Deep water culture
Deep water culture (DWC) is a hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Bubbleponics is a related method of plant production that involves a top-fed deep water culture system.
Traditional methods favor the use of plastic buckets with the plant contained in a net pot suspended from the center of the lid and the roots suspended in the nutrient solution. An air pump powered aquarium airstone oxygenates the nutrient solution; if sufficiently oxygenated, the plant roots can remain submerged indefinitely. Once the plants are ready to flower, the level of the nutrient solution is gradually reduced to expose the roots to the air.
Plants absorb vastly more oxygen directly from the air than from the oxygen dissolved in water. Deep water culture allows plant roots to absorb large quantities of oxygen while also allowing the uptake of nutrients. This leads to rapid growth throughout the life of the plant.
Recirculation deep water culture
Recirculating direct water culture systems (also known as RDWC) use a reservoir to provide water for multiple buckets. Traditional methods using unconnected buckets require individual testing for pH and conductivity factor (CF). This has led to innovations that have seen the removal of air stones in favor of connecting multiple buckets together and recirculating the water. As the water is reintroduced to the bucket it is broken up and aerated with the use of spray nozzles. Constant recirculating oxygenates the water and ensures a good mix of nutrients CF and stabilizes pH throughout the entire system so testing is required only at one point, which would be at the 'Tub' like reservoir. The deep water culture system requires adequate water + oxygen nourishing solution.
The solution is oxygenated (possibly near, or equal to, oxygen saturation) from an air pump combined with porous stones. With this method the plants may grow faster because of higher amounts of oxygen that the roots receive, versus other forms of deep water culture.
The term "Bubbleponics" describes a top-fed deep water culture hydroponic system. Basically, the water is pumped from the reservoir up to the top of the roots (top feeding). The water is released over the plant's roots and then runs back into the reservoir below in a constantly recirculating system. As with traditional deep water culture, there is an airstone in the reservoir to help add oxygen to the water. Both the airstone and the water pump run 24 hours a day.
The biggest advantages with Bubbleponics over deep water culture involve increased growth during the first few weeks. With deep water culture, there is a time where the roots haven't reached the water yet. With Bubbleponics, the roots get easy access to water from the beginning and will grow to the reservoir below much more quickly than with a deep water culture system. Once the roots have reached the reservoir below, there is not a huge advantage with Bubbleponics over deep water culture. However, due to the quicker growth in the beginning, a few weeks of grow time can be shaved off.
DWC hydroponic system usage
It is advisable to start this type of indoor cultivation with cubes of rock wool. Once the seeds are germinated in cubes of rock wool, put them into the DWC baskets previously filled with expanded clay pellets. Fill the DWC system with water and fertilizers that are hydroponic specific up to the level of the solution in contact with the base of baskets.
In this way, the clay will be in contact with the solution that will be absorbed by the plants roots. Soon the plant will develop a large root system that will naturally immerse in the nutrient solution. It will not be necessary to maintain the level of nutrient solution to the same level of the base of the baskets, but results will come with a lower level. It is recommended replacing the nutrient solution approximately once a week and wash the container / tank with hot water to remove any algae, mold and salt deposits. Every time you fill the tank, measure the pH of the solution and ensure that its appropriate for the plant and growth phase. Revise with the pH indicator. Constantly monitor the pH. The well-oxygenated and enlightened environment promotes the development of algae. It is therefore necessary to wrap the tank with black film obscuring all light.
Ebb and flow
Ebb and flow (also called ebb and flood and flood drain) are two phases of the tide or any similar movement of water. The ebb is the outgoing phase, when the tide drains away from the shore; and the flow is the incoming phase when water rises again. The terms are also common in figurative use.
Ebb and Flow is a form of hydroponics that is known for its simplicity, reliability of operation and low initial investment cost. Pots are filled with an inert medium which does not function like soil or contribute nutrition to the plants but which anchors the roots and functions as a temporary reserve of water and solvent mineral nutrients. The hydroponic solution alternately floods the system and is allowed to ebb away.
Under this system a water-tight growing bed, containing either clean gravel or coarse sand as the rooting medium, is periodically flooded for a short period (5 to 10 minutes) with a nutrient solution pumped from a supply tank. By placing the nutrient solution supply tank below the growing bed, the nutrient solution can drain back by gravity. This hydroponic growing system is little used today other than for hobby-type systems. The method is inefficient in its use of water and plant nutrient reagents. Root disease occurrence and nutrient element insufficiencies can occur with repeated use of the nutrient solution. Because it is a "closed” system, the re-circulated nutrient solution will require reconstitution, filtering, and sterilization. Within the growing period, the nutrient solution may require replacement. The rooting medium will require washing to remove root debris and accumulated precipitates as well as sterilization before reuse.
