1. Leaf area:fruit (m2/kg)
Abstract
Pruning Systems and Applied Water Amounts Interact on Productivity and Phenolic Composition of Zinfandel
Clinton C. Nelson and S. Kaan Kurtural*
1Department of Viticulture and Enology, 1 Shields Avenue University of California Davis USA
The objective of this study was to evaluate the interactive effects of three pruning systems with phenology based irrigated treatments on ‘Zinfandel clone 1A/Freedom’. Irrigation treatments were sustained deficit irrigation (SDI) that were maintained at a mid-day leaf water potential (Ѱ) of -1.2MPa and were irrigated to 80% of evapotranspiration (ETo) from bud break until harvest, and regulated deficit irrigation (RDI) that received 80% of ETo from bud break to fruit set, where after 50% ETo was replaced to maintain (Ѱ) at -1.4MPa until veraison, but not thereafter. Pruning treatments consisted of cane-pruned (CP), spur-pruned (HP) and mechanically-pruned (MP). Treatments were arranged factorially with four replicated blocks. Yield components, yield efficiency, exhaustively extracted skin anthocyanin composition measured. The effects of the prolonged California drought was evident throughout the study period. The crop coefficient (Kc) declined by 30% from 2013 to 2015, hence affecting applied water amounts. The MP treatments had the most consistent yield after a brief decline in 2013 as vineyard adjusted to mechanical management. The SDI treatment consistenly had greater yield than RDI The skin weight of Zinfandel was not affected by pruning treatments however, there was a consistent effect of irrigation treatments. Seed weight increased as well as number of seeds per berry as drought conditions worsened. The leaf area to fruit ratio of MP vines were managed within the optimum zone after the second year of the trial where as CP and HP indicated too much leaf area for the amount of fruit carried on the vine. The total anthocyanin produced per hectare was greatest with the MP treatment in the two of the three years of the experiment. The MP treatment also had the least water footprint compared to HP and CP, respectively. Likewise the RDI treatment also decreased the water footprint, However, the yield decline with RDI was too great to be economically viable for the study area. The total skin anthocyanin concentration per unit of berry skin weight consistently greater with the MP treatment in two of three years of the experiment. Based on consistent yield component, yield efficiency and superior water footprint and anthocyanin content per berry and produced per hectare, MP with SDI is recommended for growers of Zinfandel in hot climates.
Figure 2. (A) HP: hand-pruned to 22 buds, (B) architecture of pruning system at canopy closure
Figure 3. (A) CP: cane-pruned to six, eight node long canes with canopy separation (B) architecture of pruning system at canopy closure.
Figure 4. (A) MP: mechanically box-pruned to 100 mm spur height, (B) architecture of pruning system at canopy closure A A A B B B
Figure 1. Development of estimated crop coefficient at a commercial Zinfandel/Freedom
vineyard in 2013,2014 and 2015
Berry weight (g)
Cluster no.
Cluster wt (g)
Yield (kg/vine)
Skin wt (mg/berry)
Seed wt (mg/berry)
Seed count
Leaf area:fruit (m2/kg)
(TACY/ha)
Water
Footprint (m3/t)v
TSA (mg/kg)
Pruning systems
2013 SP
2.24
139 au
196.8
26.9 a
47.6
50.4
1.84
0.59 a
7698
166 a a CP
2.16
145 a
195.9
27.5 a
52.5
1.96
0.38 b
7189
157 a ab MP
2.22
121 b
193.4
23.0 b
56.1
53.4
1.90
0.70 a
6377
195 b b
Pr>F
0.5975
<0.0001
0.6400
0.3794
0.0844
0.1281
0.5944
0.0510
Deficit irrigationy
SDI
2.40 a
133
196.4
25.9
53.6
53.1 a
1.92
0.58
6971
193 b
1688.2
RDI
2.01 b
138
194.4
26.5
49.2
50.9 b
1.88
0.52
7205
152 a
1572.8
0.1351
0.5635
0.5355
0.3504
0.0563
0.4459
0.2894
0.8262
0.4407
Pruning system × irrigation (Pr>F)
0.8342
0.5223
0.0661
0.3230
0.5327
0.4229
0.6863
0.0317
0.9470
0.1456
0.7179
2014
1.80
79 b
183.4
14.2 b
45.2
63.0
2.13
0.79 a
4136 b
137 b b
1.79
196.9
13.9 b
50.1
65.8
2.18
0.42 b
3823 b
136 b b
1.78
100 a
172.8
17.5 a
40.2
67.0
2.30
0.68 a
5098 a
111 a a
0.9572
0.5926
0.1764
0.2565
0.2186
0.0193
0.0009
0.0038
Deficit irrigation
1.89 a
92 a
184.7
16.9 a
50.9 a
69.3 a
2.19
0.57
4987 a
1192.1
1.69 b
80 b
184.0
13.4 b
39.1 b
61.2 b
0.69
3714 b
119 a
1341.4
0.0007
0.9719
0.0113
0.0002
0.6673
0.0602
0.0014
0.0011
0.1582
Pruning system × irrigation (Pr>F)
0.8000
0.0144
0.4940
0.0093
0.3518
0.9025
0.9472
0.4997
0.0030
0.2325
0.8461
2015
1.81
172.5
13.8 b
46.1
62.1
2.11
0.78 a b
135 b b
1.89
155.7
12.3 b
50.0
66.3 b
134 b b
102 a
175.5
18.0 a
54.1
66.8
2.33
0.69 a a
110 a a
0.8765
0.0005
0.2311
0.0001
0.3478
0.3298
0.2087
1.90 a
94 a
181.9 a
17.1 a
52.1 a
69.8 a
2.17
0.60 a
137 a
1421.4
