Soilless cultivation is an innovative process that was introduced in recent years for protected crops.
This practice has been established for the large-scale production of fresh vegetables and ornamental plants, especially in the countries of Northern Europe, with the main purposes of:
- Increasing production
- Reducing working times
- Reducing the need for water and fertilizers
- Optimizing climatic conditions
The continuous climate changes, the increasing interest in environmental impacts, and the availability of cheap facilities and simple technologies all lead to an increased use of soilless cultivation in commercial applications.
When talking about soilless crops, we’re referring to two types of systems:
- Real hydroponics, without substrate: the root system of a plant is directly in contact with the water and the nutrient solution (floating system, nutrient film technique, aeroponics)
- Hydroponics with substrate: the plant grows on inert, organic materials, or a mixture between them (cultivation bags, slabs, pots or bins)
In these systems, fertigation feeds the plants and involves the use of water-soluble fertilizers. In the most sophisticated and technological systems, the nutrient solution is recycled continuously, thus ensuring maximum efficiency of the water resources used (closed cycle). In the simplest systems, however, especially in those based on the use of the substrate, the drained nutrient solution is dispersed (open cycle).
Advantages and disadvantages of soilless cultivation
Soilless cultivation has numerous advantages like:
- Increasing unit yields and anticipating harvest
- Improving the quality of the final product, such as the size and uniform physical-chemical characteristics of the fruits, due to the controlled and accurate management of nutrition and climatic parameters
- Using easily replaceable structures in case of reconversion
- Reducing the labor for demanding processing operations, such as tillage and soil disinfection
- Reducing water consumption, especially in plants managed in a closed cycle in areas with limited water availability
- Reducing the use of pesticides and adopting integrated pest management strategies more easily
Although the advantages can be very encouraging in the decision to adopt these systems, it is also necessary to consider the disadvantages and difficulties that must be faced:
- Insufficient know-how to understand how to manage fertigation, irrigation, crop care and automatic control unit technology
- Need for constant monitoring of various parameters, such as EC, pH, nutrient solution recipe and climate
- Greater risk of incurring water or saline stress in case of a blackout, which renders the whole system unusable
- Medium-high initial investments
- Difficulty in reaching potential productions in the first years, due to facilities management problems
- Difficulty in disposing of inorganic substrates at the end of use
- Dispersion of the exhausted nutrient solution in the surface layers when using open-cycle systems
When you decide to cultivate with a soilless system, you need to choose the ideal system type depending on the place where you intend to work, the plant species, the size, and the budget available.
The floating system is generally suitable for the cultivation of leafy vegetables. The plants are placed on floating panels and the roots are immersed in the nutrient solution. It is a simple system, as the realization is rather cheap, and the short crop cycle of leafy vegetables does not require the constant reintegration of the nutrient solution.
Oxygenation is the only parameter to be carefully checked: it must be guaranteed with the installation of a pump and periodically checked to ensure its concentration is between 5 and 7 mg/L (or parts per million). Furthermore, even with a blackout, the plants would survive.
1: Floating system scheme. Source: Agricultural Research & Technology: Open Access Journal
The NFT system is more versatile and can accommodate different plant species, from salads and strawberries to larger plants, since it’s possible to vary the size of the channels, the distance between the holes and the arrangement in space, which can also be vertical.
These systems are composed of perforated channels, within which a thin layer (film) of nutrient solution feeds the plants and continuously flows. A storage tank collects the nutrient solution and a pump ensures continuous recirculation in the system. In this case, the pump should always work well and power outages must be avoided to ensure the efficiency of the system.
In the absence of the recirculating nutrient solution, the plants could survive for just a few hours.
The distribution of the nutrient solution can be continuous or intermittent: in the latter case, the electricity consumption is reduced and greater ventilation is favored, but the roots could suffer from thermal shocks and excessive salinity. Being a closed cycle, periodic checks and reintegrations of the nutrient solution are necessary.
2: NFT system scheme. Source: Agricultural Research & Technology: Open Access Journal
3: NFT system example. Source: Growilla Hydroponic
In systems that involve the use of pots and the substrate, the nutrient solution is provided by a drip irrigation system. The inert materials used as a substrate have a good drainage capacity, which guarantees the air circulation and, therefore, oxygen.
On the other hand, organic materials ensure the buffering capacity, limiting radical changes in pH at the root system level, due to incorrect management of the nutrient solution. The advantage of using the pots is varying the distance between them, moving them from one place to another and distributing them on different floors.
However, the irrigation system requires special attention: periodic maintenance and disinfection are necessary to avoid the occlusion of the drippers.
4: Soilless system with pots for grape cultivation. Source: Manisa Viticulture Research Institute
5: Soilless system with pots for tomato cultivation. Source: NPK Technology
The cultivation on slabs allows growers to improve production in a very limited space. In the USA, peat is the most used and requested material, as it has a good water retention capacity, good physical and chemical characteristics, low nutrient content and it is cheap. However, coir is also an excellent organic material that can replace peat.
The advantage of growing in bags is reusing the same material for 2-3 production cycles, after disinfection, as well as guaranteeing good buffering capacity and good water retention.
The number of plants to be placed per bag depends on the selected species: a high density leads to competition between the roots of the plants, causing stunted development and, therefore, a lower final yield. On the other hand, choosing a low density could be counterproductive and not guarantee to obtain the best from the productive potential. Furthermore, also, in this case, it is essential to periodically check the drippers to avoid any occlusion and the EC and pH values of the nutrient solution.
6: Tomato cultivation in peat bags. Source: Soilless Culture - Use of Substrates for the Production of Quality Horticultural Crops
7: Strawberry cultivation in coir bags. Source: Colture protette.
The irrigation plan management is equally important so that water imbalances do not occur: ideal irrigation must return a drainage water volume of around 30% of the volume applied.
Values lower than this percentage cause saline stress and difficulties in the absorption of nutrients, while higher values cause water stagnation and nutrients leaching.
Practical tips for optimal management of soilless cultivation
Regardless of the type of cultivation system, some operations must be carried out for appropriate and efficient cultivation management.
The main periodical or daily activities are:
- Monitoring the pH and EC in the nutrient solution (Inlet, outlet and on the drained one)
- Monitoring the applied and drained irrigation volumes (make sure that the drainage is 30% of the volume applied)
- Monitoring the temperature, humidity and solar radiation
- Checking the occlusion status and the correct positioning of the drippers (they must not be too far from the root zone)
- Monitoring oxygenation level in the nutrient solution, in the case of the floating system
- Monitoring periodic plants health (physiological alterations, pests or fungal attacks)
- Wearing protective suits and shoe covers. It avoids bringing from the outside pathogens that can infest or damage crops.
- Disinfecting the slabs, bags and drippers with a suitable solution, after each crop cycle
- Integrating and varying the nutrient solution for each phenological phase
To ensure optimal management, it is advisable to have sensors that continuously monitor environmental parameters and irrigations. The data recorded by the sensors must be easily accessible from the computer or even from the phone, so it is possible to intervene immediately, if there are warnings or even just to keep the cultivation under control.
The main sensors that must be present are:
- Air temperature sensor
- Relative air humidity sensor
- PAR sensor
- CO2 sensor
- Inlet and outlet flow meters
- Possible IWET probe for substrate water content
- EC and pH probe for management of inlet and outlet nutrient solution
- Portable EC and pH probe to evaluate the nutrient solution coming out of the dripper