In protected cultivation the delivery of water and nutritional substances, based on various factors such as the type of ground utilised (open ground, containers, hydroponics) the type of crop, the density of the plants, the quality of the water, the aims of irrigation (true irrigation or climatising irrigation) can be effected in various ways.
Currently the great majority of systems are based on micro-irrigation in which water is supplied to the plant utilising a low delivery capacity and pressure with a high level of uniformity that is essential in protected environments where intensive cultivation is practiced.
Micro-irrigation is based on a system of pumps, water treatment, devices for the distribution of fertilisers and a system of pipes that feed the lateral tubes equipped with water distribution devices.
The punctiform distributors can either be formed by drippers with a turbulent flow of the type on-line or in-line (driplines) or by capillary systems.
The on-line drippers distribute between 2 and 8 litres per hour at a working pressure of 1.0 Bar and they have a turbulent flow so as to reduce the risk of sediment and blocking. They can either be normal (when the pressure increases, also the quantity of water per hour increases) self-compensating (the quantity of water remains constant in a range of pressure from 6 to 50 m .c.a.) or with anti-dripping devices. All the drippers stop functioning at the same moment when the pressure in the lateral pipe drops to 0.3 Bar so avoiding drainage of the solution to the advantage of the plants placed at a lower level. In the same way, all the drippers will start functioning again when the pressure rises to 0.4 Bar. It is possible to install a manifold with 1 – 4 outlets on each dripper in order to attach micro-tubes in polyethylene that in turn deliver water to dripper stakes. In this way the system is able to deliver water to four or more pots if they are placed close to each other or to distribute water in several points if the plants are in large containers. Another system of punctiform distributors makes use of capillary systems with laminar flow. These are micro-tubes in PE with an internal diameter of about 0.6 – 1.5 mm produced in different lengths with a co-extrusion process and inserted at pre-established distances directly into the lateral PE tube which has a diameter of 16, 20 and 25 mm .   At the end of each capillary tube there is a stake that is normally self-threading. Thanks to the reduced internal diameters you get a laminar flow that produces a constant delivery in function with the length and the pressure.
In this case the designer must pay great attention because even the smallest variation in the pressure could cause considerable changes in the delivery capacity.
It is a common practice to resort to driplines either light (hoses) or heavy. The driplines, whether normal or self-compensating, are made of PE tubes with a diameter of 16, 20 and 22 mm with drippers inserted at pre-established distances during the extrusion phase of the tube itself. The driplines, either normal or self-compensating, are usually utilised for several seasons and they normally have a cylindrical dripper equipped with an input filter and turbulent flow labyrinth. The delivery capacity varies (1.5 – 2.1 – 3 – 4 - 8 - 15 Lit/h at a working pressure of 1.0 Bar); the distance between the drippers also varies considerably. Other lighter driplines such as the P1 produced by A.I.T. present a flat dripper welded to the internal wall with consequent reduction of the delivery capacity. Their duration depends on the thickness expressed in mil (1 mil = 0.0254 mm ) and consequently on the price.
The dripping hoses are very thin polyethylene tubes (6 – 8 mil) with turbulent flow labyrinth drippers along its whole length and it has exit holes made with laser technology at varying distances: 10 – 15 – 20 – 30 – 40 cm . In this case the pressure is very low, equal to 0.7 – 1.0 Bar. The short distance between the drippers allows you to create a uniformly damp area that helps the plant develop, especially during the early phases of its growth and particularly in well-drained soil.
Almost always in protected cultivation it is common practice to utilise an irrigation system of micro-sprinklers to water the entire surface, overlapping totally or partially the areas covered by the sprinklers. There is a vast range of distributors and depending on the requirements they can be static, dynamic or vaporising. Some of them have devices to prevent the intrusion of insects while other components are especially studied to eliminate drainage from the tubes with consequent damage to the plants below. The distributors that produce extremely fine drops are used to modify the microclimate. They are usually used very frequently but only for brief periods throughout the day.
For plants grown in cell-like containers or for very intensive cultivation there is a special system known as “mobile bar”. This is a metal bar equipped with sprinklers that runs along a suspended guide that is automatically controlled.
For cultivating plants in vases it is common practice to employ capillary sub-surface irrigation that makes use of the movement of water in a non-saturated sub-soil. The pots are normally placed on tables where the water and nutritive solution is absorbed into the pot through the hole in the base of the pot in function with the physical characteristics of the material lining the tables. This system is known as “closed circuit system” because the nutritive solution that is not used by the plant is returned to the cycle after the conductivity and pH values have been re-established and sanitary checks have been made. In this way the upper part of the plant does not come into contact with water and you obtain a high level of uniformity of distribution as well as reducing excess waste of water even though you increase the risk of fungus disease.
  There are several variations of subsurface capillary irrigation. When the pots are placed on tables or on concrete floors, it is possible to utilise subsurface irrigation with a “carpet” system. This system utilises a material with a high level of water retention and which is always kept damp by periodical additions of nutritive solution. Moisture is constantly drawn up from the “carpet” into the pots by means of capillary action. This system is suitable only for plants that require a constant level of moisture. Subsurface irrigation of “flow and de-flow” is utilised for cultivation in pots placed on tables equipped with containers in moulded plastic. The base of these gutter-shaped containers is moulded in order to facilitate the flow of nutritive solutions. Every table is connected to a tank and a collection tank that recuperates the solution and puts it back into circulation. A variation of this method is that which utilises the concrete floors in greenhouses. This system is used by large companies and for crops with a long growth cycle. It is known as “ subsurface irrigation with grooves ” when the plants are cultivated in long gutter-shaped containers about 10- 30 cm wide that are placed side by side on a surface with a 0.5% slope. Water enters at one end and forms a stream about 3- 5 mm deep for about 30 minutes, while, at the other end, there is a drainage channel that collects the solution and returns it the fertiliser/irrigator to repeat the cycle.


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