When we talk about irrigation methods (or irrigation systems) we mean the way in which water is distributed in the soil.
The choice of one method over another depends on many factors, such as the availability of water, the morphology and location of the soil, the climate, the source of water supply, the type of crop, the degree of mechanization of the crop, etc.
The following irrigation methods are distinguished:
- submersion method;
- sliding method;
- sprinkling or sprinkling method;
- micro-flow or drop method;
- subirrigation method.
The irrigation method by submersion provides for the permanence on the ground for more or less long periods of a layer of water of variable thickness. In some cases, arrangements are envisaged in more or less large rectangles (sunflower or flower beds, see fig. 1) delimited by small embankments or arrangements in real basins (fig. 2) circular in correspondence with the crown of the trees. In other cases, however, the ground is divided into compartments (fig. 3) or more or less rectangular and more or less leveled rooms, dependent or independent from each other. The latter is the irrigation system adopted for rice paddies, applicable on flat land, not very permeable and adopting very high seasonal volumes. In general it can be said that the submerged irrigation system is a system that requires more or less expensive arrangements, clayey soils and substantial bodies of water; if in the rice fields the type of irrigation is still present, the same can no longer be said for citrus groves first irrigated with basin irrigation systems.
Fig. 1 - Irrigation scheme for submersion of flower beds or sunflower.
The sunflowers have a rectangular shape and dimensions of about 100 square meters and are irrigated by a head watering machine with a modest longitudinal and transverse slope and connected to other watering machines. It is widespread in alfalfa meadows.
Fig. 2 - Irrigation scheme for submerged basins.
The system allows you to wet only circular portions of soil around the stem of tree plants. It was widespread in citrus areas, required high manpower and led to heavy losses due to evaporation and deep percolation. Now replaced by more modern systems such as the rain or drip system.
Fig. 3 - Irrigation scheme for compartments.
Each compartment can have sizes ranging from 0.5 to 2 Ha perfectly flat surrounding by small embankments. The various compartments can be dependent or not depending on whether they are communicating with each other. Typical of rice fields, the system requires significant and continuous bodies of water; seasonal volumes are high.
The irrigation method by scrolling instead, it provides a veil of constant water throughout the watering which then goes along its course to infiltrate the ground. Most of the time, the method requires rather expensive and accurate ground arrangements which are distinguished in simple wing (fig. 4), double wing (fig. 5), flat (fig. 6), small pitch (fig . 7), with horizontal pits, with lateral infiltration (fig. 8). The various types of accommodation change based on the arrangement of the watering machine with respect to the plot and the slope of the latter. Flow irrigation is suitable for lawns and grasslands where high watering volumes (1000 m3 / ha) and large surfaces are required.
Fig. 4 - Irrigation scheme for single wing sliding.
The fields are rectangular in shape with the longer side located upstream where the water tap is located which distributes the water by overflow.
Fig. 5 - Irrigation scheme for double wing sliding.
The water passes from a head watering machine to a smaller watering machine and then enslaves the two plots located on the sides of the latter. Expensive and permanent accommodation.
Fig. 6 - Irrigation scheme for level sliding.
The watering machine is located at the top of the plot and stops irrigation when it has wet about 80%. Used for fodder crops.
Fig. 7 - Irrigation scheme for creep sliding.
Compared to the level system, there is a head watering machine and two lateral orthogonal to it.
Less used than the esplanade for excessive maintenance required.
Fig. 8 - Irrigation scheme for lateral infiltration sliding.
The furrows are spaced to varying degrees according to the type of soil and crop.
The part between two furrows is called porca and houses one or more rows. The water will tend to infiltrate laterally leading to serious problems along the line. The method is applicable where there is high water availability.
The irrigation method by sprinkling (photo n. 1) provides for the supply of water by simulating a rain thanks to the use of suitable equipment. These devices consist of medium or long range and medium to large flow sprinklers arranged in a triangle, square or rectangle feed according to the degree of overlap desired. In fact, the sprinklers can, based on the operating pressure, cause a nebulized irrigation with a more than humectant conditioning effect. Undoubtedly one of the limiting factors for the rain system is represented by the wind that conditions the trajectories of the sprinklers themselves; in these cases it is always advisable to bring the sprinklers closer to each other and to choose low-range sprinklers.
Compared to other methods, sprinkler or sprinkler irrigation does not require special arrangements, it has good irrigation efficiency as it does not cause losses due to sliding and deep percolation.
Photo 1 - Sprinkler irrigation on nurseries.
The sprinkler irrigation system can also be used on nurseries and shadows. By choosing the appropriate sprinkler, humectant or air-conditioning irrigation can be obtained.
The irrigation method drop (photo n. 2) it is also called micro-irrigation as the water is dispensed through dispensers called micro-flow and low pressure drippers. The drippers are divided into online drippers and online drippers. The first are dispensers that are inserted on pipes placed on the ground or at a certain height along the row of plants. These dispensers can be button or cigar and have a flow rate from 2 to 16 l / h.
The in-line drippers, on the other hand, are co-extruded dispensers inside polyethylene pipes, self-cleaning thanks to the presence of small filters at the inlet of the dripper itself. Both in the on-line and in-line drippers there is the possibility of having self-compensating dispensers which keep the flow constant as the pressure increases.
The drip irrigation method is currently the most used method in fruit growing, horticulture, greenhouses and nurseries for which water saving is essential, saving labor and costs for arranging the land, the possibility of carrying out fertigation interventions. On the other hand, since the dispensers have very limited dimensions, the system requires more or less pushed and variable filter systems from the most common mesh and disc filters (ideal for well water), to the more sophisticated sand filters (ideal for water from lake or open-air channels).
The underground irrigation method (subirrigazione, photo n. 3) it constitutes the most modern irrigation system ever. The most effective systems require the use of dripping wings (in-line drippers) buried in number and with variable distances depending on the type of crop and the morphological conditions of the soil. Obviously, the system allows to obtain a good water saving as compared to a normal drip system it does not cause losses due to evaporation of the soil.
Subirrigation is a very effective system for supplying water to crops even in conditions of scarce water availability; a limit is represented by its lack of feasibility on land rich in skeleton or where too deep work is carried out. Another limit is represented by the intrusion both from the roots and from the earth particles surrounding the dripper.
If this last aspect has been resolved thanks to the use of air vent valves that prevent the entry of air and with it also the muddy material around the problem of any radical intrusion remains. In some cases the radical intrusion is avoided thanks to the use of herbicides (mostly antigerminative) mixed with the polyethylene itself or added to the plant. In other cases, on the other hand, the coverage of the system for a possible radical intrusion is ensured by a hydraulic closing of the in-line drippers by means of a chamber which then acts by exploiting the depression effect of closing the system.
Photo 2 - Dripline (in-line sprinkler).
The dripping wing can be stretched on the ground along the row of plants. Obviously this arrangement hinders cross-cutting on the ground. Depending on the type of crop and the type of soil, the spacing and the most congenial flow rate can be chosen.
Photo 3 - In-ground dripline.
The radical intrusion is averted thanks to the presence of anti-germinative herbicides which are mixed with polyethylene or introduced into the system.
Figures from Principles and Irrigation Technique - Vito Lombrado - Ed. LEpos
Fact sheet by Dr. Andrea Palazzo