Crop NPK Removal Estimator
Calculate nitrogen, phosphate, and potash removed at harvest for corn, soybean, and wheat crops across any field acreage.
Use the Crop NPK Removal Estimator
Crop & Yield Inputs
Calculates total nutrient export mass across the entire field.
Select a grain crop, enter your yield goal and field area, and click Calculate to view harvested nutrient removal.
Harvested Nutrient Removal
lb/ac
N
Nitrogen
—
lb / acre
Field Total:
—
P
Phosphate (P₂O₅)
—
lb / acre
Field Total:
—
K
Potash (K₂O)
—
lb / acre
Field Total:
—
Agronomic Limitation: Soybean Biological Nitrogen Fixation
Soybean grain exports nitrogen (3.44 lb/bu / 57.33 kg/t), but soybean obtains substantial nitrogen through biological fixation. Do not treat the displayed grain N removal as a synthetic nitrogen recommendation; use locally calibrated Extension guidance and a soil test.
Harvest Removal Breakdown
| Nutrient | Removal Coeff. | Rate / Area | Field Total |
|---|
Primary Source Provenance & Limitations
- Nitrogen Coefficients: 0.69 lb/bu corn, 3.44 lb/bu soybean, 1.05 lb/bu wheat. Source: University of Delaware Cooperative Extension (Nitrogen Removal in Delaware Crops).
- P₂O₅ & K₂O Coefficients: Corn (0.32 P₂O₅ / 0.22 K₂O lb/bu), Soybean (0.72 P₂O₅ / 1.20 K₂O lb/bu), Wheat (0.55 P₂O₅ / 0.27 K₂O lb/bu). Source: Iowa State University Extension & Outreach (crop removal table).
- Removal ≠ Fertilizer Prescription: Nutrient removal measures grain export only. Fertilizer application must be guided by calibrated soil tests (e.g., Bray-1, Mehlich-3, Olsen), soil pH, buffer capacity, subsoil fertility, and local Extension recommendations.
Standard Test Weights & Chemical Relationships
Standard Grain Test Weights
Corn Grain: 56 lb/bushel (0.0254 t/bu)
Soybean Grain: 60 lb/bushel (0.0272 t/bu)
Winter Wheat: 60 lb/bushel (0.0272 t/bu)
Soybean Grain: 60 lb/bushel (0.0272 t/bu)
Winter Wheat: 60 lb/bushel (0.0272 t/bu)
Elemental vs. Oxide Conversions
P₂O₅ = Elemental P × 2.2914
Elemental P = P₂O₅ × 0.4364
K₂O = Elemental K × 1.2046
Elemental K = K₂O × 0.8302
Elemental P = P₂O₅ × 0.4364
K₂O = Elemental K × 1.2046
Elemental K = K₂O × 0.8302
Metric conversion rule: kg nutrient / metric tonne = (lb nutrient per bushel / standard lb grain per bushel) × 1000.
Summary
Calculate nitrogen, phosphate, and potash removed at harvest for corn, soybean, and wheat crops across any field acreage.
How it works
- Select your grain crop: Corn Grain (56 lb/bu), Soybean Grain (60 lb/bu), or Winter Wheat Grain (60 lb/bu).
- Choose your measurement system: Imperial (bu/ac yield, lb/ac removal) or Metric (t/ha yield, kg/ha removal).
- Enter your yield goal and field area (defaults to 1 acre or 1 hectare).
- Click Calculate to view per-area removal rates and total field mass of N, P2O5, and K2O leaving the field in harvested grain.
Use cases
- Quantify total nitrogen, phosphate, and potash leaving the field in harvested grain.
- Calculate multi-year crop nutrient removal to track long-term soil nutrient balance.
- Scale removal rates across entire field acreage for farm-level nutrient planning.
- Distinguish harvested crop removal from fertilizer prescriptions and soil-test credits.
- Convert between imperial (bu/ac, lb/ac) and metric (t/ha, kg/ha) nutrient removal units.
Frequently Asked Questions
Last updated: 2026-09-22 ·
Reviewed by Nham Vu