Plant Macronutrients and Micronutrients

Plants get three elements viz. Carbon(C), Hydrogen (H) and Oxygen (O) from air and water. During the process of Photosynthesis, these three elements are combined to make carbohydrates, with subsequent releasing of Oxygen. While roots absorb water, CO2 enters the plants via stomata (the small leaf openings).

Apart from air, 15 of the essential nutrients are supplied by the soil to plants. Out of them, Nitrogen, Phosphorus and Potassium are called primary nutrients or macronutrients. They are called primary nutrients because they are required by plants in large amount relative to other nutrients and deficiency of them is most likely to limit the plant growth and healthy development.

Three more elements viz. Calcium, Magnesium and Sulphur are known as secondary nutrients because the deficiency of them is less likely to be a growth limiting factor. Calcium and Magnesium are generally added to soil to adjust soil pH. Sulphur generally gets added to soil via rain and release from organic matter in soil.
Further, nine more elements viz. Zinc, Chlorine, Boron, Molybdenum, Copper, Iron, Manganese, Cobalt and Nickel are called micro-nutrients. They are called so because they are found and needed by plants in very small amount relative to other nutrients and are least likely to be limiting plant growth and healthy development.