In the past, irrigation in the vineyard was associated with low quality wine as it was considered forcing and permissible only as an “emergency” measure.
Today, in the light of recent studies which have highlighted the negative effects of even brief periods of water stress on wine quality, irrigation strategies are discussed in terms of the desired quality of the end product.
Drip micro irrigation is the most suitable method for the vineyard, because of the series of agronomic benefits it brings and its irrigation efficiency, which reaches levels of 85-90% in surface systems and as much as 95% in subsurface systems. These methods meet the requirement to reduce wetting of the foliage, facilitate mechanisation of the vineyard and at the same time rationalise the use of increasingly precious water supplies.
Choosing the specific drippers to be used in the vineyard is a complex task as it requires knowledge of the area’s climatic conditions, the hydrological properties of the soil, the variety of vine, the growing system and techniques used etc.
From an analysis of these variables a choice of suitable dripper is established, along with hourly flow rate, distance between drip points, irrigation cycle and volume of water to be used.
It is extremely important to analyse the soil type in order to know how the root systems develop. In loose, well-drained soils, in times of water stress, the plant is forced to develop a root system which can reach deeper and damper layers of soil. In this case, drip irrigation favours greater root growth and rapid development of the plant in its early years. Heavy clay soils can retain greater quantities of water, but this does not mean that irrigation is superfluous. In fact, being compact and airless, this type of soil tends to force the roots to colonise the more superficial layers of soil, making the plants more susceptible to high temperatures and water stress.
Irritec solutions for vine irrigation are extremely diverse and suitable for any habitat: from ordinary drippers JUNIOR® and TANDEM® to the self-compensating MULTIBAR®, ideal for sloping land and long rows. ROOTGUARD® is the subirrigation dripline most commonly used in viticulture.
When the dripline is attached to the supporting wires, the Irritec hooks (GRG®) facilitate installation and are also ideal for machine harvesting and to drip water steeply sloping vineyards.
Distance between the drippers depends of the plantation density and above all on soil type: in looser soils shorter intervals (40 – 50 cm) are used, while for heavier clay soils the distance is greater, 80-100 cm. Hourly flow rates generally used in viticulture vary between 1.5 and 2.2 litres/hour.
With subirrigation the driplines are buried at an average depth of 30 – 40 cm, so as to deliver water right into the rhizosphere, thus enhancing the effects of fertigation. When calculating the distance from the dripline to the plants, the soil type must be taken into account. In loose soils a distance of around 40 cm from the row is recommended, while in heavier soils the line can be installed midway between rows, to encourage the development of root systems which establish themselves over the whole surface.
Vine growers are increasingly resorting to fertigation, which can be enhanced by micro irrigation techniques and subirrigation in particular. In fact the irrigation system becomes the method of conveying nutrient solutions to the root apparatus, for easy absorption especially of those elements with low mobility such as phosphorus and potassium. Fertigation systems can vary according to the level of technology desired: from the simple VENTURI unit to comprehensive fertigation machines (DOSAPRO®, SHAKER SET®, DOSABOX®).
The irrigation strategy to be implemented in the vineyard needs to seek a balance between perfect plant development and crop yield on the one hand, and a harmonious ratio of plant growth to input of high quality compounds which are characteristic of the vine variety on the other.
There are two critical points for watering in the vine: flowering and following veraison. The two week before flowering and the 3-4 weeks afterwards are essential for the formation and development of the grapes, and therefore an adequate water supply is indispensable.
During the veraison phase, watering should be more restrained, and diminish gradually as the fruit approaches full maturity, restricting foliage growth and maintaining leaf function. In red grapes, controlled water stress should be more rigorous to encourage the synthesis of colouring substances (anthocyanins), while in white varieties a less intensive stress level is advisable to retain the sharp freshness of the fruit. It is always advisable to carry out fertigation interventions following harvest, to facilitate absorption and storage of elements which the plant will use to renew its foliage the following year.
Thanks to automatic irrigation systems, this can be done at night, which is when the plant tissues are rehydrating.
The volume of water used and the length of the irrigation cycles depend on the hydrological characteristics of the soil: in loose, stony soils short, frequent cycles are best, carried out daily or on alternate days. In heavy soils weekly cycles can be used, delivering up to 10 – 12 mm of water. Accurate management of irrigation schedules can be obtained by the use of suitable equipment such as the Scholander pressure chamber, which allows leaf water potential to be calculated with a degree of precision.
The experienced vine grower can also determine the water condition of his vineyard by examining shoots and leaves. Under optimum conditions the leaves of the vine are turned towards the sun and the tendril on the shoot is longer than the tip, which is bent. Conversely, signs of lack of water which indicate a need to irrigate include leaves bent away from the direction of the sun, straight tips on the shoots and shorter tendrils.