Irrigation for arable crops
Which irrigation method to choose, which equipment...
Installing an irrigation system has a significant cost if you start from scratch. You need to find a place to draw the water from, dig a well of varying depths to reach the water table and then install a suitable pump (thermal or electric). Next, you'll need to lay a network of pipes (overhead or underground) to the plots and, finally, you'll need to invest in irrigation equipment : cannon + reel, pivot, boom, cover with sprinklers, drip irrigation, etc.
The equipment is not the only important point to consider, there is also the technique (pressure, flow rate, head losses, etc).
With the right equipment and the right technical skills, you can achieve precision irrigation.
All this can represent an investment of several tens of thousands of euros. But the crops that require this type of installation are well worth it financially.
Optimising irrigation requires technical knowledge ( crop physiology, soil, equipment), economic knowledge and the use of appropriate control tools.
Different types of irrigation equipment
The machine most commonly used in arable farming is the hose reel. The principle is simple : a spool on a frame unwinds in the field and then rolls up once it has been irrigated. Different models are available, depending on the length of the spool, its diameter, the method of installation, etc. The last element in contact with the water, at the end of the coil in the case of a reel, will determine the irrigation method. There are several types of equipment :sprinkler irrigation, with a cannon or boom, and drip irrigation.
Irrigation cannons
The cannon is the simplest and least expensive irrigation system. It uses pressure to send water to the field. Robust and mobile, they are widely used on fragmented plots of land, as they are easy to transport with the tractor. By adjusting the spraying angle, they can also be adapted to all plot shapes and crop rotations. The spraying width will depend on the pressure of the pipe. As a general rule, the spraying width is 72 metres with a gun pressure of around 5-6 bars.
Weak points :
- They consume a lot of energy (high pressure is required to spray the water) and the reel has to be moved every time it changes position.
- When there's too much wind, the water jet doesn't cover the entire surface area required and the jet is less precise.
- The water sent out by the cannon is very violent when it lands on the ground. It is therefore not advisable to use this equipment on fragile crops.
Irrigation ramps
The ramp is a spreading system that allows you to irrigate in a "softer" way. The water is not sent into the field but deposited on the plant by a fine rain. They can be front-mounted or pivot-mounted. They are better suited to large plots of land and can increase the precision of spreading, even in difficult conditions such as windy days. As the pressure required is lower than with a reel gun, energy consumption is reduced. The quality of water distribution is also better, and the booms allow ferti-irrigation.
The pivots can be programmed, freeing the farmer from a major labour burden.
Weak points :
- This type of equipment also represents a significant cost.
- More difficult to install. This is why it is mainly used for very fragile crops such as vegetables.
- Cannot be moved.
Integral covers
These are booms laid on the ground that distribute water to sprinklers. They can be adapted to any plot (or to supplement watering in corners not covered by reels or pivots). They can be installed on slopes and require less pressure than cannons. They need to be dismantled and reassembled every year.
Ramps on reels
.JPG)
These combine the versatility of the hose reel with improved watering performance (25 % less water required). This type of equipment combines finesse and precision in the delivery of water with the adaptability of a conventional cannon, although it is not suitable for all types of plot. However, it is still expensive. In the north of France, reel-mounted booms are used more often.
Micro-irrigation
Micro-irrigation is based on the principle of drip irrigation (surface or underground) at root level, at a low flow rate. Highly efficient, micro-irrigation is by far the most economical technique, both in terms of energy and water consumption. The advantage of this type of installation is that, once in place, no additional work is required to operate it (apart from emergency maintenance and repairs, of course). It has other advantages, but costs around 50 % more than a conventional irrigation system.
This type of system requires more work to install and dismantle at the start and end of the season than the sprinkler system. This involves placing pipes with holes in them in the rows of the crop and sending water through them. As the holes are very fine, the water escapes drop by drop.
You might think that this system is more efficient than a sprinkler system, but that's not necessarily the case. In fact, for the same level of yield, the difference in the quantity of water used between a sprinkler system and a drip system is not significant.
| Type of
equipment |
Efficiency
efficiency |
Quality of
distribution |
Energy consumption
consumption |
| Rewinder | 80 to 95 % | Average to good | High |
| Pivot, ramp | 90 to 95 | Excellent | Moderate |
| Boom on reel | 90 to 95 | Good to excellent | Moderate |
| Full coverage | 70 to 95 | Good to excellent | Low to moderate |
| Micro-irrigation | Close to 95 | Excellent | Poor |
Advantages and disadvantages
Advantages
- The larger the irrigable area of the farm, the greater its potential.
