Abstract
Purpose A three-year study was carried out in a steep vineyard to study inter-annual and within-season vigor variability by proximal sensing. Methods Each season, vigor maps were obtained around veraison when a full canopy status was achieved; in 2021 and 2022, within-season vigor variability was assessed at 9 and 8 dates. Every year, main yield components, grape composition and pruning weight were determined. In 2022, dynamic in vegetative growth, canopy density, leaf gas exchange and water status, soil temperature and water status were also performed. Results Mostly due to more rapid soil warming, vines growing in low vigor (LV) plots had fostered leaf area development and shoot growth over the first three dates of measurements before high vigor (HV) fully made up at pre-flowering. From flowering onward, vine growth in LV was totally checked and the gap versus the HV kept widening. Over summer, in LV, leaf water potential assessed pre-dawn and midday reached the quite limiting thresholds of −0.6 and −1.4 MPa, whereas in HV water stress was rather moderate. Gas exchange limitations in LV essentially mirrored the above with stomatal conductance decreased to 0.03 mmol m −2 s −1 at pre-veraison. Final vine size and yield were severely curtailed in LV (−49% and −62% as compared to HV, respectively) which, on the other hand, achieved much better and complete grape maturity. Conclusion This trial confirms that even within a tiny and steep vineyard, spatial variability between vigor zones evaluated at full canopy tends to be maintained over years, thus justifying, for instance, a selective harvesting approach. However, it is quite meaningful that, in both 2021 and 2022, the ultimately defined LV vigor initially developed bigger canopy, balanced with HV at pre-flowering and then re-entered in their standard classification of “low vigor” plots. This behavior is relevant anytime a variable management strategy is planned. Indeed, early season fertilization should be adjusted with a logic opposite to that applicable to a “low vigor” level while, real-time canopy spray is recommended.