Crop Fertilizer NPK Calculator
Calculate fertilizer amount to meet crop NPK requirements.
Convert between fertilizer grades, find nutrient rates per hectare or acre, and plan applications.
NPK: The Three Major Nutrients Nitrogen (N): promotes vegetative growth, leaf and stem development. Phosphorus (P₂O₅): root development, flowering, fruiting, energy transfer. Potassium (K₂O): disease resistance, water regulation, fruit quality. Fertilizer grades (e.g., 10-20-10) show % N — % P₂O₅ — % K₂O by weight.
How to Read Fertilizer Labels A 46-0-0 bag (urea): 46% N, 0% P₂O₅, 0% K₂O → 460 g of N per kg of fertilizer. A 10-10-10 bag: 10% N + 10% P₂O₅ + 10% K₂O → 300 g of nutrients per kg. Elemental P = P₂O₅ × 0.436 | Elemental K = K₂O × 0.830
Calculating Fertilizer Rate Fertilizer needed (kg/ha) = Nutrient required (kg/ha) / (Grade% / 100) Example: Need 100 kg/ha of N using Urea (46% N) → 100/0.46 = 217 kg/ha urea.
Typical Crop Nutrient Requirements (kg/ha) Corn/Maize: N=150–200, P₂O₅=60–80, K₂O=100–150 Wheat: N=100–150, P₂O₅=50–70, K₂O=60–90 Rice: N=80–120, P₂O₅=40–60, K₂O=60–80 Soybean: N=20–40, P₂O₅=40–60, K₂O=60–100 (fixes atmospheric N) Potato: N=150–200, P₂O₅=100–150, K₂O=200–300 Tomato: N=100–150, P₂O₅=80–120, K₂O=150–250 Pasture grass: N=100–200, P₂O₅=20–40, K₂O=40–80
Soil Test Adjustments Subtract existing soil nutrients from target rates. Build-up applications may exceed maintenance rates in first year. Always apply based on current soil test — over-application wastes money and pollutes waterways.