Interpolation of Nitrogen Fertilizer Use in Canada from Fertilizer Use Surveys

Canadian nitrogen (N) fertilizer use has more than doubled since 1990 (1.2 to 2.9 MtN by 2021). Consequently, a better understanding of this trend is needed. A comprehensive set of recommended N rates (RNRs) that agreed with the fertilizer sales data from 1996 and 2001 was compared with the Fertilizer Use Survey (FUS). The FUS was conducted from 2014 to 2021, with 2017 being the most representative year for these data. Using non-parametric statistics, confidence intervals were derived from the histograms used to present the FUS data. N application rates from the RNR for canola, spring and Duram wheat, and oats in the west were all below their respective FUS confidence intervals, whereas N application rates for grain corn showed almost no difference in N use between the RNR and FUS. Crop-specific N application rates interpolated from the RNR and FUS were integrated over their respective crop areas and plotted against national fertilizer sales records from 1990 to 2021. The rapid increase in N use between 2001 and 2017 (0.89 MtN), 90% of it (0.80 MtN) in Western Canada, was primarily due to the increased application rates per crop, rather than crop area changes. The RNR-FUS interpolations were a good approximation of N sales records and could improve farm GHG emissions modelling. The economically important crops in Western Canada should be the main focus for N-related GHG reduction measures, but production losses need to be avoided.