Manual of techniques for sustainable mountain viticulture Josep Lluís Pérez Verdú

3.3.3. Control of the hydrous state of the plant

The plant behaves like a water deposit that absorbs it from the soil and loses it through its leaves.

When the vine uses its extracellular water to transpire with greater or less intensity, its volume redu-

ces. During times of low demand (night time, cloudy days), the plant collects water through its roots

from the moisture in the soil and recovers its initial volume. This activity is constant and the contrac-

tions it causes (of several tenths of a micron) can be measured in the trunk using movement sensors

known as dendrometers, made using alloys that do not dilate with temperature.

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Figure 3.5 Ratio between the effective leaf area and the root soil volume: a key parameter

1.2m

0.5m

2.5m

Double vine training

Production arm 

per stock =1 m

1 shoot every 7 cm

14 shoots per stock 

ELA of 1 shoot=0.14 m

2

PF=2 x 0.5=1 m

2

RSV=1 m

2

x 1 m=1 m

3

ELA=14 s x 0.14 m

2

/s=1.96 m

2

ELA/PF=1.96

Ring vine training

Distance between stock=0.8 m

Production arm per 

stock=1.88 m

1 shoot every 7 cm

26 shoots per stock 

ELA of 1 shoot=0.14 m

2

PF=0.8 x 2.0=1.6 m

2

ELA=26 s x 0.14 m

2

/s=3.64 m

2

ELA/PF=2.27

2.0m

0.4m

Cordon royat vine training

(2.5x1.2) (illustrative example)

Production arm per

stock=1.2 m

1 shoot every 10 cm

12 shoots per stock 

ELA of 1 shoot=0.14 m

2

PF=2.5 x 1.2=3 m

2

RSV=3 m

2

x 1 m=3 m

3

ELA=12 s x 0.14 m

2

/s=1.68 m

2

ELA/PF=0.56

If the middle is reduced 

to 2 m: ELA/RSV=0.7

Note that, for each type of vine training, the ELA/RSV ratio does not depend on the distance between stock on the same

row. When the distance between rows of stock increases, the ELA/RSV ratio decreases. Therefore, for a good ELA/RSV ratio,

the passageway between rows of stock should be the minimum compatible with the passing of machinery (greater planta-

tion density) 

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The extent of daily trunk contraction reflects the intensity of the demand on the hydrous reserves of

the plant.

Between the minimum value of one particular day and the maximum value of the following day, the

increase corresponds to the hydric recovery plus the vegetative growth. 

Figure 3.6 Daily dendrometer oscillations

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Dendrometers (to measure stock trunk diameter

variations)

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Trunk diameter variations (TDV) give two indicators of great value for the hydric control of the plant

(Figure 3.7): the maximum daily contraction (MDC) and daily growth (DG). If this latter parameter is

accumulated over time, this gives the accumulated daily growth (ADG). 

The daily growth (DG) is a good indicator of the plant’s hydrous state. Under severe hydric stress, the

trunk diameter decreases continuously that is only recovered when the plant has enough water avai-

lable again to transpire. 

Depending on the water needs of the vine during its vegetative cycle described in the previous sec-

tion, the dendrometer graph must appear as indicated in Figure 3.8:

•

During the spring months, the dendrometer graph must be ascending. The daily growth (DG) indi-

cator must be regularly positive, i.e. the ADG must increase. 

•

During hot months and until the harvest, the dendrometer graph must be primarily flat. The DG is

nil or of a small value. 

The only exception may arise during veraison (two or three weeks during which the grape changes

colour, early July in Figure 3.8): The sugar concentration increases considerably and, with this, the

osmotic potential, which creates strong demand on the plant’s hydrous reserves leading to the

consequent decrease in the trunk. 

After veraison, where the dendrometer shows a continued drop, the plant is suffering from hydric

stress that puts ripening at risk: Irrigation is necessary for the plant to be able to cool itself and so

that the leaves do not close its stomata and photosynthesis

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detained. Where the graph is ascen-

ding, this indicates excess supply and irrigation must be reduced or stopped. 

•

After the harvest, the day is shorter and cooler and natural humidity is normally high. As such, irri-

gation loses relevance. During this part of the cycle, maintaining the leaves in good phytosanitary

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Figure 3.7 Indicators for the hydrous

control of the plant based on dendro-

meter readings. 

On the Y-axis: dendrometer reading in

microns 

Source: Moisés Cohen et al. Nutri-fitos

2003.

MDC

DG

Days

500

400

300

200

100

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condition (fungus free) is considered most important so that the residual chlorophyll function can

remain active. The synthesised sugars will be used to start growth the following spring. 

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Figure 3.8 Balanced dendrometer graph

In red: dendrometer graph

In blue: graph of the soil moisture sensor at a depth of 50 cm. 

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Some grape varieties have response behaviours to weather and soil parameters that are somewhat different to the general rule.

A very notable case is that of the Merlot variety, as was seen on the Mas Martinet estates in the Priorat region. In situations of

high temperatures and low relative humidity, the plant is incapable of absorbing irrigation water through its root system to over-

come stress, even with the soil at field capacity. This affects photosynthesis and, as a result, the quality of the grape and the

wine. Relative humidity is a decisive factor in the plant restarting its hydrous functions. Experiments show that the Merlot variety

does not find its best potential in semi-arid areas such as the Priorat region (Merlot is from the Bordeaux region, with high rela-

tive humidity as it is where two large rivers join). 

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