Abstract
The training system Semi-Minimal-Pruned Hedge (SMPH) blends features of traditional Vertical Shoot Positioning-type (VSP) trellising systems with the concept of minimal pruning. While saving labor, this training system results in relatively high crop load and a poor leaf area to fruit weight-ratio (LFR), and thus, needs to be able to ripen grapes in a cool to moderate climate. For these reasons the impact of yield regulation strategies, including (i) shoot thinning (Darwin-Rotor), (ii) biotechnological thinning (Gibberellic acid), and (iii) bunch thinning (harvest machine) were trialed in a three year study at Geisenheim, Germany between 2017 and 2019 using Riesling (Vitis vinifera L.). The average yield per vine in SMPH (5.34 ± 1.10 kg) was 61.1% higher with a narrower LFR (14.01 cm2 g−1), compared with VSP (3.32 ± 1.02 kg, LFR: 16.99 cm2 g−1). The yield was successfully reduced and LFR simultaneously increased with shoot thinning (−33.1%, LFR: 19.04 cm2 g−1), biotechnological thinning (−18.3%, LFR: 16.69 cm2 g−1) and bunch thinning (−37.3%, LFR: 21.49 cm2 g−1). Ripening was delayed in SMPH. On average, two maturity thresholds (14.1 °Brix and 18.2 °Brix) were achieved 129 GDD (seven days according to the recorded daily mean temperatures, respectively) and 269 GDD (16 days) later in non-thinned SMPH, compared to VSP. All thinning treatments accelerated maturity progress ranging from 27 GDD (two days) to 58 GDD (three days) for 14.1 °Brix and 59 GDD (three days) to 105 GDD (six days) for 18.2 °Brix. Apart from immediate benefits on the economic efficiency, the adaption of the leaf area to fruit weight ratio using SMPH holds high potential to, (i) produce grapes targeting specific wine profiles and/or (ii) reducing the velocity of ripening under conditions of climatic change.
Highlights
Modern viticulture is challenged from various sides
The Semi-Minimal-Pruned Hedge (SMPH) training system was generally characterized by higher nodes and shoot number, but shorter shoot length, as well as less inflorescences and lower leaf area per shoot compared to Vertical Shoot Positioning-type (VSP) (Table 2)
The average number of nodes was 20 times higher in SMPH resulting in 10 times higher number of shoots per meter, due to a significantly lower bud burst-rate compared to VSP (Table 2)
Summary
Modern viticulture is challenged from various sides. On the one hand, labor shortages and a trend towards larger winery sizes create the demand for increased mechanization and automatisation of vineyard and winery tasks. Changes in average season temperature (Northern Hemisphere: Apr-Oct; Southern Hemisphere: Oct-Apr) show a high variability but seem to be less pronounced in cool climate regions, i.e., Rhine valley showing an average warming of 1.51 ◦ C [2] Phenological stages, such as bud break, flowering and veraison are projected to occur earlier in the year in European viticulture [3,4]. An earlier ripening period will expose the ripening grapes to higher temperatures [4], and lead to a higher degree of alcohol, a lower concentration of organic acids, especially malic acid, and to changes in the aroma composition of wines [8] This may impact on the typicity of regional wine profiles.
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