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Literature review and database of P and K research data to develop sound best management practices for P and K

Principal Investigator: Greg Stewart and Ian MCDonald

Research Institution: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)

Timeline: December 2012 – March 2015


  • Identify studies that evaluated optimal phosphorus (P) soil levels, optimal potassium (K) soil levels or both for corn, soybean, wheat, alfalfa, canola and edible beans and field crop yield response.
  • Update crop nutrient removal tables based on a targeted maintenance approach.
  • Develop a P and K Recommendation Calculator based on a targeted maintenance approach to encourage greater adoption of Best Management Practices (BMPs) for P and K.


  • Updated, or reaffirmed P and K recommendations for Ontario field crops supported by more recent research.

Scientific Summary:

Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) phosphorus (P) and potassium (K) recommendations for major field crops (corn, soybeans and winter wheat) were last updated in the 1970’s.  These P and K recommendations were developed based on the sufficiency approach which suggests P and K rates that are most likely to optimize economic returns for the crop produced that year.  Using this approach would result in yearly applications of P and K on lower testing soils in order to avoid risk of yield loss due to inadequate P and/or K fertility. OMAFRA’s P and K recommendations are often ignored because of a perception that crop yields have significantly increased since their introduction and the recommendations are no longer sufficient to support current high yielding corn hybrids and soybean and wheat varieties. 

The objective of the project was to provide science based information that farmers, agronomists, researchers, and others can use with confidence to select environmentally and agronomically sound P and K application rates, methods and timing of these important nutrients and to achieve industry stakeholder confidence in Ontario P and K best management practices. A total of 368 Ontario research trials that evaluated field crop response to P and/or K fertilizers were identified and databased.  The current data base consists of 347 distinct research trials that evaluated P and/or K fertility research for corn, soybeans, cereals and alfalfa based forages.  Whenever possible the replicated data was included in the database.  Unfortunately, for many of the trials only treatment average data was available.  Data basing included information on the location of the trial, relevant cropping history (when reported), tillage (when reported) pesticide inputs (when reported) and P and K fertilizer applied (including description of product, rates application timing and application methods).  Data included in the database includes crop yield, soil fertility and soil texture and series (when reported).  Crop nutrient removal tables were reviewed and updated.  The proposed updated tables now provide nutrient concentrations for corn stover, soybean stalks and cereal straw. Updated crop nutrient removal tables for major field crops in Ontario have been completed and included in the 3rd edition of the Agronomy Guide.

External Funding Partners: Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA)