How Exactly Does Drip Irrigation Work?

Over recent years, there have been considerable technological advancements in irrigation. One of the more effective of which is drip irrigation. Irrigation technologies, put simply, provide water to plants, and methods for doing so can vary widely. Techniques for irrigation can range from surface irrigation techniques, either through channels or completely flooding the field, to the more precise and controlled method of drip irrigation. Other examples include overhead irrigation which, consequently, creates a lot of runoff.

For anyone who has played the Civilization series of games, or has an interest in the development of civilizations, you'll quickly appreciate that irrigation was a very early technological advancement of our species. It allowed for the development of more efficient farming and subsequently provided stable, more or less, food supplies. Drip irrigation is, in effect, a modern "tweak" of the time old technique.

In the following article, we'll quickly gloss over what drip irrigation is and the components of a typical system. Let's get stuck in then.

Example of a commercial setup [Image Source: Wikimedia Commons]

What is drip irrigation?

Drip irrigation is renowned for being a very efficient method of watering plants. By way of example, the average sprinkler system has an efficiency of around 75-85%. Drip irrigation, in contrast, has efficiencies in excess of 90%. Over time this difference in water delivery efficiency will make a considerable difference in crop production and the company's bottom line. In areas where water is short supply, such as the desert regions of the US, drip irrigation has, unsurprisingly, become the preferred method of irrigation. Drip irrigation systems are relatively inexpensive and easy to install, simple to design, and help maximize plant health due to the reduced moisture levels on fields.

This form of irrigation, sometimes called trickle irrigation, applies water directly and slowly to the soil. The technique's efficiency is provided by two major factors. The first is that water is absorbed by the soil for access to the plant roots rather than running off or evaporating. Secondly, the water is only supplied to those areas of the field that actually need the water, i.e. the plant roots. Most drip irrigation systems are simple to design which minimizes design errors and installation flaws. There are some great guidelines out there if you are interested in perhaps installing one.

Why irrigation is important

Irrigation is one of the oldest technologies mankind developed. It is used extensively across the world. Countries with the largest populations (USA, China, India etc.) have over 100,000 km2 of irrigated land! Wow!

Irrigation consumes a lot of fresh water and can result in water logging of crops and build up of salts. Salinization is a big problem in places like Egypt. The riverbed of the Nile has been irrigated from close to 5000 years since around 3100 BCE. These practices draw salt from lower horizons in the soil to upper levels. This is so bad in some places that the soil is actually whitish in areas! This isn't an issue isolated to Egypt and occurs wherever irrigation has been employed for a long period of time.

Drip irrigation offers a great solution to this potential problem. Historic practices such as centre-pivot irrigation are not sustainable in the long term. They consume large amounts of water and are potentially damaging to the "health" of the soil. Drip irrigation allows the user to better control the amount of water plants receive, rather than blanket watering the area. Eutrophication is massively decreased by drip irrigation as fertilizers are not carried away by water runoff into watercourses.

Drip irrigation might be the future

Italy is one of the world's largest agrarian countries and has a large percentage of land given over to growing wheat, corn, rice and fruits etc. Italy began implementing drip irrigation in 2011. Italy's adoption of drip irrigation is estimated to save the country 4.3 billion Euros over the next thirty years! According to the World Water Development Report (WWDR), 47% of the world's population are likely going to live in "areas of high water stress" by 2030! If this warning is to be believed, it is essential that we develop and implement ways to better use and conserve water supplies. Drip irrigation might just be the perfect solution for farming.

How does it work?

In effect, drip irrigation places small drip emitters in close proximity to the crops' root systems. This provides a much-improved efficiency and makes the system much more controllable compared to other methods. The emitters release water in a slow and steady fashion. The emitters are very small, about the size of a US quarter and are arranged in an array in the ground. These emitters are directly connected to the water source by feeder hoses. Another setup is to have the emitters built into the feeder hose instead of rows of independent emitters. This is called a trickle hose.

Who invented it?

The invention of drip irrigation is often attributed to one Simcha Blass. Simcha was an Israeli engineer and inventor who lived between 1897 and 1982. Simcha was an important figure in water development in Israel and he, with his son, initiated, introduced and developed drip irrigation systems.

Drip irrigation was tested in a primitive form in the 1920's but the modern technology as we know it was properly developed by Simcha in the 1930's in Israel. Its discovery seems to have been something of an accident. Blass, whilst spending some time in the desert regions of Southern Israel noticed something strange. He noticed that one tree near his location was performing much better than all other vegetation nearby.

When Blass went for a closer look, he noticed that a water pipe near the tree had a small leak supplying its root system with its very own regular slow supply. This accidental discovery led Blass to embark on a journey of trial and error testing various materials and water pressures for an ideal solution. It wasn't until the 1950's with modern plastics that Blass could take his technology to the next level. In the 1960's Blass was able to finalize the technology and patent the design.

