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Hyperphonic agriculture

Hydroponic is a type of horticulture and a subset of hydroculture which involves growing plants, usually crops, without soil, by using water-based mineral nutrient solutions in aqueous solvents. Terrestrial or aquatic plants may grow with their roots exposed to the nutritious liquid, or, in addition, the roots may be physically supported by an inert medium such as perlite, gravel, or other substrates. Despite inert media, roots can cause changes of the rhizosphere pH and root exudates can affect rhizosphere biology and physiological balance of the nutrient solution by secondary metabolites.

The nutrients used in hydroponic systems can come from many different sources, including fish excrement, duck manure, purchased chemical fertilizers, or artificial nutrient solutions.

Plants commonly grown hydroponically in a greenhouse, on inert media, include tomatoes, peppers, cucumbers, strawberries, lettuces, and cannabis, usually for commercial use, and Arabidopsis thaliana, which serves as a model organism in plant science and genetics.

Hydroponics offers many advantages, notably a decrease in water usage in agriculture. To grow 1 kilogram (2.2 lb) of tomatoes using intensive farming methods requires 400 liters (88 imp gal; 110 U.S. gal) of water; using hydroponics, 70 liters (15 imp gal; 18 U.S. gal); and only 20 liters (4.4 imp gal; 5.3 U.S. gal) using aeroponics. Since hydroponics takes much less water to grow produce, it could be possible in the future for people in harsh environments with little accessible water to grow their own food.

History

Further information: Historical hydroculture

The earliest published work on growing terrestrial plants without soil was the 1627 book Sylva Sylvarum or ‘A Natural History’ by Francis Bacon, printed a year after his death. As a result of his work, water culture became a popular research technique. In 1699, John Woodward published his water culture experiments with spearmint. He found that plants in less-pure water sources grew better than plants in distilled water. By 1842, a list of nine elements believed to be essential for plant growth had been compiled, and the discoveries of German botanists Julius von Sachs and Wilhelm Knop, in the years 1859–1875, resulted in a development of the technique of soilless cultivation. To quote Sachs directly: “In the year 1860, I published the results of experiments which demonstrated that land plants are capable of absorbing their nutritive matters out of watery solutions, without the aid of soil, and that it is possible in this way not only to maintain plants alive and growing for a long time, as had long been known, but also to bring about a vigorous increase of their organic substance, and even the production of seed capable of germination.” Growth of terrestrial plants without soil in mineral nutrient solutions was later called “solution culture”.It quickly became a standard research and teaching technique and is still widely used. Solution culture is now considered a type of hydroponics where there is an inert medium for stabilizing plant growth.

Around the 1930s plant scientists investigated diseases of certain plants, and thereby, observed symptoms related to existing soil conditions such as salinity. In this context, water culture experiments were undertaken with the hope of delivering similar symptoms under controlled conditions. This approach forced by Dennis Robert Hoagland led to model systems (e.g., green algae Nitella) and standardized nutrient recipes playing an increasingly important role in modern plant physiology. In 1929, William Frederick Gericke of the University of California at Berkeley began publicly promoting that solution culture be used for agricultural crop production. He first termed this cultivation method “aquaculture” but later found that aquaculture was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato vines twenty-five feet (7.6 metres) high in his back yard in mineral nutrient solutions rather than soil. He then introduced the term hydroponics, water culture, in 1937, proposed to him by W. A. Setchell, a phycologist with an extensive education in the classics. Hydroponics is derived from neologism υδρωπονικά (derived from Greek ύδωρ=water and πονέω=cultivate), constructed in analogy to γεωπονικά (derived from Greek γαία=earth and πονέω=cultivate), geoponica, that which concerns agriculture, replacing, γεω-, earth, with ὑδρο-, water.

Gericke, however, underestimated that the time was not yet ripe for the general technical application and commercial use of hydroponics for producing crops because the system he employed was at that time too sensitive and required too much monitoring to be used in commercial applications. Reports of Gericke’s work and his claims that hydroponics would revolutionize plant agriculture prompted a huge number of requests for further information. Gericke had been denied use of the university’s greenhouses for his experiments due to the administration’s skepticism, and when the university tried to compel him to release his preliminary nutrient recipes developed at home, he requested greenhouse space and time to improve them using appropriate research facilities. While he was eventually provided greenhouse space, the university assigned Hoagland and Arnon to re-evaluate Gericke’s claims and show his formula held no benefit over soil grown plant yields, a view held by Hoagland. In 1940, Gericke, whose work is considered to be the basis for all forms of hydroponic growing, published the book, Complete Guide to Soilless Gardening, after leaving his academic position in 1937 in a climate that was politically unfavorable. Therein, for the first time, he published his basic formula involving the macro- and micronutrient salts for hydroponically-grown plants.

