Water needs of the vine: When and how much to water the vine?

The vine is one of the crops that has the least water needs when it comes to forming a kilogram of dry matter: around 300 liters, so that, in general, the vine would survive with around 300 mm of water throughout its entire vegetative cycle , either as rainwater or as an external contribution in the form of irrigation.

However, the amount of water that a particular vineyard requires depends on many factors:

1. Variety. Each variety has different water needs.
2. The field capacity of the terrain. A clay soil stores more water than a sandy one.
3. Evapotraspiration. Directly related to the temperature, lighting, soil and arrangement of the plant.
4. Planting density. If the plant has more land for its root development, it will also have more water from the soil.
5. Fertilization. A deficiency of mineral nutrients can limit the water conductivity of the roots.
6. The vineyard driving system. Their demands are increased if the vineyard is under an extended and highly productive driving system.

2- Distribution of the water needs of the vine in the vegetative cycle.

On the other hand, the approximately 300 mm of water required during the vine cycle is not distributed evenly throughout it.

Expressed as a percentage, it is known that it needs around 44% between veraison and leaf fall , 2% during winter rest , 10 % between sprouting and fruit set , and around another 44% between fruit setting and veraison.

3- Effects of irrigation on the vine:

Irrigation in general helps to avoid the effects produced by the absence of water. The main effect of irrigation is to increase production , which affects the quality of the wines.

You have to be careful with watering since it is always not good (for example during the veraison to harvest phase).

The winegrower will be especially careful that the vine meets its water needs , especially at times when it needs water the most.

If the contribution of rain is not enough, it is when it must rely on external irrigations that guarantee, at least, the survival of the plant. If the plant suffers stress in any of its phases, its external manifestations are different.

4- Effects of water stress in the different growth phases:

1. Sprouting: An irregular sprouting with few flowers and short branchesis achieved in the overflow.
2. Flowering: A lack in flowering causes a decrease in fruit set , with small berries.
3. Fruit set: After flowering, the lack of water causes poor foliage and harvest development ; if the stress is severe it can even cause a delay in maturation. It is important that in this phase there is no water deficit, since if it exists it will considerably reduce the harvest and the foliar area.
4. Verage: If the foliar area is reduced, it causes a decrease in the development and quality of the berries as well as in the acclimatization of the strain, which causes an increase in the susceptibility to autumn frosts and low winter temperatures.
5. Harvest: A lack of water in the harvest causes senescence and premature fall of the leaves , and an advance in the withering of the stems. After the harvest, the scarcity of water can lead to the reduction of carbohydrate and nitrogen reserves in the perennial parts.

5- Effects of excess water on the vine.

If, on the contrary, the plant receives more water than necessary and the excess is evident, a series of equally negative manifestations arise in it.

1. At the time of overflow , a lack of oxygen can occur due to waterlogging, externalized in short shoots, yellowed leaves and even the death of the shoot.
2. In the long term, both the veraison and the start of ripening are delayed. Excess moisture at the time of flowering causes excess vigor in the branches causing deficiencies in fruit set and causing bleeding.
3. After veraisoning, the excess humidity increases the size of the grape, but with a lower concentration of sugar and a higher concentration of acids.

Therefore, a balance is essential not only in the amount of water supplied to the vineyard, but also at the time when it is supplied.

6- When to water the vine?

The moment in which the irrigation occurs is almost more important than the amount of water supplied.

The irrigation of the vine must take into account the rainfall of the registered area.

The highest water needs of the vine range from sprouting to veraison , decreasing from this phase.

7- How much to water? Calculation of the water needs of the vine.

Drip irrigation allows an adequate adjustment of the amounts of water to the needs of the crops, but for this, these needs must be known by technicians and farmers.

Calculation of water needs of the vine: This is the method proposed by the Food and Agriculture Organization of the United Nations (FAO) that is based on the publication Evapotranspiration of the crop.

The procedure estimates the water needs from:

1. The climatological variables that determine the reference evaporative or evapotranspiration demand (ETo).
2. A factor linked to the crop , called the crop coefficient (Kc).

In this way, the water needs or evapotranspiration of the crop (ETc) are calculated as:

ETc = ETo * Kc

In the previous expression, we must consider:

The effect of rain , in the event that it occurs.

The amount of rain that is actually used by a crop is a very difficult value to parameterize.

Therefore, simple models for estimating the Effective Precipitation (Pef) have been taken into account to calculate the Net Irrigation Needs.

NRN = ETc – Pef

From here, the Gross Irrigation Needs are obtained taking into account the Efficiency of the Installation and, where appropriate, the Washing Fraction when it is necessary to compensate with irrigation management.

ETo and Precipitation is obtained from the information provided by the meteorological stations integrated in the  SIAR Network .

Regarding Kc , the coefficients of the most representative crops have been compiled and incorporated into the water needs calculation module.

These coefficients are either the result of works published by different national agricultural research centers or the result of experimentation plans developed at the IVIA in recent years.

In this way, this methodology makes it possible to obtain a fairly accurate estimate of the irrigation needs of the majority of species cultivated in our territory.

8- Irrigation in the vineyard. Do I do them right?