Choosing the Right Cultivation Systems in Aquaponics or Hydroponics
In aquaponics as in hydroponics, different cultivation systems can be implemented to grow plants. A cultivation system is characterized by a technique of irrigation and a typical growing medium (with or without substrate). They differ from each other by specific features that make them more or less suitable for the varieties of plants grown, the cultivation practices (hydroponics or aquaponics), and the environmental conditions of the environment. Let’s explore these different approaches together.
Soilless cultivation techniques
Nutrient Film Technique (NFT)
This technique is based on the continuous flow of a thin film of water loaded with nutrients over the roots of the plants. The nutrient solution (fish water in aquaponics or mineral nutrient solutions in hydroponics) flows at the bottom of perforated gutters (standard diameters from 32 to 50 mm) to accommodate young plants, inclined to ensure gravity-driven water flow, on a slope of 1% to 3% between the inlet and outlet of the nutrient solution.
Advantages
- This technique allows roots to absorb nutrients and water efficiently while maintaining a good supply of oxygen, essential for healthy plant development thanks to roots simultaneously submerged and exposed.
- This technique is particularly suited to fast-growing plants, such as leafy plants (lettuces, herbs, cabbages, etc.), with relatively low water and nutrient needs compared to plants with more extensive root development.
- It is a low-cost system to set up, simple to assemble, lightweight and easy to maintain. It optimizes transplanting, harvesting, and cleaning times compared to a raft system.
- This system can be easily adapted into sliding tables to saturate a production area and increase the number of plants per m², but beware of labor time if this sliding NFT system is not automated. Sliding NFT systems are among the most efficient technologies for leafy plant cultivation, widely used in the United States for over a decade.
- NFTs can be supplied with continuous or intermittent flow to save some energy. The advantage in aquaponics of coupling NFT systems is to have a minimal filtered flow continuously used by the plants grown.
Disadvantages
- Excessive root growth can clog the gutters and limit the proper flow of the nutrient solution, which will then flood the roots and reduce oxygenation.
- Using this technique for plants with long growth cycles (fruit plants or production cycles longer than 2 months) is therefore not recommended.
- A power outage of a few hours or even a few tens of minutes during the day can cause root drying and thus total crop loss.
- The water temperature is very important in soilless cultivation systems and must be maintained optimally between 15 and 25°C. However, NFT gutters act as large heat exchangers, so double-wall systems should be prioritized in hot or very cold regions. Also, limiting the length of each gutter to 15 m max in temperate climates and 8 m max in tropical climates will reduce the impact of ambient temperature and ensure homogeneous distribution of nutrients and oxygen from the inlet to the outlet of the gutter, otherwise growth heterogeneity on the same gutter may occur (which will degrade your rotations and yields).
- It is necessary to supply filtered water with a maximum of 200 µm and to ensure regular maintenance of the network. Since the system has many capillaries, the development of biofilm and/or significant accumulation of organic matter can quickly hinder the flow of the nutrient solution.
Deep Water Culture (DWC) and RAFTS
Often referred to as "Raft", due to the widespread use of floating growing media (various plastics are used) in commercial hydroponic or aquaponic plant production systems, deep water culture is a system where plant roots are submerged in a nutrient solution often aerated. It consists of a reservoir in which a nutrient solution circulates and air diffusers; this is called active aeration.
Advantages
- Like the nutrient film technique (NFT), deep water culture allows plant roots, directly in contact with the nutrient solution, to easily absorb oxygen (provided the rafts are well elevated above the water level) and nutrients present in the water.
- Easy to set up and inexpensive, this cultivation technique allows efficient production of large quantities of leafy plants. Benefiting from a large immersion volume, it also allows the cultivation of fruit and vegetable plants with longer cycles and thus more developed root systems.
- The thermal inertia of the nutrient solution, more or less significant depending on the depth of the reservoir used, prevents rapid temperature rises or drops. The large volume of water in DWC systems provides thermal and nutritional inertia and thus facilitates the control of these parameters. Although inertia is a major advantage of DWC systems, it is also one of their main disadvantages.
Disadvantages
- Deep water culture requires permanent aeration or intense circulation of the nutrient solution and thus the use of aerators or pumps that may consume significant electricity compared to NFT systems, and in case of prolonged failure, root necrosis can quickly occur.