"Gubbins" of a drip irrigation system

Drip irrigation systems are pretty simple setups but do consist of several constituent parts. A typical simple system will consist of the following components.

Simplified drip irrigation system [Image Source: IrrigationTutorials]

Valves

The role of valves in the drip irrigation system is very simple. They turn the water flow on or off. Valves come in various "flavors". Isolation valves are manually operated for systems that require an infrequent shut-off of the water. These valves are typically sited close to the water supply to enable isolating the system for repairs or off season. These can be installed anywhere in the system to enable isolation of segments of the system for localized repairs but this is usually only employed in larger systems.

Control valves are valves that turn the water on and off to individual "circuits" or areas of the yard that are perhaps irrigated separately from one another. These can be automatic (using solenoids) or manually operated. Depending on the system design there can be just one or many installed. For instance, you may have one control valve that controls water supply to the emitters in a vegetable garden. Yet another may be present that controls water supply to shrubs or hanging pots around the house and patio.

Drip irrigation system [Image Source: Wikimedia Commons]

Backflow preventer

This is a piece of kit employed within the system to prevent, hence the name, dirt, bacteria, other contaminants from being sucked back up into the drinking water supply for the drip system. This device is essential for all drip irrigation systems.

Backflow preventers are essential because drip emitters rest directly on the soil and are potential very susceptible to water contamination from soil born diseases etc.

Pressure regulators and pressure reducing valves

These devices, as the name implies, reduce the pressure of water flowing through the system and keep it at a constant level. Pressure reducing valves and pressure regulators are in this instance synonyms and essentially the same thing.

Drip irrigation systems, on the whole, perform best at lower water pressures than typical water supply systems. These devices also enable a constant system pressure even if the supply pressure fluctuates periodically, which is nice. Designers need to be conscious of areas with low water pressure as these devices will clearly further reduce the system pressure.

Usually, two types of pressure regulators are employed in drip irrigation systems. Non-adjustable ones with pre-set outlet pressures and user adjustable types. In general, small homeowner system will use non-adjustable valves if they have less than 3 control valves. You can, of course, install adjustable valves if you want full control of your system. Non-adjustable regulators must be installed after the control valve and in cases where multiple control valves are present, pressure regulators are needed for each one. Accidental installation before the control valves can cause pressure surges that will damage the system.

Adjustable pressure regulators, on the other hand, can be installed before or after the control valves. In large systems, you can install a single or fewer adjustable pressure regulators in the main supply line before control valves to save on costs.

Filters

The filter is obviously used to, well, filter the water. Drip emitters have very small openings which are easily clogged up so employing filters earlier in the system is essential for increasing the life span of the irrigation system. Recommendations for filters are that they are between 150 and 200 mesh. High-quality filters are often installed before the valves or pressure regulator but lower quality ones can be installed after the pressure regulator. High-quality filters usually have a maximum pressure rating of 10.3 bars (150PSI).

Emitters

Now we come to the "guts" of the drip irrigation system. The emitters are responsible for directly controlling the rate of water supply to the soil. Emitters are usually small plastic devices that either screw or snap onto the drip tube or pipe. In trickle pipe systems they are pre-assembled and part of the pipe assembly. Common emitters, emit, water at around 4 liters per hour.

As a general rule of thumb 1 or 2 emitters are usually required per plant. This does, of course, depend entirely on the size of the plant in question. Trees or shrubs will clearly need more than a small plant. Use of multiple emitters also provides the system with backups in case of a blockage in one or more of the emitters. The more emitters present the wider the area of irrigation and hence the increased growth of roots for healthier crops and plants. Of course, if plants tend to be planted close together the system may only need 1 per plant depending on the system design and "coverage" of the emitters.

Emitters are usually installed at least 450 mm apart. As a rule, some sources suggest installing emitters 600 mm apart under 80% of the plant's leaf canopy, this is where the roots are after all. For highly permeable soils emitters should be placed 300 to 450 mm apart. Emitters should never be buried unless they are specifically designed for this purpose.

[Image Source: Wikimedia  Commons]

Mainline and lateral/sub-main pipes

This pipe is the main connection between the water supply to the control valves of the drip irrigation system. It can be made of galvanized steel, copper, PVC or heavy wall Polyethylene. Each type has the inherent limitations and strengths. PVC, for example, is easily damaged by sunlight and is usually buried or protected. Polyethylene has a low burst pressure and is usually only used where water pressures are lower than 50 PSI.

Lateral/sub-main pipes are located between the control valve and drip emitter assemblies. These can again be made of PVC, PEX or Polyethylene. As these are generally placed downstream of the pressure regulator high-pressure ratings are not essential.