Principles of operation
The fundamental principle of hydroponics relies on fertilized and aerated water which provides both nutrition and oxygen to a plant's root zone. It often involves relatively sophisticated mechanization processes which can be daunting to casual hobbyists. Nutrient solutions must usually be below the temperature at which pathogen growth can begin, yet not so cool that root activity is suppressed. Active aeration of the fertilizer solution is common, since root systems themselves remove oxygen, creating conditions which also can promote pathogenic bacteria and water-borne molds.
E&F utilizes the fact that the solution is not left in constant contact with the roots of plants, to avoid the need for oxygenating or chilling of the solution. Instead it relies on characteristics of root function to provide passive oxygenation at a high level which tends to suppress pathogen growth.
Simplicity is maintained through usage of a single, two-directional path for the solution. Water flows in and out using the same tube. When the pump has raised water into the tray, briefly submerging the roots, the pump is rendered inactive using a switch, typically a timer, and the water flows back down the same tube. This eliminates the need for more than one sealed fitting and reduces overall complexity of the system.
Ebb and flow systems come on according to the water-holding capacity of the medium in which the roots sit. Highly water-retentive media can require watering only once a day, while others require two to as many as six floodings, with each "flood" stage only lasting a few minutes. The time it takes to flood the roots is not a critical parameter, which means that pumps are often moderate in capacity and can be small for systems sustaining indoor plants. This makes the method popular with amateur and urban gardeners. Gravity acts as drain pump, and aeration is accomplished through thin-filming and positive displacement of air as it is forced out of the root zone by water.
Aeration in ebb and flood systems
Aeration of an ebb and flood system is an important aspect of its operation. Automatic displacement eliminates air which has been de-oxygenated by the roots as the water rises to its highest flood stage. When the pump turns off, gravity pulls the water downwards, which re-exposes the space around the roots to the air.
The film of water left around the roots during ebb has a high surface-to-mass ratio, which means that even as the roots absorb oxygen, its high surface area facilitates re-oxygenation, which can sustain the roots as long as their surfaces remain damp. The high oxygen content of water filmed in this way suppresses most harmful lifeforms, keeping the root zones disease free. In other types of hydroponics this function must be performed by cooling the solution to protect it from pythium, a form of water mold responsible for a condition called 'root rot', in which the outer cells of the roots die, turn brown and slough off when handled. Need for supplementary oxygenation using air pumps is also eliminated, which increases reliability and reduces complexity.
Ebb and flow hydroponic systems are also quiet, while using less power than other hydroponic systems, which means that they can be used in environments where acoustic signature and excessive plumbing is objectionable, such as residential or classroom applications where space is at a premium.
Drawbacks to E&F systems
Ebb and flow systems are flexible, with few practical drawbacks. Though typically known for compact cultivation of plants having smaller stature, it has been used for growing large plants, using buckets ranging in size from 1 gallon to 5 gallons, making use of high-volume pumps such as those in large aquariums, decorative fountains and koi ponds.
There are facets to these systems that present some labor investment in large-scale applications. These are primarily management of media between uses, such as washing and sterilization. This can be done by dumping into the tray and filling with a sterilizing solution such as hydrogen peroxide or chlorine solution, temporarily plugging the drain, with hand removal of root fragments. Larger containers require transferring the media to a suitable surface after sterilization to permit removal of leftover plant material.
A second drawback is that the roots tend to grow together, meaning removal of harvested or damaged plants can be somewhat problematic in plants having well-developed root systems. Commercial crops harvested at one time are somewhat immune to concerns related to that aspect of the system, but in the event of pathogenic invasion the problem can quickly spread, as all the roots share the same flood source.
Also, most ebb and flow systems use a recycling reservoir to flood the table. Over a period of time the pH of the nutrient solution may fluctuate to a range which is unhealthy for the plant. If the pH is not corrected, various problems may occur, including but not limited to poor nutrient absorption and leaf cannibalization. As the name implies, leaf cannibalization occurs as the plant takes nutrients from one part of the plant and uses those nutrients in a different part of the plant. Leaf cannibalization appears as yellow or brown spots on leaves.
During Flower pH rises quite a bit each day. It is best to adjust first thing and last thing each day. Also, during Flower nutrients and water absorption increases, while root exudate gets carried back to the reservoir. This causes ppms to increase significantly. Proper control requires routine checking and replacing with fresh nutrients ~ 5 days to avoid toxicity.
Since the plant(s) is being fed several times a day, lower ppm nutrients (600–800) are sufficient. Pushing with higher ppms can cause the plant to burn up from the inside, especially when significant water evaporation/usage causes the remaining nutrient concentration to increase beyond 1500 ppms.
