Modern Pressurised Irrigation

Perfect irrigation means that plants get the water they need every day, when they need it. This scenario is rarely the case; there are simply too many variables that
have to be built into the irrigation design. However, we have means and methods to continually optimise the irrigation.

Modern pressurised irrigation – methods and equipment

Sprinkler systems

Sprinkler systems effectively produce artificial rain. Sprinklers can provide a uniform application, with the correct sprinkler and nozzle size for accuracy, adequate pressure flow, correct mounting on a riser at the correct height, and if they are spaced evenly so that the degree of overlap is uniform. Weather conditions must be considered when installing these systems, because wind gusts can disturb the uniformity of a system.
These systems are normally designed to apply water at a lower rate than the soil’s infiltration
rate, so that the amount of water infiltrated at any point on the field depends on the application
rather than the soil infiltration rate. They can be used on a wide variety of applications, including
agriculture and landscaping. There are different categories of sprinkler systems, and many types
of systems within each category.
Major categories of sprinkler irrigation are traveling irrigators, where a sprinkler, or a set of
sprinklers, is attached to equipment that can be moved around, and fixed sprinklers, which are
favored where traveling sprinkler systems would be hard to maneuver in irregular shaped fields.

A pressurised irrigation system consists of a water source, a pump to pressurise the water, a pipe system to distribute the water from the pump, and a means of distributing the water to the crop. Means of distributing the water in the field are primarily sprinkler irrigation, where sprinklers spray the water across the ground, and drip irrigation, where water and nutrients are applied directly to the root zone.

Fixed sprinkler systems

Fixed sprinklers are mounted on pipes that are either above or below ground. Some types are:
Hand move sprinkler systems consist of 6 to 12 meters long sections of aluminum pipe, with quick coupling connections at each joint. Sprinklers are installed on pipe risers, which are then connected to the pipe couplings on each of the lateral pipelines. These lateral lines are assembled and operated in one area, and are then disassembled and moved to another area to apply water. The sprinkler systems themselves are low cost, but they do require a large amount of labor. They can be used on just about any crop, however they can be hard to move if they are used on land with sticky soil.Solid set (or Permanent) systems are similar to hand move except the field has been installed with all the pipe and fittings and no moving of anything is required to irrigate. Only valves need to be turned on or off for each zone.

Pop up sprinklers are typically used on turf areas but not sod farms, are installed at ground level with all the plumbing buried beneath the ground level and water pressure brings them up to irrigate. These systems normally have a permanent, buried water supply line, meaning the sprinklers cannot be moved. This type of irrigation system is designed to make sure that every inch of ground receives a minimum amount of water. This type of sprinkler system is not ideal for growing crops.

Traveling sprinkler systems

Side roll systems are a type of traveling irrigator where the structure is a mechanised variation of the hand move system. A lateral pipeline that has sprinklers connected to it is mounted on wheels, with the pipeline acting as the axle. Wheel size is chosen to ensure the axle clears the crop as it moves through the field. A drive system, located near the center of the lateral pipeline, moves the system from one position to the next.

Traveling gun systems, also known as hose reel irrigators, involve a high volume sprinkler gun mounted onto a trailer that typically covers a large area. This system can easily be hauled into a field, and moved around from location to location. Water is delivered to the system by a hose hooked up to a water supply. Traveling gun systems usually produce large droplets and high application rates, so they are best suited for coarse soils with high intake rates.

Center pivot systems are lateral pipelines with sprinklers, which rotate around a central point. They are constructed in segments, each with a wheel at the end and can run off of any type of water source, with water pumped through the center of the pivot from where it flows through the pipes and out of the sprinklers. Each sprinkler has a pressure regulator right before the sprinkler head, and the sprinkler nozzles are smaller near the center of the pivot and get bigger further out on the pivot. The pivot’s sprinkler system is designed this way because the end of the pivot covers more ground than the inner parts of the pivot. An end gun at the end of the pivot turns on when the pivot reaches a corner to irrigate the land that the pivot does not cover. Pivots may contain an arm that swings out to irrigate corners of a field, instead of end guns. Most center pivots require dismantling to be transferred to another location. This system is known for its great efficiency in water application and the high initial cost is usually balanced out by its low cost in labor.

Linear move systems are similar to the center pivot, because they are both made up of series of aluminum pipe towers with sprinklers attached however both ends of the linear move system migrate along the field. This system is designed to irrigate a rectangular field that does not contain any large trees or obstructions. Water is supplied to the linear move system by hose. One of the greatest problems and costs of the linear move system is that it starts at one end of the field and
ends at the other, meaning the return run along the field is without spraying water, adding to the energy expense of irrigation.

Drip irrigation

Drip irrigation is arguably the most efficient form of irrigation, because there is minimal runoff and evaporation; water and nutrients are applied directly to the root zone, and the design of the system is with tubing either buried underground or lying flat near the plants. Emitters evenly spaced on the tubing ensure that water is distributed uniformly to each plant. The emission device, its flow rate and spacing, depends on the crop being grown and the soil texture.

