Corn Nutrient Guide

Essential Corn Nutrients

Corn requires 17 essential nutrients for growth and development:

Primary macronutrients:

• Nitrogen (N): Most yield-limiting. 1.0-1.2 lb N/bu of yield. 200 bu/ac needs 200-240 lb N/ac.
• Phosphorus (P): Critical for root development and energy transfer. 0.30-0.35 lb P₂O₅/bu. 200 bu/ac needs 60-70 lb P₂O₅/ac.
• Potassium (K): Important for stalk strength and disease resistance. 0.22-0.25 lb K₂O/bu. 200 bu/ac needs 44-50 lb K₂O/ac.

Secondary macronutrients:

• Sulfur (S): Increasingly important with reduced atmospheric deposition. 0.05-0.10 lb S/bu. 200 bu/ac needs 10-20 lb S/ac.
• Calcium (Ca): Usually adequate in soils with pH 6.0+
• Magnesium (Mg): Usually adequate; deficient in sandy, low-OM soils

Micronutrients:

• Zinc (Zn): Most common micronutrient deficiency in corn. 0.005 lb/bu
• Boron (B): Sometimes deficient in sandy, low-OM soils
• Iron (Fe), manganese (Mn), copper (Cu), molybdenum (Mo), chlorine (Cl): Rarely deficient in corn

Corn Nutrient Removal Rates

Knowing what your crop removes helps plan fertilizer replacement:

Note: These are removal rates — actual fertilizer needs may be higher to build soil test levels or lower if soil tests are already high.

Nitrogen Management

Nitrogen is the most yield-limiting nutrient and typically the most expensive single input:

Requirement: 1.0-1.2 lb N per bushel of yield. A 200 bu/ac crop needs 200-240 lb N/ac total.

Credits:

• Soil organic matter: 30 lb N per 1% OM above 1%
• Soybean previous crop: 50 lb N credit
• Alfalfa previous crop: 100-150 lb N credit
• Manure: variable — test manure for nutrient content

Timing: Split applications — 30-50% pre-plant + 50-70% sidedress at V3-V8.

Sources: Anhydrous ammonia (82-0-0, cheapest), urea (46-0-0, easy handling), UAN (32-0-0, flexible liquid).

Use our Nitrogen Calculator for instant N rate calculations.

Phosphorus Management

Phosphorus is critical for root development, early growth, and energy transfer:

Requirement: 0.30-0.35 lb P₂O₅ per bushel of yield.

Soil test levels:

• Low (<10 ppm Bray P): Apply 80-120 lb P₂O₅/ac (build + removal)
• Medium (10-20 ppm): Apply 50-80 lb P₂O₅/ac (removal)
• High (20-30 ppm): Apply 30-50 lb P₂O₅/ac (maintenance)
• Very high (>30 ppm): Skip P application (draw down)

Sources: DAP (18-46-0), MAP (11-52-0), APP (10-34-0 liquid).

Placement: Banded placement (starter or in-furrow) is 2-4x more efficient than broadcast on low-P soils.

Potassium Management

Potassium is important for stalk strength, disease resistance, and water regulation:

Requirement: 0.22-0.25 lb K₂O per bushel of yield.

Soil test levels:

• Low (<120 ppm): Apply 100-180 lb K₂O/ac
• Medium (120-180 ppm): Apply 60-100 lb K₂O/ac
• High (180-250 ppm): Apply 40-60 lb K₂O/ac
• Very high (>250 ppm): Skip K application

Sources: Potash (0-0-60), potassium magnesium sulfate (0-0-22-11Mg-22S) for low-Mg soils.

Timing: Fall or spring application. Potassium doesn't leach, so timing is flexible.

Sulfur Management

Sulfur is increasingly important with reduced atmospheric deposition from clean air regulations:

Requirement: 0.05-0.10 lb S per bushel of yield. 200 bu/ac needs 10-20 lb S/ac.

Deficiency symptoms: Yellow striping on younger leaves (sulfur is immobile in plant). Often confused with nitrogen deficiency, but N deficiency shows on older leaves.

Sources:

• Ammonium sulfate (21-0-0-24S): Both N and S
• Gypsum (calcium sulfate): 17% S, also provides Ca
• Elemental sulfur: 90% S, must be oxidized by soil bacteria
• Potassium magnesium sulfate (K-Mag): 22% S + 11% Mg + 22% K₂O

Timing: Apply sulfate-S in spring (immediately available). Apply elemental S in fall (oxidizes over winter).

Zinc Management

Zinc is the most common micronutrient deficiency in corn:

Requirement: 0.005 lb Zn per bushel of yield. 200 bu/ac needs 1.0 lb Zn/ac.

Deficiency symptoms: Interveinal chlorosis (yellow striping) on new leaves, stunted plants, 'white bud' syndrome.

Deficient conditions: High-pH soils (>7.0), low-OM sandy soils, recently limed soils, high-P soils.

Sources:

• Zinc sulfate: 36% Zn, broadcast or banded
• Zinc chelate (Zn-EDTA): 14% Zn, foliar or in-furrow
• Zinc oxide: 70-80% Zn, slowly available

Application rate: 5-10 lb Zn/ac as broadcast (lasts 3-5 years) or 1-2 lb Zn/ac banded annually.

Soil Testing for Corn

Soil testing is the foundation of any fertilizer program:

Test frequency: Every 2-4 years per field. More often on sandy or high-value ground.

Sample depth: 6-7 inches for conventional till; 3-4 inches for no-till or permanent sod.

Sample density: 15-20 cores per 20-acre sample area. Mix thoroughly.

Sample by soil type: Don't mix samples from different soil types.

Lab analysis: pH, organic matter, P, K, Ca, Mg, S, micronutrients. Cation exchange capacity (CEC) calculated.

Recommendations: Lab provides fertilizer recommendations based on soil test levels and yield goal.

Fertilizer Application Best Practices

Follow these best practices for effective fertilizer use:

1. Soil test every 2-4 years — don't guess on fertility
2. Set realistic yield goals — base on 5-year average plus 5%
3. Time N applications — split pre-plant and sidedress
4. Place P near roots — band or in-furrow for efficiency
5. Apply K in fall or spring — flexible timing
6. Use variable rate — apply more on high-testing zones, less on low
7. Account for credits — manure, soybean/alfalfa previous crop
8. Use inhibitors — N-serve for fall anhydrous, Agrotain for surface urea
9. Monitor with tissue tests — confirm nutrient uptake during season
10. Record results — track yield response to inform future decisions