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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 language: aer (air) and ponos (labor, hardship, or toil). It falls under the category of hydroponics, as water is employed in aeroponics to deliver to the plants.
The goal is to maintain an environment free from pests and , allowing the plants to thrive and grow faster than those cultivated in a growing Growth 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 .
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 (550 kPa).
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 (1988) 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.
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.
One significant benefit of aeroponic technology is the ability to quickly remove a Plant pathology from the plant support structure without disrupting or infecting other plants, thanks to the isolated nature of the system.
Due to the disease-free environment unique to aeroponics, many plants can be grown at higher densities (plants per square meter) compared to more traditional cultivation methods like hydroponics, soil, and Nutrient Film Technique (NFT). 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.
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.
To ensure long-term growth, the mist system must possess significant pressure to effectively penetrate the dense root system(s). 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.
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 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.Hoehn, A. (1998). Root Wetting Experiments aboard NASA's KC-135 Microgravity Simulator. BioServe Space Technologies.
Atomization at pressures exceeding 65 pounds per square inch (450 kPa) 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.
The precise control over root zone moisture levels and water delivery makes aeroponics particularly well-suited for studying water stress. K. Hubick evaluated aeroponics as a means to consistently produce plants with minimal water stress, which can be utilized in drought or flood physiology experiments.Hubick, K.T., D.R. Drakeford and D.M. Reid (1982). A comparison of two techniques for growing minimally water-stressed plants. Canadian Journal of Botany 60: 219–223.
Aeroponics are a better choice when it comes to investigating root morphology. The absence of aggregates enables researchers to easily access the entire, intact root structure without causing damage that may occur when removing roots from soils or aggregates. It has been observed that aeroponics yields more natural root systems compared to hydroponics.Coston, D.C., G.W. Krewer, R.C. Owing and E.G. Denny (1983). "Air Rooting of Peach Semihardwood Cutting." HortScience 18(3): 323.
Aeroponic growth specifically refers to the process of growing plants in an air culture.
An aeroponic system refers to the collection of hardware and components designed to support plant growth in an air culture.
An aeroponic greenhouse is a controlled environment structure made of glass or plastic, equipped with the necessary tools to cultivate plants in an air/mist environment.
Aeroponic conditions pertain to the specific environmental parameters required to sustain plant growth in an air culture, tailored to the needs of a particular plant species.
Aeroponic roots refer to the root system that develops when plants are grown in an air culture.
High-pressure aeroponic systems incorporate advanced technologies for air and water purification, nutrient sterilization, the utilization of , and pressurized nutrient delivery systems. These features enhance the efficiency and effectiveness of the aeroponic setup.
Biological subsystems and hardware components encompass several features and functionalities, such as effluent control systems, disease prevention measures, pathogen resistance mechanisms, precise timing and pressurization of nutrient solutions, sensors for heating and cooling, thermal control of solutions, efficient light arrays with optimized photon flux, spectrum filtration capabilities, fail-safe sensors and protection mechanisms, reduced maintenance and labor-saving features, as well as Ergonomics design and long-term reliability features.
These commercial aeroponic systems, including the high-pressure devices, are primarily utilized for cultivating high-value crops, enabling multiple on a continuous commercial scale.
Advanced commercial systems go a step further by incorporating data gathering, monitoring, analytical feedback, and internet connectivity to various subsystems, enhancing overall efficiency and productivity.Stoner, R.J. (1989). Aeroponic Taxus Growth Experiment., Internal Report, Hauser Chemical
In 1942, W. Carter conducted pioneering research on air culture growing and described a method for growing plants in water vapor to facilitate root examination.Carter, W.A. (1942). A method of growing plants in water vapor to facilitate examination of roots. Phytopathology 732: 623–625. Since 2006, aeroponics has been widely used in agriculture worldwide.NASA Spinoff (2006) Progressive Plant Growing Has Business Blooming. Environmental and Agricultural Resources NASA Spinoff 2006, pp. 68–72.
In 1944, L.J. Klotz made an important discovery by misting citrus plants, which facilitated his research on diseases affecting citrus and avocado roots. In 1952, G.F. Trowel successfully grew apple trees using a spray culture technique.
In 1957, F. W. Went coined the term "aeroponics" to describe the air-growing process. He grew coffee plants and tomatoes with air-suspended roots, nourishing them through the application of a nutrient mist to the root section.
