Evaluation of site-specific management practices to reduce the heterogeneity in grapevine vigor, yield, and grape composition: Doctoral thesis abstract
Authors: Pereyra Alpuín Cesar Gustavo 
Published: March 2024

During eight consecutive seasons (2014-2021) the intra-plot heterogeneity of vigor in a cv. Tannat vineyard in Uruguay was studied. Such variability was assessed during three years (2015, 2016 and 2017) using the Normalized Difference Vegetation Index (NDVI), calculated from aerial images. High-resolution (0.2 m) multispectral images were obtained over the ground to define contrasting vigor zones: high (HV) and low (LV). In winter 2020, trunk diameter was assessed to corroborate the interannual stability of vigor, and positive correlations were established between NDVI and vegetative growth parameters. A complete description of soil physical and chemical parameters was carried out. Climate data (rainfall, temperature, relative humidity and light), vegetative growth (leaf area; leaf nitrogen and potassium; pruning weight), yield (number of bunches per plant, bunch weight, berry weight) and grape composition (total soluble solids, acidity, pH, anthocyanins and total phenols) were used. In addition, site-specific management techniques were employed according to vigor zone to influence yield and grape quality and reduce heterogeneity. For HV, treatments were aimed at reducing water and nitrogen inputs and improving microclimatic conditions in the cluster zone. In LV, on the other hand, treatments were aimed at increasing vegetative growth and yield with water and nitrogen supplementation. Although a 1 ha plot can be considered homogeneous from a topographic, edaphological and climatic point of view, this study demonstrated the existence of great variability in soil variables, production parameters and grape composition. The HV zone was associated with higher levels of leaf area, pruning weight, yield (higher berry and bunch weight) and bunch disease incidence than the LV zone. These HV zone characteristics were the result of a deeper and more structured soil, with higher organic matter content, nitrogen reserves and clay content, and abundance of montmorillonite-type clay. These soil properties in the HV zone proved to be more conducive to root growth, particularly fine roots, with better vertical and horizontal distribution. The LV zone, was distinguished by a shallower and more compact soil which negatively conditioned root growth. New information was provided on the interaction of the soil-plant-atmosphere system. In particular, the dominant role of water availability in the first place and soil nitrogen availability in the second place in establishing plant vigor. The effect of nitrogen on plant response was highly dependent on soil water availability. The gradient of vine vigor and yield between the two zones remained stable over the years, regardless of climatic conditions. This indicates that soil characteristics can mitigate or enhance the effects caused by climatic conditions. The determination (possible by remote sensing) of the vigor zones of a plot is a prerequisite for proposing soil and crop management practices that optimize the use of resources and ensure the economic and environmental sustainability of wine production.