As a result of research of Gericke’s claims by order of the Director of the California Agricultural Experiment Station of the University of California, Claude B. Hutchison, Dennis Robert Hoagland and Daniel Israel Arnon wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil, which made the claim that hydroponic crop yields were no better than crop yields obtained with good-quality soils. Ultimately, crop yields would be limited by factors other than mineral nutrients, especially light.However, this study did not adequately appreciate that hydroponics has other key benefits including the fact that the roots of the plant have constant access to oxygen and that the plants have access to as much or as little water as they need.This is important as one of the most common errors when cultivating plants is overwatering and underwatering; and hydroponics prevents this from occurring as large amounts of water, which may drown root systems in soil, can be made available to the plant in hydroponics, and any water not used, is drained away, recirculated, or actively aerated, thus, eliminating anoxic conditions in the root area. In soil, a grower needs to be very experienced to know exactly with how much water to feed the plant. Too much and the plant will be unable to access oxygen because the air in the soil pores is displaced; too little and the plant will lose the ability to absorb nutrients, which are typically moved into the roots while dissolved, leading to nutrient deficiency symptoms such as chlorosis. Hoagland’s views and helpful support by the University prompted these two researchers to develop several new formulas for mineral nutrient solutions, universally known as Hoagland solution.

One of the earliest successes of hydroponics occurred on Wake Island, a rocky atoll in the Pacific Ocean used as a refueling stop for Pan American Airlines. Hydroponics was used there in the 1930s to grow vegetables for the passengers. Hydroponics was a necessity on Wake Island because there was no soil, and it was prohibitively expensive to airlift in fresh vegetables.

From 1943 to 1946, Daniel I. Arnon served as a major in the United States Army and used his prior expertise with plant nutrition to feed troops stationed on barren Ponape Island in the western Pacific by growing crops in gravel and nutrient-rich water because there was no arable land available.

In the 1960s, Allen Cooper of England developed the nutrient film technique.The Land Pavilion at Walt Disney World’s EPCOT Center opened in 1982 and prominently features a variety of hydroponic techniques.

In recent decades, NASA has done extensive hydroponic research for its Controlled Ecological Life Support System (CELSS). Hydroponics research mimicking a Martian environment uses LED lighting to grow in a different color spectrum with much less heat. Ray Wheeler, a plant physiologist at Kennedy Space Center’s Space Life Science Lab, believes that hydroponics will create advances within space travel, as a bioregenerative life support system.

In 2007, Eurofresh Farms in Willcox, Arizona, sold more than 200 million pounds of hydroponically grown tomatoes. Eurofresh has 318 acres (1.3 km²) under glass and represents about a third of the commercial hydroponic greenhouse area in the U.S. Eurofresh tomatoes were pesticide-free, grown in rockwool with top irrigation. Eurofresh declared bankruptcy, and the greenhouses were acquired by NatureSweet Ltd. in 2013.

As of 2017, Canada had hundreds of acres of large-scale commercial hydroponic greenhouses, producing tomatoes, peppers and cucumbers.

Due to technological advancements within the industry and numerous economic factors, the global hydroponics market is forecast to grow from US$226.45 million in 2016 to US$724.87 million by 2023.

Techniques

There are two main variations for each medium: sub-irrigation and top irrigation^[specify]. For all techniques, most hydroponic reservoirs are now built of plastic, but other materials have been used, including concrete, glass, metal, vegetable solids, and wood. The containers should exclude light to prevent algae and fungal growth in the nutrient solution.

