Hydroponics

NASA researcher checking hydroponic onions with Bibb lettuce to his left and radishes to the right

File:Autotrophic-Metabolism.jpg

Example of Autotrophic Metabolism

Hydroponics is a method of growing plants using mineral nutrient solutions instead of soil. Terrestrial plants may be grown with their roots in the mineral nutrient solution only or in an inert medium, such as perlite, gravel or Rockwool. A variety of techniques exist.

Plant physiology researchers discovered in the 1800s that plants absorb essential mineral nutrients as inorganic ions in water. In natural conditions, soil acts as a mineral nutrient reservoir but the soil itself is not essential to plant growth. When the mineral nutrients in the soil dissolve in water, plant roots are able to absorb them. When the required mineral nutrients are introduced into a plant's water supply artificially, soil is no longer required for the plant to thrive. Almost any terrestrial plant will grow with hydroponics, but some will do better than others. It is also very easy to do; the activity is often undertaken by very young children with such plants as watercress. Hydroponics is also a standard technique in biology research and teaching and a popular hobby.

History

Researcher with hydroponic strawberries

The term hydroponics is derived from Greek and literally means 'working water'. Many people use the term hydroponics to describe any methods of growing that does not use soil (although some scientists dispute this definition) and in that sense ancient peoples such as the Babylonians and Aztecs used hydroponics, as nutrients were obtained from other sources. The mineral nutrient solutions used today for hydroponics were not developed until the 1800s.

The earliest published work on growing terrestrial plants without soil was the 1627 book, Sylva Sylvarum by Sir Francis Bacon, although Bacon died in 1626. Water culture became a popular research technique after that. 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. Mineral nutrient solutions for soilless culture of plants were first perfected in the 1860s by the German botanists, Julius von Sachs and Wilhelm Knop. Growth of terrestrial plants without soil in mineral nutrient solutions was called solution culture. It quickly became a standard research and teaching technique and is still widely used today. Solution culture is now considered a type of hydroponics where there is no inert medium.

In 1929, Professor William Frederick Gericke of the University of California at Berkeley was first to suggest that solution culture be used for agricultural crop production. He first termed it aquiculture but later found that aquaculture was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato and other plants to a remarkable size in his backyard in mineral nutrient solutions rather than soil. By analogy with the ancient Greek term for agriculture, geoponics, the science of cultivating the earth, Gericke introduced the term hydroponics in 1937 (although he asserts that the term was suggested by Dr. W. A. Setchell, of the University of California) for the culture of plants in water (from the Greek hydros, water, and ponos, labor).

Reports of Gericke's work and his claims that hydroponics would revolutionize plant agriculture prompted a huge number of requests for further information. Gericke refused to reveal his secrets because he had done the work at home on his own time. This refusal eventually resulted in his leaving the University of California. In 1940, he wrote the book, Complete Guide to Soilless Gardening.

Two other plant nutritionists at the University of California were asked to research Gericke's claims. Dennis R. Hoagland and Daniel I. Arnon wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil, debunking the exaggerated claims made about hydroponics. Hoagland and Arnon found that hydroponic crop yields were no better than crop yields with good quality soils. Crop yields were ultimately limited by factors other than mineral nutrients, especially light. This research, however, overlooked the fact that hydroponics has other advantages 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 growing is over and under-watering and active hydroponics prevents this from occurring as large amounts of water can be made available to the plant and any water not used is drained away or recirculated. In soil growing a grower needs to be very experienced to know exactly how much water to feed the plant. Too much and the plant will not be able to access oxygen, too little and the plant will go dry.

These two researchers developed several formulas for mineral nutrient solutions, known as Hoagland solutions. Modified Hoagland solutions are still used today.

One of the early 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.

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 their Controlled Ecological Life Support System or CELSS.