- Since plant roots are permanently submerged in water, it is necessary to regularly monitor the temperature of the nutrient solution to avoid stressing the plants and slowing their growth.
- Maintenance of these systems is complex because they act as large settling tanks accumulating all particles and debris. Therefore, sanitary drains must be performed, as with all other cultivation systems, requiring thorough cleaning of the DWC bottoms and a large amount of fresh water to restart production. A nutritional collapse is often observed after each sanitary drain, causing deficiencies or requiring significant nutrient supplementation.
- Cultivation stages are often longer than in NFT systems, due to raft plate handling, cleaning (which should be automated quickly via a raft washing machine), and transfers. Plan for DWC systems at human height (about 80 cm to 1 m), even if this costs more for the supporting structure, as it will save labor time and greatly improve employee comfort.
- As with NFTs, ensure to use food-grade certified materials to prevent any release of chemical molecules or microparticles into your system, as DWC and RAFT systems are very risky in this regard if early tool deterioration occurs.
Dynamic Root Floating Technique (DRFT)
This technique is similar to RAFT deep water culture since it also uses floating rafts as growing media. However, it uses a thin water layer (maximum 5 cm), which still allows significant root development (because the available surface remains large) but uses a much smaller water volume that can be more easily moved or renewed intermittently; this is called passive aeration.
Advantages
This system combines the advantages of NFT and RAFT cultivation systems.
- The cultivated plants can survive several hours in case of power failure.
- The system also benefits from good thermal inertia, as the water is insulated within the structure often made of XPS panels and covered by the rafts. Thermal regulation of this water volume is easier than in a DWC system since the volume is much smaller (5 to 10 times less than in DWC).
- Adjustments of nutrient solution parameters can be more finely controlled and sanitary drains can be performed more regularly.
Disadvantages
- A precise water level adjustment is necessary to ensure good circulation of the air layer located between the plant base and the submerged part of the roots.
- System cleaning, as with DWC, remains a heavy but necessary step, although sedimentation is lower. Water volumes being much smaller than those used in deep water culture systems, filling is faster and less prone to nutritional collapse.
Cultivation techniques with substrate
"Soilless cultivation" does not necessarily mean without substrate. If plant roots, in hydroponics or aquaponics, absorb nutrients that ensure their growth directly from the nutrient solution with which they are irrigated, an organic or inorganic substrate can be used as a base for root system anchorage throughout growth. There are different types of substrates used in hydroponics and aquaponics. The most popular, expanded clay pellets, coconut fiber, rockwool, or perlite, each have advantages and disadvantages related to their capacity for water and nutrient retention, drainage, pH stability, or environmental impact.
They must also be adapted to the cultivation techniques used. Coconut fiber, for example, with its high water retention capacity, is particularly suited to drip irrigation, whereas clay pellets, which are more draining, are preferred for submerged cultures with "flood table" systems.
Flood table systems (Flux-Reflux – Ebb & flow)
Flood tables operate on a cycle of filling and draining a growing tray filled with substrate (clay pellets, gravel, perlite, etc.) or a tray where plants are placed in individual pots or trays (notably for seedlings), also filled with substrate. This system is inspired by the natural movement of tides, hence its name.
The system works by automatic filling and controlled draining. At regular intervals, a pump sends nutrient-enriched water to the table. The water gradually floods the growing substrate, submerging the plant roots. Once the water level is reached (usually a few centimeters above the substrate), the water drains, allowing oxygen to reach the roots. The tide cycle lasts from a few minutes to a few hours depending on the system. This process can be repeated several times a day.
Advantages
- The filling and draining cycle allows alternation between irrigation and oxygenation, which is beneficial for roots. Air entering the substrate when drained promotes healthy root growth.
- Flood tables can be sliding to optimize the number of plants per m².
- Management of irrigation and nutrients is often very simplified.
Disadvantages
- In case of malfunction of the siphon system or pumping, excessive water level fluctuations can harm root health due to under- or over-irrigation.
- Using flood tables filled with substrate allows a wide variety of crops but will accumulate organic matter and become an uncontrolled reservoir in the short or medium term, requiring heavy cleaning and sanitary draining. Therefore, this tool should be favored for seedling trays or potted cultures.
