WATERING PROBLEMS UNDER GLASS AND PLASTICS ON THE CANARY ISLANDS
Our basic problem is how to get water. The Canadas Mountains act as a barrier on which the Passat unloads its moisture. Water leaks through the volcanic rocks and is accumulated in subterranean reservoirs formed by impermeable soil. By drilling horizontal tunnels into the rocks we try to reach these reservoirs which will provide for us with water. There is no underground water to be worth drilling. Drilling is done cooperatively.
Steel tubes and open concrete channels conduct the water to the reservoirs. Water stored in this open reservoirs has to be filtered before use, because it is very dirty. Quality of water much depends on the content of soluble salt of the subsoil which water passes on its way through the rocks. It varies very much and you may have to adapt your crop to the water or use the hydroponic system.
Due to the difference of height we are forced to built terraces to obtain a profitable size of the fields. Fields have to be equipped with a good drainage system, because we aim at watering our crops more frequently. On the Canaries wind is blowing very often, therefore irrigation by nozzles can only be used under cover. As there is not enough room between grown up plants and the netting which covers our fields, and there is still too much draught, sprinklers covering a big area cannot be installed. The same problems affect the installation of nozzles above the plants; only in propagation houses, which do not have any draught, there is no problem for it.
Nozzles installed 2 cm above the ground are an obstacle for working on the soil and can only be used for plants which remain longer in the soil.
Due to the difference of height we are provided with high pressures, nearly 8 atmospheres, in the water tubes. As we do need much water at the same time for irrigation, the main tube has a diameter of four inches, with two inch side arms, where the nozzles are.
When irrigation takes place, 80 to 100 cubic metres of water per one hour flow through the main tube. We still could not find an exactly working dosing equipment for these conditions, as Osmometers do not work satisfactorily.
The disadvantages of this irrigation system are small compared with the advantages. They lie in the high costs of making terraces, not exactly working dosing equipment and a higher rate of Botrytis.
The most important advantage for us is the saving of an amount of nearly 50% of water compared with the ancient irrigation systems, the