Sixteen chemical elements are required for the growth of all plants: carbon, oxygen, and hydrogen (these three are obtained from carbon dioxide and water), plus nitrogen, phosphorus, potassium, calcium, magnesium, sulfur, iron, manganese, zinc, copper, boron, molybdenum, and chlorine.

Fertility levels can vary from a deficiency to a sufficiency, or even toxicity (too much), of one or more nutrients.

soil considered fertile in all other ways could have levels of available potassium too low for optimum plant growth