By 1983, Superior Growers Supply was one of the first hydroponic merchants in the United States, helping to introduce gardening techniques using all the different methods of hydroponics to the general public. Forming international relationships with the worlds leading hydroponic company Growth Technology, and together launching Hydrodynamics International, another company dedicated to the evolution of the hydroponics industry. Gardeners can buy a complete kitchen hydroponics growing system for under 200USD, with the new Aerogarden plant growing system, or a number of other hydroponics systems on the market. Consumers can grow certain plants year-round that are superior to soil-grown plants, and use less space. Currently, there are well over 100 hydroponic gardening centers throughout United States.

Soilless culture

Gericke originally defined hydroponics as crop growth in mineral nutrient solutions, with no solid medium for the roots. He objected in print to people who applied the term hydroponics to other types of soilless culture such as sand culture and gravel culture. The distinction between hydroponics and soilless culture of plants has often been blurred. Soilless culture is a broader term than hydroponics; it only requires that no soils with clay or silt are used. Note that sand is a type of soil yet sand culture is considered a type of soilless culture. Hydroponics is always soilless culture, but not all soilless culture is hydroponics. Many types of soilless culture do not use the mineral nutrient solutions required for hydroponics.

Billions of container plants are produced annually, including fruit, shade and ornamental trees, shrubs, forest seedlings, vegetable seedlings, bedding plants, herbaceous perennials and vines. Most container plants are produced in soilless media, representing soilless culture. However, most are not hydroponics because the soilless medium often provides some of the mineral nutrients via slow release fertilizers, cation exchange and decomposition of the organic medium itself. Most soilless media for container plants also contain organic materials such as peat or composted bark, which provide some nitrogen to the plant. Greenhouse growth of plants in peat bags is often termed hydroponics, but technically it is not because the medium provides some of the mineral nutrients. Peat has a high cation exchange capacity and must be amended with limestone to raise the pH.

Advantages

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Disadvantages

• If timers or electric pumps fail or the system clogs or springs a leak, plants can die very quickly in many kinds of hydroponic systems.
• Hydroponics usually requires a greater technical knowledge than geoponics.
• For the previous two reasons and the fact that most hydroponic crops are grown in greenhouses or controlled environment agriculture, hydroponic crops are usually more expensive than soil-grown crops.
• Solution culture hydroponics requires that the plants be supported because the roots have no anchorage without a solid medium.
• The plants will die if not frequently monitored while soil plants do not require such close attention.

Common misconceptions

Hydroponics has been widely misconceived as miraculous. There are many widely held misconceptions regarding hydroponics, as noted by the following facts:

• Hydroponics will not always produce greater crop yields than with good quality soil.
• Hydroponic plants cannot always be spaced closer together than soil-grown crops (geoponics) under the same environmental conditions.
• Hydroponic produce will not necessarily be more nutritious or better tasting than geoponics.

Techniques

The two main types of hydroponics are solution culture and medium culture. Solution culture does not use a solid medium for the roots, just the nutrient solution. The three main types of solution culture are static solution culture, continuous flow solution culture and aeroponics. The medium culture method has a solid medium for the roots and is named for the type of medium, e.g. sand culture, gravel culture or rockwool culture. There are two main variations for each medium, subirrigation and top irrigation. For all techniques, most hydroponic reservoirs are now built of plastic but other materials have been used including concrete, glass, metal and wood. The containers should exclude light to prevent algae growth in the nutrient solution.

Static solution culture

In static solution culture, plants are grown in containers of nutrient solution, such as glass Mason jars (typically in-home applications), plastic buckets, tubs or tanks. The solution is usually gently aerated but may be unaerated. If unaerated, the solution level is kept low enough that enough roots are above the solution so they get adequate oxygen. A hole is cut in the lid of the reservoir for each plant. There can be one to many plants per reservoir. Reservoir size can be increased as plant size increases. A homemade fugifilm system can be constructed from plastic food containers or glass canning jars with aeration provided by an aquarium pump, aquarium airline tubing and aquarium valves. Clear containers are covered with aluminum foil, butcher paper, black plastic or other material to exclude light. The nutrient solution is either changed 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 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

