Assessing grapevine water status and rootstock effects using vegetation indices from UAV and proximal sensors

Unmanned aerial vehicle (UAV)-based sensing and proximal sensing are effective techniques for monitoring grapevine canopies through vegetation indices (VI), enabling the assessment of plant growth-related factors. This study aimed to evaluate whether VIs derived from both sensing platforms correlate with leaf grapevine and soil water status. The similarity between the two platforms in estimating VI and their effectiveness in detecting variations in plant growth associated with different rootstocks were examined. Grapevines cv. Syrah grafted onto IAC 572 and Paulsen 1103 rootstocks were monitored across a 1.1 ha vineyard in Southeastern Brazil. UAV-based sensing involved capturing images with a multispectral sensor mounted on an UAV, while proximal sensing was conducted by measuring canopy reflectance with an active sensor. The Normalized Difference Red Edge (NDRE) derived from UAV-based sensing showed the strongest correlation with stomatal conductance g_s (r = 0.84, p < 0.001, pseudo-R² = 0.73) and relative leaf water content RLWC (r = 0.73, p < 0.001, R² = 0.60). No significant correlation was observed between the soil water parameter θ at 0–0.2 m and VI estimates from either platform (p > 0.05). Significant correlations (p < 0.001) were found between NDRE (r = 0.70, pseudo-R² = 0,58) and Normalized Difference Vegetation Index (NDVI) (r = 0.72, pseudo-R² = 0,54), derived from both sensing methods. Both indices also detected differences in grapevine vigor related to rootstock influence. UAV-based measures provided stronger correlations with these traits than proximal measurements.