Which component of fertilizer is used for stimulating early growth purpose ?
Phosphorus
Phosphorus is the nutrient associated with early growth and root development — option 4.
The three primary nutrients and what each does. Fertilisers are described by their N-P-K rating, and the three elements have quite distinct roles in the plant:
| Nutrient | Main role | Deficiency shows as |
|---|---|---|
| Nitrogen (N) | Vegetative growth — it is a constituent of amino acids, proteins and chlorophyll, so it drives leaf and stem development | Yellowing of older leaves, stunted shoots |
| Phosphorus (P) | Early growth, root establishment, flowering, seed and fruit formation; it is part of ATP, DNA, RNA and cell membranes | Poor root growth, delayed maturity, purple tinge on leaves |
| Potassium (K) | Regulation — opening and closing of stomata, water balance, enzyme activation, resistance to disease and cold | Scorched leaf margins, weak stems |
Why phosphorus in particular. A germinating seedling must build a root system before it can do anything else, and root growth depends on a supply of energy in the form of ATP — adenosine triphosphate — and on the phosphate backbone of DNA for cell division. Both require phosphorus. It also moves very poorly through the soil, reaching roots only by slow diffusion, so it must be placed near the seed at sowing rather than applied later. This is exactly why “starter” fertilisers such as di-ammonium phosphate are drilled with the seed, and why phosphorus is the nutrient named for early growth.
Why oxygen is not an answer. Oxygen is essential to the plant for respiration, but it is taken from the air and from soil water. It is not supplied as a fertiliser component, and no fertiliser is rated for its oxygen content.
A note on Indian practice. Urea supplies nitrogen, DAP and single super phosphate supply phosphorus, and muriate of potash supplies potassium. Over-use of urea relative to the other two has skewed the N-P-K ratio in Indian soils well away from the recommended balance, which is one reason nutrient-based subsidy was introduced.
Hence, the answer is Phosphorus.
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