Drip tube or hose

This is a special type of tube common in most drip systems. They tend to be laid on the ground surface between plants. Emitters are generally installed to these tubes. Drip tubes tend to be made of thin-walled polyethylene and consequently have a much lower pressure rating than other parts of the system. It is generally recommended that these stay above ground as they can commonly be nibbled on by pesky local rodents! In large commercial setups, these tubes are usually "hard-piped" in these systems and the emitters are installed directly onto the laterals.

Drip tube tends to not exceed 60 meters in length from the point where water enters the tube. Tubes can be extended so long as the point of entry of the water supply never exceeds 60 meters from entry to pipe termination point. e.g. a 120-meter tube where the water entry point is at the center point.

Air vent

Air vents are installed in systems that are turned off at any time. They prevent air from being sucked up into the emitters. As the water pressure falls away, air can be sucked back through the emitters and entrain dirt or soil into them. Clearly not desirable. The presence of an air vent mitigates this problem by drawing in air through it rather than the more delicate emitter openings.

End cap or flush valve

Unless you want water to run out of the end of the drip tube you'll need to install an end cap! All well and good but this do introduce another issue for the drip irrigation system. The water flow within the drip system is very slow which can allow sediment to build up, even allow algae to grow within the pipes. Normally drip tubes are flushed about once a year, more if an algae problem is persistent.

Benefits of drip irrigation

Given the technology's setup, the greatest benefit this method provides to the producer is control. Given the amount of control it provides, the technique offers great economic benefits as well as reduced waste. A typical lawn sprinkler will use between 4 and 20 liters of water per minute. A standard drip irrigation system, on the other hand, measures water use in liters per hour. This slower supply of water to the crops improves root take up and reduces water loss through ground percolation. This allows the water to be used more efficiently and reduce waste through evaporation for example. The direct application of water to the soil also prevents drift. Drift is the phenomena of water being blown or dispersed to other parts of the site where water is not required, e.g. walkways etc.

A well maintained and managed drip irrigation system can, all but eliminate, water waste through surface runoff. Drip irrigation systems rarely need excavations and rarely disrupt the integrity of landscapes during installation. Tubing can be weaved throughout the site where irrigation is required. Drip irrigation systems can, therefore, also be moved and are not required, which is nice.

The design of drip irrigation provides maximum crop yield and increased fertilizer use on crops. Its localized supply of water results in reduced weed growth and also restricts the population of potential hosts. Drip irrigation systems result in minimal, if any, soil erosion as there is no surface runoff. This also controls potential fertilizer pollution in natural groundwaters and surface waters. The use of emitters, control valves etc. allows the user to provide ready adjustment and sophisticated control of water supply to areas of the site. Seed germination is greatly improved and tillage operations are decreased.

Disadvantages of drip irrigation

There are many advantages for using drip irrigation over other irrigation methods and they are usually a great solution for commercial properties. Drip irrigation is not without its problems, as you'd expect. They do tend to require more maintenance than a more conventional system.

As previously discussed the slow water flow rate and low pressure can cause sediment to build up in pipes. Algae can even grow where climates permit. Mitigation of these issues requires regular flush outs of the system. This is usually required at least annually but can be more frequent in the case of algal build up. Non-potable water contains more particles which can easily clog filters and drip emitters in particular. Drip emitter nozzles also require regular cleaning. These irrigation systems can also have an issue with salinity hazards.

[see-also]

Drip irrigation is best used for beds rather than say a lawn. Large open spaces that do require regular watering are better served with more conventional irrigation systems. For larger commercial applications, regular monitoring of plant health should be carried out to make sure the system is working at peak efficiency. Clogged or block emitters can cut off the water supply to "spots" in the field that will cause the gradual decline in health of the plants in the affected areas. This obviously adds an extra manpower cost to the facility. A well organized and managed monitoring system will identify problems early on, allowing for repairs to be carried out in a timely manner.

Water distribution elements of the system can also be damaged by exposure to sunlight especially if made of PVC. This can cause ongoing maintenance and repair costs that may not be the case with alternative irrigation systems.

The last word

So there you go. Drip irrigation has come a long way since the random observations of one engineer and inventor. With future water supplies potentially becoming stretched, the need to improve water use wherever we can will likely see drip irrigation becoming ever more important to our agricultural needs. Drip irrigation is a relatively simple technology and offers a fantastic alternative to more traditional, water "hungry" or should we say "thirsty", irrigation methods. It is seeing ever increasing popularity in more arid regions of the world and you can even install a simple one in your garden! It is of course not perfect but the benefits and reduced water consumption and environmental impacts of the tech more or less outweigh its limitations.

Sources: IrrigationTutorials, NKOLandscaping, AgriInfo, LearnTravelArt, MyOliveTree