Re-evaluating phosphorus and potassium management for corn, soybeans and wheat in Ontario

Principal Investigator

Horst Bohner & David Hooker

Research Institution

Ontario Ministry of Agriculture, Food and Rural Affairs (OMAFRA) / University of Guelph

External Funding Partners

OMAFRA/University of Guelph funding partnership

Project Start

January 2012

Project End

February 2018


  • Evaluate the ability of current OMAFRA phosphorus (P) and potassium (K) fertilizer recommendations for ensuring maximum economic returns for modern, high yielding, corn hybrids, soybean cultivars and wheat cultivars.
  • Identify over the long term whether meeting fertilizer recommendations for a given soil test (i.e. the sufficiency approach) will provide the net return equivalent to the build and maintenance approach. Is the sufficiency approach currently used by OMAFRA adequate for high yield environments?
  • Investigate fertilizer rates and application methods to maximize net returns during the year of application.


  • The most economically effective phosphorus (P) and potassium (K) fertility program (sufficiency vs. build-and-maintain approaches) will allow for increased economic sustainability by allowing farmers to be more efficient in their use of P and K fertilizer.

Scientific Summary

Current phosphorus (P) and potassium (K) recommendations for Ontario are based on data from the 1960-1970s. Doubling of phosphorus and potassium fertilizer prices over the past 10 years has led some producers to reduce P and K fertilizer application rates. Crop yields during this same time period increased resulting in greater demand for, and removal in grain, of P and K. Currently, corn yields exceeding 200 bu/ac, soybean yields exceeding 50 bu/ac and wheat yields exceeding 100 bu/ac are becoming increasingly common. When these three crops are planted in rotation at yields of 200 bu/ac for corn, 50 bu/ac for soybeans and 100 bu/ac for wheat; the average yearly phosphorus and potassium removal is about 65 lb/ac for both P and K. There is concern that current OMAFRA P and K recommendations do not adequately provide for yields that are much higher than those of 25 years ago. There is very little long term research in Ontario comparing grain yields on soils with lower P and/or K levels (where only maintenance P and K fertilizer rates were applied) against yields on soils where P and K levels were built to relatively high levels.

This proposed research will investigate the best P and K fertility approach with today's grain yields: current sufficiency approach versus "build and maintain" approach. The project will establish four long-term field trials to evaluate corn, soybean and wheat response. Yields will be measured where only sufficiency P and K fertilizer rates are applied on low testing soils against where soil-test P and K levels were built to greater than 21 ppm P and 120 ppm K and then maintained. A three-year soybean-winter wheat-corn rotation will be established with each crop present for each year of the trial. The goal is to maintain these trials for at least 10 years.

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