The Ohio State University, Michigan State University, and Purdue University have coordinated to provide tri-state fertilizer recommendations based on soil phosphorus tests, yield potential, and crop nutrient removal.1 If soils are deficient in phosphorus, the recommendations advise adding fertilizer to reach "optimal" levels. To maintain these levels, farmers should apply fertilizer based on crop removal rates and yield potential.
Precision agriculture and variable rate technology can optimize fertilizer use by applying it based on yield and soil characteristics, potentially reducing phosphorus waste.2
NRCS recommendations for when to apply phosphorus.
Resources:
1 Developing Phosphorus and Potassium Recommendations for Field Crops
2 2023 WLEB Conference: Soil Testing and Nutrient Management