الصباح النجار
04-10-2009, 12:59 PM
Hydroponics
http://www.hydroponicist.com/images/hydroponics-grow-room.gif
http://upload.wikimedia.org/wikipedia/commons/b/b3/Hydroponic_onions_nasa.jpg
History
http://www.odec.ca/projects/2005/lees5s0/public_html/Hydroponics_files/image006.jpg
The study of crop nutrition began thousands of years ago. Ancient history tells us that various experiments were undertaken by Theophrastus (http://en.wikipedia.org/wiki/Theophrastus) (372-287 B.C.), while several writings of Dioscorides (http://en.wikipedia.org/wiki/Dioscorides) on botany dating from the first century A.D., are still in existence.[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0)
The earliest published work on growing terrestrial plants without soil was the 1627 book, Sylva Sylvarum by Sir Francis Bacon (http://en.wikipedia.org/wiki/Francis_Bacon), printed a year after his death. Water culture became a popular research technique after that. In 1699, John Woodward (http://en.wikipedia.org/wiki/John_Woodward_(naturalist)) published his water culture experiments with spearmint (http://en.wikipedia.org/wiki/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 to plant growth had been made out, and the discoveries of the German botanists, Julius von Sachs (http://en.wikipedia.org/wiki/Julius_von_Sachs) and Wilhelm Knop, in the years 1859-65, resulted in a development of the technique of soilless cultivation.[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0) 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 began publicly promoting that solution culture be used for agricultural crop production. He first termed it aquaculture but later found that aquaculture (http://en.wikipedia.org/wiki/Aquaculture) was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato vines twenty-five feet high in his back yard in mineral nutrient solutions rather than soil.[2] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-1#cite_note-1) By analogy with the ancient Greek (http://en.wikipedia.org/wiki/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").[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0)
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 claiming 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 (http://pmb.berkeley.edu/newpmb/faculty/hoagland/NAS_Memoir.pdf) and Daniel I. Arnon (http://pmb.berkeley.edu/newpmb/faculty/deceased.shtml) wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil,[3] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-2#cite_note-2) 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 hydroponics prevents this from occurring as large amounts of water can be made available to the plant and any water not used, drained away, recirculated, or actively aerated, eliminating anoxic conditions which drown root systems in soil. In soil, 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 lose the ability to transport nutrients, which are typically moved into the roots while in solution.
These two researchers developed several formulas for mineral nutrient solutions, known as Hoagland solutions (http://en.wikipedia.org/wiki/Hoagland). Modified Hoagland solutions are still used today.
One of the early successes of hydroponics occurred on Wake Island (http://en.wikipedia.org/wiki/Wake_Island), a rocky atoll in the Pacific Ocean used as a refueling stop for Pan American Airlines (http://en.wikipedia.org/wiki/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 (http://en.wikipedia.org/wiki/Nutrient_film_technique). The Land Pavilion (http://en.wikipedia.org/wiki/The_Land_(Disney)) at Walt Disney World's EPCOT Center opened in 1982 and prominently features a variety of hydroponic techniques. In recent decades, NASA (http://en.wikipedia.org/wiki/NASA) has done extensive hydroponic research for their Controlled Ecological Life Support System (http://en.wikipedia.org/wiki/Controlled_Ecological_Life_Support_ System) or CELSS. Hydroponics intended to take place on Mars are using LED lighting to grow in different color spectrum with much less heat.