In continuous flow solution culture the nutrient solution constantly flows past the roots. It is much harder to automate than the static solution culture because sampling and adjustments to degree and nutrient concentrations can be made in a large storage tank that serves potentially thousands of plants. A popular variation is the nutrient film technique or NFT. In NFT, the plants grow through light-proof plastic films placed over shallow, gently sloping channels. A steady flow of nutrient solution is maintained along the channel, and the roots grow into dense mats, with a thin film of nutrient passing over them (hence the name of the technique). 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.

Aeroponics

Main article: Aeroponics

Aeroponics is similar to hydroponics but instead of submerging the roots in a liquid, a fog or mist of the nutrient solution is sprayed over the root system. This has the advantage of minimizing water usage as well as giving the roots ample access to oxygen. Aeroponics have been given special attention from NASA since a mist is easier to handle than a liquid in a zero gravity environment.

Passive subirrigation

The medium generally has large air spaces, allowing ample oxygen to the roots, while capillary action delivers water and nutrients to the roots from the base of the medium. The simplest method has the container constantly sit in a shallow layer of nutrient solution or on a capillary mat saturated with nutrient solution. A variety of materials can be used for the medium: vermiculite, perlite, clay granules, rockwool, or gravel. This method requires little maintenance, requiring only occasional refilling and replacement of the nutrient solution. This keeps the medium regularly flushed with nutrient solution and air.

Additional advantages of these sterile porous media are the reduction of root rotting conditions and the additional ambient humidity provided. These advantages are particularly important in the use of hydroponics for orchid cultivation.

It is important in passive subirrigation to wash out the system from time to time to remove salt accumulation. This may be checked with an electrical conductivity or ppm meter, a good average reading would be about 1500 ppm. Lettuce grows well at about 800 ppm and tomatoes to 3000 ppm but both will grow reasonably well on 1500 ppm. It is important to keep the pH reading at about 6.3 to enable nutrient uptake. Data are available for the optimum settings for most plants.

This is commonly employed for large display plants in public buildings: in Europe a system using small clay granules is marketed for growing houseplants. A similar subirrigation method uses a wick. The wick runs from the base of the plant container (e.g. a pot or a tray) down to a bottle of nutrient solution. The solution travels up the wick into the medium through capillary action.

Flood and drain (or ebb and flow system) subirrigation

In its simplest form, there is a tray above a reservoir of nutrient solution. The tray is either filled with growing medium (clay granules being the most common) and planted directly, or pots of 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.

Top irrigation

In top irrigation, nutrient solution is periodically applied to the medium surface. This may be done manually once per day in large containers of some media, such as sand. Usually, it is automated with a pump, timer and drip irrigation tubing to deliver nutrient solution as frequently as 5 to 10 minutes every hour.

Deep water culture

Main 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.

Organoponics

Main article: Organoponics

In a hydroponic system the roots need to be able to absorb nutrients as they touch the roots hairs. There is no soil for organic fertilizer to sit in and release nutrients. So far, many chemical additives and root stimulators have done a great job adding nutrients to the plant through hydroponic gardening. Some claim that soil grown plants produce better tasting and possibly more nutritious food than hydroponically grown plants althought this statement is not proven.

Media

One of the most obvious decisions a hydroponicist has to make is which medium they should use. Different media are appropriate for different growing techniques.

Diahydro

Natural sedimentary rock medium. Diahydro consists of the fossilized shells of algae (diatoms) that lived millions of years ago. Diahydro is extremely high in Silica (87-94%), an essential component for the growth of plants and strengthening of cell walls.

Expanded clay

Also known as 'Hydroton' or 'leca' (light expanded clay aggregate), trademarked names, these small, round baked spheres of clay are inert and are suitable for hydroponic systems in which all nutrients are carefully controlled in water solution. The clay pellet is also inert, pH neutral and do not contain any nutrient value.

