Research Project

Revisiting nitrogen fertilizer recommendations for Saskatchewan: Are we measuring the right soil nitrogen pool?

AWC contribution: $30,000

Start date: April 1, 2018

End date: March 31, 2022


Nitrogen (N) is an essential plant nutrient and, along with water, is the factor that most frequently limits crop production. In recent years, however, soil N tests have come under considerable scrutiny and criticism, leading some to suggest that the lack of an appropriate soil N test is one of the biggest limitations to developing appropriate fertilizer N recommendations and, hence sustainable N use. Indeed, Les Henry (Grainews; September 17, 2015) has stated that “the biggest current limitation to soil testing is a lack of a test for N that will be mineralized during the growing season.” Indeed, when we test a soil for N, what we are really asking is how much N this soil is likely to supply during the growing season. Although measuring N released through mineralization during the growing season is possible, the real challenge is forecasting this N release. The typical approach to soil testing is to measure the amount of N present in the soil, specifically soil inorganic N—either in the fall or spring—and plug this information into a mathematical algorithm that predicts N release based on soil characteristics (for example, organic matter content) and provides a “best estimate” of the additional N required to reach a target yield. The question is: can we replace this algorithm with a rapid soil N test that directly measures the organic N fraction contributing to N release during the growing season? 


Develop a rapid soil test to determine potentially mineralizable N.

Benefits to producers:

Fertilizer, and in particular, N fertilizer, represents one of the highest single input costs for wheat and canola growers[1] yet there is growing concern that current soil N tests and soil N recommendations do not provide the information that farmers need to make informed fertilizer N decisions. Indeed, some soil testing labs limit their soil test reports to providing only the measured levels of inorganic N, leaving it to the farmer or local agronomist to interpret these levels and develop their own fertilizer plans. Our project aims to develop a new soil N test that provides a rapid assessment of potentially mineralizable N, correlates to crop yield outcomes, and can be used to improve fertilizer N recommendations. Such a test could then be commercialized and licensed to others or developed further in-house. This will provide a better means of estimating fertilizer needs.


Dr. Richard Farrell holds a B.Sc. in resource development from the University of Rhode Island and M.Sc. and Ph.D. degrees in soil chemistry from Iowa State University. Rich joined the faculty of the Department of Soil Science at the University of Saskatchewan in 1997 and is currently an Associate Professor and Saskatchewan Ministry of Agriculture Strategic Research Program (SRP) Chair in Soil Biological Processes. The focus of the SRP Chair is to conduct research on soil-plant relationships, focusing on soil biological processes and inputs that enhance crop production, optimize nutrient use efficiency, maintain or enhance soil quality, and provide definable environmental benefits that support marketing initiatives. Rich is also the co-director of the Prairie Environmental Agronomy Research Laboratory (PEARL) at the University of Saskatchewan. Together with his students, Dr. Farrell has published 87 peer reviewed scientific papers and 9 book chapters, as well as numerous conference proceedings and presentations to producer groups. 
Dr. Fran Walley is a Professor in the Department of Soil Science, and the Associate Dean (Academic) in the College of Agriculture and Bioresources at the University of Saskatchewan. She holds a Ph.D. in soil microbiology from the U of S and maintains an active research program in the area of soil nitrogen dynamics. One aspect of this research deals with the impact of cropping systems on bioavailable N-pools in soil, which ties into her work in the area of soil N testing for improved fertilizer N recommendations. A second focus is pulse crop fertility, with an emphasis on nitrogen fixation and the development of effective inoculation strategies, including the application and use of arbuscular mycorrhizal inoculants in pulse crop systems. One goal of her research program is to improve predictions of N bioavailability (and, in turn, potential contributions to plant productivity and environmental loss) and identify practices for maintaining or enhancing soil quality, including mitigation of greenhouse gases and reduced nutrient losses. Fran is author or co-author of more than 65 refereed journal articles and book chapters. She has served on several provincial and federal research committees, and is the current president of the Canadian Society of Soil Science.