Watering of vineyards in the Douro region
The Douro is the oldest demarcated wine region, having been given this status in 1795 by the Marquis of Pombal and in 2001 being recognised by Unesco as a World Heritage Site.
The soils are, in this area, predominantly anthrosols, where the action of man was very marked in the lands occupied with vineyards, the soil having a granite base with shale formation. Regarding the climate, it is mainly continental, characterised by rainy winters with low temperatures and dry summers with high temperatures.
The profound relationship between human activity and nature allowed for the creation of an ecosystem where the characteristics of the land are used in a unique way, with the transformation of the land into terraces, thus preserving the soil from erosion and allowing the cultivation of the vineyard.
The new vineyards were installed in levels with one or two planting lines or “at the top”, in order to facilitate mechanisation and reduce the difficulty of the work.
Although traditionally the vineyard is not a watered crop in this region, several studies show that the water shortage seen in some edapho-climatic situations, such as sloping soils, very permeable and dry soils has an impact on the quality and production of the vineyard. For this reason, the use of irrigation is increasing.
In the Douro, due to the steep slopes, the particularity of the area, it is possible to irrigate by gravity. In this situation, and due to energy savings, water is pumped from the river to a storage tank, from which irrigation is carried out, without energy costs. If the gap does not allow it, pumping is the solution, using a conventional method.
The filtration system, which is very important to prevent the passage of particles that could block the emitters, must be suitable for the type of water, the most common being mesh filtration. This must be placed in a place where the working pressure is respected, for its proper functioning.
The ducts installed are made of polyethylene, a material resistant to the stony soil of the place. The nominal pressure of the pipes used must be chosen according to the specificity of the project.
To protect the irrigation components, they are placed along the suction ducts, which allows for air to be admitted and expelled, which prevents their collapse, and the retention valves to prevent shock waves resulting from the pumping being stopped (when filling the deposits, installed at a higher level). Pressure reducing valves are also installed, so that the excess pressure that comes from the slope does not damage the system, nor make it difficult to regulate pressure for the irrigation sectors.
Drip irrigation is the most suitable for the cultivation of vineyards, and self-compensating drippers should be chosen, which charge the same flow within the working pressure range, in order to ensure a uniform water flow along the line.
The most common spacing between emitters is 0.5m, and the emitter flow rate is 1.6L/h. The distance between drippers should allow a sufficient supply of water to create a wet strip suitable for the development of plant roots.
The dimensioning of the lateral piping is of great importance in this type of irrigation installations because the pressure required at the beginning of the line conditions the pressure within the same sector. Since the entire sector has to be in the working range of the pipe, the choice of pipe diameter is essential to take into consideration.
The application of water to the vineyards when planting has been found to be quite determinant for good rooting. Although the availability of water in this area is not very high, irrigation allows producers to have considerable increases in production.
For success it is fundamental to having an irrigation system that is well-sized, well installed and with the appropriate protection and control equipment, as well as proper maintenance. These factors allow the producer to make the most of his investment.