In 1978, hydroponics pioneer Dr. Howard Resh published the first edition of his book "Hydroponics Food Production." This book (now updated) spurred what has become known as the 3-part base nutrients formula that is still a major component of today's hydroponics gardening. Resh later went on to publish other books, and is currently in charge of a highly advanced hydroponics research and production facility in the Caribbean.
http://avocado99.files.wordpress.com/2008/09/hydro-garden-sept-2008.jpg
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 (http://en.wikipedia.org/wiki/Sand) is a type of soil yet sand culture is considered a type of soilless culture. Hydroponics is a subset of soilless culture. 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 (http://en.wikipedia.org/wiki/Fertilizers), cation exchange and decomposition of the organic medium itself. Most soilless media for container plants also contain organic materials such as peat (http://en.wikipedia.org/wiki/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.
http://www.marklaurence.com/articles/pics/homemade_hydroponics.jpg
Advantages>
Today, hydroponics is an established branch of agronomical science. Progress has been rapid, and results obtained in various countries have proved it to be thoroughly practical and to have very definite advantages over conventional methods of horticulture (http://en.wikipedia.org/wiki/Horticulture). The two chief merits of the soilless cultivation of plants are, first, much higher crop yields, and secondly, the fact that hydroponics can be used in places where ordinary agriculture or gardening is impossible. Thus not only is it a profitable undertaking, but one which has proved of great benefit to humanity. People living in crowded city streets, without gardens, can grow fresh vegetables and fruits in window-boxes or on house tops. By means of hydroponics all such places can be made to yield a regular and abundant supply of clean, health-giving greens. Not only town dwellers, but also country residents have cause to be thankful to soiless culture. Deserts, rocky and stony land in mountainous districts or barren and sterile areas can be made productive at relatively low cost.
Other advantages include faster growth combined with relative freedom from soil diseases, and very consistent crops, the quality of produce being excellent. There is also a considerable reduction in growing area, weeds are practically non-existent, while standard methods and automatic operations mean less labor, less cost, and no hard manual work. Some plants can be raised, out of season, better control of crops naturally results in addition to no dirt and no smells. Waterlogging (http://en.wikipedia.org/wiki/Waterlogging) never occurs now. Chemically grown plants are not inferior to naturally reared ones in point of flavor, nor have analyses shown any deficiency in vitamin content.[citation needed (http://en.wikipedia.org/wiki/Wikipedia:Citation_needed)]
http://www.1-hydroponics.co.uk/images/hydroponic-systems/thumbs/hydroponics-vertical-garden.jpg
Disadvantages</>
The hydroponic conditions (presence of fertilizer and high humidity) create an environment that stimulates salmonella (http://en.wikipedia.org/wiki/Salmonella) growth.[4] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-3#cite_note-3) Another disadvantage is pathogens attacks including damp-off due to Verticillium wilt (http://en.wikipedia.org/wiki/Verticillium_wilt) caused by the high moisture levels associated with hydroponics and overwatering of soil based plants.[5] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-4#cite_note-4)
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 (http://en.wikipedia.org/wiki/Irrigation). 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 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 (http://en.wikipedia.org/wiki/Mason_jar) (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 system can be constructed from plastic food containers or glass canning jars with aeration (http://en.wikipedia.org/wiki/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 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 (http://en.wikipedia.org/wiki/EC_meter). Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A Mariotte's bottle (http://en.wikipedia.org/wiki/Mariotte%27s_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.
http://www.hydroponics.co.nz/images/large/EDENVALE-italian-parsley2.jpg
Continuous flow solution culture>
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 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 (http://en.wikipedia.org/wiki/Nutrient_film_technique) or NFT whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated past the bare roots of plants in a watertight gully, also known as channels. Ideally, the depth of the recirculating stream should be very shallow, little more than a film of water, hence the name 'nutrient film'. This ensures that the thick root mat, which develops in the bottom of the channel, has an upper surface which, although moist, is in the air. Subsequently, there is an abundant supply of oxygen 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, providing 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. Consequently, 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 waterlogging may occur. The slope may be provided by the floor, or 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 1 liter per minute. At planting, rates may be half this and the upper limit of 2L/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 metres 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. Consequently, channel length should not exceed 10-15 metres. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed half way along the gully and reducing flow rates to 1L/min through each outlet.
