Browsing by Author "Jasse, Aladino"

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    A study of spatial and temporal natural intra-block variability of plant water status in a commercial vineyard
    (Stellenbosch : Stellenbosch University, 2021-03) Jasse, Aladino; Poblete-Echeverria, Carlos; Aleixandre-Tudo, Jose Luis; Stellenbosch University. Faculty of Agrisciences. Dept. of Viticulture and Oenology.
    ENGLISH ABSTRACT: Water is one of the main elements responsible for plant growing and functioning. The most reliable method to measure the availability of water in plants is through the analysis of plant water status. Since plant water conditions have a significant role in grape and wine composition it is of utmost importance to control and manage the level of water deficit during the whole phenological cycle, more specifically during the ripening period. Plant water status variations during the ripening period have several consequences for the evolution of grape berry parameters and the biosynthesis of phenolic compounds in grape berries. In this period, water-stressed plants are prone to increase the concentration of certain parameters, such as sugar, and modify the biosynthesis of phenolic compounds. Plant water status is variable between plants within the vineyard block because several surrounding aspects influence the availability of water, and therefore, the absorption of water from the soil and the loss of water from the plant. Therefore, plant water status variability can be temporal according to the variability in the ripening period or spatial depending on plant conditions, soil characteristics and topography. Temporal and spatial variability can be monitored and evaluated by Precision Viticulture techniques. Precision Viticulture is an agricultural management approach that evaluates variability in vineyards with a focus on applying differentiated management practices to control intrinsic variability of vineyard blocks. The aim of this study was to evaluate natural temporal and spatial variability of plant water status during the growing season and to further investigate the effect that plant water status has on grape composition parameters (pH, TA, sugar) and wine phenolic compounds (Anthocyanins and Tannins). The existing literature concerning spatial variability of plant water status in vineyards was reviewed. Most studies in the field devote attention to the effect of Regulated Deficit Irrigation in the spatial variability of plant water status between plants. However, further work is needed to fully understand the implications of the natural spatial variability between plants in a vineyard block where also the surrounding characteristics (soil, diseases, microclimate) of each plant affect grape and wine composition. In Chapter 3, the natural spatial and temporal variability of plant water status in a commercial vineyard of cv. Cabernet Sauvignon was evaluated and mapped. Remote sensing measures of soil electrical conductivity, trunk circumference and satellite NDVI (Normalized Difference Vegetation Index) were used to select target vines in the block in addition to an unsupervised k- means function in order to create a grid of the spatial variability. Soil analysis and topography were also included in the analysis. As a result of the evaluation, 43 target plants were selected to be monitored from September to February. At the end of the season, three classes of plant water status were defined, and each target vine was assessed for yield, ripeness as well as standard juice parameters. Micro-vinification was done for each target vine and the concentration of anthocyanins and tannins was analysed. The results showed that the spatial and temporal variability of plant water status was evident along the season, affecting the grape parameters and wine concentration of phenolic compounds. An evident relationship between plant water status and soil texture and topography characteristics was noticed. Plants with a lower water status were located in steeper regions of the block with a higher water run-off and less water penetration in the soil. Compared with plants with a higher plant water status distributed in more flat regions of the block, plants with a low water status presented a significant increase in sugar content, anthocyanins and tannins and a strong decrease in yield. The findings of this thesis are a contribution to understand and quantify how spatial variability is naturally distributed and its effect on grape and wine parameters.