RAS question
Which of the following is the PRIMARY macronutrient directly responsible for promoting leafy/vegetative growth in plants?
Correct answer: (B) Nitrogen (N).
Nitrogen (N) is the primary macronutrient that most directly promotes leafy and vegetative growth in plants.
Explanation
Nitrogen is the N in the N-P-K group of primary macronutrients and is linked most directly with green, leafy growth. It is a key component of chlorophyll, amino acids and proteins, so its deficiency appears as yellowing of older leaves, or chlorosis. University of Minnesota Extension guidance distinguishes nitrogen's role in rapid green, leafy growth from phosphorus's role in early root growth, blooming and seed or fruit formation and potassium's role in drought resistance, disease resistance and seed quality. Therefore, nitrogen is the primary macronutrient most directly associated with vegetative shoot and leaf growth.
Why the other options are wrong
- (A) Phosphorus is a primary macronutrient, but it is associated with early root growth, blooming and seed or fruit formation rather than leafy vegetative growth.
- (C) Potassium is a primary macronutrient, but it is associated with drought tolerance, disease resistance, plant hardiness and seed quality rather than the primary promotion of leafy shoots.
- (D) Zinc is a micronutrient involved in enzyme systems and auxin synthesis, so it is not the primary macronutrient driving leafy growth.
Concept
Basic plant nutrition requires knowing the distinct roles of N, P and K. RAS questions on agriculture, the environment and general science often require a precise match between a nutrient and its function rather than only a general understanding of fertiliser use.