Optimize inputs, save money, and protect Iowa's water. It's the same goal.
Based on ISU Extension recommendations (MRTN approach for nitrogen). Adjust based on YOUR soil test results.
| Nutrient | Rate | Timing | Source | Cost/Acre |
|---|---|---|---|---|
| Nitrogen (N) | 150 lbs N/acre | Split: 40 lbs at planting, 110 lbs sidedress (V6) | Anhydrous ammonia or 28% UAN | $78 |
| Phosphorus (P2O5) | 50 lbs P2O5/acre (if soil test < 16 ppm) | Fall broadcast or spring band | MAP (11-52-0) or DAP (18-46-0) | $36 |
| Potassium (K2O) | 60 lbs K2O/acre (if soil test < 131 ppm) | Fall broadcast | Potash (0-0-60) | $23 |
| Lime | Apply if pH < 6.0 | Fall — needs 6-12 months to react | Ag lime or pelletized lime | $25-45 (when needed) |
N: Soybean credit: ~45 lbs N/acre already in soil. ISU recommends MRTN approach.
P: Skip if soil test is Optimum or higher. Maintenance rate only at High.
K: Corn removes ~0.27 lbs K2O per bushel. Test every 4 years.
Lime: One application lasts 4-6 years. Critical for nutrient availability.
| Nutrient | Rate | Timing | Source | Cost/Acre |
|---|---|---|---|---|
| Nitrogen (N) | 190 lbs N/acre | Split: 50 lbs at planting, 140 lbs sidedress | Anhydrous ammonia | $101 |
| Phosphorus (P2O5) | 50 lbs P2O5/acre | Fall or spring | MAP or DAP | $36 |
| Potassium (K2O) | 60 lbs K2O/acre | Fall broadcast | Potash (0-0-60) | $23 |
| Lime | Apply if pH < 6.0 | Fall | Ag lime | $25-45 (when needed) |
N: No soybean credit. Higher rate needed. MRTN for continuous corn in Iowa: 180-200 lbs.
P: Same as rotation corn if soil tests warrant.
K: Higher stover means more K removal. Consider stover management.
Lime: Anhydrous ammonia acidifies soil faster in continuous corn.
| Nutrient | Rate | Timing | Source | Cost/Acre |
|---|---|---|---|---|
| Nitrogen (N) | 0 lbs (soybeans fix their own N) | N/A | Rhizobium bacteria on roots | $0 |
| Phosphorus (P2O5) | 45 lbs P2O5/acre (if soil test < 16 ppm) | Fall broadcast | MAP or DAP | $32 |
| Potassium (K2O) | 90 lbs K2O/acre | Fall broadcast | Potash (0-0-60) | $35 |
| Lime | Apply if pH < 6.0 | Fall prior | Ag lime | $25-45 (when needed) |
N: Do NOT apply nitrogen to soybeans. Waste of money and can reduce nodulation.
P: Soybeans respond well to P. Critical for root development.
K: Soybeans remove 1.2 lbs K2O per bushel — they're heavy K users.
Lime: Soybeans are sensitive to low pH. Nodulation suffers below 6.0.
These are general recommendations. Your fields are unique. A $10-15/acre soil test every 3-4 years prevents thousands in wasted fertilizer. ISU recommends grid sampling at 2.5-acre grids for variable-rate application.
ISU Cost of Production Calculator| Practice | N Reduction | P Reduction | Cost | Incentive |
|---|---|---|---|---|
| Cover Crops | 25-40% | 15-25% | $25-40/acre | Iowa PFI cost-share, EQIP payments |
| No-Till / Strip-Till | 5-15% | 30-50% | $0-10/acre savings | EQIP, CSP |
| Nitrogen Management (MRTN) | 10-20% | N/A | Saves $10-25/acre | None — just good economics |
| Saturated Buffers | 40-90% | Minimal | $5,000-8,000 install | EQIP: up to 75% cost-share |
| Bioreactors (Woodchip) | 20-50% | Minimal | $8,000-12,000 install | EQIP: up to 75% cost-share |
| Wetlands (Constructed) | 40-70% | 30-50% | $50,000-150,000 | CREP, EQIP, RCPP |
| Grassed Waterways | 5-10% | 40-60% | $3-5/linear foot | EQIP, CRP |