Mineral solutions to provide the nutrients required for hydroponic crops were not developed until the 20th century. The gardens to cover parts of lakes of the Aztecs (chinampas) used earth. The Hanging Gardens of Babylon were gardens supposedly irrigated from the roof but there is no evidence that they used hydroponics.

The idea of ​​growing plants in environmentally controlled areas also existed in Rome. The Roman emperor Tiberius introduced the cultivation of cucumber[3]​ using hydroponic techniques.

The study of hydroponics dates back to 382 BC. C. but the first written information is from 1600, when the Belgian Jan van Helmont documented his experience that plants obtain nutritional substances from water. The first published work on the growth of terrestrial plants without soil was,

Sylva Sylvarum (1627) by Francis Bacon. After that, the water technique became popular in research. In 1699, John Woodward grew plants in water and found

that their growth was the result of certain substances in the water obtained from the soil, this when observing that the plants grew worse in distilled water than in sources of

not so purified water. With this he published his experiments of this technique with spearmint. In 1804, De Saussure expounded the principle that plants are composed

by chemical elements obtained from water, soil and air. The first to perfect mineral nutrient solutions for soilless cultivation were the German botanists Julius von Sachs.

and Wilhelm Knop") in the 1860s. The growth of terrestrial plants without soil in mineral solutions (solution culture) quickly became a standard research technique

and teaching and continues to be widely used. This technique is now considered a type of hydroponic farming.[4]​.

In 1928, Professor William Frederick Gericke of the University of California at Berkeley in California was the first to suggest that solution cultures be used for agricultural plant production. Gericke caused a sensation by growing tomatoes and other plants that reached remarkable sizes (larger than those grown in soil) in mineral solutions which led to his article entitled "Aquaculture: A Means of Producing Crops" (1929). By analogy with the term geoponics (meaning agriculture in ancient Greek) called this new branch hydroponics in 1937, although he claims that the term was suggested by Dr. W.A. Setchell of the University of California from hydros (water) and ponos (culture/cultivation).

Reports of this work and Gericke's fervent claims that hydroponics would revolutionize agriculture sparked a flurry of requests for additional information. Gericke refused to reveal his secrets, since he had done the studies at home and in his free time. This fact caused him to drop out of the University of California. In 1940, he wrote the book, Complete Guide to Soilless Gardening.

Two other plant nutrition specialists at the University of California were asked to investigate Gericke's claims. Dennis R. Hoagland and Daniel I. Arnon wrote the typical agriculture newsletter in 1938, debunking exaggerated claims made about hydroponics. Hoagland and Arnon concluded that hydroponic crops were no better than crops grown on good soil. Crops were limited by factors other than mineral nutrients, especially light. These investigations, however, overlooked the fact that hydroponics had other advantages including that the roots of the plant have constant access to oxygen and that the plant can have access to as much or as little water as it needs. This is one of the most common mistakes when the crop is over-irrigated or under-irrigated. Hydroponics is capable of preventing this from happening by draining or recirculating the water that is not absorbed by the plant. In crops on land, the farmer needs to have enough experience to know how much water he should water the plant with. The solution with which the roots will be in contact must be sufficiently oxygenated so that root metabolism is not impeded.

These two researchers developed several formulas for mineral nutrient solutions. Modified versions of Hoagland's solutions are still in use today.

One of the first successes of hydroponics occurred during World War II when American troops in the Pacific implemented large-scale hydroponic methods to provide fresh vegetables to troops at war with Japan on islands where land was not available and it was extremely expensive to transport them.

In the 1960s, Alen Cooper in England developed the Nutrient Film Technique. The Earth Pavilion at Disney's Epcot Center, opened in 1982, highlighted various hydroponic techniques. In recent decades, NASA has conducted extensive research for its CELSS (Controlled Ecological Life Support System).

Also in the 1980s, several companies began marketing hydroponic systems. Currently (2010) it is possible to purchase a kit to set up a small home hydroponic growing system for less than €200. Soilless cultivation (CSS) techniques are used on a large scale in commercial circuits for the production of tobacco plants, (floating) thus discarding the "Match (seedbed)") in soil that requires methyl bromide to disinfect the soil from weeds, pathogens and insects. Also in Holland and other countries with a high degree of development in intensive farming, CSS techniques have advanced, developing related industries and numerous technologies related to the development of new growing media such as perlite, rock wool, coconut fiber or cocopeat, toasted rice husk and other appropriate media.