GTi's device featured an open-loop water-driven system controlled by a microchip. It delivered a high-pressure hydro-atomized nutrient spray within an aeroponic chamber. The Genesis Machine was designed to be connected to a water faucet and an electrical outlet, providing the necessary resources for operation.
Aeroponics plays a crucial role in propagating plants that have low success rates in vegetative propagation, plants with significant medicinal uses, high-demand plants, and in creating new cultivars of specific plant species. For instance, Leptadenia reticulata, an important medicinal plant with low reproductive rates through both seeds and cuttings, has found easier propagation through aeroponics (Mehandru et al., 2014). Aeroponics has also contributed to the availability of elm trees, including Ulmus Americana cultivars, which were severely affected by Dutch elm disease (Oakes et al., 2012).Oakes, A. D., N. A. Kazcmar, C. A. Maynard, and W. R. Argo. (2009). Vegetative propagation of American elm (Ulmus americana) varieties from softwood cuttings. Journal of Environmental Horticulture, 30(2):73–76.
Aeroponics serves as a more advantageous alternative to the traditional method of using overhead misters (Peterson et al., 2018).Peterson, B. J., S. E. Burnett, O. Sanchez. (2018). Submist is effective for propagation of Korean lilac and inkberry by stem cuttings. HortTechnology. 28(3):378–381. It boasts a higher success rate compared to overhead misters, which have drawbacks such as the need for large volumes of water, potential unsanitary conditions, uneven misting coverage, and possible leaching of foliar nutrients (Peterson et al., 2018). In essence, cloning has become easier with the use of aeroponic apparatus, as it initiates faster and cleaner root development through a sterile, nutrient-rich, highly oxygenated, and moist environment (Hughes, 1983).
By utilizing aeroponics, growers can directly clone and transplant air-rooted plants into field soil. The aeroponic roots are more resistant to wilting, leaf loss, and transplant shock compared to traditional methods like hydroponics. Moreover, air-rooted plants tend to be healthier and less susceptible to pathogen infections. However, it is important to maintain the root chamber's relative humidity (RH) below to prevent the development of issues like fungus gnats, algae, and anaerobic bacteria.
The efforts of GTi in developing an all-plastic aeroponic method and apparatus controlled by a microprocessor have ushered in a new era of artificial life support for plants, allowing them to grow naturally without the use of soil or traditional hydroponics. In fact, GTi obtained a patent for their innovative aeroponic system in 1985.
Aeroponics has gained recognition as a time- and cost-saving technique. The economic application of aeroponics in agriculture is under development in the 21st century.
It is worth noting that many of these early open-loop and closed-loop aeroponic systems continue to operate successfully to this day.
In 1982, Isaac Nir in Israel developed a patent for an aeroponic apparatus that utilized compressed low-pressure air to deliver a nutrient solution to suspended plants held by styrofoam inside large metal containers.Nir, I. (1982), Apparatus and Method for Plant growth in Aeroponic Conditions., Patent United States
In 1976, British researcher John Prewer conducted a series of aeroponic experiments in the UK, where were grown from seed to maturity in 22 days using polyethylene film tubes. The fog droplets used in these experiments were generated by equipment supplied by Mee Industries of California.The system employed is described in detail in UK patent No.1 600 477 (filed 12 November 1976 - Complete Specification published 14 October 1981 - title IMPROVEMENTS IN AND RELATING TO THE PROPAGATION OF PLANTS). In collaboration with John Prewer, a commercial grower named Kings Nurseries on the Isle of Wight used a different design of aeroponics system in 1984 to grow strawberry plants. The strawberries flourished, yielding a bountiful crop that was highly appreciated by customers, especially the elderly, who valued the cleanliness, quality, and flavor of the fruit, as well as the convenience of picking it without stooping.
In 1983, Richard Stoner filed a patent for the first microprocessor interface designed to deliver tap water and nutrients into an enclosed aeroponic chamber made of plastic. Stoner subsequently established several companies dedicated to researching and advancing aeroponic hardware, interfaces, biocontrols, and components for commercial aeroponic crop production.
