Micro-irrigation to save water

Micro-irrigation is an effective water-saving technique that offers a solution of choice for both gardeners and agricultural companies. With an incomparable efficiency, this system allows to water the plants at the right time and at the right dose.

What is micro-irrigation?

Developed in the early sixties, micro-irrigation ensures optimal distribution of water under low pressure directly to the feet of the plants concerned. Of course, already in ancient times, the issue had been addressed by the use of oyas, these porous buried jars that ensured effective watering close to the roots.

But let's go back to the current system which has the advantage of being able to be planned by cycles, according to the climatic conditions, and which allows to choose the flow intended for each plant.

Otherwise known as 'localized irrigation', this technology was created in Israel in 1959, when the advent of plastic pipes allowed its development. Patented in 1960, drip irrigation quickly took off in America and Australia. Nowadays, this system is recommended in arid countries and in hot climates. Unlike conventional irrigation, which waters the entire soil indiscriminately using maximum pressure, micro-irrigation provides water in a punctual manner, on a well-defined area of the soil and at low pressure.

What does a micro-irrigation system look like?

There are several micro-irrigation media, although drip irrigation is the best known and most widely used, especially by individuals.

• The drippers work under a pressure of 1 bar. Each dripper is fixed independently on the whole length of a pipe of 0,5 to 1,5 mm of diameter. With one or more holes for water flow, the dripper can be chosen or adjusted (depending on the model) to the right flow rate for each plant (from 0 to 20 l/h).
• Micro-sprinklers, micro-diffusers or micro-sprayers are generally used in arboriculture. They can be fixed on a stake and diffuse water on 40 cm by rotation of the cap with an adjustable flow from 0 to 60 l/h.
• Micro-porous pipes are perforated with a multitude of small holes from which the water flows at low pressure along the whole length.

Advantages of micro-irrigation

This controlled watering technique allows enormous water savings (25 to 40%) compared to flood or runoff irrigation techniques with an efficiency 40% higher.

• Micro-irrigation can be coupled with a programmer, or even a weather station or an application to manage the watering according to the real needs corresponding to the climatic conditions. You can even be notified in case of water shortage or technical problem.
• Evaporation is less, especially when the system is activated at the end of the day. It also helps avoid many cryptogamic diseases that spread through the watering of foliage.
• The hydric shocks so harmful to plants are avoided. Plants not stressed by the lack of water are more vigorous and less sensitive to parasites.
• In a large farm, it allows to reduce labor costs.
• The rooting of the plants is favored by this system.
• There are far fewer weeds, which avoids competition for cultivated plants and tedious and time-consuming weeding.
• This technique allows for the direct addition of fertilizer during watering in large-scale agricultural operations.
• Knowing that the water consumption of intensive agriculture corresponds to nearly 70% of the world consumption, that water resources are beginning to decline or even disappear in some areas, the problem of food security may become burdensome. Micro-irrigation helps to overcome this problem.

Disadvantages of micro-irrigation

Although few in number, there are some disadvantages to installing a micro-irrigation system.

• The cost can be prohibitive when it comes to irrigating a large plot of land. However, at the level of a medium-sized private garden (500 m²) or even better, a simple balcony or terrace, it is possible to obtain very affordable kits that will quickly pay for themselves.
• Another concern is the technical nature of the installation (calculation of pressure losses, installation of the pressure reducer, knowledge of the right pipe diameters, creation of the different circuits, adjustment of the flow rate of the drippers and their number, installation and adjustment of a possible programmer...) which can frighten the novice gardener or those who are not very handy.
• The drip system should be checked often enough because some drippers can be clogged, especially by ants or soil debris.
• Leaks and breaks are not impossible, especially after the brushcutter has been used! If you don't do your own brush cutting or mowing, always remember to tell the person in charge of this work that an automatic watering system is in place, otherwise your garden will be compared to the water games in Versailles as soon as the watering system is turned on!

The installation seen from the trenches

You have now the technical study in hand to realize your underground watering system. Now it's time to tackle one of the most difficult parts (for the arms...): the earthwork.

Let's see the steps and our advice for the earthwork for the installation of your underground sprinkler.

