When talking about diet and food, macronutrients almost always mean carbs, protein,
and fat.
When talking about soil, fertilizer, or plant health, macronutrients/macroelements
refer to the key
elements that are analyzed in plants in high amounts (as opposed to micrnutrients/microelements).
- This classification is based on the
concentrations in which nutrients are present in plant
tissue. The reference value is the dry plant matter. The amount of nutrient needed and
accumulated in the plant is not related to "optimum" A plant deficient of a few micrograms
of a
microelement, e.g. ZN, will probably grow as badly as a plant deficient in a few milligrams of a
macroelement, e.g. K.
(primary nutrients,
macroelements): C, O, H, N, P, K, S, Ca, Mg, Cl
Primary Macronutrients:
Needed in the greatest amounts: Nitrogen (N), Phosphorus (P),
Potassium (K) – These are the famous "NPK" on fertilizer labels.
Secondary Macronutrients:
Needed in moderate amount: Calcium (Ca), Magnesium (Mg),
Sulfur (S).
Carbon (C), Oxygen
(O), Hydrogen (H) are the macroelements present in the highest
amounts
- Microelements (trace nutrients):
Cu, Zn, Mn, Fe, B, Mo
