Background and Aims: Knowing the impact of cultural practices on nitrogen (N) dynamics in perennial crops is critical to
promote N use efficiency. This study focused on the impact of crop regulation on the plant N dynamics, on the fruit N composition,
and on the N fertilisation use efficiency.
Methods and Results: A large crop load gradient was set in a homogeneous plot of the grape cultivar Chasselas.
Fertilisation in the form of 15N-labelled foliar urea allowed the measurement of N uptake and partitioning among plant fractions.
Dry mass, carbon, and N dynamics were assessed over two consecutive seasons. Crop regulation did not affect grape N
concentration at harvest. Both N uptake and root N mobilisation were reduced in response to crop regulation. Fertilisation
efficiency was higher under high-yield conditions in terms of N uptake and grape N accumulation. The carry-over effects of
crop regulation in the following year were highlighted.
Conclusions: Crop regulation strongly affects the overall plant N cycle, that is, uptake, distribution and release. Crop regulation
improves must sugar concentration at harvest, while N concentration remained unchanged. The efficiency of N
fertilisation varies greatly with crop load, which limits the interest of fertilisation under low-yield conditions.
Significance of the Study: These results contribute to the development of accurate nutrition models and sustainable cultural
practices.