Aeroponics

Aeroponics_Lettuce

Aeroponic Loose Leaf Lettuce

Aeroponics is the process of growing plants in an air or mist environment without the use of soil or an aggregate medium (known as geoponics).  Unlike hydroponics, which uses water as a growing medium and essential minerals to sustain plant growth, Aeroponics is conducted without a growing medium. Because water is used in Aeroponics to transmit nutrients, it is sometimes considered a type of hydroponics. Ideally, the environment is kept free from so that the plants may grow healthier and more quickly than plants grown in a medium. However, since most Aeroponic environments are not perfectly closed off to the outside, pests and disease may still cause a threat. Controlled environments advance plant development, health, growth, flowering and fruiting for any given plant species and cultivars. 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 leaves and crown, often called the “canopy”, extend above.

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. 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 micro-meter mist heads using a high-pressure (80 poundsper square inch (550 kPa)) diaphragm pump.

Benefits and drawbacks

Ecological advantages

Aeroponic growing is considered to be safe and ecologically friendly for producing natural, healthy plants and crops. The main ecological advantages of Aeroponics are the conservation of water and energy. When compared to hydroponics, Aeroponics offers lower water and energy inputs per square meter of growing area. When used commercially, Aeroponics uses one-tenth of the water otherwise necessary to grow the crop but this can be reduced to as little as one-twentieth.

Increased air exposure

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.

Benefits of oxygen in the root zone

Aeroponic-propagation-soft-tissue

Aeroponic-propagation-soft-tissue

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 of 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.

Other benefits of air (CO2

Plants in a true Aeroponic apparatus have 100% access to the  concentrations ranging from 450 ppm to 780 ppm for photosynthesis.  At one mile (1.6 km) above sea level the CO2s concentration in the air is 450 ppm during daylight. At night the CO2s 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 CO2s in the air for photosynthesis. Growing under lights during the evening allows Aeroponics to benefit from the natural occurrence.

Disease-free cultivation

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 sq 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 crops 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.

Water and nutrient hydro-atomization

Aeroponic-wheat-roots

Aeroponic wheat roots

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.

Advanced materials

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 systems.  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 innext generation hydro-atomizing misting and spray jets.

Nutrient uptake

Aeroponic_wheat

Aeroponic wheat

The discrete nature of interval and duration Aeroponics allows the measurement of nutrient uptake over time under varying conditions. An Aeroponic system was used for non-destructive measurement of water and ion uptake rates for cranberries. In the study, these researchers found that by measuring the concentrations and volumes of input and efflux solutions, they could accurately calculate the nutrient uptake rate. After verification of their analytical method, they went on to generate additional data specific to the cranberry, such as diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Work such as this not only shows the promise of Aeroponics  as a research tool for nutrient uptake, but also opens up possibilities for the monitoring of plant health and optimization of crops grown in closed environments.

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.

Types of Aeroponics

Low-pressure units

Aeroponic_Basil

Aeroponic Basil

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 in-continuities, debris, and unwanted pathogens. Such units are usually suitable for bench top growing and demonstrating the principles of Aeroponics.

High-pressure devices

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.

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