- Possibility of growing a more diversified crop rotation.
- Maintains yields during hot, dry spells.
- Easier to produce crops with high added value.
Disadvantages
- Having a water resource nearby.
- Regulations are changing. Access to natural resources such as water is becoming more difficult. Acquiring an irrigation well is becoming more difficult, prompting some farmers to invest now to secure the future of their production facilities.
Investment costs
The cost of all the necessary equipment can be quite high, depending on requirements. The irrigation station is one of the biggest expenses, but once it has been purchased, there will be no need to replace it. What's more, with an electric motor/pump, maintenance is almost non-existent. Once the well is operational, you need pipes to bring the water to the field and a spreading system. The cost of a 5-inch diameter mobile overhead pipe (flow rate of 60m³/h) is around €13,000 for 1km of pipe (i.e. €13/m). The price of a reel, on the other hand, is also highly variable, depending on the choice of machine and options.
To get an idea of costs, consult the irrigation cost calculation tables provided by the Hauts de France Chamber of Agriculture.
The average cost of electrical energy varies widely. It includes the cost of electricity and meter rental. However, if electricity is not available at the foot of the well, you will have to install an electricity line to the well at your own expense.
Similarly, if the public electricity line you want to use is not suitable for an irrigation station like ours, you will need to have a transformer installed to standard at your own expense, by an approved company.
Regulatory point
Irrigation regulations mainly relate to drilling and well approval. It is forbidden to drill without authorisation and/or declaration. Two bodies are involved in declarations and authorisations for water abstraction : the DDT (departmental directorate for the territories) and the water police.
Any drilling project requires a declaration to be filed under the Water Act (article R.214-1 of the Environment Code - section 1.1.1.0). The associated abstractions are subject to the Water Act in the following cases :
- Heading 1.1.2.0 : withdrawal from an aquifer (excluding groundwater) :
- For a volume greater than or equal to 200,000 m³/year : authorisation is required.
- For a volume greater than 10,000 m³/year but less than 200,000 m³/year : a declaration is sufficient.
- Heading 1.2.1.0 : abstraction from groundwater accompanying watercourses :
- Greater than 1000m³/h or 5 % of the watercourse flow : Authorisation.
- Between 400 and 1000 m³/h or between 2 and 5 % of the watercourse flow : Declaration.
- Heading 1.3.1.0 : abstraction in a water distribution zone :
- Greater than 8 m³/h : Authorisation.
- In other cases : Declaration.
To drill an agricultural irrigation well, you need to submit a dossier to the DDT with the following information :
- Details of the applicant.
- Location of well.
- Technical specifications.
- A letter of request.
- A hydrogeological study.
A hydrogeologist should be contacted to carry out this study to check the impact of the abstraction on water resources and water quality.
Boreholes must be drilled in accordance with good practice, in compliance with the decree of 11 September 2003 on the general requirements applicable to boreholes, boreholes and the creation of wells under the Water Act, the dedicated standard NF X10-999 and the application guide for this decree drawn up by BRGM (Bureau de recherches géologiques et minières).
Rationalising irrigation
Good irrigation management means preserving water resources by combining natural elements with new technologies. There are many tools available to help you manage water efficiently : electronic regulators, probes, decision support tools such as Irré-LIS®, IRRINOV®, etc. But you also need to think carefully about your system to optimise irrigation.
Better irrigation means taking into account 4 elements: water, soil, climate and the plant :
- Knowing more about water means knowing where irrigation water comes from (groundwater or rivers) and its availability (in limited quantities or not).
- Understanding the soil means knowing its capacity to store water.
- Knowing the climate means knowing the site's potential evapotranspiration and rainwater supply.
- Knowing the plant means knowing the needs of each plant and the drought-sensitive phases of the crop. For example, maize has high water requirements around flowering (from 2 weeks before to 3 weeks after).
Irrigating plots of land takes a lot of time, especially monitoring time. Two tools make it easier to control irrigation : GPS and mobile phones. GPS lets you know where the reel or pivot is. Using a mobile phone (or GSM), you can remotely control the pumping station, check the system parameters, check the progress of water turns, etc.
For more information on this subject, please consult the leaflet Irrigation equipment for field crops : how can you save water ? published by the Centre Chamber of Agriculture and Cuma Centre.
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