With climate change, the farmers are having to deal with an increase in extreme weather events, such as periods of drought occurring earlier in the year and for longer periods, hail, frosts, violent storm and heat stress. With so many weather events. we must look for ways of mitigating their effects on the productions.

Among the factors influenced by this climate change, water stands out in particular. Even though the total amount of water available each year hardly changes, distribution is the problem. However, water plays a vital role in agricultural production, particularly in citrus growing. To mitigate these effects, the farmers have a number of tools available. Among these, precision irrigation is particularly significant. It is not so much a solution but rather a powerful tool to help the agricultural industry cope with these new challenges and become more resilient. The same applies to the citrus fruit sector, where irrigation has now become an essential production tool.

At the same time there is increased pressure on the “water” resource. So how can we conserve this recourse while ensuring the security of food production? The challenge facing precision irrigation is to deliver the water to “precisely the right place” and “at the right time”. Precision irrigation, which includes drip irrigation systems (above or below ground) and micro-sprinkling, is the most effective system with respectively 90% and 80% efficiency. In the case of subsurface drip irrigation, the efficiency is almost 100%.

The “soil x plant” relationship: “In the right place”

In our endeavour to achieve irrigation efficiency, there is one essential prerequisite, which is that we must have an understanding of the soil and the distribution of the roots. It is important, if not essential, to take your soil into consideration, if your irrigation project is to be successful. And this applies no matter what irrigation system you have chosen. Above all, it is important to know the following components of your soil:

• Texture (percentage of clay, silt and sand) with the soil texture triangle
• Depth
• Structure

Do not be content with a 2D observation of your soil. Look at what lies below it. This is particularly important when expecting any hydromorphic zones to appear, for example. For subsurface drip irrigation, you need to know your soil in order to choose the proper device and manage the orchard correctly.

Once we understand the soil, then we must also determine the root distribution of our crop. For citrus fruits, the active roots (or rootlets) are concentrated within the first 60 cm of soil. This is the area that we intend to cover with our irrigation.

Understanding this “soil-plant” relationship is essential for deciding upon the most efficient irrigation system. It will also provide us with the keys for scheduling our irrigation in the future. Therefore, to ensure that the amounts applied are “actually” absorbed by the roots, then the optimal soil conditions must be maintained with a proper water/oxygen balance, which is not only indispensable for allowing the roots to breathe, but also for having an active soil life. Maintaining this balance will permit maximum assimilation of the water and nutrients. It is from this perspective that low flow drippers have been developed (1.6 l/h, 1 l/h or even lower). The general idea behind this concept is entirely agronomic by stimulating the distribution of the water in the soil while maintaining optimum conditions for absorption and soil structure.

Root suffocation is undesirable for any crop and even more so for citrus fruits, where it can lead to the development of fungal diseases (such as Phytophthora) and root rot.

With this knowledge, as well as an understanding of the producer’s crop husbandry practices and the availability of the water resource, it will be possible to determine the most suitable irrigation system.

For a drip irrigation system, this allows the user to determine the spacing between the drippers as well as their flow rate to obtain a uniform and continuous distribution along the entire length of the dripline.

  Fulfilling the plant’s needs = “at the right time”

Once the system has been chosen, it will have to be managed correctly so as to fulfil the crop’s requirements precisely. The citrus fruit’s crop and nutrient requirements differ in the course of its phenological cycle. That is the advantage of micro-irrigation, which is able to meet the demands at the opportune moment and thus maximise the agronomic benefits of the system.

For citrus fruits, water forms a key part of their production, both in terms of quantity and quality (size, acidity, sugar content, etc.). Generally-speaking, the citrus fruit orchards are kept in a state of optimum humidity, i.e. with no excess or constraints. This optimum management pattern is particularly important during the flower induction, flowering and fruit set stages. This also applies to the rest of the cycle.

As water is an improtant vehicle for carrying nutrients, we use the precision irrigation system to apply nutrients to the crop at the exact moment when they are required, which is called fertigation. 

This practice can help to avoid leaching of the nutrients (particularly nitrates) and to apply the nutrients according to the plant’s uptake rate.

With drip irrigation, we are targetting the root system in a more precise manner resulting in a more efficient application of the nutrients, particularly for non-mobile elements in the soil, such as Phosphorous and Potassium. This is particularly true with subsurface drip irrigation where the drippers are located “right at the heart” of the rooting system.

Precision irrigation for citrus fruits

What are the choices for irrigating a citrus fruit orchard efficiently? There are two main types of precision irrigation systems:

• Micro-sprinklers
• Drip irrigation, which can be above ground or subsurface.

The choice of system is determined by the specific features of the project: water resource (availability, analysis), cultivation practices (tillage of the soil, harvest,weeds, environmental approach, etc.) and the wishes of the producer. Whatever the system chosen, it will be a self-regulating system allowing for the water to be distributed evenly and optimally at every point of your orchard. This is particularly important for perrenial crops in order to achieve a uniform production, whatever the characteristics of the field (topography, shape).

In micro-sprinkling, you have the choice of a system laid on the ground or suspended above ground. Although it is less efficient than drip irrigation, around 80%, a larger soil surface can be irrigated with micro-sprinkling and it is compatible with fertigation. Depending on the type of water, soil and operating constraints, this system could be the most suitable for a citrus orchard. The main disadvantages are: weed management and creating obstrucions in the field during harvest.

Another option is drip irrigation, to which the citrus orchards respond very well. A large part of the surface area of irrigated citrus fruits in the world are irrigated with this system. With maximum application efficency, this system has the advantage of applying the water as close as possible to the root system.

With this system you need to anticipate when to start irrigation (do not allow the soil to dry out too much) and divide up the amounts of water applied. The other advantages are:

• Less weeds
• Less fungal diseases

For the citrus fruit orchards, there are always drip irrigation lines on both sides of the row in order to balance the tree’s supply, maximise the root volume and respond to the crop’s needs. In practice, 2⁄3 of the height of the foliage is available. Even though this can depend on the variety, generally speaking the lines are positioned between 0.8 and 1 m from the trunk.

The subsurface drip irrigation system is commonly regarded as being the most efficient of the irrigation systems with an efficiency close to 100%. To ensure the longevity of this system, and thus its effciency, the drippers used are equipped with innovative anti-syphon and anti-root intrusion technologies (root barrier, dripper impregnated with iron oxide, etc.). A subsurface irrigation system meets the most demanding technical and agronomic requirements to ensure the system’s longevity and efficiency.

This type of system can just as easily be installed on mature orchards (under certain conditions) as young plantations. Young seedlings are left on the surface for the first 2⁄3 years before burying the lines, whenever possible. The aim is to encourage the young trees’ roots to develop before postioning the lines. They are buried at a maximum depth of 30 cm. However, depending on the “soil-plant” relationship, they can be buried at a shalllower depth.

Whatever the precision irrigation system, the hydraulic design, installation and maintenance are key factors conributing towards its longevity and efficiency. For a project to be efficient, the greater the need for paiyng special attention to the preliminary study, installation and maintenance.

Conclusion

As far as citrus trees are concerned, there is no simple option. Each solution responds to the agronomic, technical and operational demands that are specific to each project. That is why it is so important to take the time to prepare the preliminary study and follow the manufacturer’s recommendations with regard to the installation and maintenance of the system. Technology represents the path to the success of your project.

Going even further in the research to find greater efficiency and ways of scheduling the irrigation system more effectievly and sustainably, we have seen the development of digital tools. We are standing on the threshold of a digital revolution aimed at helping the farmers to achieve their production objectives while preserving the resources and the environment.    

Author : Netafim