1/ The trenches

Make the trenches as shown on the plan

The width does not matter. A trencher makes cuts 9 cm wide and this is more than enough to pass pipes and sprinklers. If you are working with a backhoe, there are small buckets that make narrow trenches (so there is less soil to put back in place afterwards!). Finally, with a spade, there is no choice but to get the width of the tool.

Remove all the stones if possible.

In terms of depth, there are several opinions...

• I often advise 35 cm minimum (a little more than a spade).
• It is useless to dig at 60cm to protect yourself from frost. In some regions, if the winter is very hard, the ground can freeze very deeply. It is better to foresee anti-freeze systems as soon as the installation is done.
• The idea of putting the pipes at 90 cm to be sure that nothing freezes is very risky: the sprinklers are on the surface, and they will be damaged by the cold: it is therefore better to have the possibility of draining the whole installation. Moreover, at this depth, when it is necessary to intervene to modify or repair, it is very complicated. Think about the hole that will have to be made for a simple connection to be added.

Don't forget when opening the trenches to foresee the location for the manholes (see manhole picture).

2/ Setting up the pipe network

Unroll the polyethylene pipe at the bottom. In case of important presence of stones or pebbles, put a bed of sand under the pipes (in this case, dig deeper).

Install fittings and sprinklers.

DO NOT PLUG UP!

At the end of the line, do not put the plugs in yet. You must first send water into the pipes to clean them of all the debris that could have slipped inside. (see photo turbine380)

Screw in the plugs once this step is completed. Shim and adjust your sprinklers. Leave the system running and check ALL the connections.

There are no leaks after your installation? You can now fill in the gaps...a little...

3/ Locate the water network

3) If you have a 40 cm deep trench, put 20 cm of earth and then put a blue wire mesh. This will avoid piercing the pipes if you have to work on them in a few years: it will indicate the presence of pipes underneath. The blue color of this plastic mesh is important, it is a recognized standard for water (for information, green = telephone, red = electricity, yellow = gas).

4/ End of the earthwork

That's it, you can fill it in completely. Let the soil settle for several days before renovating the damaged lawn.

Technically, the trenches are not the most difficult part, but a well done earthwork allows an easy maintenance during the following years.

Underground irrigation programmers

The use of a buried automatic watering controller allows you to control the watering time at the most convenient time of the day. 

One of the most important ways to save water is to water only as long as you need to, when evaporation is lowest, i.e. in the middle of the night or early morning.

To do this, your underground watering system must include an important element: the programmer. It will allow your installation to start and stop at the desired time; it will control the solenoid valves, so that your garden is watered in successive sequences: we speak then of several networks or ways.

There are four main types of multi-network programmers:

1. The battery-operated programmer, connected to the solenoid valves by a cable with many wires. This is a choice to be reserved exceptionally for places where there is no power supply. Compared to other options, this product is quite expensive. (main manufacturer: RAIN BIRD).
2. The wireless battery or current programmer. This one is connected by waves to the solenoid valves. The installation is thus strongly facilitated.
3. On the other hand, it is still a very expensive product, but practically all suppliers are trying to develop this type of programmer. We can therefore hope that the prices will decrease in the years to come. (Main manufacturers: RAIN BIRD, GARDENA...).
4. The wall-mounted programmer, with a separate transformer (photo opposite), connected to the solenoid valves with a multi-core cable. This is the best quality/price ratio. There are, apart from the "first prices", very reliable models at around 75 Euros that can control up to 6 solenoid valves. The only problem is that these products must be installed indoors (garage, cellar, storeroom, etc.), near a power outlet, as the electrical transformer (220v/24v) is not protected from water projections. (main manufacturers: RAIN BIRD, NELSON...).

The wall-mounted programmer, with an integrated transformer, connected to the solenoid valves with a multi-core cable. This is the largest choice available on the market. There are all models (from 2 to 48 networks) and all prices (from 170 Euros for the big brands). These devices have the particularity to be in the standards for a wall installation outside, even in the rain.
They are also products that can be installed inside. The advantage is that there are less visible wires, the transformer being included with the programmer in a single box, with a door that can be closed. (see photo below)

Logically, the many existing models and the discretion in terms of wall installation make these products very often preferred by craftsmen. (Main manufacturers: HUNTER, RAIN BIRD...).

