The Ontario Phosphorus and Potassium Database

corn field with blue sky in background

Did you know that a review of Ontario phosphorus (P) and potassium (K) fertilizer guidelines was undertaken? The work looked at crop responses to P and K for corn, soybeans, winter wheat and alfalfa from 368 trials conducted over the last several decades. It compared most economic rates to current Ontario fertilizer guidelines as found in the Agronomy Guide for Field Crops, Publication 811.

So what did the report find out? The main conclusions were as follows:

  • Economic yield responses for corn, soybeans, wheat and alfalfa were generally small where soil test phosphorus (Olsen) was over 12 ppm and could be obtained with P application rates that didn’t exceed 20 kg-P2O5/ha
  • Band applications of P for corn and wheat were a more effective and efficient application method when compared to broadcast
  • Applying K usually did not result in economically significant corn or soybean yield increases where soil test K was over 100 ppm. For alfalfa, applying removal rates of K is more than sufficient to ensure adequate K fertility where soil test K is over 100 ppm.

Current sufficiency-based Ontario fertilizer guidelines were found to be adequate for phosphorus and potassium based on the database. However, the authors noted that the maximum soil test level that provided a nutrient recommendation equivalent to crop nutrient removal decreased over the past 30-35 years due to higher crop yields. In other words, soil test values for P and K would be maintained at lower levels if following only the Ontario sufficiency-based recommendations. In response to this concern, they suggested a possible “target and maintain” approach whereby soil test ranges of 12-18 ppm for P (Olsen) and 100-130 ppm for K could be targeted and maintained.

The full report can be downloaded by clicking here.