Final answer:
Iron (Fe) is the element needed in the least amount for turfgrass growth and metabolism, functioning as a crucial micronutrient for chlorophyll formation and other processes.
Step-by-step explanation:
The element needed in the least amount for turfgrass growth and metabolism is iron (Fe). While all plants require nutrients to grow, some elements are needed in larger quantities than others. The three main macro-nutrients that plants typically consume in larger amounts are nitrogen (N), phosphorus (P), and potassium (K). Iron is considered a micronutrient, which is needed in lesser quantities compared to these macro-nutrients but is still vital for various functions within the plant.
Iron plays a crucial role in the formation of chlorophyll and is not required in the same amounts as nitrogen, phosphorus, or potassium, hence it is the correct answer to the question.