Drip irrigation is known for its flexibility. Each system is custom designed to fit the needs of the crop and the land, in order to maintain optimum moisture at the plant root zone. Since they apply water directly to a plant’s roots, a minimal amount of water is wasted, and drip systems can operate at up to 95% uniformity. These systems are therefore perfect for drought plagued areas. Drip irrigation systems may be convenient during harvest, because they can run while crops are being picked. Moreover, these systems can last as long as twenty years, if they are properly maintained.

Unfortunately, these systems do require a lot of maintenance; they can be damaged easily as well. Since drip emitters are so small, they are susceptible to clogging, even at mineral concentrations as low as 0.1 ppm, and it is necessary to analyze and treat the water that is going into the system. Identifying emitters that are clogged can also prove difficult, because they are usually buried underground.

These systems should be flushed periodically, their filters need to be cleaned frequently, and pressure gauges should be checked regularly to make sure the system is running correctly and there is no buildup. The drip tape is susceptible to damage from for example installation equipment, tillage equipment, insects, birds, rodents, excessive pressure, and direct sunlight.

Types of punctured emitters

NoN Pressure Compensating (non-PC) emitters have a maximum pressure variation of approximately 0.69 bars or 7 meters of elevation change. Large changes in discharge
rates. Non-PC drippers should be used on fields with small variations in elevation.

Laminar flow (Flag emitters) work well on very low-pressure systems, such as gravity-flow drip systems, where the water follows a short path before it is emitted. Inexpensive, they work well, although with a tendency of clogging up. The emitter can be taken apart and cleaned. Typically used on landscape residential irrigation systems.

Turbulent-Flow emitters run water through a path with sharp turns and obstacles before the water is released. With a shorter length and larger diameter, they are less susceptible to clogging.

Vortex emitters run water through a little whirlpool to reduce its flow and pressure. Most emitters have a small inlet and outlet hole, which can lead to clogging.

Pressure Compensating (PC) emitters deliver the same amount of water over a wide range of pressures. Pressures can range from 1-3.44 bars or 24.4 meters of elevation change. PC drippers should be used on fields with large variations in elevation.

Drip irrigation is suitable for all crops, although it is costly to install for closely spaced crops and is therefore not the ideal irrigation system for all fields. As noted, the different types of drip emitters that can be used to regulate the flow of water are classified as no pressure compensation (non-PC) or pressure
compensating (PC) emitters. The emitters can be on-line, which means they are held on to the tubing with typically a barb, or inline, meaning they have been inserted into the tubing as during manufacture.

Water can also be applied from a drip system using either micro sprinklers or micro sprays. These operate at a low pressure, produce small to medium sized droplets, have a low precipitation rate, and allow for a longer watering time. Micro sprays or sprinklers are typically used on tree crops to spread the water droplets out over a larger surface. Micro sprays and sprinklers may provide some frost protection if sufficient water amounts are designed for that application. Furthermore, they can be
used for agriculture practices such as nurseries, greenhouses, landscapes, and home gardens. The major difference between the two is that micro sprinklers have moving parts, while micro sprayers do not.

All drip/micro irrigations, micro sprays or sprinklers require
some degree of filtration to prevent clogging.

Types of preinstalled emitters

Dripline (dripperline) is a polyethylene (PE) hose with a wall thickness of about 1.27 mm and a diameter of 1.9 cm or smaller, with the emitters molded and inserted inside the tubing. The only visible part is the hole or holes in the tubing where water is emitted (in-line emitters). If the emitters are installed on the hose in the field it is called on-line. The type of emitter used is usually a pressure compensating diaphragm emitter. Dripline is usually used in agriculture, vegetable gardens, and can be installed below ground for some agricultural crops and for lawns.

Drip tape is relatively inexpensive and is manufactured as a thin flat plastic tube with closely spaced built-in water outlets. Common diameters are 16 mm, 22 mm and 35 mm. The inlet pressures to a drip tape are usually less than 1 bar. The wall thickness can range from 4 to 25 mil. Outlet spacing can vary from 10 to 61 cm, and 30,5 cm is common. This type of product is ideal for row crops. A low cost drip system, water uniformity is usually very good when designed properly. Since the emission holes are so small, they can clog extremely easily and proper filtration is required. Drip tape can in some cases be used for more than one year inagriculture but is typically removed and discarded at the end of each growing season in high cash crops such as strawberries.

Components for pressurised irrigation
Pressurised irrigation is more efficient than flood irrigation, because all open channels are removed and closed pipes are used. Adding pressure boosting means that the right amount of pressure can be applied to get the water to where it needs to be. The farmer should try to achieve the highest possible efficiency;
because once the equipment is paid for, total cost of ownership can be kept down. The best example is the cost of energy, which is the biggest single cost item for the farmer.

To get the best out of a pressurised system, a full irrigation design and analysis of flow and pressure requirements is needed, followed by water source pumping needs and efficiency analysis of the pumps, to get the real and substantial benefits that are possible in the system – this is much more than looking at the pump.

