Optimization of 4R nitrogen fertilization practices in response to production system uncertainties

Nitrogen (N) fertilization provides essential benefits for food production, but its optimal management is subject to a high level of complexity. The fertilizer industry, agronomists, consultants, and farmers recognize the 4Rs as the basis for optimum fertilization, but their implementation is knowledge-intensive and site-specific. For a full implementation of the 4R strategy for N, it is necessary to address the risks and opportunities at the field scale, with respect to weather and its interactions with soils and other management factors.

The goal of this project is to quantify the influence of soil and weather conditions (i.e., temperature, precipitation): (1) experienced prior to the growing season; (2) from sowing to topdressing application (if applicable); and 3) after the last N application on the potential for crop yield response and N losses. For this matter, it will be necessary to study the accuracy of site-specific weather forecasts and the opportunity for their inclusion in a probabilistic strategy to optimize N use efficiency, while safeguarding crop yield potential, and to explore system sensitivity to possible interactions with other soil amendments, cultivar specification, tillage systems, and different influential management-induced factors.

In 2015, a decision-support tool called webSCAN was developed based on a dataset of 322 site-years of corn N response data from Ontario and Quebec. The webSCAN tool adjusts N rates for rainfall prior to and around sidedress application time. This tool, combining the "right time" and "right rate" approaches was found to enhance profitability of N use on corn. Work in 2016 expanded the crop response database to include 302 site-years for potatoes.

In 2017, the decision-support tool was implemented online at www.numericag.com. As detailed in a paper submitted for the 14th International Conference on Precision Agriculture to be held June 24-26, 2018 in Montreal, Canada, NumericAg enables the determination of the optimum average application rate that maximizes expected profits for farm specific conditions including soil texture, weather, and price variability. The current version is illustrated using nutrient application with only one crop and only one fertilizer. The tool is evolving with ongoing advancements, and will help farmers and crop advisers not only to select the most profitable application rate, but also to manage risks associated with over and under application.