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

Nitrogen 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.

The results of an initial meta-analysis of Ontario and Quebec corn responses to N were presented at the 2015 meetings of the American Society of Agronomy. This dataset is comprised of 322 site-years in which N was applied with sidedress timing. The results provide strong support for including rainfall 15 days before and after the time of sidedess as a factor governing crop response to N. An interaction with soil texture was also elicited. A decision support tool called webSCAN, which uses these findings, has been tested from 2013 through 2015 and was found to improve N rate selection over grower's practice, achieving either the same yield with less N, or higher yields where it recommended more N.

Further work is continuing to expand the database to include potato, barley, and wheat crops. A postdoctoral fellow has been hired for 2016 and 2017 to establish a statistical framework for managing uncertainties on soil, crop status and weather assessment. In addition, some of the work will evaluate use of the North American Ensemble Forecast System (NAEFS) provided by Environment Canada.