Pressurised irrigation systems can be designed so that the entire block or field is irrigated, without any need for zone valves, if the quantity of water is sufficient and the entire crop in the field requires the same application and water quantity. If the irrigation blocks are broken into smaller blocks and one or more is irrigated at a time due to different application rates and crop requirements, a pump with a variable frequency drive (VFD) may make sense, to achieve the highest efficiency while irrigating all of the blocks. Flow requirements in each block may vary with the same operating pressure, so regulating the pressure with a variable frequency drive (VFD) is important. If the entire field is irrigated, a VFD pump also makes sense if the water source fluctuates, for example with seasonal fluctuations in groundwater level.

A pressurised irrigation system is about much more than just the pump. The benefits of a fully designed system can be substantial – especially savings on energy.

Control, monitoring and data management equipment is increasingly important in simple to complex irrigation systems. Pump control and monitoring can be accomplished remotely so the farmer may not need to drive out to a field to turn on or off the irrigation system. The system can also be monitored for operating pressure, flow and chemical dosing. If an issue occurs an alarm will notify the grower of the issue so it can be corrected. Remote monitoring and controls as well as data collection is becoming more commonplace, saving time, money and resources that make the overall irrigation and pumping system more efficient.

Dosing and disinfection

Many types of chemical injection products are available, from dosing and disinfection pumps, all with their particular advantages and disadvantages. The initial high cost of smart digital dosing pumps is quickly countered by their extremely high precision and uniformity. Some pumps have two way communications and can be remotely monitored. The dose and injection rate can also be changed remotely.
When installing dosing equipment, it is important to ensure compatibility with any additives, such as chemicals that can react with the current water conditions, potentially damaging the pump or components of the irrigation system. For example,iron oxide precipitate in the water can cause clogging, so care must be taken if chlorine is used to treat the water as it can cause iron to percolate out. Test your water and know what issues may occur with the chemicals you plan to apply in any irrigation system.
When the irrigation system works correctly and the water application is uniform, then the application of any fertiliser or chemical will also be uniform.

Filtration

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 filteration equipment. Some chemicals well react with the materials from which the filters are manufactured. Water soluble fertilisers are typically injected after the filters and must be in solution, and chemicals must be tested prior to injection into the irrigation system.

A filtering system should be chosen based on budget, the irrigation system used and water quality. Sometimes a combination of more than one type of filter will need to be used. The degree of filtration is noted by microns or mesh. Filters are solely used to remove particles from water; they cannot take out dissolved solids, salts, and other toxic elements. To change the chemistry of the water, other types of treatment are needed.

Four main methods are used to filter water for irrigation systems: screen filters, media filters, disk filters and centrifugal filters. Media filters backed up with a screen filter may work best for water with organic and inorganic particles. Check with the manufacture of the emission device for their recommendations on the mesh or micron size of filtration.

Filtration systems require routine maintenance, because they constantly need to be inspected for wear, clogging, tears, and corrosion. They also need to be flushed periodically to remove debris and prevent the growth of microorganisms in the system by injecting algaecides or other chemicals to be preventative. Filtration systems for microirrigation have to be monitored closely. Even the smallest sand particle can cause damage to the system and a strict flushing routine needs to be followed.
A sight glass needs to be installed on the back flush outlet pipe, allowing visible control that the filter is being flushed correctly. Pressure gauges after the pump, before the filters and before the water enters the field also help ensure the system is working properly. Other components of any filter system must include air vents and a pressure relief valve. Check local regulations on the proper use and installation of backflow prevention devices to ensure chemicals and water do not flow
back into your well or water source.

Four main methods are used to filter water for irrigation systems: screen filters, media filters, disk filters and centrifugal filters

Types of filtration equipment

Screen filters are very common and usually the least expensive type of filter. Great for removing hard particles such as sand from water, they do not remove organic
matter very well because non-solid materials tend to either slip through the screen or insert themselves in the screen material, where they can be difficult to remove. Screen filters can be washed by hand or flushed with water. Cartridge filters are a variation of screen filters that are able to remove organic matter moreeffectively.

Media filters force water through a tank that is full of small, sharp-edged objects. These objects are uniform in size, and sharp crushed silica sand is typically used. The sharp edges on these particles will snag organic material, making media filters excellent for removing nonsolid matter. However, they are not able to remove hard matter such as sand particles that get mixed in with the media particles. Media filters are cleaned, by back flushing clean, filtered water through the tank.

Disk filters are a cross between a screen filter and a media filter, because they can efficiently remove sand and organic matter. Round disks, each with grooves on
one side, are stacked on top of each other, creating tiny spaces where water flows through, trapping all matter that does not fit through the gaps. These disks can easily be cleaned by unshackling them and washing by hand.

Centrifugal filters are also known as sand separators, because their primary function is removing sand from water. Dirty water enters the filter, where centrifugal forces cause the sand to move to the outside edge of the cylinder and then collect at the bottom of the tank. Sand particles can pass through the system if the filter
is not sized properly and at the initial startup and shut down of the flow. A sand separator system is not effective in removing organic matter, as it will only remove
particles that are heavier than water.