When it comes to hydroponic crop production, plants may be grown in water culture systems or substrate or aggregate systems. This article will focus on the most common types of water culture systems and what should be considered when choosing a system. Future articles will follow, focusing on water quality, root zone and nutrient solution management, common issues in water culture systems, and more. In commercial operations, water culture systems are almost exclusively used for leafy green production. Large scale commercial water culture systems often do not offer labour access to plants, which is necessary for long term fruiting crops. While leafy greens may be seeded, transplanted, and then allowed to grow until harvest, long term fruiting crops (i.e. tomato, cucumber, pepper) must be maintained as they grow (leaf pruning, harvesting, etc.) to maximize yields. However, for hobby and home growers water culture systems are much smaller and access to plants is usually not limited, making these types of systems a very productive, affordable, and relatively simple hydroponic system for home growers looking to grow just about anything.
Healthy spinach roots growing in a water culture system. Tomatoes growing in a substrate (aggregate) system.
WATER CULTURE SYSTEMS
Nutrient Film/Flow Technique (NFT)
Nutrient film technique is among the most popular hydroponic systems for both commercial operations and hobby growers. Nutrient film technique consists of a reservoir of nutrient solution, a gutter like a trough where plants are located, and a pump that supplies nutrient solution to the trough and plant roots. The excess nutrient solution is then recirculated to the reservoir. High technology commercial operations will sometimes disinfect nutrient solution before recirculating to plants in order to decrease disease pressure.
NFT is an active system, meaning that some type of water pump is pumping nutrient solution to plants. The fact that NFT is an active system is something that should be considered when choosing a growing system, a chance of failure is increased with an active hydroponic system due to pump failure. However, NFT systems typically require less volume of nutrient solution than other systems and are therefore lighter in weight, making them favourable for rooftops and locations where weight is a concern. In commercial operations, NFT systems are primarily used for leafy green production, as large root systems of fruiting crops tend clog gutters and emitters. In most cases, dissolved oxygen is maintained at adequate levels due to the consistent circulation of nutrient solution, so aeration may not be necessary. However, it cannot hurt to add additional aeration to ensure sufficient dissolved oxygen levels in nutrient solution.
Lettuce growing in NFT gutter. Source: https://www.maximumyield.com/advantages-of-nft-hydroponic-systems/2/3892
Deep Water Culture (DWC)
Deep water culture is sometimes referred to as deep flow technology, a pond system, or a raft system, but they all referred to the same type of system that consists of a large volume of nutrient solution with some type of raft that anchors plants and allows roots to grow into the large volume of solution and uptake nutrients and water. Deep water culture is usually a passive system, meaning that a pump is ordinarily not used to supply nutrient solution to plants. However, depending on the volume of nutrient solution, aeration is usually required to maintain dissolved oxygen at appropriate levels for optimum growth. The fact, that this is a passive system, decreases its chance of failure, making this a very simple, stress-free, and popular system for both commercial and home growers. It is important for growers to ensure that material being used as the reservoir of nutrient is dark enough, so light does not penetrate and induce algae growth. It is equally important that the reservoir material is strong enough to hold the desired volume of nutrient solution without bowing or leaking when filled.
Ebb and Flow
Ebb and flow systems are not as popular as NFT or DWC in commercial leafy green production, however, it is still used and can be an effective system when employed correctly. Ebb and flow systems are active systems that consist of a nutrient solution reservoir, a planting area, and a pump that floods the planting area with a nutrient solution. This nutrient solution is then drained from planting area and is either discarded or recirculated to the reservoir. Like NFT, in high tech operations, recirculated nutrient solution may be treated with ultraviolet light or some other disinfectant system. In many cases, ebb and flow tables are used as the planting area with this type of system. These tables are built for this type of system and allow to be flooded and then drained quite easily and efficiently.
Potted lettuce being grown on ebb and flow tables
Aeroponics is an active system where plants are anchored to some sort of board and roots are suspended in air and supplied nutrient solution in form of mist rather than liquid. Because roots are suspended in the air, they are exposed to very high amounts of oxygen, which can lead to increased plant vigour and yields and decreased disease pressure. However, the chance of failure can be increased as precipitation of fertilizer salts often leads to nutrient solution emitters becoming clogged. Commercially, aeroponics is not utilized as often as NFT, DWC, or ebb and flow, but there are large commercial operations using this system for leafy greens, root and tuber crops, and medicinal crops
Aeroponics - https://www.igrow.news/news/how-does-aeroponics-work
Undercurrent systems are an active system that can be thought of as a recirculating deep-water culture system. In this type of system, plants are typically grown in a grow basket placed in a bucket filled with nutrient solution. Multiple buckets are connected via PVC plumbing and nutrient solution is recirculated between buckets. Circulation of nutrient solution provides constant dissolved oxygen to the root system, which can decrease disease pressure and increase yields. A benefit of using this type of active system is that the reservoir of nutrient solution in this system is often large enough to buffer against failure. If a pump fails and recirculating ceases, plant roots will typically still access to a sufficient volume of nutrient solution (assuming reservoir is filled), as opposed to an NFT system that only has access to a film of the solution if recirculation ceases.