http://www.hydroponicist.com/images/hydroponics-grow-room.gif
http://upload.wikimedia.org/wikipedia/commons/b/b3/Hydroponic_onions_nasa.jpg
History
http://www.odec.ca/projects/2005/lees5s0/public_html/Hydroponics_files/image006.jpg
The study of crop nutrition began thousands of years ago. Ancient history tells us that various experiments were undertaken by Theophrastus (http://en.wikipedia.org/wiki/Theophrastus) (372-287 B.C.), while several writings of Dioscorides (http://en.wikipedia.org/wiki/Dioscorides) on botany dating from the first century A.D., are still in existence.[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0)
The earliest published work on growing terrestrial plants without soil was the 1627 book, Sylva Sylvarum by Sir Francis Bacon (http://en.wikipedia.org/wiki/Francis_Bacon), printed a year after his death. Water culture became a popular research technique after that. In 1699, John Woodward (http://en.wikipedia.org/wiki/John_Woodward_(naturalist)) published his water culture experiments with spearmint (http://en.wikipedia.org/wiki/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 to plant growth had been made out, and the discoveries of the German botanists, Julius von Sachs (http://en.wikipedia.org/wiki/Julius_von_Sachs) and Wilhelm Knop, in the years 1859-65, resulted in a development of the technique of soilless cultivation.[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0) 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 began publicly promoting that solution culture be used for agricultural crop production. He first termed it aquaculture but later found that aquaculture (http://en.wikipedia.org/wiki/Aquaculture) was already applied to culture of aquatic organisms. Gericke created a sensation by growing tomato vines twenty-five feet high in his back yard in mineral nutrient solutions rather than soil.[2] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-1#cite_note-1) By analogy with the ancient Greek (http://en.wikipedia.org/wiki/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").[1] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-references-0#cite_note-references-0)
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 claiming 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 (http://pmb.berkeley.edu/newpmb/faculty/hoagland/NAS_Memoir.pdf) and Daniel I. Arnon (http://pmb.berkeley.edu/newpmb/faculty/deceased.shtml) wrote a classic 1938 agricultural bulletin, The Water Culture Method for Growing Plants Without Soil,[3] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-2#cite_note-2) 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 hydroponics prevents this from occurring as large amounts of water can be made available to the plant and any water not used, drained away, recirculated, or actively aerated, eliminating anoxic conditions which drown root systems in soil. In soil, 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 lose the ability to transport nutrients, which are typically moved into the roots while in solution.
These two researchers developed several formulas for mineral nutrient solutions, known as Hoagland solutions (http://en.wikipedia.org/wiki/Hoagland). Modified Hoagland solutions are still used today.
One of the early successes of hydroponics occurred on Wake Island (http://en.wikipedia.org/wiki/Wake_Island), a rocky atoll in the Pacific Ocean used as a refueling stop for Pan American Airlines (http://en.wikipedia.org/wiki/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 (http://en.wikipedia.org/wiki/Nutrient_film_technique). The Land Pavilion (http://en.wikipedia.org/wiki/The_Land_(Disney)) at Walt Disney World's EPCOT Center opened in 1982 and prominently features a variety of hydroponic techniques. In recent decades, NASA (http://en.wikipedia.org/wiki/NASA) has done extensive hydroponic research for their Controlled Ecological Life Support System (http://en.wikipedia.org/wiki/Controlled_Ecological_Life_Support_ System) or CELSS. Hydroponics intended to take place on Mars are using LED lighting to grow in different color spectrum with much less heat.
In 1978, hydroponics pioneer Dr. Howard Resh published the first edition of his book "Hydroponics Food Production." This book (now updated) spurred what has become known as the 3-part base nutrients formula that is still a major component of today's hydroponics gardening. Resh later went on to publish other books, and is currently in charge of a highly advanced hydroponics research and production facility in the Caribbean.
http://avocado99.files.wordpress.com/2008/09/hydro-garden-sept-2008.jpg
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 (http://en.wikipedia.org/wiki/Sand) is a type of soil yet sand culture is considered a type of soilless culture. Hydroponics is a subset of soilless culture. 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 (http://en.wikipedia.org/wiki/Fertilizers), cation exchange and decomposition of the organic medium itself. Most soilless media for container plants also contain organic materials such as peat (http://en.wikipedia.org/wiki/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.
