Which of the following nutrients is classified as a secondary macronutrient?

Calcium is classified as a secondary macronutrient because it plays a crucial role in plant health and development but is required in smaller quantities compared to primary macronutrients like nitrogen, phosphorus, and potassium. Secondary macronutrients, which also include magnesium and sulfur, help support fundamental physiological processes, including cell wall structure and stability, enzyme function, and overall plant growth.

While nitrogen, phosphorus, and potassium are vital for plants in larger amounts—contributing primarily to growth and productivity—calcium helps with cellular function and soil health, often aiding in the development of root systems and the prevention of physiological disorders. Understanding the different classifications of nutrients can help in managing soil health and plant nutrition effectively.