Static solution culture

 The deep water raft tank at the Crop Diversification Centre (CDC) South Aquaponics greenhouse in Brooks, Alberta

In static solution culture, plants are grown in containers of nutrient solution, such as glass Mason jars (typically, in-home applications), pots, buckets, tubs, or tanks. The solution is usually gently aerated but may be un-aerated. If un-aerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen. A hole is cut (or drilled) in the top of the reservoir for each plant; if it is a jar or tub, it may be its lid, but otherwise, cardboard, foil, paper, wood or metal may be put on top. A single reservoir can be dedicated to a single plant, or to various plants. Reservoir size can be increased as plant size increases. A home-made system can be constructed from food containers or glass canning jars with aeration provided by an aquarium pump, aquarium airline tubing and aquarium valves. Clear containers are covered with aluminium foil, butcher paper, black plastic, or other material to exclude light, thus helping to eliminate the formation of algae. The nutrient solution is changed either on a schedule, such as once per week, or when the concentration drops below a certain level as determined with an electrical conductivity meter. Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A Mariotte’s bottle, or a float valve, can be used to automatically maintain the solution level. In raft solution culture, plants are placed in a sheet of buoyant plastic that is floated on the surface of the nutrient solution. That way, the solution level never drops below the roots.

Continuous-flow solution culture

 The nutrient film technique (NFT) being used to grow various salad greens

In continuous-flow solution culture, the nutrient solution constantly flows past the roots. It is much easier to automate than the static solution culture because sampling and adjustments to the temperature, pH, and nutrient concentrations can be made in a large storage tank that has potential to serve thousands of plants. A popular variation is the nutrient film technique or NFT, whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated in a thin layer past a bare root mat of plants in a watertight channel, with an upper surface exposed to air. As a consequence, 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 all other forms of production, there is 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 where 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 practised. 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 probably 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 are 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, 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 one liter per minute. At planting, rates may be half this and the upper limit of 2 L/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 meters 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 meters. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed halfway along the gully and halving the flow rates through each outlet.

Aeroponics

Main article: Aeroponics

Aeroponics is a system wherein roots are continuously or discontinuously kept in an environment saturated with fine drops (a mist or aerosol) of nutrient solution. The method requires no substrate and entails growing plants with their roots suspended in a deep air or growth chamber with the roots periodically wetted with a fine mist of atomized nutrients. Excellent aeration is the main advantage of aeroponics. A diagram of the aeroponic technique

Aeroponic techniques have proven to be commercially successful for propagation, seed germination, seed potato production, tomato production, leaf crops, and micro-greens. Since inventor Richard Stoner commercialized aeroponic technology in 1983, aeroponics has been implemented as an alternative to water intensive hydroponic systems worldwide.The limitation of hydroponics is the fact that 1 kilogram (2.2 lb) of water can only hold 8 milligrams (0.12 gr) of air, no matter whether aerators are utilized or not.

Another distinct advantage of aeroponics over hydroponics is that any species of plants can be grown in a true aeroponic system because the microenvironment of an aeroponic can be finely controlled. The limitation of hydroponics is that certain species of plants can only survive for so long in water before they become waterlogged. The advantage of aeroponics is that suspended aeroponic plants receive 100% of the available oxygen and carbon dioxide to the roots zone, stems, and leaves, thus accelerating biomass growth and reducing rooting times. NASA research has shown that aeroponically grown plants have an 80% increase in dry weight biomass (essential minerals) compared to hydroponically grown plants. Aeroponics used 65% less water than hydroponics. NASA also concluded that aeroponically grown plants require ¼ the nutrient input compared to hydroponics. Unlike hydroponically grown plants, aeroponically grown plants will not suffer transplant shock when transplanted to soil, and offers growers the ability to reduce the spread of disease and pathogens. Aeroponics is also widely used in laboratory studies of plant physiology and plant pathology. Aeroponic techniques have been given special attention from NASA since a mist is easier to handle than a liquid in a zero-gravity environment.

Fogponics

Main article: Fogponics

Fogponics is a derivation of aeroponics wherein the nutrient solution is aerosolized by a diaphragm vibrating at ultrasonic frequencies. Solution droplets produced by this method tend to be 5–10 µm in diameter, smaller than those produced by forcing a nutrient solution through pressurized nozzles, as in aeroponics. The smaller size of the droplets allows them to diffuse through the air more easily, and deliver nutrients to the roots without limiting their access to oxygen.

