The primary nutrients are nitrogen, phosphorus and potassium. You may be most familiar with these three nutrients because they are required in larger quantities than other nutrients. These three elements form the basis of the N-P-K label on commercial fertilizer bags. As a result, the management of these nutrients is very important. However, the primary nutrients are no more important than the other essential elements since all essential elements are required for plant growth. Remember that the ‘Law of the Minimum’ tells us that if deficient, any essential nutrient can become the controlling force in crop yield.
The intermediate nutrients are sulfur, magnesium, and calcium. Together, primary and intermediate nutrients are referred to as macronutrients. Macronutrients are expressed as a certain percentage (%) of the total plant uptake. Although sulfur, magnesium, and calcium are called intermediate, these elements are not necessarily needed by plants in smaller quantities. In fact, phosphorus is required in the same amount as the intermediate nutrients, despite being a primary nutrient. Phosphorus is referred to as a primary nutrient because of the high frequency of soils that are deficient of this nutrient, rather than the amount of phosphorus that plants actually use for growth.
The remaining essential elements are the micronutrients and are required in very small quantities. In comparison with macronutrients, the uptake of micronutrients is expressed in parts per million (ppm, where 10,000 ppm = 1.0%), rather than on a percentage basis. Again, this does not infer that micronutrients are of lesser importance. If any micronutrient is deficient, the growth of the entire plant will not reach maximum yield (Law of the Minimum).
Hydrogen also is necessary for building sugars and building the plant. It is obtained almost entirely from water. Hydrogen ions are imperative for a proton gradient to help drive the electron transport chain in photosynthesis and for respiration
Oxygen by itself or in the molecules of H2O or CO2 are necessary for plant cellular respiration. Cellular respiration is the process of generating energy-rich adenosine triphosphate (ATP) via the consumption of sugars made in photosynthesis. Plants produce oxygen gas during photosynthesis to produce glucose but then require oxygen to undergo aerobic cellular respiration and break down this glucose and produce ATP.
Carbon forms the backbone of many plants biomolecules, including starches and cellulose. Carbon is fixed through photosynthesis from the carbon dioxide in the air and is a part of the carbohydrates that store energy in the plant.