Fertilizer Calculator
Calculate NPK fertilizer application rates per acre based on soil test results and crop nutrient requirements.
Results
Visualization
How It Works
Fertilizer recommendations are based on crop nutrient removal and soil test levels. Corn needs about 1.2 lbs of nitrogen per bushel of yield goal. Phosphorus and potassium recommendations are based on soil test levels — "build" if low, "maintain" if optimal, "draw down" if high.
The Formula
Gross N = Yield Goal × N Per Bushel
Net N = Gross N − Previous Crop N Credit
P₂O₅ and K₂O based on soil test level thresholds
Net N = Gross N − Previous Crop N Credit
P₂O₅ and K₂O based on soil test level thresholds
Variables
- N Per Bushel — Nitrogen uptake per bushel of grain (corn: 1.2 lb, wheat: 1.4 lb)
- N Credit — Nitrogen from previous legume crop (soybeans: 45 lbs, alfalfa: 80-150 lbs)
- Soil Test P/K — Current nutrient levels in ppm from a recent soil test
Example
200 bu corn after soybeans: Gross N = 240, less 45 credit = 195 lbs N/acre. At $0.55/lb = $107/acre just for nitrogen.
Tips
- Split nitrogen applications (pre-plant + side-dress) improve efficiency by 10-15%.
- Soil test every 2-3 years — nutrient levels change with removal and application.
- Don't apply nitrogen for soybeans — they fix their own from the atmosphere.
- The MRTN (Maximum Return to Nitrogen) rate is more economical than yield-goal-based rates.
- Consider soil organic matter — each 1% OM mineralizes ~20 lbs N/acre/year.