The thing to remember about this slightly off-putting term is that, strictly speaking, it is an agricultural practice aimed at growing a plant in a media without soil, often more simply called “soil-less” cultivation. It is not new and the earliest practices go back to ancient times: we have all heard of the Hanging Gardens of Babylon ! Moreover it is no accident that the word « hydroponic » has its roots in the Greek language: « hudor, water » and « ponos, labour or effort». In these types of cultivation, which can currently be applied to vegetables (tomatoes, cucumbers, peppers…) or many kinds of commercialised cut flowers, the soil is replaced by an inert pH neutral substrate (rock wool, coconut fibre, peat, pine bark, pozzolana, clay granules…) !
WHY RESORT TO HYDROPONICS OR SOIL-LESS CULTIVATION ? If it was already an attractive proposition in ancient times, it is creating even more interest today, especially if we take into account the difficult equation that mankind will soon have to solve: feeding an increasing world population with the use of fewer resources ! The reason is that this method of forced cultivation (which we will explain in detail a little further on), requires less agricultural land (the crop density is much higher), water (there is less loss through percolation and the water lost can possibly be collected and recycled), nutrients (they are almost all easily absorbed by the plant), plant health products (generally speaking soil-less cultivation goes hand in hand with the protected environment of a closed greenhouse) and even labour (crop density and support systems allow for substantial savings to be made). Some installations allow for crops to be produced by drastically restricting the interferences of the natural environment, because, by way of an example, all liquid waste is often collected for recycling or treatment in situ. The only down side relates to the need for heating if there is a desire to grow forced crops out of season. However, this constraint can be reduced in the case of a crop that is more in harmony with the prevailing climatic conditions WHAT IS THE COMPOSITION OF A TYPICAL SYSTEM ? The first component is the substrate itself. It is chosen for its water retention qualities and pH neutrality vis-à-vis the intended crop. Rock wool placed in bags has dominated the market for some time now, but from now on other neutral products of biological origin, such as coconut husk, are also appearing on the market. Pots containing pozzolana or clay granules are also available (flower crops). These hydroponic growing media are generally placed in rows in order to be able to form squares and make the best use of the available surface area of the closed structure (plastic, glass greenhouse…), the reason being to maximise the light available to the plant while providing protection from the weather (low temperatures, wind…). Therefore, this facilitates the creation of a favourable climate for crop growth (controlling the humidity, temperature and even maintaining a carbon dioxide [CO2] enriched environment). This optimum arrangement will have a very beneficial effect on the crop management conditions (size, upkeep…) and also the harvest (in the majority of cases the crop is raised off the ground and the vegetable can be gathered from a reachable height, with the pickers moving around on a mobile trolley, in an organised, ergonomic and comfortable manner). This allows for costs to be optimised in our regions where labour is expensive and it also enables us to compete with countries where labour prices are low and welfare issues have less recognition (daily working hours, no minimum wage, child labour…). In each bag of substrate there is a self-regulating anti-drain dripper applying an irrigation amount via specific tubing and an adapted stake. Therefore, in such a system where the plant has a minimum buffer volume, micro-irrigation has the capacity to provide water and nutrients at the right time and in the right proportions. The reliability and precision of the system must, therefore, be very high level. NETAFIM was one of the first firms in the world to become involved in this technical growing method. Having developed drip-feed methods since the fifties, for the very reasons that make this growing method so relevant (feeding more people with fewer resources in arid regions), NETAFIM has become a forerunner in developing extremely sophisticated and efficient products. The challenge consisted of ensuring that all the emitters supply the irrigation water at the same flow rate: the idea was to obtain even and controlled growth over the whole surface area. The reason is, obviously, that if the plants at the beginning of the row receive more water than those at the end, then the first ones will end up maturing more quickly, which could result in the producer having to stagger the harvest and spread out the marketing period. NETAFIM very soon solved this problem in the late sixties by developing self-regulating drippers (whatever the pressure in the dripline may be, the flow of each dripper is the same). Producers had the possibility of extending the length of their driplines and building larger area greenhouses, which allowed them to reap the benefits of the economies of scale. Given the low buffer capacity of the substrates, it was also necessary for the producers to increase the number of daily irrigations. By doing this, between two irrigations, draining the pipes of water at the low points (which is always there, in spite of what people say) posed the problem of not having a uniform level of irrigation. The company NETAFIM very quickly resolved these difficulties, by perfecting the Anti-drainage system before its competitors: the emitter orifice only opens during irrigation and closes between the two applications, thus avoiding this unnecessary phenomenon. It is easy to imagine the work involved in assembling such drip feed systems: different crop varieties, different structures, different cultivation techniques… producing a different end product on each occasion… a unique and specific project. NETAFIM very quickly identified this problem and