaf injury may result