The clay is formed into round pellets and fired in rotary kilns at 1200°C. This causes the clay to expand, like popcorn, and become porous. It is light in weight, and does not compact over time. Shape of individual pellet can be irregular or uniform depending on brand and manufacturing process. The manufacturers considers expanded clay to be an ecologically sustainable and re-usable growing medium because of it's ability to be cleaned and sterilized, typically by washing in solutions of white vinegar, chlorine bleach or hydrogen peroxide (H2O2), and rinsing completely.

Another viewpoint is clay pebbles are best not re-used even when they are cleaned due to root growth which may enter the medium. Breaking open a clay pebble after a crop has been grown will reveal this. However, this view is generally not widely shared.

Rockwool

Rockwool is probably the most widely used medium in Hydroponics. Made from basalt rock it is heat-treated at high temperatures then spun back together like candy floss. It comes in lots of different forms including cubes, blocks, slabs and granulated or flock. When this medium is dry, care needs to be taken so as not to inhale any particles — inhaling such particles may carry a health risk. Rockwool initially causes an increase in pH level. You must adjust the pH level of the nutrient solution to counteract this. A pH level of 5.5-6.5 should suffice to create a suitable pH.

Coir

Coir, from coconut husk fiber, can be used as a compressed medium. Coir comes also in bags and in slabs. Some types of coir are very high in sodium (salt) due to the nature of coconut palms growing on island environments and being processed in the salt air.

Perlite

Perlite is a volcanic rock that has been superheated into very lightweight expanded glass pebbles. It is used loose or in plastic sleeves immersed in the water. It is also used in potting soil mixes to decrease soil density. Perlite has similar properties and uses to vermiculite but generally holds more air and less water. If not contained, it can float if flood and drain feeding is used.

Vermiculite

Like perlite, vermiculite is another mineral that has been superheated until it has expanded into light pebbles. Vermiculite holds more water than perlite and has a natural "wicking" property that can draw water and nutrients in a passive hydroponic system. If too much water and not enough air surrounds the plants roots, it's possible to gradually lower the medium's water-retention capability by mixing in increasing quantities of perlite.

Sand

Sand is cheap and easily available. However, it is heavy, it does not always drain well, and it must be sterilized between use.

Gravel

The same type that is used in aquariums, though any small gravel can be used, provided it is washed first. Indeed, plants growing in a typical traditional gravel filter bed, with water circulated using electric powerhead pumps, are in effect being grown using gravel hydroponics. Gravel is inexpensive, easy to keep clean, drains well and won't become waterlogged. However, it is also heavy, and if the system doesn't provide continuous water, the plant roots may dry out.

Brick Shards

Broken up brick has been used in the place of gravel, works just like it, the disadvantage being that it may alter the pH and if recycled, has to be cleaned first.

Polystyrene Packing Peanuts

Very lightweight. Cheap, readily available and they drain well. They can be too light, and are mainly used in closed tube systems. Only polystyrene peanuts can be used: the biodegradable ones will become a sludge.

Nutrient Solutions

Plant nutrients are dissolved in the water used in hydroponics and are mostly in inorganic and ionic form. Primary among the dissolved cations (positively-charged ions) are Ca²⁺ (calcium), Mg²⁺ (magnesium), and K⁺ (potassium); the major nutrient anions in nutrient solutions are NO₃⁻ (nitrate), SO₄²⁻ (sulfate), and H₂PO₄⁻ (phosphate).

Numerous 'recipes' for hydroponic solutions are available. Many use different combinations of chemicals to reach similar total final compositions. Commonly-used chemicals for the macronutrients include potassium nitrate, calcium nitrate, potassium phosphate, and magnesium sulfate. Various micronutrients are typically added to hydroponic solutions to supply essential elements; among them are Fe (iron), Mn (manganese), Cu (copper), Zn (zinc), B (boron), Cl (chlorine), and Ni (nickel). Chelating agents are sometimes used to keep Fe soluble. Many variations of the nutrient solutions used by Arnon and Hoagland (see above) have been styled 'modified Hoagland solutions' and are widely used.

