Aeroponics

Aeroponics is the process of cultivating plants in an air or mist environment, eliminating the need for soil or an aggregate medium. The term "aeroponic" originates from the ancient Greek: aer and ponos. It falls under the category of hydroponics, as water is employed in aeroponics to deliver nutrients to the plants.

Methods

The fundamental principle of aeroponic growing entails suspending plants in a closed or semi-closed environment whilst spraying their dangling roots and lower stems with a nutrient-rich water solution in an atomized or sprayed form. The upper portion of the plant, including the leaves and crown, referred to as the canopy, extends above. The plant support structure keeps the roots separated. To minimize labor and expenses, closed-cell foam is often compressed around the lower stem and inserted into an opening in the aeroponic chamber. In the case of larger plants, trellising is employed to support the weight of the vegetation and fruits.
The goal is to maintain an environment free from pests and diseases, allowing the plants to thrive and grow faster than those cultivated in a growing medium. However, since most aeroponic environments are not completely sealed off from the outside, pests and diseases can still pose a threat. Controlled environments facilitate the advancement of plant development, health, growth, flowering, and fruiting for various plant species and cultivars.
Due to the sensitivity of root systems, aeroponics is often combined with conventional hydroponics. This serves as a backup nutrition and water supply in case of any failure in the aeroponic system, acting as an emergency "crop saver."
High-pressure aeroponics refers to the method of delivering nutrients to the roots using mist heads with a size range of 20-50 micrometers. This is achieved using a high-pressure diaphragm pump operating at around 80 pounds per square inch.

Benefits and drawbacks

Increased air exposure

Air cultures maximize air exposure to facilitate optimal plant growth. The materials and devices that hold and support aeroponically grown plants must be completely free from disease or pathogens. A vital characteristic of a genuine aeroponic culture and apparatus is minimal plant support features. This design allows maximum airflow around the plant by minimizing contact between the plant and the support structure. In long-term aeroponic cultivation, it is crucial to ensure that the root systems are unconstrained, allowing unrestricted growth, root expansion, unhindered access to pure water, adequate air exchange, and disease-free conditions.

Benefits of oxygen in the root zone

Adequate oxygen availability in the rhizosphere is essential for promoting healthy plant growth. In aeroponics, where plants are grown in an environment of air and micro-droplets of water, almost any plant can thrive and reach maturity with an abundant supply of oxygen, water, and nutrients.
Some growers prefer aeroponic systems over other hydroponic methods, since the increased aeration of the nutrient solution provides greater oxygenation to the plant roots, stimulating growth and aiding in the prevention of pathogen formation.
Clean air plays a crucial role in purifying the environment for plants in aeroponics. Unrestricted access to air is necessary for natural plant growth and successful physiological development. If the support structure restricts the plant's natural growth, it can increase the risk of plant damage and subsequent disease formation.
Researchers have utilized aeroponics to study the impact of gas composition in the root zone on plant performance. Soffer and Burger conducted a study on the effects of dissolved oxygen concentrations in a system they termed "aero-hydroponics," which involved a 3-tier hydro and aero system with distinct zones within the root area. Their results indicated that dissolved oxygen is crucial for root formation. Additionally, they found that in the misted section, where nutrient mist was provided, the number and length of roots were consistently greater compared to the submerged or un-misted sections. Even at the lowest oxygen concentration tested, the misted section demonstrated successful root development.

Other benefits of air (CO₂)

Aeroponics also entails the management of CO₂ levels in the system's air, which subsequently impacts the rate of photosynthesis in plants.
Utilizing artificial lights for growth offers advantages such as increased growth rates and enhanced reliability compared to solar lighting. This lighting method can be effectively combined with aeroponics to optimize plant growth.