1.71 b
82 b
157.3 b
12.9 b
40.2 b
60.1 b
2.23
0.71 b
120 b
1401.1
0.0004
0.0987
0.2541
0.1672
0.2345
0.3451
0.5467
0.4321
0.7621
0.5632
0.8721
0.4311
0.0345
0.7421
Introduction and Objectives
For many San Joaquin Valley (SJV) wine grape growers in California, management of their vineyards with insufficient guidelines regarding the capacity of vigorous cultivars, such as ‘Zinfandel,’ to produce high quality fruit, is a challenge. Much of the wine grapes planted in the SJV are grown on a two or three wire single-curtain, non-shoot positioned trellis commonly referred to as the California sprawl. This trellis type while not capital intensive to install is often utilized improperly, resulting in excessive fruit zone shading under vigorous conditions. This results in large canopies with declining yield and less than ideal fruit composition at the farm gate. The declining yields in the SJV were also attributed to mechanical box pruning that also exacerbates the excessive fruit zone shading. Since more than 30 buds per 30 cm of cordon are retained by the bearing surface management method, fruit zone shading in the current season depresses fruitfulness of buds in subsequent seasons.
There does no appear to be a general agreement in hot viticulture regions on how best to apply irrigation stress based on phenological indicators. Recently, applying 50% of ETo demand with a mid-day leaf water potential (Y) of -1.4 MPa between fruit set and veraison was shown to improve berry skin phenolics when combined with mechanical crop load management. However, application of management required two cultural practices, pruning and shoot thinning which was deemed uneconomical within the region.
The objective of this project was to investigate the effects of three pruning systems and two regulated deficit irrigation methods on components of yield, berry skin phenolics, and water foot print of Zinfandel grapevine in a resource limited environment.
Experimental design and Methods
Experimental design:
The experiment was arranged factorially in a randomized complete block with four replications. There were three pruning systems and two regulated deficit irrigation treatments applied.
Treatments applied:
Regulated deficit irrigation treatments:
SDI: Sustained deficit irrigation was applied two weeks post bud-burst to end of harvest where mid-day Y was maintained at -1.2 MPa. The following formula was used to apply fractions of ETo throughout the season with weekly Kc measurements based on canopy shade.
ETcSDI = [ETo x {(percent shaded area x 0.016)+0.02} x 80%]
RDI: Deficit irrigation amount was regulated based on phenology indicators with the goal of maintaining Y at -1.2 MPa between bud-burst to fruit set, and veraison to harvest; and Y at -1.4 MPa between fruit set to veraison. The following formulae were used to apply fractions of ETo at the prescribed times with weekly Kc measurements based on canopy shade.
ETcRDI bb-fs;ver-har = [ETo x {(percent shaded area x 0.016)+0.02} x 80%]
ETcRDI fs-ver= [ETo x {(percent shaded area x 0.016)+0.02} x 50%]
Evolution of crop coefficient is presented in Figure 1.
Pruning systems: The three pruning systems with the goal of achieving three different canopy architectures are as follows:
HP: Spur-pruned manually to 22 buds (Figs 2A, 2B)
CP: Cane pruned manually to six, 8-node long canes with horizontal canopy separation (Figs 3A, 3B)
MP: Mechanically box-pruned to a 100 mm spur height (Figs 4A, 4B).
Conclusions
The crop coefficient of Zinfandel was affected by the prolonged drought in California. The reduction of crop coefficient by approximately 30 % from 2013 to 2014 and 2015 henceforth affected estimated crop evapotranspiration and water footprint during the experimental period.
The MP treatment had the highest clusters harvested, yield, lowest leaf area to fruit ratio, and water foot print. The CP and SP treatments had the lowest yield and the highest water foot print.
The SDI treatment most consistent yield response, but a slightly greater water footprint than the RDI.
The MP treatment had the greatest anthocyanin concentration on gravimetric basis. The total anthocyanin content was not affected by applied water amounts possibly due to macroclimate of the region.
The SDI treatment had the greatest anthocyanin content when extrapolated to a per-hectare basis
A combination of MP and SDI are recommended based on exceptional yield, water foot print, and acceptable phenolic compounds concentrations.
Acknowledgements:
The study was partially funded by the American Vineyard Foundation. The authors would like thank Geoffrey Dervishian, Faustino Valdez, Michael Blaine for their technical assistance during the execution of this trial.