Long-term impacts of nitrogen application methods and rates on blueberry yield

We assessed the long-term impact of nitrogen (N) fertilizer rates and application methods on blueberry yield in two field experiments at the Agassiz Research and Development Centre, Agassiz, British Columbia. In the first experiment, N fertilizer rates above BC recommendations (≥100% of the recommended rate) have been applied as ammonium sulfate through broadcast and fertigation since 2008. In the second experiment, nitrification inhibitors (dicyandiamide; applied as UMAXX) combined with N fertilizer rates below BC recommendations (≤100% of the recommended rate) have been applied through fertigation using suspended and buried irrigation lines since 2016. In the first experiment, berry yield data collected in 2020 and 2021 are consistent with previously published data confirming the trend of decreased berry yield with time when N fertilizer rates are above BC recommendations. Data collected in the second experiment during the same period showed no particular effect of nitrification inhibitors or lower N rates (50% of local recommended rate) on berry yield. Based on these results, we suggest that while higher N fertilizer rates and incorporation of dicyandiamide are not beneficial in increasing berry yield, there is an opportunity to reduce nitrogen fertilizer rates without compromising the berry yield.