Choosing a medium like lava rock is ideal for flood and drain in that it drains quickly, and due to its rough texture, it traps small amounts of oxygen and nutrients which keeps the root zone moist between feedings. Also, because it drains quickly, the number of feedings can be increased to roughly every 45–60 minutes during lights on, producing explosive growth. Should the grower opt for this method, the nutrient ppm should be kept below 800, better still 600.
Poor drainage, or incomplete drainage, may cause a condition wherein dense roots are exposed to stagnant water which is trapped by the root mass. Root rot and fungal growth are the most common result of stagnant water. Some E&F systems are not as immune to root rot as a well-designed system would be. In tables where plants are larger than optimal for the system, this can create the need for modifications such as screens or beds of medium-sized gravel to prevent standing water. Tilting the tray is one way to achieve better drain characteristics. In bucket E&F this problem can be dealt with in a similar manner, ensuring good drainage through using medium of adequate size and ensuring that drainage of the container between flood cycles is complete.
Hydrogen peroxide is also added to nutrient solutions when there is suspicion that the anaerobic pythium root rot mold has begun to proliferate on the roots' surfaces. The oxygen liberated from the hydrogen peroxide is destructive to single-celled organisms and is administered in dosages which vary with the concentration of the peroxide. Typically several tablespoons or more of 3.5% peroxide solution per gallon of water are used. The temporary rise in the oxygen level is only minimally damaging to roots, while eradicating the water-borne mold can significantly increase yield or even save a crop's viability.
Nutrient film technique
Nutrient film technique (NFT) is a hydroponic technique wherein a very shallow stream of water containing all the dissolved nutrients required for plant growth is re-circulated past the bare roots of plants in a watertight gully, also known as channels. In an ideal system, the depth of the recirculating stream should be very shallow, little more than a film of water, hence the name 'nutrient film'. This ensures that the thick root mat, which develops in the bottom of the channel, has an upper surface, which, although moist, is in the air. Subsequent to this, an abundant supply of oxygen is provided to the roots of the plants. A properly designed NFT system is based on using the right channel slope, the right flow rate, and the right channel length. The main advantage of the NFT system over other forms of hydroponics is that the plant roots are exposed to adequate supplies of water, oxygen and nutrients. In earlier production systems, there was a conflict between the supply of these requirements, since excessive or deficient amounts of one results in an imbalance of one or both of the others. NFT, because of its design, provides a system wherein all three requirements for healthy plant growth can be met at the same time, provided that the simple concept of NFT is always remembered and practiced. The result of these advantages is that higher yields of high-quality produce are obtained over an extended period of cropping. A downside of NFT is that it has very little buffering against interruptions in the flow, e.g., power outages, but, overall, it is one of the more productive techniques.
The same design characteristics apply to all conventional NFT systems. While slopes along channels of 1:100 have been recommended, in practice it is difficult to build a base for channels that is sufficiently true to enable nutrient films to flow without ponding in locally depressed areas. As a consequence, it is recommended that slopes of 1:30 to 1:40 be used. This allows for minor irregularities in the surface, but, even with these slopes, ponding and water logging may occur. The slope may be provided by the floor, or benches or racks may hold the channels and provide the required slope. Both methods are used and depend on local requirements, often determined by the site and crop requirements.
As a general guide, flow rates for each gully should be 1 litre per minute. At planting, rates may be half this, and the upper limit of 2L/min appears about the maximum. Flow rates beyond these extremes are often associated with nutritional problems. Depressed growth rates of many crops have been observed when channels exceed 12 metres in length. On rapidly growing crops, tests have indicated that, while oxygen levels remain adequate, nitrogen may be depleted over the length of the gully. As a consequence, channel length should not exceed 10–15 metres. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and reducing flow rates to 1L/min through each outlet. Care needs to be taken to maintain hygienic conditions and to avoid heavy metal contamination of NFT systems by using mainly plastic or stainless steel pumps and components.
A leading protagonist of NFT was Dr Alan Cooper, a scientist at the Glasshouse Crops Research Station in England who published the book "The ABC of NFT" (Grower Books, London, UK, 1979, 1844pps,Reprinted by Casper Press, Narrabeen, Australia). NFT systems were used by a significant proportion of commercial growers in the UK through the 1980-1990 period but were only used for lettuce in Europe. Dutch growers particularly rejected NFT because of the perceived high risk of disease spread by the recirculating solution. NFT ensures that plants have unlimited access to water at all times, but it is now recognized that fruiting crops can benefit from carefully limited water supplies. Leafy crops like lettuce benefit from unlimited water supplies and are still widely grown using NFT, but now most commercial greenhouse crops of tomatoes, capsicums and cucumbers are grown hydroponically using some kind of inert media, with rockwool being the most important media worldwide. NFT remains a very popular system for home use.
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