Rapid fertilizer turnover and dominant soil N mineralization in a cool-climate vineyard revealed by 15N tracing, biological N availability, and N exposure

The relative contributions of fertilizer N and native soil N cycling to seasonal vine N supply remain unclear in cool-climate vineyards. We conducted a two-year field experiment in a Chardonnay vineyard in Nova Scotia, Canada, to quantify soil N supply, fertilizer fate, and whole-system N use efficiency (NUE) using 15 N-labelled ammonium sulfate, biological N availability, and in situ ion-exchange membrane measurements of N exposure. Three N fertilizer rates (0, 25, 50 kg N·ha − 1 ) were tested. Fertilizer N generated only a short-lived mineral N pulse, with a half-life of about 18–20 d, and contributed only ~ 12% of seasonal N exposure in the labelled treatment. By contrast, native soil organic N mineralization was estimated to provide ~ 80–90% of seasonal vine-available N. Fertilizer increased vegetative growth and early-season tissue N status, but did not improve berry yield or fruit quality. NUE remained low and similar among treatments (26–35%). By harvest, only ~ 9% of applied fertilizer N was recovered in berries, while most fertilizer N was no longer recovered in the measured aboveground biomass and 0–50 cm soil pools. N exposure was moderately associated with total N supply estimated from biological N availability (R 2 ≈0.5), supporting its value as a time-integrated indicator of vineyard N availability. These findings indicate that seasonal vine N supply in this cool-climate vineyard was driven mainly by native soil N cycling rather than spring fertilizer input, highlighting the need to explicitly account for soil N supply in vineyard N budgeting and fertilization strategies.