Stoner's company, Genesis Technology Inc, played a pioneering role in manufacturing, marketing, and applying large-scale closed-loop aeroponic systems in greenhouses for commercial crop production.Stoner, R.J. and J.M. Clawson (1999–2000). Low-mass, Inflatable Aeroponic System for High Performance Food Production. Principal Investigator, NASA SBIR NAS10-00017
In the 1990s, General Hydroponics Europe (GHE) attempted to introduce aeroponics to the hobby hydroponics market and introduced the Aerogarden system. Although the Aerogarden did not meet the criteria of "true" aeroponics as it produced droplets instead of a fine mist, it created a demand for aeroponic growing in the hobby market. The distinction between mist aeroponics and droplet aeroponics became blurred in the eyes of many. However, a UK firm called Nutriculture conducted trials of true mist aeroponics, which showed positive results compared to traditional growing techniques like Nutrient Film Technique (NFT) and Ebb & Flood. Despite the drawbacks of cost and maintenance, Nutriculture developed a scalable, easy-to-use droplet-aeroponic system called the Amazon, acknowledging that better results could be achieved by propagating plants in their branded X-stream aeroponic propagator and then transferring them to the specially designed droplet-aeroponic growing system.
Following these early endeavors, plant experiments were conducted on various missions involving Bangladesh, China, and joint Soviet-American efforts, including Biosatellite II, Skylab 3 and 4, Apollo-Soyuz, Sputnik, Vostok programme, and Zond program. Initial research findings shed light on how low gravity affected the orientation of roots and shoots (Halstead and Scott, 1990).
Subsequent research delved into investigating the impact of low gravity on plants at different levels, such as organismic, cellular, and subcellular. At the organismic level, several species including pine, oat, mung bean, lettuce, Watercress, and Arabidopsis thaliana exhibited decreased seedling, root, and shoot growth under low gravity conditions. However, lettuce grown on the Cosmos mission showed the opposite effect, displaying enhanced growth in space (Halstead and Scott, 1990). Mineral uptake in plants grown in space was also found to be affected. For instance, peas grown in space demonstrated increased levels of phosphorus and potassium, while the divalent cations calcium, magnesium, manganese, zinc, and iron exhibited decreased levels (Halstead and Scott, 1990).Tibbitts, T.W., W. Cao and R.M. Wheeler (1994). Growth of Potatoes for CELSS. NASA Contractor Report 177646.
Results from NASA's enclosed environment bean experiments on the MIR space station and shuttle confirmed that ODC promoted increased germination rates, better sprouting, enhanced growth, and activated natural plant disease mechanisms. Although initially developed for NASA, ODC is not limited to space applications. Soil and hydroponics growers can also incorporate ODC into their planting techniques, as it complies with USDA NOP standards for organic farming.
One notable example of ODC's expansion in agriculture is its application in the cannabis industry. The ODC product line has been developed specifically for emerging agricultural crops like cannabis. The active ingredients in the ODC cannabis line include the original chitosan ingredient at a concentration of 0.25%, as well as 0.28% colloidal nitrogen and 0.05% calcium.
In order to enhance the resilience of hydroponic and aeroponic systems against plant diseases and reduce reliance on chemical additives, NASA explores the integration of environmental biocontrols into the design of these systems. The Advanced Plant Habitat (APA), deployed on the International Space Station (ISS) since 2018, exemplifies this approach. Equipped with over 180 sensors, the APA optimizes plant growth and health while decreasing the need for chemical additive biocontrols. The sensors monitor various environmental factors, including lighting intensity, spectrum, and photoperiod, temperature, CO2 levels, relative humidity, irrigation, as well as plant-derived ethylene and volatile organic compound (VOC) scrubbing. Additionally, the APA features leaf and root zone temperature sensors, root zone moisture sensors, and oxygen concentration meters.
These environmental controls serve two main purposes in inhibiting plant diseases. Firstly, they maintain environmental conditions that directly hinder the growth of diseases, fungi, and pests. By carefully regulating factors like temperature and humidity, the risk of infections, such as botrytis in leaves, is reduced as the environment becomes less conducive to disease proliferation. Secondly, these controls create conditions that promote the plant's natural disease prevention mechanisms, indirectly inhibiting the effects of plant diseases. For instance, experiments with peppers conducted under blue light conditions have shown increased resilience to powdery mildew.
Research efforts have focused on identifying and developing technologies for rapid plant growth in different gravitational environments. Low-gravity environments present challenges such as efficient delivery of water and nutrients to plants, as well as the recovery of waste products. Food production in space also requires addressing issues like water management, minimizing water usage, and reducing system weight. Additionally, future food production on planetary bodies like the Moon and Mars will involve dealing with reduced gravity environments. Given the varying fluid dynamics at different levels of gravity, optimizing nutrient delivery systems has been a major focus in developing plant growth systems.