Drip system
The drip system relies on a network of pipes and capillaries to deliver the nutrient solution, from a fertigation tank or directly from an aquaculture fish tank, to plants grown in substrate blocks (coconut fiber, peat, bark, rockwool, etc.) or pots (clay pellets, pumice, coconut, etc.).
Drippers are installed at each block or pot. These drippers are connected to a flow regulator often ranging from 2 to 4 L/h. The volume delivered per dripper depends on pump running time and must be carefully adjusted according to substrate type, crops, and development stage. It must be corrected based on measured drainage rate. The drained nutrient solution can be recovered, filtered, and reinjected into the irrigation network, called a closed system, as opposed to an open system where excess water is not recovered. In a closed system, substrate blocks are placed in collecting gutters where excess nutrient solution flows by gravity.
Advantages
- Water and nutrients are delivered with precision directly to the roots, reducing losses.
- This irrigation technique suits almost all crops.
- Blocks or pots are easy to set up and remove in case of sanitary drain or contamination (be careful to separate drained solution from the growing substrate).
- Roots develop easily in the substrate allowing long cultivation cycles, provided the physico-chemical properties of the substrate meet plant needs.
- Organic substrates are reusable for other uses (flower strips, fruit trees, etc.).
Disadvantages
- Irrigation management must be precise to avoid over- or under-irrigation which can quickly damage the crop and negatively impact an entire growing season. It must be adjusted according to daily climate, substrate moisture, drainage rate, crop stage, and obviously the type of substrate used.
- Stakes connected to capillaries must be equipped with anti-clogging systems, although this does not prevent close monitoring. Water must be filtered at 130 µm and strong network prophylaxis ensured with regular purging.
- Drippers can clog due to mineral deposits, algae, or fine particles, especially in aquaponic systems where water contains fish waste and microorganisms. Water distribution may be uneven if the system is poorly designed or drippers have inconsistent flow rates. This can cause differences in plant growth. The substrate must retain water but also allow good root aeration.
- Planting time can be significant if perforations are not adapted. Drainage slots must match your growing media to facilitate drainage flow which must be light-proof (otherwise algae will develop).
Sprinkling
Sprinkler irrigation consists of spraying a nutrient solution (in hydroponics) or fish water (in aquaponics) as fine droplets onto plants (notably for orchid cultivation) or their root system (aeroponics). This method uses sprinklers or nozzles to distribute water evenly.
Advantages
- Sprinkler irrigation allows uniform distribution of water and nutrients, ensuring each plant or root system receives necessary inputs evenly.
- It offers excellent root oxygenation, promoting healthy plant growth, especially in aeroponics.
- It can be used both for irrigation and for thermal regulation (fogging) or to apply treatments or boosters.
Disadvantages
- The system requires significant filtration upstream of the sprinkling network, as nozzles can clog due to particles or mineral deposits, especially in aquaponics.
- Sprinklers require a minimum operating pressure: low or high pressure systems, which can result in sometimes significant electricity consumption.
- In case of system failure or pump malfunction, roots can quickly dry out, causing water stress for plants.
- It may be less suitable for dense leafy crops, where sprinkling does not effectively reach roots or substrate.
Summary
| System | Principle | Suitable plant types | |
|---|---|---|---|
| Without substrate | NFT (Nutrient Film Technique) | Thin film of nutrient solution continuously flowing over roots. | Leafy vegetables, short-cycle aromatic plants (max. 2 months) |
| DWC (Deep Water Culture) | Roots permanently submerged in a large water layer (> 20 cm) | Leafy vegetables, aromatic plants | |
| DRFT (Dynamic Root Floating Technique) | Combination of raft system and thin water layer (< 5 cm) | Leafy vegetables, aromatic plants | |
| With substrate | Flood tables | Periodic flooding and draining of growing tables filled with substrate or potted/tray cultures (seedlings) | Seedlings, flowering plants, potted herbs, fruit plants |
| Drip irrigation | Precise drip delivery of nutrient solution at plant base | Fruit plants (tomatoes, strawberries), flowers, root plants | |
| With substrate or bare roots | Sprinkling and aeroponics | Spraying fine droplets on roots or substrate | Aromatic herbs, young plants, aerial root plants |
