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Agronomic Crops Network

Ohio State University Extension


Executive Summary

The Tri-State Field Crop Fertilizer Recommendations for Indiana, Michigan, and Ohio have been revised and updated. Extensive research station and on-farm trials have been conducted over the past decade to validate and refine the guidelines. In general, the fertilizer recommendations originally published in 1995 provide a solid framework for managing fertilizers and soil fertility. However, some changes have been made to the recommendations:

View these changes in table form:
Quick Reference Guide to Tri-State Recommendation Changes.

  • Soil sampling remains a critical component of effective nutrient management.
    • Sample soil in a consistent way every 3 to 4 years, with samples representing no more than 25-acres.
    • Adapt nutrient management based on trends over time.
  • Soil pH remains one of the most important aspects of supplying adequate nutrition to crops.
    • Soil pH should be kept between 6.0 and 6.8 for field crops.
  • Optimizing nitrogen management is challenging and requires careful consideration of many factors.
    • Nitrogen rate recommendations for corn are based on an economic model designed to maximize farmer profitability (maximum return to N (MRTN)) available at
  • Framework for P and K fertilizer management has been updated to reflect current economic and soil sampling realities.
    • Build-up range is recommended but not required.
    • Drawdown range has been removed from the framework.

General Guidelines for Fertilizer Application

Build-up and Maintenance Guidelines

  • Mehlich-3 is now the default soil extractant that has replaced Bray P1 for phosphorus and ammonium acetate for base cations. Mehlich-3 P returns approximately 35% higher soil test phosphorous (STP) values than Bray P1. Mehlich-3 K returns approximately 14% higher soil test potassium (STK) ammonium acetate, as discussed in the fact sheet Converting Between Mehlich-3, Bray P, and Ammonium Acetate Soil Test Values. See
  • Critical levels for all crops are largely consistent with the original recommendations, except for revising the values to reflect Mehlich-3 as the soil extractant. Critical levels for corn silage and alfalfa were not evaluated, but are assumed to be consistent and remain unchanged from the original Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa:

New Mehlich-3 P and K Critical Levels for Field Crops in the Tri-State Region

  • Crop removal rates were updated with current analyses of grain P and K concentrations.
    • Nutrient removal rates per bushel of grain have decreased, especially with potassium. This represents an opportunity to save on fertilizer costs. See

Nutrients Removed in Harvested Grain

  • Updated P and K fertilizer rates are based on expected yield goals when soil test P and K are in the maintenance range:

 Recommended Fertilizer Rates by Expected Yield

  • Soils in the tri-state region typically supply adequate Ca, Mg, S, and micronutrients for crop production.
    • S deficiencies remain infrequent but are increasing.
  • The judicious use and placement of fertilizer remains a key factor in running a profitable farming operation.
  • The concept of soil fertility should be extended beyond fertilizer management to include sound agronomic practices that promote soil biology and physical structure in field crop systems.

See a Quick Reference Guide to Tri-State Recommendation Changes.

Tri-State Fertilizer Recommendations for Corn, Soybeans, Wheat, and Alfalfa

Executive Summary  |  Soil Sampling, Handling, and Testing  |  Soil pH and Lime Recommendations  |  Nitrogen  |  Phosphorus and Potassium  |  Calcium, Magnesium, and Sulfur  |  Micronutrients  | Additional Resources  |  Authors and Acknowledgements

This website provides a summarized version of the Tri-State Fertilizer Recommendations, reporting the main points of the document but lacking comprehensive detail. For complete information, please see the full version which is available from The Ohio State University Extension Publications Store.