The purchase of a programmer should not be based solely on its price: it is the submerged part of the iceberg (the rest of the installation being buried) and you will use it frequently (changing the watering times according to the season for example).

So you need a model that is easy to modify.

More and more products are available with hundreds of programming options. Even if you don't need all of them, the more options a controller has, the easier it is to adjust if you only focus on what you need for your garden.

So don't necessarily look for the cheapest one that seems simple, as this may limit the use you want to make of it.

Finally, in addition to the notions of saving water, a programmer is obviously a comfort of use, like all the rest of an underground watering installation.

Note that there are now programmers accessible from your smartphone.

Installation of a solenoid valve manhole for an underground irrigation system

Here is an illustrated example of a solenoid valve assembly in a manhole. This one, as well as those that could follow, is only an example among many solutions or preferences that each installer may have. Nevertheless, some basic principles are stated.

1/ Mounting the manifold

Here two solenoid valves with the water inlet in the center. Although there is a main water cut-off, a shut-off valve is always placed at the manhole inlet. The solenoid valves are removable before and after, by the "removable union" type fittings. The solenoid valves have been disassembled so as not to bother with the wires, protective tape (orange here) prevents the intrusion of earth. Pipe primers allow the manifold to be mounted completely without worrying about the rest of the piping.

2/ Positioning the collector

After the hole has been made for the manhole (wider than necessary), the bottom is laid flat, the solenoid valve manifold is placed, as well as a sheath here to allow the cable to be passed later. The pipes under the manifold allow to raise it a little with respect to the level of the manhole (the usefulness of this will be seen later).

3/ Arrival of the manhole

The manhole has been cut with a hole saw in order to let the pipes pass. It is positioned over the collector. We check that it is level and aligned with the limits of the garden (wall, alley, ...). Note that the manhole is deliberately larger than necessary: it is a false economy to try to put a maximum number of valves in a small manhole; maintenance and repairs are difficult, the connections are not accessible, ...

4/ Wedge the manhole

Once the manhole is correctly in place, we start to backfill all around it, gently so as not to shift it. The geotextile film is pulled up along the outside walls so that the soil does not enter the manhole.

5/ Backfilling

Once the manhole is in place, it can be completely filled in. The pipe primers are useful on some sites where the manholes are installed well before the garden pipes.

6/ Manhole bottom 

The bottom of the manhole is filled with pebbles. The pieces of pipe which supported the collector are removed.

7/ Cleaning

The manhole is cleaned with water. All the components of a collector are watertight, so it can be washed with water. The solenoids are screwed -by hand- on the solenoid valves, the wires will not interfere anymore. The multi-core cable coming from the programmer is brought into the manhole, longer than necessary (it will not be cut).

8/ Connections

All that remains is to connect the wires of the solenoids with the cable, using waterproof connections. Here, the connections are enclosed in a box, for cleanliness reasons, so as not to leave unsightly connections lying around: be careful, it is never the box that makes the watertightness, but the specific connections used.

Renovation of a solenoid valve manhole for underground watering

Here is an example of a manhole installation using existing cables or pipes.

1/ Assembly of the new manhole

After the old manhole with its solenoid valves has been completely dismantled (the cables are not cut, it is better to keep the connections), a new complete manifold is assembled, adapting to the existing one.

Here, three watering networks, drip, so three solenoid valves. A stop valve was added at the entrance of the collector, as well as a second valve to easily purge the collector before the winter.

This is a solution that I recommend very regularly (even if it is not systematic). Removable fittings before and after the solenoid valves.

2/ The manhole

We check and try the positioning of the manhole. In renovation, it is always a little more complex than in a new creation. It is necessary to check that a maximum of elements and connections are inside the manhole (and not under the edges, the walls, inaccessible).

3/ Connections

The manhole has been installed, wedged and filled, it is time to make the watertight connections.

Here you can see the old connections (brown), which have not been removed in order to identify the wires as the new connections are installed (blue or black).

4/ Finishing

Once finished, a bottom of garviers or pebbles, then we wash the manhole; the old grey cable has not been shortened, and there is room in this large manhole to work if needed.

