Question 1

How do I calculate how much fertilizer my crop needs?

Accepted Answer

Multiply your target yield (tons per hectare) by the crop's nutrient removal coefficient (kg N, P₂O₅, K₂O per ton harvested), then add a 10-20% buffer for losses. Subtract any soil-test-measured available nutrients. The result is the fertilizer rate to apply per hectare. Example: 10 t/ha corn × 17 kg N/ton × 1.15 buffer = 195 kg N/ha gross; minus 20 kg N/ha from soil = 175 kg N/ha.

Question 2

What is nutrient removal?

Accepted Answer

Nutrient removal is the amount of N, P, K, and micronutrients that leaves the field with the harvested product (grain, fruit, tuber). Typical values (kg per ton of yield): corn 17 N / 8 P₂O₅ / 5 K₂O; wheat 25 / 10 / 6; soybean 65 / 14 / 20 (high N because grain is protein-rich); potato 3.3 / 1.2 / 5.5. Source: IPNI (International Plant Nutrition Institute) crop nutrient removal tables.

Question 3

What is NPK fertilizer?

Accepted Answer

NPK stands for the three primary macronutrients: Nitrogen (N), Phosphorus (as P₂O₅ on labels), and Potassium (as K₂O on labels). A bag labeled 20-10-10 is 20% N, 10% P₂O₅, 10% K₂O by weight. A 50 kg bag of 20-10-10 contains 10 kg N, 5 kg P₂O₅, and 5 kg K₂O. See our glossary entry for NPK for the full explanation.

Question 4

Should I split fertilizer applications?

Accepted Answer

Yes — especially for nitrogen. Splitting nitrogen into 2-3 applications (pre-planting + mid-season + optional late-season) typically raises nitrogen-use efficiency 10-20% compared to a single pre-plant dose (IFA, 2022). Phosphorus and potassium are usually applied all at once before planting because they move slowly in soil. Splitting also reduces leaching losses after heavy rain.

Question 5

Does this calculator replace a soil test?

Accepted Answer

No. This calculator provides a planning-quality estimate of fertilizer need based on target yield and crop-specific removal rates. A current soil test (every 2-3 years) is still essential to measure actual available nutrients, pH, CEC, and micronutrient status. Use this calculator to estimate fertilizer budgets, then refine rates with an agronomist and soil-test results before applying.

Question 6

What crops does this calculator support?

Accepted Answer

15 crops with validated nutrient removal coefficients: corn (maize), wheat, rice, barley, soybean, cotton, potato, tomato, onion, sugarcane, canola/rapeseed, oats, cabbage, carrot, banana. WiseYield's full platform extends this to 221 crops with AI-powered, zone-specific recommendations based on soil test, satellite NDVI, and real-time weather.

Question 7

Is this fertilizer calculator free?

Accepted Answer

Yes — completely free, no signup or credit card required. The calculator runs entirely in your browser; your farm data never leaves your device. For AI-driven variable-rate recommendations that combine soil tests, satellite imagery, and real-time weather for your specific fields, try WiseYield's 14-day free trial.

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