Passive sub-irrigation

Main article: Passive hydroponicsWater plant-cultivated crocus

Passive sub-irrigation, also known as passive hydroponics, semi-hydroponics, or hydroculture, is a method wherein plants are grown in an inert porous medium that transports water and fertilizer to the roots by capillary action from a separate reservoir as necessary, reducing labor and providing a constant supply of water to the roots. In the simplest method, the pot sits in a shallow solution of fertilizer and water or on a capillary mat saturated with nutrient solution. The various hydroponic media available, such as expanded clay and coconut husk, contain more air space than more traditional potting mixes, delivering increased oxygen to the roots, which is important in epiphytic plants such as orchids and bromeliads, whose roots are exposed to the air in nature. Additional advantages of passive hydroponics are the reduction of root rot and the additional ambient humidity provided through evaporations.

Hydroculture compared to traditional farming in terms of crops yield per area in a controlled environment was roughly 10 times more efficient than traditional farming, uses 13 times less water in one crop cycle than traditional farming, but on average uses 100 times more kilojoules per kilogram of energy than traditional farming.

Ebb and flow (flood and drain) sub-irrigation

 An ebb and flow, or flood and drain, hydroponics systemMain article: Ebb and flow

In its simplest form, there is a tray above a reservoir of nutrient solution. Either the tray is filled with growing medium (clay granules being the most common) and then plant directly or place the pot over medium, stand in the tray. At regular intervals, a simple timer causes a pump to fill the upper tray with nutrient solution, after which the solution drains back down into the reservoir. This keeps the medium regularly flushed with nutrients and air. Once the upper tray fills past the drain stop, it begins recirculating the water until the timer turns the pump off, and the water in the upper tray drains back into the reservoirs.

Run-to-waste

In a run-to-waste system, nutrient and water solution is periodically applied to the medium surface. The method was invented in Bengal in 1946; for this reason it is sometimes referred to as “The Bengal System”. A run-to-waste hydroponics system, referred to as “The Bengal System” after the region in eastern India where it was invented (circa 1946)

This method can be set up in various configurations. In its simplest form, a nutrient-and-water solution is manually applied one or more times per day to a container of inert growing media, such as rockwool, perlite, vermiculite, coco fibre, or sand. In a slightly more complex system, it is automated with a delivery pump, a timer and irrigation tubing to deliver nutrient solution with a delivery frequency that is governed by the key parameters of plant size, plant growing stage, climate, substrate, and substrate conductivity, pH, and water content.

In a commercial setting, watering frequency is multi-factorial and governed by computers or PLCs.

Commercial hydroponics production of large plants like tomatoes, cucumber, and peppers uses one form or another of run-to-waste hydroponics.

In environmentally responsible uses, the nutrient-rich waste is collected and processed through an on-site filtration system to be used many times, making the system very productive.

Some bonsai are also grown in soil-free substrates (typically consisting of akadama, grit, diatomaceous earth and other inorganic components) and have their water and nutrients provided in a run-to-waste form.

Deep water culture

 The deep water culture technique being used to grow Hungarian wax peppersMain article: Deep water culture

The hydroponic method of plant production by means of suspending the plant roots in a solution of nutrient-rich, oxygenated water. Traditional methods favor the use of plastic buckets and large containers with the plant contained in a net pot suspended from the centre of the lid and the roots suspended in the nutrient solution. The solution is oxygen saturated by an air pump combined with porous stones. With this method, the plants grow much faster because of the high amount of oxygen that the roots receive.The Kratky Method is similar to deep water culture, but uses a non-circulating water reservoir.

Top-fed deep water culture

Top-fed deep water culture is a technique involving delivering highly oxygenated nutrient solution direct to the root zone of plants. While deep water culture involves the plant roots hanging down into a reservoir of nutrient solution, in top-fed deep water culture the solution is pumped from the reservoir up to 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 deep water culture, there is an airstone in the reservoir that pumps air into the water via a hose from outside the reservoir. The airstone helps add oxygen to the water. Both the airstone and the water pump run 24 hours a day.

The biggest advantage of top-fed deep water culture over standard deep water culture is increased growth during the first few weeks. With deep water culture, there is a time when the roots have not reached the water yet. With top-fed deep water culture, 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 top-fed deep water culture over standard deep water culture. However, due to the quicker growth in the beginning, grow time can be reduced by a few weeks.

Rotary

 A rotary hydroponic cultivation demonstration at the Belgian Pavilion Expo in 2015

A rotary hydroponic garden is a style of commercial hydroponics created within a circular frame which rotates continuously during the entire growth cycle of whatever plant is being grown.

