The basic principle of aeroponic growing is to grow plants suspended in a closed or semi-closed environment by spraying the plant's dangling roots and lower stem with an atomized or sprayed, nutrient-rich water solution. The roots of the plant are separated by the plant support structure. Many times closed cell foam is compressed around the lower stem and inserted into an opening in the aeroponic chamber, which decreases labor and expense; for larger plants, trellising is used to suspend the weight of vegetation and fruit.
Ideally, the environment is kept free from pests and disease so that the plants may grow healthier and more quickly than plants grown in a medium. Due to the sensitivity of root systems, aeroponics is often combined with conventional hydroponics, which is used as an emergency "crop saver" – backup nutrition and water supply – if the aeroponic apparatus fails. High-pressure aeroponics is defined as delivering nutrients to the roots via 20–50 micrometre mist heads using a high-pressure (80 pounds per square inch (550 kPa)) diaphragm pump.
Close-up of the first patented aeroponic plant support structure (1983). Its unrestricted support of the plant allows for normal growth in the air/moisture environment, and is still in use today.Air cultures optimize access to air for successful plant growth. Materials and devices which hold and support the aeroponic grown plants must be devoid of disease or pathogens. A distinction of a true aeroponic culture and apparatus is that it provides plant support features that are minimal. Minimal contact between a plant and support structure allows for 100% of the plant to be entirely in air. Long-term aeroponic cultivation requires the root systems to be free of constraints surrounding the stem and root systems. Physical contact is minimized so that it does not hinder natural growth and root expansion or access to pure water, air exchange and disease-free conditions.
Oxygen in the rhizosphere (root zone) is necessary for healthy plant growth. As aeroponics is conducted in air combined with micro-droplets of water, almost any plant can grow to maturity in air with a plentiful supply of oxygen, water and nutrients.Some growers favor aeroponic systems over other methods of hydroponics because the increased aeration of nutrient solution delivers more oxygen to plant roots, stimulating growth and helping to prevent pathogen formation.
Clean air supplies oxygen which is an excellent purifier for plants and the aeroponic environment. For natural growth to occur the plant must have unrestricted access to air. Plants must be allowed to grow in a natural manner for successful physiological development. The more confining the plant support becomes, the greater incidence of increasing disease pressure of the plant and the aeroponic system.
Plants in a true aeroponic apparatus have 100% access to the CO2 concentrations ranging from 450 ppm to 780 ppm for photosynthesis. At one mile (1.6 km) above sea level the CO2 concentration in the air is 450 ppm during daylight. At night the CO2 level will rise to 780 ppm. Lower elevations will have higher levels. In any case, the air culture apparatus offers ability for plants to have full access to all the available CO2 in the air for photosynthesis.Growing under lights during the evening allows aeroponics to benefit from the natural occurrence.
Aeroponics can limit disease transmission since plant-to-plant contact is reduced and each spray pulse can be sterile. In the case of soil, aggregate, or other media, disease can spread throughout the growth media, infecting many plants. In most greenhouses these solid media require sterilization after each crop and, in many cases, they are simply discarded and replaced with fresh, sterile media. A distinct advantage of aeroponic technology is that if a particular plant does become diseased, it can be quickly removed from the plant support structure without disrupting or infecting the other plants. Due to the disease-free environment that is unique to aeroponics, many plants can grow at higher density (plants per square meter) when compared to more traditional forms of cultivation (hydroponics, soil and Nutrient Film Technique [NFT]). Commercial aeroponic systems incorporate hardware features that accommodate the crop's expanding root systems.
Researchers have described aeroponics as a "valuable, simple, and rapid method for preliminary screening of genotypes for resistance to specific seedling blight or root rot.” The isolating nature of the aeroponic system allowed them to avoid the complications encountered when studying these infections in soil culture.
Aeroponic equipment involves the use of sprayers, misters, foggers, or other devices to create a fine mist of solution to deliver nutrients to plant roots. Aeroponic systems are normally closed-looped systems providing macro and micro-environments suitable to sustain a reliable, constant air culture. Numerous inventions have been developed to facilitate aeroponic spraying and misting. The key to root development in an aeroponic environment is the size of the water droplet. In commercial applications, a hydro-atomizing spray at 360° is employed to cover large areas of roots utilizing air pressure misting.
A variation of the mist technique employs the use of ultrasonic foggers to mist nutrient solutions in low-pressure aeroponic devices.Water droplet size is crucial for sustaining aeroponic growth. Too large a water droplet means less oxygen is available to the root system. Too fine a water droplet, such as those generated by the ultrasonic mister, produce excessive root hair without developing a lateral root system for sustained growth in an aeroponic system.