Disease-free cultivation

Aeroponics offers the advantage of limiting disease transmission since it reduces plant-to-plant contact, and each spray pulse can be kept sterile. In contrast, diseases can easily spread throughout soil, aggregate, or other growing media, affecting multiple plants. Traditional greenhouses often require sterilization of solid media after each crop, and sometimes these media are simply discarded and replaced with fresh, sterile ones.
One significant benefit of aeroponic technology is the ability to quickly remove a diseased plant from the plant support structure without disrupting or infecting other plants, thanks to the isolated nature of the system.
Image:aeroponic-plants.jpg|thumb|The first successful cultivation of basil from seed in an aeroponic system inside a modern greenhouse was achieved in 1986.
Due to the disease-free environment unique to aeroponics, many plants can be grown at higher densities compared to more traditional cultivation methods like hydroponics, soil, and Nutrient Film Technique. Commercial aeroponic systems incorporate hardware features that accommodate the expanding root systems of crops.
Researchers have highlighted aeroponics as a valuable, simple, and rapid method for preliminary screening of genotypes for resistance to specific seedling blights or root rots. The isolating nature of aeroponic systems enables researchers to avoid complications encountered when studying these infections in soil cultures.

Water and nutrient hydro-atomization

Aeroponic equipment employs sprayers, misters, foggers, or other devices to create a fine mist of solution for delivering nutrients to plant roots. Aeroponic systems are typically closed-looped systems designed to provide macro and micro-environments that sustain reliable and consistent air cultures. Several inventions have been developed to facilitate aeroponic spraying and misting. The size of the water droplet is critical for root development in an aeroponic environment. In commercial applications, a 360° hydro-atomizing spray is used, which utilizes air pressure misting to cover large areas of roots.
A variation of the mist technique, known as fogponics, utilizes ultrasonic foggers to mist nutrient solutions in low-pressure aeroponic devices.
Water droplet size plays a vital role in maintaining aeroponic growth. Water droplets that are too large can limit the availability of oxygen to the root system. Conversely, excessively fine water droplets generated by ultrasonic misters can lead to excessive root hair growth without developing a lateral root system necessary for sustained growth in an aeroponic system.
Mineralization of ultrasonic transducers requires maintenance and presents a potential risk of component failure. This is also a drawback of metal spray jets and misters. Restricted access to water can cause plants to lose turgidity and wilt.

Advanced materials

has provided funding for research and development of new advanced materials aimed at improving the reliability and reducing maintenance in aeroponics. It has been determined that a high-pressure hydro-atomized mist with micro-droplets ranging from 5 to 50 micrometers is necessary for sustained aeroponic growth.
To ensure long-term growth, the mist system must possess significant pressure to effectively penetrate the dense root system. Achieving repeatability is crucial in aeroponics, and this includes maintaining the appropriate hydro-atomized droplet size. The degradation of the spray caused by mineralization of mist heads hampers the delivery of the water nutrient solution, resulting in an environmental imbalance within the air culture system.
To address this issue, special low-mass polymer materials have been developed and are utilized to prevent mineralization in the next generation of hydro-atomizing misting and spray jets. These materials help maintain the efficiency and effectiveness of the misting system.

Nutrient uptake

The discrete nature of interval and duration aeroponics allows for the measurement of nutrient uptake over time, even under varying conditions. Barak et al. conducted a study using an aeroponic system to non-destructively measure water and ion uptake rates in cranberries.
In their research, the team found that by measuring the concentrations and volumes of input and efflux solutions, they could accurately calculate the nutrient uptake rate. To validate their findings, they compared the results with N-isotope measurements. Once their analytical method was verified, Barak et al. proceeded to gather additional data specific to cranberries. This included studying diurnal variations in nutrient uptake, examining the correlation between ammonium uptake and proton efflux, and exploring the relationship between ion concentration and uptake. These findings highlight the potential of aeroponics not only as a valuable research tool for studying nutrient uptake but also as a means to monitor plant health and optimize crop cultivation in closed environments.
Atomization at pressures exceeding 65 pounds per square inch increases the bioavailability of nutrients. Consequently, nutrient strength must be significantly reduced to prevent leaf and root burn. It's worth noting the large water droplets in the photo on the right, which indicate that the feed cycle may be too long or the pause cycle too short. Both scenarios discourage lateral root growth and root hair development. Optimal results are achieved when feed cycles are as short as possible, with roots remaining slightly damp but never excessively dry. A typical feed/pause cycle is less than 2 seconds of feeding followed by approximately 1.5–2 minutes of pause, maintained continuously. However, when an accumulator system is incorporated, cycle times can be further reduced to less than approximately 1 second of feeding and around 1 minute of pause.