Crop Fertilizer NPK Calculator
Calculate the amount of fertilizer needed to meet crop NPK requirements.
Convert between common fertilizer grades, find nutrient rates per hectare or acre, and plan fertilizer 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.