Plants will change the composition of the nutrient solutions upon contact by depleting specific nutrients more rapidly than others, removing water from the solution, and altering the pH by excretion of either acidity or alkalinity. Care is required not to allow salt concentrations to become too high, nutrients to become too depleted, or pH to wander far from the desired value.

Commercial

Due to their arid climate, Israel has developed advanced hydroponic technology. They have marketed their system to Nicaragua, which uses it to produce more than one million pounds of peppers annually for sale abroad, including the United States.

The largest commercial hydroponics facility in the world is Eurofresh Farms in Willcox, Arizona, which sold 125 million pounds of tomatoes in 2005. Eurofresh has 256 acres under glass and represents about a third of the commercial hydroponic greenhouse area in the U.S. Eurofresh does not consider their tomatoes organic, but they are pesticide-free. They are grown in rockwool with top irrigation.

Some commercial installations use no pesticides or herbicides, preferring integrated pest management techniques. There is often a price premium willingly paid by consumers for produce which is labeled "organic". Some states in the USA require soil as an essential to obtain organic certification. There are also overlapping and somewhat contradictory rules established by the US Federal Government. So some food grown with hydroponics can be certified organic. In fact, they are the cleanest plants possible because there is no environment variable and the dirt in the food supply is extremely limited. Hydroponics also saves an incredible amount of water; It uses as little as 1/20 the amount as a regular farm to produce the same amount of food. The water table can be impacted by the water use and run-off of chemicals from farms, but hydroponics may minimize impact as well as having the advantage that water use and water returns are easier to measure. This can save the farmer money by allowing reduced water use and the ability to measure consequences to the land around a farm.

The environment in a hydroponics greenhouse is tightly controlled for maximum efficiency and this new mindset is called Soil-less/Controlled Environment Agriculture (S/CEA). With this growers can make ultra-premium foods anywhere in the world, regardless of temperature and growing seasons. Growers monitor the temperature, humidity, and pH level constantly.

Hydroponics have been used to enhance vegetables to provide more nutritional value. A hydroponic farmer in Virginia has developed a calcium and potassium enriched head of lettuce, scheduled to be widely available in April of 2007. Grocers in test markets have said that the lettuce sells "very well," and the farmers claim that their hydroponic lettuce uses 90% less water than traditional soil farming.

Present and future

With pest problems reduced, and nutrients constantly fed to the roots, productivity in hydroponics is high, plant growth being limited by the low levels of carbon dioxide in the atmosphere, or limited light. To increase yield further, some sealed greenhouses inject carbon dioxide into their environment to help growth (CO₂ enrichment), or add lights to lengthen the day, control vegetative growth etc.

This technology allows you to grow where no one has grown before, be it underground, or above, in space or under the oceans this technology will allow humanity to live where humanity chooses. If used for our own survival or our colonisation, hydroponics is and will be a major part of our collective future.

External links

• Barak, P. 2002. Essential Elements for Plant Growth: Hydroponics.
• Hershey, D.R. 1994. Solution culture hydroponics: history and inexpensive equipment. American Biology Teacher 56:111-118.
• Jensen, M.H. 1997. Hydroponics. HortScience 32
• Hydroponics as a Hobby: Growing Plants Without Soil. University of Illinois Circular 844
• Utah State Univerisity Hydroponics
• Hydroponics at McMurdo Station Antarctica
• Antarctic Hydroponics
• Cornell University Commercial Hydroponic Lettuce, Spinach and Pak Choi Grower's Handbooks
• Hydroponics and Soilless Cultures on Artificial Substrates as an Alternative to Methyl Bromide Soil Fumigation

See also

• Growroom