Which component of fertilizer is used for stimulating early growth purpose ?

Question

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Correct — C, Phosphorus. In the standard NPK division of labour taught in every agronomy text, each of the three primary nutrients owns a distinct job, and phosphorus owns root establishment, seedling vigour and early maturity. The reason is biochemical rather than descriptive. Phosphorus is a structural part of ATP and ADP, of the nucleotides that make up DNA and RNA, and of the phospholipids in every cell membrane. A germinating seedling is doing two things at maximum rate — dividing cells and transferring energy — and both of those processes consume phosphate directly, which is why a shortage of P at the two-to-four leaf stage stunts a plant permanently in a way a later shortage does not. There is a second, purely physical reason phosphorus is the 'early' nutrient. Phosphate ions are strongly fixed by soil minerals and are almost immobile in the soil solution; a nitrate ion moves with soil water to the root, but a phosphate ion must effectively be met by the root. A young seedling has a tiny root system and cannot go looking for it. That is exactly why 'starter' fertiliser is phosphatic and why it is drilled or banded next to the seed rather than broadcast over the field — di-ammonium phosphate, DAP, graded 18-46-0, meaning 18 per cent nitrogen and 46 per cent P2O5, is the fertiliser most Indian farmers use for basal application at sowing. The same immobility is why plants evolved mycorrhizal partnerships: fungal hyphae are far finer than root hairs, reach soil the root cannot, and secrete acids that release phosphate the root could never absorb by itself. Read the stem's three qualifiers together — a component of fertiliser, aimed at growth, and specifically early growth — and only phosphorus satisfies all three at once.

Why the other options are wrong — (a) The intended trap, and it wins if you read only the word 'growth'. Nitrogen is the nutrient of vegetative growth — it builds amino acids, proteins and the chlorophyll molecule itself, so it drives leaf area and the deep green colour of a healthy crop, and India consumes more of it than of P and K combined. But it acts across the whole season, and nitrate is mobile in soil, so it is top-dressed in splits rather than placed under the seed.  (b) Potassium is the regulator rather than a builder: it is not incorporated into any structural molecule of the plant but stays as a free ion controlling stomatal opening, water balance, enzyme activation and the translocation of sugars, which is why K-sufficient crops resist drought, lodging and disease better. Its classic deficiency sign is scorching along the margins of the older leaves — a mid-to-late-season symptom, not a seedling one.  (d) Oxygen is genuinely essential to a plant — roots respire and drown in waterlogged soil without it — but it is not a component of any fertiliser. Along with carbon and hydrogen it comes free from air and water, which is precisely why the three of them never appear on a fertiliser bag. Anything sold as fertiliser exists to supply what the atmosphere cannot.

Concept: Plants need seventeen elements to complete their life cycle. Three of them — carbon, hydrogen and oxygen — are taken from air and water and cost nothing. The remaining fourteen come from the soil and are split by the quantity required: the primary macronutrients nitrogen, phosphorus and potassium, which soils run short of first and which fertiliser exists to supply; the secondary macronutrients calcium, magnesium and sulphur; and the micronutrients — iron, manganese, zinc, copper, boron, molybdenum, chlorine and nickel — needed in traces but no less essential, since a plant starved of any one of them dies just as surely as one starved of nitrogen. Fertiliser grades are written as three numbers in the fixed order N–P–K, expressed as per cent N, per cent P2O5 and per cent K2O: urea is 46-0-0, di-ammonium phosphate is 18-46-0, and muriate of potash is 0-0-60. Reading a bag correctly is itself an examinable skill, because the middle number is the phosphate figure and the order never changes.

State PCS 2024 Q102 — Science & Technology PYQ with Answer

State PCS 2024 Q102 — Science & Technology PYQ with Answer