Micro irrigation, also known as drip or trickle irrigation is a system of applying regulated amounts of water directly to the root zones of plants. The chief advantage of a micro irrigation system lies in its potential to minimize transfer and evaporative loss and to conserve water by applying it only to the areas where it can best be utilized by the plant. Additionally these systems lend themselves well to automation, irrigation scheduling and low-labor watering. It is estimated that a drip irrigation system coupled with needs-based irrigation scheduling (based on soil moisture readings) can result in water savings of up to 60 percent over traditional watering methods. Especially for gardeners or landscapers using metered water from a municipal supply, this translates to significant monetary savings.
Micro irrigation in some form has been practiced since ancient times. Historical records show early Mesopotamian farmers using buried clay pots to slowly ooze water to the root zones of trees and grape vines. Development of modern systems came about in the 1860’s when researchers in Afghanistan began using buried clay pipes for the same purpose. The development of modern plastics technology post-World War 2 enabled many improvements in irrigation systems. Today drip irrigation is in wide use, particularly in those arid regions of the world where water is scarce and expensive.
Components of a micro irrigation system
The typical system generally consists of several basic parts:
1. A water source, generally delivered under pressure. Most systems operate under relatively low pressures, typically 5-30 PSI.
2. A filtration device to prevent plugging of small lines and emitter orifices.
3. An injection port, to introduce fertilizers, pesticides or cleaning compounds
4. A main supply line, generally running the length of the area to be irrigated.
5. Lateral carrying lines running to individual plants or rows of plants.
6. Emitters that drip, stream or spray a measured amount of water to a plant or limited area
7. Pressure regulater(s) to maintain a constant pressure within the system
Most systems will also have some or all of the following accessories:
8. Manual or automatic control valves to control flow to various laterals
9. Backflow valve to prevent water in the system from mixing back with the source
10. Air injection point near the head of the system, with vents or blowout valves at the end of laterals. This allows pressurized air to be introduced to evacuate water from the system for winterizing.
Benefits and Disadvantages of Drip Systems
The primary incentive for a home gardener or landscaper to install a micro system is economic. In places where water is scarce or expensive the reduction in water use of up to 60% can result in significant monetary savings. The highly efficient use of scarce resources may allow planting of water-loving species that would otherwise be impractical to grow.
These systems are highly adaptable to automated control, which can result in greatly reduced labor requirements once the installation is in place. Different types of emitters may be attached to a single lateral line, which enables the practice of zoned planting, wherein various types of plants are grouped according to their water requirements. Plant nutrients and certain pesticides may also be applied through the irrigation system in a process known as fertigation or chemigation. As with water, chemical use can also be reduced by making application only to the area of the root zone.
Drip or micro irrigation is not suitable for every situation. Although it has been adapted for turf or broadcast seedings, it is more applicable to row crops and especially to perennials where a system, once installed, can remain in place for years.
In regions with high levels of precipitation where irrigation is required only occasionally the water savings may be insufficient to offset the relatively high installation cost. In addition to initial cost, micro systems require a fairly high level of maintenance. The components tend to be fragile, especially those related to automated control. Micro irrigation does not allow the heavy application of water needed to flush salts from soil, which may require some sort of supplemental equipment if flushing becomes necessary.
Although a micro irrigation assembly can be as simple as laying a soaker hose along a row of plants, the major components of most systems, particularly source assemblies, main supply lines and controls are a semi-permanent installation. Main lines are of PVC pipe and are buried below the frost line. Lateral lines are usually of soft plastic with compression fittings and may be sub-surface or above-ground. Above-ground lines may be laid directly on the surface or attached to support structures such as trellises. When used on annual plantings, sub-surface lines are generally removed and discarded at the end of each growing season.
Emitters may be of several types. Drippers produce a slow drip of water, generally at a rate of 0.5 – 4 gallons per hour (GPH). Bubblers emit a small stream of water at rates up to 16 GPH. Micro-sprinklers direct a fine spray or mist at rates from 15 – 40 GPH and may cover a circular area of up to 40 ft. in diameter.
Water filtration is a warranty requirement of most equipment manufacturers and an essential for proper operation of most systems. Well water and treated water from municipal delivery sources generally need minimal filtration while ditch or cistern water will require a higher level of treatment. Primary filtering devices are often in the form of sand spinners or disc filters, while final cleaning is done by cartridge or sand media filters.
All but the most primitive drip systems require water to enter the system under pressure. Standard operating pressures typically range from 5-30 PSI. The relatively low pressure and volume requirements compared to more traditional irrigation methods enable the use of smaller, lower-horsepower pumps, which results in reduced energy use and lower pumping costs. Conversely, older pumping stations already in place to serve traditional irrigation methods can spread water over a much larger acreage when retrofitted to a micro system.
Most installations require a backflow preventer at the water source to prevent any return of water from the system to the source. This is particularly important where water is taken from a well or municipal supply, or where chemigation is practiced
Considerations for Use
When contemplating the installation of a drip or other micro irrigation system over more traditional irrigation methods, several important points must be considered.
Cost: The initial investment in equipment and installation is apt to be considerably higher than for more traditional methods such as flood, furrow or overhead irrigation. Because micro irrigation applies water directly and only to the zones where it is needed, extensive linear footage of supply lines must be extended to reach all parts of the planted area. Considerable excavation is needed to accommodate these lines. Consequently material cost and labor may result in a capital outlay several times that of other systems.
Water use efficiency: Efficient water use can result in overall water savings, but the two terms should not be confused. The efficiency of most drip systems is 90% or higher. That is to say, 90% or more of the water that enters the system is deposited in such a way that plants can utilize it. By comparison, overhead sprinklers are about 75-80% efficient while flood irrigation efficiency hovers around 60%. Thus the technical efficiency advantage of micro irrigation is 10-30%. However, since a drip system also enables more precise management of irrigation, the actual water savings of a drip system can be higher – up to 60% in some cases.
Maintenance: Micro irrigation systems require a higher level of ongoing maintenance than other types. The soft plastic that makes lines and appliances affordable has a relatively short working life and is susceptible to damage from a number of outside sources. Plugging of small apertures from sand or algae is common, even with good filtration. Buried or ground-level carrying lines may be damaged by burrowing rodents and require repair or replacement. Electronic controllers tend to be fragile and may require occasional replacement. Most system components are designed for a functional life span of 5-10 years before replacement is required. Most importantly, in regions where winter temperatures fall below freezing it is imperative that all water be evacuated from the system at the end of the growing season.
The decision to install a micro irrigation system for gardens or landscaping must take into account several considerations. Chief among these is the economic; does the reduction in water use and labor justify the capital outlay and maintenance costs? In areas with high precipitation levels, where irrigation is only an occasional supplement during dry spells, the time required to recover installation cost by water savings may far exceed the practical lifespan of the system. Conversely, where water is scarce and expensive the initial outlay may be amortized within a year.
The degree of automation allowed by a drip system allows a significant reduction in labor requirements. This can be particularly important in cases where hourly or contract labor is engaged for irrigating. A single individual can operate multiple systems simultaneously, as the only requirements are monitoring and, perhaps startup and shutdown depending on the degree of automation. Furthermore, plants with vastly different water requirements can be accommodated by designing the system to simultaneously deliver varying quantities of water to individual zones.
Ultimately the decision to install a micro system may be dictated by the desire to practice conservation, the satisfaction of achieving maximum efficiency of water and power use and the inclination to engage in wise resource management.
Drip irrigation vs. other irrigation systems
Schematic diagram of a typical micro irrigation system from Irrigation Tutorials