Secondary macronutrients are essential to plant function and are required in quantities less than N, P, and K, but more than micronutrients. These include calcium (Ca), magnesium (Mg), and sulfur (S). Each are described briefly below:
- Calcium: Primarily a component of cell walls and structure. Found in gypsum, limestone, and calcium chloride.
- Magnesium: Central ion in the chlorophyll molecule and chlorophyll synthesis. Found in S-Po-Mg, dolomitic limestone, and magnesium sulfate.
- Sulfur: Metabolized into the amino acid, cysteine, which is used in various proteins and enzymes. Found in ammonium sulfate, elemental sulfur, gypsum, and potassium sulfate.