got around it by having a machine-tool in-house capable of manufacturing tailor-made assemblies, customised for each individual client. Type of dripper (model, capacity in litres…), spacing between the drippers (there are as many different requirements as there are different scenarios), type of dripline, lengths of the customised driplines (each greenhouse is unique) and delivery schedule… we can respond flexibly without having to use any subcontractor in order to guarantee quality and delivery date and dealing with any unexpected anomalies. This is a service that is very much appreciated by French and European customers who have been coming to us for more than 25 years… Thus these systems represent a chain where all the links must be under perfect control (for example there is only one window of opportunity lasting a few days for the producer to close one growing campaign and begin another). PLANT ENVIRONMENT CONTROL TOOLS Equipped nowadays with NETAFIM self-regulating anti-drain dripper systems, producers can implement dozens of daily irrigations of varying frequency and duration according to the climatic conditions and season: strong sunshine, increased frequency and duration according to the calculated value. A greenhouse climate management computer continuously monitors the input variables (external sunlight, temperature, humidity…) and reacts quickly to adjust the output variables (precise and appropriate management of the irrigation, and also heating, opening of vents,…). A plant has to be irrigated and kept in an environment that is favourable to its development if optimum growth is to be achieved. One determining factor must not to be forgotten: the application of nutrients required for cell development (mineral salts, trace elements…). The water being used for irrigation is an ideal vector for these substances: applying them directly to the rooting system, which has developed in the hydroponic growing medium with optimum efficiency. The surplus fertilisers are not leached via the streams and waterways towards the sea as often happens with traditional farming methods. It is even possible to apply fewer nutrients since they are absorbed completely. For a number of years, many firms such as NETAFIM have been developing technologies for applying fertilisers in this irrigation water. After years of using the traditional dosing pumps, which were the preferred option for greenhouses in the 70s and 80s, we are now going to see the arrival of technologies known as multi-dosing channel methods (one dedicated channel for each type of fertiliser to be applied and measured out independently of the others, allowing for the limitless creation of fertilisation « recipes », which are very close to the ideal, (fulfilling the plant’s requirements in terns of Nitrogen, Phosphorus and Potassium, which vary according to its growth stage). NETAFIM very soon distinguished itself (early 2000) with the use of the direct action VENTURI injector technology. The fertiliser is introduced continuously into the water in a programmed and proportional manner (e.g.: 0.1 % nitrogen applied with each irrigation dose) and monitored (measuring one of the effects of applying the fertiliser: the variation in the electrical conductivity). A part of this irrigation water recovered through the drainage of the growing media can even be recycled for the next irrigation so as to maximise fertiliser consumption by the crop and thus limit the subsequent leaching of fertilisers into the environment. These are pragmatic, economical and efficient solutions, which help the producer benefit from a perfectly managed irrigation schedule, producing an optimum product with the minimum of resources. SOIL-LESS CULTIVATION: An EFFICIENT AND SUSTAINABLE FORM OF CROP-GROWING? By using « artificial soil », which is free of parasites or diseases, the use of not only plant protection inputs but also water and fertilisers, logically, is greatly reduced. The closed structure of the greenhouse allows for an Integrated Biological Control (IBC) to be exercised, effectively introducing useful insects for the role of combating harmful insects: bumble bees, ladybirds and « specialists ». Thus practically all plant protection products become redundant, and there is no longer the risk of seeing the harmful insects and organisms becoming resistant to increasingly concentrated doses of chemicals… a well-known and dangerous consequence. Through this system of limited soil use and drip irrigation, in merely 30 years the amount of water consumed to produce 1 kg of tomatoes has been halved. We have now reached a rationale of producing more food with the use of far less resources, made necessary by the growth of the world population. Pollution of the groundwater has become almost nonexistent with greenhouse water recycling. A growing method that minimises the impact on the environment while, while at the same time being capable of meeting the needs of the populations, will inevitably comply with the criteria required for sound and sustainable development. CONCLUSION The soilless growing of crops has many advantages: possible traceability and monitoring of the different practices, health and safety at work (less plant protection products and ergonomic processes), efficient soil substrate management, well managed fertiliser applications, crop protection using biological rather then chemical methods, water-saving irrigation methods, properly-managed food hygiene, agricultural waste management and optimised productivity. Although, at the present time, this system is exclusively the domain of the countryside, we can only imagine that it will soon reach the towns and cities, with all the advantages this technique has to offer, principally the need to supply a fresh product as close as possible to where the consumers are located, with minimum transport (and thus a reduction in CO2) and resources (water, fertiliser…). The source of production will be closer to the distribution source: creating a virtuous circle for the future! Many architects are already planning buildings of the future covered in plants, supported by adapted irrigation systems.