SPRINKLER IRRIGATION

In sprinkler irrigation, the water is applied on the soil surface in form of a rain [1, 2].

The spray pattern is obtained when the water at pressure is expelled through small

orifices. The operative pressure is developed by an appropriate pumping unit. Use of this system expanded after the World War II with the introduction of light and movable aluminum pipes. Sprinklers and fast couplers were developed to facilitate assembly and dismantling. Manually lateral movable and rotating sprinklers were then devel-oped. Later to save energy and water, the fixed solid-set systems came into being. In plantations and fruit orchards, these consisted of lateral plastic pipes placed between or along the tree row and sprayers of low flow rates or mini sprinklers. Giant sprin-klers mounted on small carts were also developed to facilitate to coverage of extensive areas.

Figure 4.8. Sprinkler irrigation.

Figure 4.9. Overhead irrigation.

Figure 4.10. Irrigation with a tank mounted on tractor.

Figure 4.11. Center pivot with drop sprinklers.

Figure 4.12. Wheel line irrigation system.

The simple automation is carried out by means of use of volumetric metering valves to provide a known volume of water, or timed valves to provide water for a known duration. The valves can work at a predetermined sequence. Then the automa-tion systems included use of solenoid valves to close and open according to an estab-lished schedule. Several fields can be watered by connecting the units from subfield to a “Master Central Control Unit.” Although the sprinklers have increased in popularity, the surface irrigation continues to predominate. The basic components of a sprinkler system are: A water source, a pump to provide a operating pressure, one or more than one main/sub mains to distribute the water to all the field, sprinklers and control valves, etc.

Advantages:

1. Preparation of land is not required. It can be used on lands of rough topography and level lands.

2. It allows total use of the land.

3. It offers great flexibility in design.

4. It can be used in any type of soil including high permeability rates.

5. It is generally more efficient than the surface irrigation.

6. More water in comparison with the surface irrigation is saved.

7. One adjusts very well to additional irrigation. It can be used for protection against frosts and the heat.

8. The use of portable pipe reduces the cost of the equipment.

9. Fertilizers can be applied efficiently through the irrigation water.

10. The root zone is developed better than with the surface irrigation.

11. The cost for manual labor is lower than for the surface irrigation.

12. The gauging of the water is easier with this system.

13. The performance efficiency is high.

14. It is possible to make frequent applications at low volumes, when it is neces-sary.

Disadvantages:

1. Elevated initial cost.

2. The evaporation loss is high. These losses can be reduced to a minimum by watering at night.

3. Salty water can cause damage to the crop.

4. Incidence of foliage diseases is high. Some crops can suffer by loss of flowers due to the impact of the water.

5. The freezing conditions can affect the functioning of sprinklers.

6. There is interference with the pollination.

7. The wind interferes so that distribution of water is affected.

Types of Sprinkler Irrigation Systems Manually operated and portable system

These systems include lateral pipe with sprinklers installed at regular intervals. The lateral pipe is, generally, of aluminum, with Sections of 6, 9, or l2 meters in length, and fast connections for pipes. The sprinkler is installed at the top of a riser (in the or-chards, the height of a riser should go under the leaf canopy). The risers are connected to the lateral tube. The length of the tube is selected to correspond with the desired spacing of the sprinklers.

The lateral pipe with sprinklers is placed on a ground and it is used until the ap-plication has been terminated. Then, the lateral tube is dismantled and is positioned in the next section. This system has a low initial cost, but requires high manual labor. It can be used in almost all crops. However it may be difficult to move the lateral pipes when the crop is mature.

Lateral system on wheel (movable)

This system is a variation of the manual system. The lateral pipe is mounted on wheels.

The height of the wheels is chosen so that the axis exceeds height of the crop for easy movement. A drive unit is commonly a motor driven with gasoline and is located near the center of the lateral pipe. The system is moved from one place to another by wheels.

Traveling sprinkler system with progressive movements

This system uses a sprinkler (tube) gun of high pressure and high volume. The spray gun is mounted on a towable trailer. The water is supplied by means of a flexible hose or from an open ditch. The system can be used in one field for a desired time and then can be moved to the next field. The tow can be moved by means of a cable or it is pos-sible to be pulled ahead while the hose is coiled in a spool to the border of the field.

These systems can be used in almost all crops. However, due to high intensities of application, these are not suitable for clay soils.

Center pivot system

This system consists of a lateral pipe with simple sprinklers supported by a series of towers. The towers are impelled in such way so that the lateral pipe moves around the center, about the pivot point. The speed of the complete circular motion fluctuates from twelve hours to several days. The intensity of the application of water increases with the distance from the pivot in order to give a uniform amount of application. Be-cause the center pivot irrigates a circular area, it leaves non irrigated the corners of the field (unless additional special equipment is added to the system). Center pivots are able to water almost all field crops.

Linear move system

The linear move system is similar to the center pivot system. The line of the pipe extends in perpendicular direction to the lateral one. The delivery of the water to the lateral is by a flexible hose or from an open ditch. The system irrigates the rectangular fields free of high obstructions.

Low energy pressure system (LEPA)

LEPA systems are similar to the linear move systems of irrigation. The orifices in the lateral pipe and pipes can discharge at very low water pressure, exactly according to the soil moisture. Generally LEPA systems are accompanied with soil surface manage-ment regimes such as minimum tillage or most commonly micro-dams to prevent high application rates from causing runoff. With suitable soil surface management systems, high infiltration rates are not an absolute requirement.

Solid-set systems

In this system, sufficient lateral pipes are placed in the field and are not moved dur-ing the season. Solid-set systems utilize a network of aluminum tubes for irrigation.

Enough lateral lines are used to cover all the area. The system reduces to a minimum the need for manual labor during the irrigation season.

Types of Sprinklers

1. Rotating sprinklers, impact type: These are commonly used over a wide range of pressure, discharge, spacing and rate of application for different crops.

2. Sprinklers, high volume or “gum” type: These are rotating sprinklers with a discharge up to 60 M³/h at a pressure head of 60 meters. It can cover areas up to one hectare simultaneously.

3. Sprinklers with low flow rate: These sprinklers apply l20 to 350 liters per hour at a pressure head of l5–25 meters. These are used mainly in irrigation of fruit trees.

4. Mini sprinklers: Small sprinklers can apply 30–l20 liters per hour at a pres-sure head of l5–25 meters. These are used in vegetables and nurseries.