NPK Full Form — Nitrogen Phosphorus Potassium

N = Nitrogen Role in plants: Essential for chlorophyll production, protein synthesis, and overall vegetative growth (leaves and stems). Nitrogen-deficient plants show yellowing of older leaves (chlorosis).

P = Phosphorus Role in plants: Essential for root development, flower and fruit formation, seed production, and energy transfer (ATP/ADP cycle). Phosphorus deficiency causes dark purplish leaves and poor root growth.

K = Potassium (Chemical symbol K from Latin 'Kalium') Role in plants: Regulates water uptake (stomatal opening/closing), enzyme activation, disease resistance, and overall plant strength. Potassium deficiency causes brown, scorched leaf edges.

These three are called 'primary macronutrients' because plants need them in the largest quantities.

NPK ratio: The three numbers on fertilizer bags (e.g., 10-26-26, 12-32-16, 17-17-17) represent the percentage by weight of N, P₂O₅, and K₂O.

Example: 10-26-26 fertilizer contains:

• 10% Nitrogen (N)
• 26% Phosphorus (as P₂O₅)
• 26% Potassium (as K₂O)

Common NPK fertilizers in India:

• DAP (Di-Ammonium Phosphate): 18-46-0 — high phosphorus; used at sowing time
• Urea: 46-0-0 — only nitrogen (not a true NPK, but the most common N fertilizer)
• MOP (Muriate of Potash): 0-0-60 — only potassium
• Complex fertilizers: 10-26-26, 12-32-16, 17-17-17 — balanced NPK

Beyond NPK, plants also need:

Secondary macronutrients (needed in moderate quantities):

• Calcium (Ca), Magnesium (Mg), Sulphur (S)

Micronutrients (needed in very small amounts but essential):

• Iron (Fe), Manganese (Mn), Zinc (Zn), Boron (B), Copper (Cu), Molybdenum (Mo), Chlorine (Cl)

Deficiency of any essential nutrient can cause specific symptoms (e.g., Zn deficiency causes 'Khaira' disease in rice).