Automatic drip irrigation by gravity

If you don't have electricity and water near the area to be watered or you don't want to use it because it is your second home and the taps are closed and the fuses are broken when you are away, automatic gravity drip irrigation can be a solution for a self-sufficient system, but it has some implementation constraints.

Having a water tank

Automatic gravity watering requires a rainwater reservoir or a tank filled regularly with water when you are present intermittently. Its volume will depend on your autonomy. A tank of one cubic meter is a good starting point and will ensure several weeks of watering depending on your surface to cover. By connecting several tanks you will increase this autonomy. 

The advantage of the water tank in the case of a second home is to leave with peace of mind with the water meter valves closed. Who hasn't experienced a leak on his watering system?

Severity and pressure

In this type of watering, the idea is to take advantage of gravity to feed our drip system. Under its effect, the water will flow in your network which must be under the water level of the tank. In fact, a buried tank on a flat ground will not be suitable without a pump and therefore with electricity nearby.

But for the drip system to work at its best, pressure is needed to feed and distribute the water throughout the network. This is related to the height of the tank and more precisely to the height of the water level, placing the water tank as high as possible will be an asset. If your land is flat, you should consider raising the tank by a slope, a small construction, some breeze blocks or pallets, if your land is sloping, simply place it in the upper part of the garden.

The pressure is 1 bar every 10 meters vertically (editor's note: information well known to divers), a meter of difference in level between the tank and the watered area makes you gain 0.1 bar of pressure. This is only an order of magnitude, but it is important when it comes to solenoid valves.

To facilitate the flow, bring the water as close as possible to the area to be watered with large diameter pipes starting with 25 mm for example and then create a secondary network with 16 mm and finish with small pipes if necessary next to the targeted plants. The drippers can be installed directly on the secondary network or of course on the tertiary network.

Not one but many networks

Too many drippers on your network will not allow you to keep a good pressure in the whole circuit. Some branches may not be supplied. It is therefore important to define several networks operating at different times from the same tank to maximize the pressure and therefore the flow.

Create separate networks for different zones, depending on whether it is a vegetable garden, a dry rock garden, a flower bed, a hedge, etc. The watering times and frequencies will not be the same in any case. 

Adapted solenoid valves

Solenoid valves are taps whose opening and closing is controlled electrically by a nearby or remote programmer. 

Most of the solenoid valves available on the automatic watering market only work from a certain water pressure, generally between 0.5 and most often 1 bar. Be careful because this information is not always available on the technical data sheets or the packaging of the products on the market. It is unlikely that you will have such a pressure or your land is very steep, so you need to find 0 bar solenoid valves, which open without or with very little pressure. This is the case of some automatic programmers like the "tap nose" for automatic watering from rainwater harvesters. Moreover, some of them propose 2 ways, that is to say the possibility to program the watering of two different circuits. Most of them work with batteries, which is good because we don't have electricity!

Programming of the automatic watering

For a bed of flowers or a vegetable garden, a watering of approximately one hour every 48 hours in summer is a base of departure to allow a watering in depth and not just wet the surface ground. Then adapt according to the needs of your plants.

Consider starting at night when the soil starts to cool down after midnight. Distinguish and adapt the programming according to the seasons, so decrease the frequency outside the summer period by passing from 48h to 72h for example.

A drip irrigation system

With a low and variable pressure according to the level in the tank, and according to the altitude of the different circuits if your garden is not flat, an adjustment of each dripper is necessary. Also adapt the flow rate of the drippers to the needs of your plants. Over time, check that each dripper is working properly, as particles can clog them or even lime deposits can block them. Make sure that the tank remains clean and free of deposits.

Although it may be tempting to use other types of sprinkler systems such as boom sprinklers, their water consumption is not at all the same and will limit the life of your water supply. So use sparingly.

Last tips...

Place taps to purge air at the end of each of your circuits.

Connect several 1000-liter tanks together to gain autonomy depending on the space available for their installation.

Test your installation for a few weeks and measure the consumption in the tank. This will allow you to estimate the available watering time in your absence or to adapt the possible watering duration.