Secondary nutrients are those that are required in less amounts as compared to Major Plant Nutrients. Calcium, Magnesium and Sulfur are Secondary Plant Nutrients.
Calcium is a key component of cell walls, helping to build a strong structure and ensuring cell stability while Sulfur plays a role in nitrogen stabilization and in reducing the level of common and powdery scab.
Magnesium plays a crucial role in photosynthesis, as it is present in the center of each chlorophyll molecule. Magnesium is also an important nutrient as it's deficiency in potato crop can reduce yields by up to 15%.