Which nutrient in soil is most crucial for plant growth and development?

Nitrogen is the nutrient most crucial for plant growth and development because it is a key component of amino acids, which are the building blocks of proteins. Proteins play a vital role in nearly all plant functions, including growth, metabolic processes, and the formation of chlorophyll, which is essential for photosynthesis. Without adequate nitrogen, plants will exhibit stunted growth, yellowing leaves (a condition known as chlorosis), and reduced yields.

While phosphorus is important for energy transfer and root development, and potassium plays a critical role in water regulation and overall plant health, nitrogen is fundamental for vegetative growth and overall biomass production. Calcium is important for cell wall structure and stability, but it does not play as direct a role in the growth processes as nitrogen does. Thus, nitrogen's involvement in protein synthesis and its role in promoting healthy, vigorous growth make it the most critical nutrient among the options given.