Which nutrient is primarily responsible for root development in plants?

Phosphorus is primarily responsible for root development in plants due to its critical role in several physiological processes. This nutrient is essential for energy transfer and storage within the plant, notably through its involvement in ATP (adenosine triphosphate) synthesis, which is crucial for energy transfer in cellular processes.

Moreover, phosphorus is a key component of nucleic acids, which are essential for cell division and growth. This is particularly important in the early stages of plant development, where robust root systems are necessary for anchoring the plant and absorbing water and nutrients from the soil. A well-developed root system not only supports the growth of the plant but also enhances its ability to withstand environmental stresses.

In contrast, nitrogen primarily supports leaf and stem growth, potassium aids in overall plant health and stress resistance, and calcium is important for cell wall structure and plant development. Therefore, while all these nutrients play significant roles in plant growth, phosphorus is uniquely focused on promoting adequate root development, making it the correct choice for this question.