Various nutrient delivery methods are currently employed, both on Earth and in low-gravity environments. Substrate-dependent methods include traditional soil cultivation, zeoponics, agar, and nutrient-loaded ion exchange resins. In addition to substrate-dependent approaches, non-soil methods have been developed, including the nutrient film technique, ebb and flow, aeroponics, and others. Hydroponic systems, with their high nutrient solution throughput, can achieve rapid plant growth. However, this necessitates large volumes of water and significant recycling of the solution, which poses challenges for controlling solutions in microgravity conditions.
Aeroponic systems use hydro-atomized sprays to deliver nutrients, resulting in minimal water usage, enhanced root oxygenation, and excellent plant growth. The nutrient solution throughput of aeroponic systems is higher compared to other systems designed for low-gravity environments. Aeroponics eliminates the need for substrates and reduces the quantity of waste material that must be managed by other life support systems. By removing the substrate requirement, planting and harvesting processes are simplified, automation becomes easier, the weight and volume of expendable materials are reduced, and a potential pathway for pathogen transmission is eliminated. These advantages highlight the potential of aeroponic production in microgravity environments and its efficiency in food production for outer space.
On Earth, the cost of materials and transportation can pose challenges to the economic viability of aeroponic systems for commercial growers. However, these challenges become even more pronounced when considering the limitations imposed by payload mass for space transportation.
To overcome these limitations, NASA has developed specialized materials capable of withstanding the harsh space environment for inflatable habitats and structures. These materials, similar to aramid fibers, are currently being utilized in the development of expandable habitats by Bigelow Aerospace. Successful tests have been conducted in space with one of Bigelow's Expandable Activity Modules, demonstrating the feasibility of such inflatable structures in the space environment.
The reduced volume of nutrient throughput in aeroponics leads to a reduction in the overall amount of nutrients required for plant development.
Another advantage of the reduced throughput, particularly relevant for space applications, is the decreased water volume used. This reduction in water volume not only lightens the weight needed to sustain plant growth but also reduces the buffer volume. Additionally, the volume of effluent produced by the plants is minimized in aeroponics, resulting in a reduced amount of water that requires treatment for reuse.
The use of relatively small solution volumes in aeroponics, combined with the limited exposure of roots to the hydro-atomized mist, minimizes root-to-root contact and reduces the spread of pathogens among plants.
In 2000, Stoner was granted a patent for his organic disease control biocontrol technology, which enables pesticide-free cultivation in aeroponic systems.
A notable milestone in aeroponics occurred in 2004 when Ed Harwood, the founder of AeroFarms, invented an innovative aeroponic system that utilizes micro fleece cloth to grow lettuces. AeroFarms, leveraging Harwood's patented aeroponic technology, currently operates the largest indoor vertical farm in the world based on its annual growing capacity in Newark, New Jersey. This state-of-the-art farm employs aeroponic technology to produce and distribute up to two million pounds of pesticide-free leafy greens each year.
Dr. Reese considers it a significant achievement to successfully grow corn in an aeroponic system for Biomass. Previous attempts at growing various types of corn using hydroponics had been unsuccessful.
Through the implementation of advanced aeroponics techniques, Dr. Reese was able to harvest mature ears of genetically modified corn while effectively containing the corn pollen and spent effluent water, thus preventing their release into the environment. This containment ensures that the surrounding environment remains free from GMO contamination.
Dr. Reese emphasizes that aeroponics offers the potential for economically viable bio-pharming practices, making it a promising avenue for pharmaceutical production.
This development holds significant historical importance as it marks the first time a nation has specifically prioritized aeroponics to bolster its agricultural sector, promote economic growth in farming, meet rising demands, improve food quality, and increase overall production.
"We have shown that aeroponics, more than any other form of agricultural technology, will significantly improve Vietnam's potato production. We have very little tillable land, aeroponics makes complete economic sense to us," affirmed Thach.
The integration of aeroponics in Vietnamese agriculture begins with the production of low-cost, certified disease-free organic minitubers. These minitubers then serve as a local supply for farmers engaged in field plantings of seed potatoes and commercial potatoes. The adoption of aeroponics will benefit potato farmers by providing them with disease-free seed potatoes grown without the use of pesticides. Importantly, it will also reduce their operational costs and increase their yields, according to Thach.
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