Micro-irrigation Systems for Vineyards
Micro-irrigation System Components
Micro-irrigation systems can be arranged in a number of ways. The arrangement of components in Figure 13.1 represents a typical layout. Variations in pressure within the system due to changes in elevation and pressure loss within the pipes will affect the discharge of individual emitters. For a system to irrigate satisfactorily the application of water must be uniform. There should be no more than a 10 percent variation in discharge between the emitters with the lowest and highest output. To achieve this, pipes and tubing must be sized correctly. At the water source, water is controlled with automatic valves, sometimes amended with nutrients or chemicals, filtered and regulated at levels suitable for the emitters. From there, water is delivered to each emitter through a network of poly vinyl chloride (PVC) and polyethylene (PE) pipes. Some of the components used in micro-irrigation systems are discussed in the following sections.
Power Units for Pumping
Power units used for irrigation pumping include diesel engines, LP gas and gasoline engines, and electric motors. Power units should be selected to match the power requirements of the pumping application. Overloading a power unit may shorten its useful life significantly, while power units too big for the job operate at reduced efficiency.
The purpose of a pump is to deliver water evenly at the correct flow rate and pressure. There are two types of pumps─centrifugal pumps and vertical turbine pumps. Centrifugal pumps are used to pump from reservoirs, lakes, streams and shallow wells.
The volume output of the pumping station dictates the amount of area that can be irrigated. The following formula can be used to convert the maximum required evapo-transpiration rate (ETo) in inches of water per day per acre into volume of output in gallons per minute per acre.
Filters are essential to the operation of a drip irrigation system in preventing suspended materials in the water from causing system blockages, which can reduce the efficiency of the system. Suspended materials in irrigation water may be inorganic (sand, silt, and clay), organic (algae, bacteria, plant debris, fish, insects, insect larvae, and slimes), or any other floating or suspended matter. Two sets of filters are often recommended.
Centrifugal Sand Separators
Centrifugal sand separators (See Figure 13.2), in theory, are not Centrifugal sand separators (See Figure 13.2), in theory, are not actually filters but are used as pretreatment devices for other types of filters. A centrifugal sand separator removes larger particles of sand, silt, or other abrasive grit particles that can lead to the premature degradation of irrigation system components. These contaminants can reduce the efficiency of the irrigation system equipment by plugging and clogging valves and emitters. A sand separator is effective in removing up to nearly 98 percent of particle sizes too large to fit through an equivalent 200 mesh (0.074 mm) filter.
Sand Media Filters
Sand media filters (See Figure 13.3) have been used extensively for micro-irrigation systems. They consist of fine gravel and sand of selected sizes placed in pressurized tanks. The main body of the tank contains sand, which is the active filtering ingredient.
Screen filters (See Figure 13.4) are most frequently used for removing physical contaminants. They are efficient in removing very find sand from the irrigation water, but tend to be clogged rapidly by heavy loads of algae and other organic material and are not efficient as sand media filters.
Disc filters (See Figure 13.5) are relatively new devices that possess traits of both sand media and screen filters. Disc filters are better than screen filters for retaining algae. The screening element of a disc filter consists of stacks of thin, doughnut-shaped, grooved discs, forming a three-dimension filter cartridge. The stack is enclosed in corrosion and pressure resistant housing. Each individual disc contains grooves, molded into its surface.
Once the water has been filtered it is delivered to the vineyard through the mainline and submain pipelines that feed into the lateral lines in the vineyard rows.
Main and Submain Lines
The main and submain lines carry water from the control head to the manifold or directly to the lateral lines. The basic system subunit includes the manifold with attached laterals. The main line to the vineyard is buried under ground at a safe depth below the frost line. The valve assembly that makes the transition from the main lines to submains at each block location may be above ground or in a box below ground level.
Laterals or emitter lines supply water to the emission devices from the submain lines. The lateral line is either manufactured from flexible polyethylene tubing and generally ranges in size from ½ to 1 inch (1.25 to 2.54 cm), but the vast majority of vineyard irrigation systems use ½ inch tubing. The PE material is used because of its high strength and impact resistance properties.
Since micro-irrigation systems operate at relatively low pressures, even small variations in pressure can have a significant effect on how uniformly the system applies water to the vines. For this reason, pressure regulators should be used, especially on vineyards where the elevation varies considerably.
There are ranges of different types of valves that can be used in a drip irrigation system with the main types being:
Water Flow Meters
An important device for measuring water movement between the water source and the vineyard is the flowmeter. Close monitoring and accurate recordkeeping with this device will allow the irrigator to make fundamental adjustments and detect problems before they can have serious effects on the vines. Water flow meters can measure the flow rate of water or the total water that has passed by the measuring point. Flow rate is the volume of water per unit of time moving past the measuring point.
The most commonly used flowmeter is the propeller meter.
Magnetic flowmeters do not have an obstruction in the pipe so there is no opportunity for debris to get clogged in the meter. Unlike propeller meters, readings are not affected by a loss in pressure.
Automatic control systems can be controller or computer driven and range from very cheap and basic to highly sophisticated software driven programs. Pumps, valves, and injectors can be turned on and off or opened and closed to allow automatic timing and sequencing of irrigation zones.
The actual application of water in a micro-irrigation system is through an emitter. The emitter is a metering device made from plastic that delivers a small but precise discharge. The quantity of water delivered from these emitters is usually expressed in gallons per hour (gph). These emitters dissipate water pressure through the use of long-paths, small orifices or diaphragms. Some emitters are pressure compensating meaning they discharge water at a constant rate over a range of pressures. Emission devices deliver water in two different modes, either by drip or by micro-sprinkler.
Depending on how the emitters are placed in the plastic polyethylene distribution line, the drip mode can be further delineated as a line source or a point source.
Line-source Emitters: The line source type emitters are placed internally in equally spaced holes or slits made along the line (See Figure 13.6).
Point-source Emitters: The point-source type emitters are attached external to the lateral pipe (See Figure 13.7). The installer can select the desired location to suit the planting configuration or place them at equally spaced intervals.
Micro-sprinklers are emitters commonly known as sprinkler or spray heads. There are several types (See Figure 13.8). The emitters operate by throwing water through the air, usually in predetermined patterns. Depending on the water throw patterns, the micro-sprinklers are referred to as mini-sprays, microsprays, jets, or spinners. The wetted pattern is larger than that of typical drip emitter devices, and generally fewer application devices are needed per vine.
Emitters are typically manufactured in 3 flow rates; ½, 1 and 2 gallons per hour (1.9, 3.8, and 7.6 L/hr respectively). The 1 gph emitter is the most common choice in permanent plantings. However, ½ gph emitters are used frequently in sandy soils where water must be distributed over a larger area using more outlets per grapevine or where tight soils and/or slope cause runoff problems. The 2 gph emitter is used where the soil can accept a higher application rate with good lateral water movement, and runoff is not a problem.
Chemigation System Components
Chemigation, often referred to as fertigation, is an inclusive term referring to the application of chemicals into a drip irrigation system.
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