Demonstrating the effect of plant water potential-based deficit irrigation on grapevine (cv. Shiraz) in an arid climatic region

Abstract

Plant water potential has long been used as an indicator of plant stress in various crops, including grapevines. This study demonstrated the effects of plant water potential-based deficit irrigation on Shiraz vineyards cultivated in an arid region of South Africa over four consecutive growing seasons (2019–2020 to 2022–2023). Three irrigation treatments were applied, each triggered at a predetermined midday stem water potential: Treatment 1 (−1.1 MPa), Treatment 2 (−1.5 MPa), and Treatment 3 (−1.8 MPa). Irrigation treatments commenced after the pea-sized berry stage and continued until harvest. On average, 41% and 57% less irrigation water was used in Treatments 2 and 3, respectively, than in Treatment 1. Across all seasons, the total leaf area per vine was significantly higher (p < 0.05) in Treatment 1 than in Treatments 2 and 3. Mean berry mass was significantly lower in Treatment 3 than in Treatment 1. Although the number of bunches per vine did not differ significantly among the treatments, the yield followed a similar trend, with Treatment 1 producing 3.3 t/ha more than Treatment 2 and 5.8 t/ha more than Treatment 3 on average. Throughout the first three seasons, the water-use efficiency remained consistent across all treatments; however, in the final season, Treatment 3 exhibited the highest water-use efficiency. Sensory analysis of the experimental wine revealed that grapes from Treatment 2 resulted in wine with the most favourable overall composition. These results indicate that irrigation guided by a stem water potential of − 1.5 MPa can significantly conserve irrigation water while sustaining yield and enhancing the overall composition of wine.

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Acknowledgments

The authors would like to thank South Africa Wine for funding the Flagship Water 2 Project.