While system specifics vary, systems typically rotate once per hour, giving a plant 24 full turns within the circle each 24-hour period. Within the center of each rotary hydroponic garden can be a high intensity grow light, designed to simulate sunlight, often with the assistance of a mechanized timer.

Each day, as the plants rotate, they are periodically watered with a hydroponic growth solution to provide all nutrients necessary for robust growth. Due to the plants continuous fight against gravity, plants typically mature much more quickly than when grown in soil or other traditional hydroponic growing systems. Because rotary hydroponic systems have a small size, it allows for more plant material to be grown per area of floor space than other traditional hydroponic systems.

Rotary hydroponic systems should be avoided at most circumstances, mainly because of their experimental nature and their high costs for finding, buying, operating, and maintaining them.

Substrates (growing support materials)

One of the most obvious decisions hydroponic farmers have to make is which medium they should use. Different media are appropriate for different growing techniques.

Rock wool

 Rock wool

Rock wool (mineral wool) is the most widely used medium in hydroponics. Rock wool is an inert substrate suitable for both run-to-waste and recirculating systems. Rock wool is made from molten rock, basalt or ‘slag’ that is spun into bundles of single filament fibres, and bonded into a medium capable of capillary action, and is, in effect, protected from most common microbiological degradation. Rock wool is typically used only for the seedling stage, or with newly cut clones, but can remain with the plant base for its lifetime. Rock wool has many advantages and some disadvantages. The latter being the possible skin irritancy (mechanical) whilst handling (1:1000). Flushing with cold water usually brings relief. Advantages include its proven efficiency and effectiveness as a commercial hydroponic substrate. Most of the rock wool sold to date is a non-hazardous, non-carcinogenic material, falling under Note Q of the European Union Classification Packaging and Labeling Regulation (CLP).

Mineral wool products can be engineered to hold large quantities of water and air that aid root growth and nutrient uptake in hydroponics; their fibrous nature also provides a good mechanical structure to hold the plant stable. The naturally high pH of mineral wool makes them initially unsuitable to plant growth and requires “conditioning” to produce a wool with an appropriate, stable pH.

Expanded clay aggregate

Main article: Expanded clay aggregateExpanded clay aggregate

Baked clay pellets are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellets are inert, pH-neutral, and do not contain any nutrient value.

The clay is formed into round pellets and fired in rotary kilns at 1,200 °C (2,190 °F). This causes the clay to expand, like popcorn, and become porous. It is light in weight, and does not compact over time. The shape of an individual pellet can be irregular or uniform depending on brand and manufacturing process. The manufacturers consider expanded clay to be an ecologically sustainable and re-usable growing medium because of its ability to be cleaned and sterilized, typically by washing in solutions of white vinegar, chlorine bleach, or hydrogen peroxide (H
₂O
₂), and rinsing completely.

Another view is that clay pebbles are best not re-used even when they are cleaned, due to root growth that may enter the medium. Breaking open a clay pebble after a crop has been shown to reveal this growth.

Growstones

Growstones, made from glass waste, have both more air and water retention space than perlite and peat. This aggregate holds more water than parboiled rice hulls. Growstones by volume consist of 0.5 to 5% calcium carbonate – for a standard 5.1 kg bag of Growstones that corresponds to 25.8 to 258 grams of calcium carbonate. The remainder is soda-lime glass.

Coconut Coir

Regardless of hydroponic demand, coconut coir is a natural byproduct derived from coconut processes. The outer husk of a coconut consists of fibers which are commonly used to make a myriad of items ranging from floor mats to brushes. After the long fibers are used for those applications, the dust and short fibers are merged to create coir. Coconuts absorb high levels of nutrients throughout their life cycle, so the coir must undergo a maturation process before it becomes a viable growth medium. This process removes salt, tannins and phenolic compounds through substantial water washing. Contaminated water is a byproduct of this process, as three hundred to six hundred liters of water per one cubic meter of coir is needed.Additionally, this maturation can take up to six months and one study concluded the working conditions during the maturation process are dangerous and would be illegal in North America and Europe. Despite requiring attention, posing health risks and environmental impacts, coconut coir has impressive material properties. When exposed to water, the brown, dry, chunky and fibrous material expands nearly three-four times its original size. This characteristic combined with coconut coir’s water retention capacity and resistance to pests and diseases make it an effective growth medium. Used as an alternative to rock wool, coconut coir, also known as coir peat, offers optimized growing conditions.