Mineralization of the ultrasonic transducers requires maintenance and potential for component failure. This is also a shortcoming of metal spray jets and misters. Restricted access to the water causes the plant to lose turgidity and wilt.
NASA has funded research and development of new advanced materials to improve aeroponic reliability and maintenance reduction. It also has determined that high pressure hydro-atomized mist of 5-50 micrometres micro-droplets is necessary for long-term aeroponic growing.For long-term growing, the mist system must have significant pressure to force the mist into the dense root system. Repeatability is the key to aeroponics and includes the hydro-atomized droplet size. Degradation of the spray due to mineralization of mist heads inhibits the delivery of the water nutrient solution, leading to an environmental imbalance in the air culture environment.
Special low-mass polymer materials were developed and are used to eliminate mineralization in next generation hydro-atomizing misting and spray jets.
The discrete nature of interval and duration aeroponics allows the measurement of nutrient uptake over time under varying conditions. Atomization (>65 pounds per square inch (450 kPa)), increases bioavailability of nutrients, consequently, nutrient strength must be significantly reduced or leaf and root burn will develop. Note the large water droplets in the photo to the right. This is caused by the feed cycle being too long or the pause cycle too short; either discourages both lateral root growth and root hair development. Plant growth and fruiting times are significantly shortened when feed cycles are as short as possible. Ideally, roots should never be more than slightly damp nor overly dry. A typical feed/pause cycle is < 2 seconds on, followed by ~1.5-2 minute pause- 24/7, however, when an acumulator system is incorporated, cycle times can be further reduced to < ~1 second on, ~1 minute pause.>
Soon after its development, aeroponics took hold as a valuable research tool. Aeroponics offered researchers a noninvasive way to examine roots under development. This new technology also allowed researchers a larger number and a wider range of experimental parameters to use in their work.
The ability to precisely control the root zone moisture levels and the amount of water delivered makes aeroponics ideally suited for the study of water stress. K. Hubick evaluated aeroponics as a means to produce consistent, minimally water-stressed plants for use in drought or flood physiology experiments.
Aeroponics is the ideal tool for the study of root morphology. The absence of aggregates offers researchers easy access to the entire, intact root structure without the damage that can be caused by removal of roots from soils or aggregates. It’s been noted that aeroponics produces more normal root systems than hydroponics.
In most low-pressure aeroponic gardens, the plant roots are suspended above a reservoir of nutrient solution or inside a channel connected to a reservoir. A low-pressure pump delivers nutrient solution via jets or by ultrasonic transducers, which then drips or drains back into the reservoir. As plants grow to maturity in these units they tend to suffer from dry sections of the root systems, which prevent adequate nutrient uptake. These units, because of cost, lack features to purify the nutrient solution, and adequately remove incontinuities, debris, and unwanted pathogens. Such units are usually suitable for bench top growing and demonstrating the principles of aeroponics.
High-pressure aeroponic techniques, where the mist is generated by high-pressure pumps, are typically used in the cultivation of high value crops and plant specimens that can offset the high setup costs associated with this method of horticulture.Since the late 2000s, home indoor gardeners have had access to simple high pressure aeroponic (HPA) systems at affordable prices.High-pressure aeroponics systems include technologies for air and water purification, nutrient sterilization, low-mass polymers and pressurized nutrient delivery systems.
Commercial aeroponic systems comprise high-pressure device hardware and biological systems. The biological systems matrix includes enhancements for extended plant life and crop maturation.
Biological subsystems and hardware components include effluent controls systems, disease prevention, pathogen resistance features, precision timing and nutrient solution pressurization, heating and cooling sensors, thermal control of solutions, efficient photon-flux light arrays, spectrum filtration spanning, fail-safe sensors and protection, reduced maintenance & labor saving features, and ergonomics and long-term reliability features.
Commercial aeroponic systems, like the high-pressure devices, are used for the cultivation of high value crops where multiple crop rotations are achieved on an ongoing commercial basis.
Advanced commercial systems include data gathering, monitoring, analytical feedback and internet connections to various subsystems.Through trials they found that aeroponics was ideal for plant propagation; plants could be propagated without medium and could even be grown-on. In the end,
Aeroponics in space
NASA life support GAP technology with untreated beans (left tube) and biocontrol treated beans (right tube) returned from the Mir space station aboard the space shuttle – September 1997
Plants were first taken into Earth's orbit in 1960 on two separate missions, Sputnik 4 and Discover 17 (for a review of the first 30 years of plant growth in space, see Halstead and Scott 1990).
NASA's experiments aboard the MIR space station and shuttle confirmed that ODC elicited increased germination rate, better sprouting, increased growth and natural plant disease mechanisms when applied to beans in an enclosed environment. ODC is now a standard for pesticide-free aeroponic growing and organic farming. Soil and hydroponics growers can benefit by incorporating ODC into their planting techniques.
