Chapter 13

Micro-Irrigation Systems for Vineyards

Micro-Irrigation System Components

Depending on system type, site topography, soil characteristics, crop, water/fertility requirements, water availability, and water quality, vineyard systems may vary considerably in physical layout. A typical layout of a microirrigation system with the general categories is shown in Figure 13.1. 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 polyvinyl chloride (PVC) and polyethylene (PE) pipes. Some of the components used in micro-irrigation systems are discussed in the following sections. The components of a micro-irrigation system can be grouped into the following general categories: (1) the pumping station; (2)control systems; (3) filtration systems: (4) mainlines, submains, manifolds, and laterals; (5) flow control devices; (6) fertigation-chemigation systems; and (7) emitters.

Pumping Station

The pumping station consists of the power unit (internal combustion engine or electric motor) and a centrifugal, deep-well, or submersible pump. Centrifugal pumps are designed for horizontal or vertical operation. The horizontal centrifugal has a vertical impeller connected to a horizontal drive shaft.

Deep-Well Vertical Turbine Pumps

Deep-well vertical turbine pumps are centrifugal pumps adapted for use in cased wells or where the water surface is below the practical limits of a centrifugal pump. Vertical turbine pumps have the pump body submersed in the fluid, but the motor is installed above ground and connected to the pump body with a long shaft, the line shaft.

Submersible Pumps

The submersible pump is simply a turbine pump closecoupled to a submersible electric motor attached to the lower side of the turbine. Both pump and motor are suspended in the water, thereby eliminating the long-line shaft and bearing retainers that are normally required for a conventional deep-well turbine pump.

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 efficiency of electric motors ranges from 85 to 92 percent. Large electric motors (above 15 to 20 horsepower) are more efficient than small electric motors. Gasoline engines operate at efficiencies of 20 to 30 percent.

Control Systems

Control methods range from manual control valves to fully automated, computerized feedback control systems. Methods can be classified in three groups: (1) sequential operation, (2) partial automation, and (3) full automation.

Sequential Operation

Parts of the system can be operated manually or sequentially with volumetric control valves that are interconnected by hydraulic control lines. As each valve closes, the next valve opens.

Partial Automation

Volume control is well suited to micro-irrigation. Volume can be controlled most simply with some automation by use of volumetric or mechanical time clock valves. Semiautomatic volumetric control valves can be placed at the head of each subunit, or a single such valve can be used at the control head along with ordinary valves controlling each subunit.

Full Automation

Operation can be fully automated by using a central controller operated on a time or volume basis or based on soil-moisture or plant water stress sensing or by estimating Etc using a weather station reference ETo, or a National Weather Service Class A evaporation pan and a crop coefficient. In either case, automation will require a control system operating either hydraulic or electric valves.

Filtration Systems

Filtration equipment ensures that organic and inorganic particles such as sand, algae, or silt bigger than the smallest inlet or outlet hole in the system are removed, protecting the irrigation system from clogging. If chemicals or acids must be added for water treatment, be sure to determine if the materials should be injected before or after any filtration equipment. Some chemicals well react with the materials from which the filters are manufactured. Water soluble fertilizers are typically injected after the filters and must be in solution, and chemicals must be tested prior to injection into the irrigation system.

Centrifugal Sand Separators

Centrifugal sand separators (See Figure 13.2), in theory, are not actually filters but are used as pre-treatment 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.

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 that filter contaminants as the water flows through the filtering media. The main body of the tank contains sand, which is the active filtering ingredient. The sand is placed on top of a thin layer of gravel, which separates it from an outlet screen.

Disc Filters

Disc filters (See Figure 13.4) 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.

Screen Filters

Screen filters (See Figure 13.5) are most frequently used for removing physical contaminants. They are efficient in removing very fine 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. Screen filters are sometimes used as secondary filters, located downstream of sand media filters.

Main, Submain, Manifolds, and Laterals

The main objective of a micro-irrigation system is to provide an irrigation system such that when properly managed, each plant, vine, and/or tree will receive the same amount of water and nutrients, in sufficient quantity, at the proper time, and as economically as possible

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. Pressure control or adjustment points are provided at the inlets to the manifold.

Manifolds

The manifold, or header, connects the mainline to the laterals. It may be on the surface, but usually it is buried. The limit for manifold pressure loss depends on the topography, pressure loss in laterals, total pressure variation allowed for the emitter chosen, and flushing velocities.

Laterals

Laterals or emitter lines supply water to the emission devices from the submain lines. Black polyethylene (PE) is generally used as the laterals and 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.

Flow Control Devices

Any device installed in a fluid supply system, in order to ensure that the fluid reaches the desired destination, at the proper time, in the required amount (the flow rate), and under the right pressure, is called a control device. As such an appliance controls proper operation of a fluid system, selecting its type, size and placement is of uppermost importance and ought to be done with the full knowledge of the various features of the device and with complete understanding of the way it performs.

Valves

Various types of valves are used in micro-irrigation systems to protect and control the irrigation system: air and vacuum relief, flow control, pressure regulation, pressure sustaining, and safety. Valves come in various design, sizes, materials, and configuration, manual or automatic, metal or plastic, and hydraulically or electronically controlled.

Water Flow Meters

An important device for measuring water movement between the water source and the vineyard is the water flow meter. 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.

Pressure Gauges

The performance of micro-irrigation systems depends on consistent control and knowledge of water pressure. Regardless of how well the micro-irrigation system is designed or how well the emitters are manufactured, operating pressures must remain at design specifications to maintain the desired performance and distribution uniformity. Manually monitoring pressures often or continuously with automation is important because changes in pressure can indicate a variety of problems.

Fertigation-Chemigation Systems

Chemigation, often referred to as fertigation, is an inclusive term referring to the application of chemicals into a micro-irrigation system. Many different substances can be injected through irrigation systems, including chlorine, acid, fertilizers, insecticides, nematicides, and fungicides. A chemical injection system consists of an injection meter/ pump, chemical supply hose, supply tank, calibration equipment, and safety devices. See Chapter 18, Fertigation Systems for Vineyards, for a more in depth discussion on chemigation/fertigation systems.

Emitters

The actual application of water in a micro-irrigation system is through an emitter that controls the flow of water from the lateral line into the soil. The emitter decreases the pressure (reduces the head) from the lateral line to the soil. This may be done by small holes, long passageways, vortex chambers, or other mechanical means. The quantity of water delivered from these emitters is usually expressed in gallons per hour (gph). Emitters range from simple porous wall pipe (line source) to complicated mechanical passageway (point source) units.

Line-Source Emitters

Line-source emitters (dripline) is a polyethylene (PE) hose with the emitters molded and inserted inside the tubing (See Figure 13.6). The only visible part is the hole or holes in the tubing where water is emitted. This type of emitter used is usually a pressure compensating diaphragm emitter.

Micro-Sprinklers

Micro-sprinklers are a cross between surface spray irrigation and drip irrigation (See Figure 13.7). Microsprinklers have some of the advantages and some of the disadvantages of each type of irrigation. Like drip irrigation, micro-sprinklers are considered a type of low-pressure irrigation typically operating with pressures between 15 and 30 psi.

Point-Source Emitters

Point-source type emitters are attached to the lateral pipe (See Figure 13.8). The installer can select the desired location to suit the planting configuration or place them at equally spaced intervals. Point-source systems operate under somewhat higher pressures than line-source emitters. Water pressure is dissipated within the point-source emitter to achieve a low flow rate; water may flow through a long narrow path, a vortex chamber, small orifice or other arrangement before discharging.

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