Regardless of irrigation regime, canopy size can affect yield and berry quality attributes particularly under semiarid conditions. It may sound counterintuitive at first but, despite their “luxuriant look”, vines with higher canopies often experience a greater degree of water stress towards the end of the season. If there is enough water early season, vine grow fast at first. However, as the season unfolds, moisture level in the root system gets depleted faster with a larger vine. This is simply because more water is needed to sustain a larger transpiring leaf area. Thus, canopy management and irrigation can both play a role in vine water deficit variations. In the context of water scarcity, using smarter canopy practices to manipulate vine water stress instead of relying only on irrigation, is a compelling approach. In this blog we discuss the influence of canopy height on yield and berry traits.
A team of Spanish researchers, led by Mirás-Avalo tested the effect of two canopy heights on vine water deficit and fruit composition on cv. Tempranillo. They also combined different irrigation strategies, to evaluate the effect of the two training systems under contrasted water regimes. However, we will only look at the most limiting irrigation strategy called “early deficit” irrigation (ED) since it induces the most severe water stress pre veraison in the conditions of the experiment. We discussed in a previous blog why the benefits from such irrigation strategy on berry and wine quality are expected to be the highest.
Under ED treatment, no irrigation is applied during pre veraison. The first irrigation is triggered when stem water potential reached -10 bars. Then, once canopy reaches its desirable length, the “Low canopy” treatment sets a shoot length of 90 cm; the “High canopy” treatment sets a shoot length of 130 cm.
High Canopy led to more water stress and lower Berry weight
Authors reported that over 2010 and 2011, elevating the canopy increased leaf area per vine by 26%. It also induced a greater water stress. As expected from greater vine water deficit, berry weight gets lower when canopy height is taller (figure 1)
Figure 1: time profile of berry weight for the two canopy heights under Early deficit irrigation strategy ( adapted from Mirás-Avalos et al, 2017)
High canopy led to more anthocyanins with similar yield
Yield in 2011 were relatively similar (9.7 kg/vine with high canopy and 9.2 kg vine with low canopy). Thus, difference in leaf area/yield ratio are mainly due to difference in canopy height. Leaf area to yield ratio is 0.74 for low canopy and 1.01 for high canopy (figure 2)
Figure 2: average value for anthocyanins and tannins content found in 2011 under Early deficit irrigation strategy
Berries from the “high canopy” had greater anthocyanin concentrations while yield remains almost the same. Tannins concentration is not affected.
- Water demand increases in response to increased canopy height.The quantity of light intercepted is a function of canopy height. It is one of the very important factors affecting vine water deficit profile. Hence, canopy height manipulation is a very efficient practice to impose a vine water deficit profile compatible with production objectives. Its consequences can be significant on anthocyanins while yield remains almost unaffected, in the conditions of the experiment.
- When applying irrigation is not an easy option, water stress can be modified through canopy management. A lower canopy, exposing less leaf area to sunlight, will lead to lower water stress than a higher canopy. Under semi arid conditions, winegrowers can change canopy height before and after veraison. From a winemaker standpoint, it is desirable to impose a more severe vine water stress pre-veraison. This will directly benefit wine composition (as reviewed here). After veraison, it is possible to reduce water stress by reducing canopy height instead of increasing irrigation.
Irrigation is not the only way to reduce vine water stress!
Instead of increasing water supply (via irrigation) you can reduce water demand to reach similar objectives in terms of vine water stress management!
In other words, the same goal in terms of vine water use management can be obtained by:
- §Using less water pre-veraison and more water after veraison, or
- Using higher canopies (more vine water stress) pre-veraison and canopy hedging after veraison (less vine water stress).
Same yield, same tannins, more color
As a result, authors have shown that winegrowers can benefit from this practice by obtaining berries with more anthocyanins, without reducing yield.