Microirrigation Systems for Vineyards
Microirrigation 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 its general categories, is shown in Figure 14.1. 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 and consistent. 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 by automatic valves, sometimes supplemented with nutrients or chemicals, filtered, and regulated to levels suitable for the emitters. From there, water is delivered to each emitter through a network of polyvinyl chloride (PVC) and polyethylene (PE) pipes. The following sections discuss some of the components used in microirrigation systems. The components of a microirrigation system can be grouped into the following general categories: (1) the pumping station; (2) mainlines, submains, manifolds, and laterals; (3) flow control devices; (4) pressure gauges; (5) water flow meters; (6) emitters; (7) timers; (8) irrigation system controllers; (9) fertigation-chemigation systems; and (10) filtration systems.
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.
Main, Submain, Manifolds, and Laterals
The main objective of a microirrigation system is to provide an irrigation system such that when properly managed, each plant will receive the same amount of water and nutrients, in sufficient quantity, at the proper time, and as economically as possible. For this goal to be realized, the system must deliver the needed pressurized amount of water to each emitter. Main line pipe routes the water from the source to the edge of the vineyard. The submain pipe distributes the water to zones in the vineyard. The lateral pipe distributes the water to the plants via the emitters.
Main Lines and Submains
Main lines are typically high-density polyethylene or polyvinyl chloride (PVC). The main line to the vineyard is buried underground 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. Pipe size should be selected based primarily on the economic trade-off between power costs and pipe installation costs. Factors to be considered in the design and installation of pipelines include pipeline velocity, energy losses due to fittings, pressure ratings, surge pressures, temperature effects, and flushing mode.
Manifolds
The manifold, or header, connects the mainline to the laterals. Manifold pipelines are frequently installed underground with laterals on the surface, although laterals may also be underground. Underground pipelines last longer and do not interfere with vineyard operations. Main and manifold pipelines are often set 16 to 24 inches below the surface, but site conditions may require other depths.
Laterals
Laterals or emitter lines supply water to the emission devices from the manifolds. Black polyethylene (PE) is generally used as the laterals and ranges in size from 0.5 to 1 inch (1.25–2.54cm), but the clear majority of vineyard irrigation systems use 0.5-inch tubing. The PE material is used because of its high strength and impact resistance properties.
Flow Control Devices
The term “valve” applies to a variety of devices for controlling the flow of water. Various valves allow for on-off control, modulation of the flow rate through the system, and prevention of backflow. They can also be used for pressure relief or as a safety device. In general, valves can vary from simple manual on-off devices to sophisticated control equipment that acts as metering instruments and delivers predetermined amounts of water to the system. For normal on-off control, the best choices are gate, ball, and plug valves. The on-off service valves function by sliding or by turning a flat, cylindrical, or spherical flow control element over an orifice in the valve body. Leakage past the flow control element is prevented by sealing or seating surfaces at the orifice. In the fully open position, a passage through a gate, ball, or plug valve is unrestricted, resulting in a low-pressure loss through the valve.
Pressure Gauges
The performance of microirrigation systems depends on consistent control and knowledge of water pressure. Regardless of how well the microirrigation 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. Depending on the location of the instrument, a pressure drop may indicate a leak, a component or line break, a blocked filter, or a malfunctioning pump.
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 plants. Flowmeters can either be monitored manually or automatically by computerized monitoring and control systems. A key requirement of operating a microirrigation system is knowing how much water is being supplied to the vines in the vineyard. In-line flowmeters may register total flow in standard volumetric units such as gallons, cubic feet, acre-feet, or others.
Propeller Flow Meter
The most commonly used flow meter is the propeller meter. It requires installation in a straight section of pipe and for the pipe to flow at full capacity to register accurately.
Magnetic Flow Meter
Magnetic flow meters do not have obstructions in the pipe, so there is no opportunity for debris to become clogged in the meter. Unlike propeller meters, readings are not affected by pressure loss.
Emitters
The actual application of water in a microirrigation 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 can be achieved through 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 pipes (line sources) to complicated mechanical passageways (point sources) units.
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.
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
Fertigation-Chemigation Systems
Chemigation, often referred to as fertigation, is an inclusive term referring to the application of chemicals into a microirrigation 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. Refer to Chapter 18, Fertigation Systems for Vineyards, for a more in-depth discussion on chemigation/fertigation systems.
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