NASA aeroponic lettuce seed germination. Day 30.
Many hydroponic systems can provide high plant performance but nutrient solution throughput is high, necessitating large water volumes and substantial recycling of solutions, and the control of the solution in hypogravity conditions is difficult at best.Aeroponics, with its use of a hydro-atomized spray to deliver nutrients, minimizes water use, increases oxygenation of roots, and offers excellent plant growth, while at the same time approaching or bettering the low nutrient solution throughput of other systems developed to operate in low gravity.
NASA low-mass Inflatable Aeroponics System (AIS) - achieved 1999
The NASA efforts lead to developments of numerous advanced materials for aeroponics for earth and space. NASA's long range plans indicate that a human visit to Mars will need to utilize inflatable structures to house the spaceship crew on the Mars surface. Planning is under way to incorporate inflatable greenhouse facilities for food production.NASA planning scenarios also reveal the Mars surface crew will spend 60% of their time on Mars farming to sustain themselves. Aeroponics is considered the agricultural system of choice because of its low water and power inputs and high volume of food output per unit area.
NASA aeroponic lettuce seed germination- Day 3
Aeroponics possesses many characteristics that make it an effective and efficient means of growing plants.
NASA aeroponic lettuce seed germination- Day 12
Plants grown using aeroponics spend 99.98% of their time in air and 0.02% in direct contact with hydro-atomized nutrient solution. The time spent without water allows the roots to capture oxygen more efficiently. Furthermore, the hydro-atomized mist also significantly contributes to the effective oxygenation of the roots. For example, NFT has a nutrient throughput of 1 liter per minute compared to aeroponics’ throughput of 1.5 milliliters per minute.The reduced volume of nutrient throughput results in reduced amounts of nutrients required for plant development.
Another benefit of the reduced throughput, of major significance for space-based use, is the reduction in water volume used. This reduction in water volume throughput corresponds with a reduced buffer volume, both of which significantly lighten the weight needed to maintain plant growth. In addition, the volume of effluent from the plants is also reduced with aeroponics, reducing the amount of water that needs to be treated before reuse.The relatively low solution volumes used in aeroponics, coupled with the minimal amount of time that the roots are exposed to the hydro-atomized mist, minimizes root-to-root contact and spread of pathogens between plants.
Aeroponics allows more control of the environment around the root zone, as, unlike other plant growth systems, the plant roots are not constantly surrounded by some medium (as, for example, with hydroponics, where the roots are constantly immersed in water).
Improved nutrient feeding
Hydroponics Bulky Matrix
A variety of different nutrient solutions can be administered to the root zone using aeroponics without needing to flush out any solution or matrix in which the roots had previously been immersed. This elevated level of control would be useful when researching the effect of a varied regimen of nutrient application to the roots of a plant species of interest. In a similar manner, aeroponics allows a greater range of growth conditions than other nutrient delivery systems. The interval and duration of the nutrient spray, for example, can be very finely attuned to the needs of a specific plant species. The aerial tissue can be subjected to a completely different environment from that of the roots.
The design of an aeroponic system allows ease of working with the plants. This results from the separation of the plants from each other, and the fact that the plants are suspended in air and the roots are not entrapped in any kind of matrix. Consequently, the harvesting of individual plants is quite simple and straightforward. Likewise, removal of any plant that may be infected with some type of pathogen is easily accomplished without risk of uprooting or contaminating nearby plants.
Aeroponic systems are more cost effective than other systems. Because of the reduced volume of solution throughput (discussed above), less water and less nutrients are needed in the system at any given time compared to other nutrient delivery systems. The need for substrates is also eliminated, as is the need for many moving parts .
With aeroponics, the deleterious effects of seed stocks that are infected with pathogens can be minimized. As discussed above, this is due to the separation of the plants and the lack of shared growth matrix. In addition, due to the enclosed, controlled environment, aeroponics can be an ideal growth system in which to grow seed stocks that are pathogen-free. The enclosing of the growth chamber, in addition to the isolation of the plants from each other discussed above, helps to both prevent initial contamination from pathogens introduced from the external environment and minimize the spread from one plant to others of any pathogens that may exist.
Aeroponics is an improvement in artificial life support for non-damaging plant support, seed germination, environmental control and rapid unrestricted growth when compared with hydroponics and drip irrigation techniques that have been used for decades by traditional agriculturalists.
Aeroponically grown biopharma corn, 2005
Aeroponic bio-pharming is used to grow pharmaceutical medicine inside of plants. The technology allows for completed containment of allow effluents and by-products of biopharma crops to remain inside a closed-loop facility.
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