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Developing a comprehensive framework for assessing economic and environmental aspects of 4R nutrient stewardship in Ontario

Principal Investigator: Claudia Wagner-Riddle

Research Institution: University of Guelph

Timeline: October 2021 – November 2025  


  • To compare the impact of N fertilizer source (urea and UAN, with or without inhibitor) on yield and N2O emissions from winter-wheat-corn-soybean rotations with and without cover crops.
  • To compare basic and advanced 4R practices on year-round N2O emissions and corn yield at the land-scape scale in rotations with and without cover crops.
  • To evaluate soil biogeochemical models such as Daycent and DNDC to predict environmental N losses and corn yield for rotations that use cover crops and 4R practices.
  • To develop a conceptual model to determine the profit-maximizing choice of 4R practices and corn yield response functions to nitrogen and assess other factors determining adoption of 4R practices.


  • Farmers will be able to estimate the net economic and environmental benefits of adopting a variety of 4R and cover crop practices on their farm.
  • Policymakers and consumers will be able to estimate the amount that 4R practices cost farmers, should they not have a positive net return.
  • Policymakers and consumers will be able to estimate the amount of nitrogen reduction feasible with various combinations of 4R practices.

Scientific Summary:

The 4R nutrient stewardship program serves as a guideline of best management practices to improve crop N use efficiency and mitigate N losses, without compromising crop yields.  Various 4R strategies have been shown to reduce N losses from agricultural soils such as using fertilizer additives including urease and nitrification inhibitors. For example, use of urease inhibitors reduced NH3 volatilization by 64% and increased corn grain yields. However, N2O emissions were increased by 30% when urease inhibitors were applied alone, but this pollution swapping was avoided when both urease and nitrification inhibitors were used. 

On-farm nitrogen fertilizer management requires consideration of other aspects such as soil health, which has been identified as a priority for many jurisdictions including Ontario. Cover crops are a known best management practice to enhance soil health and reduce N losses through capture of residual soil N after harvest of the cash crop. In the subsequent growing season, cover crops impact plant-available N via mineralization/immobilization and can affect N2O emissions, but few studies have evaluated this impact. Application of enhanced efficiency fertilizers (e.g., with nitrification inhibitors) after cover crops has the potential to reduce N2O emissions but to our knowledge has not been studied before.

While many N reduction practices have been analysed individually in the literature, very few studies have been conducted on the economic effect of these practices. This paucity of information, especially for the province of Ontario, maintains a level of risk for farmers looking to adopt N management techniques. Nitrogen does not appear to have a significant effect on profit near the profit maximizing rate.This means that nitrogen management techniques could reduce overall nitrogen use, representing a significant cost savings, with insignificant yield losses. Understanding the practices, or combination of practices, that are most cost-effective for nitrogen reduction allows a more adept nitrogen strategy to be developed by policymakers and reduce the risk of farmers in adopting new techniques.

This research proposal is aimed at answering the following questions:

1) Can improved efficiencies through better N fertilizer source in corn and winter wheat result in reduced costs and environmental impacts?

2) Can N fertilizer source be optimized in winter wheat-corn-soybean rotations with cover crops to increase environmental and economic benefits?

3) What are the optimal 4R practices for winter wheat and corn that maximize net returns to the farmer and result in environmental benefits?

We are proposing an integrated approach that will address these questions and lead to an enhanced model that describes economic and environmental benefits of 4R practices in Ontario. 

External Funding Partners:

Fertilizer Canada

We acknowledge the support of the Natural Sciences and Engineering Research Council of Canada (NSERC).