http://www.marklaurence.com/articles/pics/homemade_hydroponics.jpg
Advantages>
Today, hydroponics is an established branch of agronomical science. Progress has been rapid, and results obtained in various countries have proved it to be thoroughly practical and to have very definite advantages over conventional methods of horticulture (http://en.wikipedia.org/wiki/Horticulture). The two chief merits of the soilless cultivation of plants are, first, much higher crop yields, and secondly, the fact that hydroponics can be used in places where ordinary agriculture or gardening is impossible. Thus not only is it a profitable undertaking, but one which has proved of great benefit to humanity. People living in crowded city streets, without gardens, can grow fresh vegetables and fruits in window-boxes or on house tops. By means of hydroponics all such places can be made to yield a regular and abundant supply of clean, health-giving greens. Not only town dwellers, but also country residents have cause to be thankful to soiless culture. Deserts, rocky and stony land in mountainous districts or barren and sterile areas can be made productive at relatively low cost.
Other advantages include faster growth combined with relative freedom from soil diseases, and very consistent crops, the quality of produce being excellent. There is also a considerable reduction in growing area, weeds are practically non-existent, while standard methods and automatic operations mean less labor, less cost, and no hard manual work. Some plants can be raised, out of season, better control of crops naturally results in addition to no dirt and no smells. Waterlogging (http://en.wikipedia.org/wiki/Waterlogging) never occurs now. Chemically grown plants are not inferior to naturally reared ones in point of flavor, nor have analyses shown any deficiency in vitamin content.[citation needed (http://en.wikipedia.org/wiki/Wikipedia:Citation_needed)]
http://www.1-hydroponics.co.uk/images/hydroponic-systems/thumbs/hydroponics-vertical-garden.jpg
Disadvantages</>
The hydroponic conditions (presence of fertilizer and high humidity) create an environment that stimulates salmonella (http://en.wikipedia.org/wiki/Salmonella) growth.[4] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-3#cite_note-3) Another disadvantage is pathogens attacks including damp-off due to Verticillium wilt (http://en.wikipedia.org/wiki/Verticillium_wilt) caused by the high moisture levels associated with hydroponics and overwatering of soil based plants.[5] (http://en.wikipedia.org/wiki/Hydroponics#cite_note-4#cite_note-4)
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 (http://en.wikipedia.org/wiki/Irrigation). 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 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 (http://en.wikipedia.org/wiki/Mason_jar) (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 system can be constructed from plastic food containers or glass canning jars with aeration (http://en.wikipedia.org/wiki/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 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 (http://en.wikipedia.org/wiki/EC_meter). Whenever the solution is depleted below a certain level, either water or fresh nutrient solution is added. A Mariotte's bottle (http://en.wikipedia.org/wiki/Mariotte%27s_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.
http://www.hydroponics.co.nz/images/large/EDENVALE-italian-parsley2.jpg
Continuous flow solution culture>
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 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 (http://en.wikipedia.org/wiki/Nutrient_film_technique) or NFT whereby a very shallow stream of water containing all the dissolved nutrients required for plant growth is recirculated past the bare roots of plants in a watertight gully, also known as channels. Ideally, the depth of the recirculating stream should be very shallow, little more than a film of water, hence the name 'nutrient film'. This ensures that the thick root mat, which develops in the bottom of the channel, has an upper surface which, although moist, is in the air. Subsequently, there is an abundant supply of oxygen 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, providing 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. Consequently, 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 waterlogging may occur. The slope may be provided by the floor, or 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 1 liter per minute. At planting, rates may be half this and the upper limit of 2L/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 metres 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. Consequently, channel length should not exceed 10-15 metres. In situations where this is not possible, the reductions in growth can be eliminated by placing another nutrient feed half way along the gully and reducing flow rates to 1L/min through each outlet.