This soilless cultivation technique avoids the impediments or limitations that soil represents in conventional agriculture through the use of substrates, any solid material other than soil that is used for hydroponic planting as support for the plant and not for its nutrition. The use of substrates allows total control over factors that affect plant development, such as humidity, oxygenation and nutrition. They are soilless crops, in that they do not contain natural soil. Agricultural perlite, pumice stone, coconut fibers, peat[5]​ or rock wool, are substrates widely used in what are called hydroponic crops. The equivalent or most commonly used name became soilless crops -CSS or soilless (in English)- since the support medium for the plants became an inorganic substance such as perlite or organic such as peat or certain agricultural waste such as fruit peels -rice, almonds, etc.-. In the case of soilless crops, as they were developed by the industry or by hobbyists, they were not analyzed at first in terms of the impact that their use would have on the environment, as occurred with other developments that were commercially profitable. In the same way, hydroponic systems were from the beginning "open" as the environmental impact that the dumping of effluents after use would have was not considered. The development of "closed" methods that mean economy in terms of the possibility of reusing nutrients and avoiding the impact it has on the external environment, pouring a solution that carries a considerable amount of ions not used by the plants being grown, also, for example, lettuce, is grown in water depending on what type it is, it also depends on its size, it must be planted in a boat with water and if the root is large, only half of it should be submerged since if it all gets wet there may be oxygen problems.

Taking into account economics and possible environmental impact, closed or recirculating systems were developed. The management of these new systems requires more complex technology. As mentioned above, there are a series of developments in the field of substrates, in addition to certain automations developed to facilitate the control of solutions so that they do not vary their chemical parameters. Both hydroponics and fertigation") have given rise to the development of control instruments such as pH-meters and online conductivity meters, as well as processors that maintain control through solenoid or hydraulic valves, so that the solution can be balanced by computer programs that determine the addition of acids when the pH rises, the dilution when the electrical conductivity rises and other control processes that interact with the environment in which the plants are evolving in size and development.

Gericke originally defined hydroponics as growing crops in mineral solutions, without any solid medium for the roots. He opposed those who applied the term hydroponics to other types of soilless cultivation such as cultivation in sand or gravel. More recently, the most classic academic author of hydroponics is Howard Resh. The distinction between hydroponics and soilless growing has often been confusing. “Soilless growing” is a broader term than hydroponics; It only requires that there be no soils with clay or silt. Note that sand is a type of soil, although it is considered soilless cultivation. Hydroponics is always an agricultural soilless crop, but not all soilless crops are hydroponic. Many types of soilless crops do not use the mineral solutions required by hydroponics.

Very recently, the use of containers in hydroponic systems has been proposed. Along with "exponentially higher" yields, the use of containers in hydroponics ensures that all growing systems will also use 90% less water and 80% less fertilizer than those used in conventional agriculture. Hydroponics in these containers require ensuring that the water passes through the same place every 12 minutes of time interval.[6] Converting a shipping container into a "portable farm" is one of the challenges that those interested in hydroponics have, so that its reuse greatly pleases environmental movements.

A very conservative calculation using hydroponics suggests harvesting 4,000 to 6,000 units of vegetables per week (40-50 tons per year), equivalent to 80 times the number of units achieved in the same space using conventional planting and harvesting systems in agriculture.

The latest addition to the growing urban agriculture sector are abandoned shipping containers that make it possible to twin high-tech hydroponic cultivation and its monitoring system with one of the demands of the reuse movement, to make use of a "box farm" that can locally produce large quantities of fresh vegetables all year round.

In the United States, more and more shipping containers are used to grow gourmet strawberries, greens, lettuce, herbs and mushrooms.

The shipping containers hold 2,800 crop germination and development tanks in the 320 square feet (approximately 30 square meters), which can be equipped with artificial lighting, planting racks, an air conditioning and ventilation system, all the necessary hydroponic components (tank, pump, and monitoring and control system), and a complete set of 18 sensors to monitor almost any environmental condition inside the container.

As for the nutrient solution, the aim is to provide the plant with the 13 main mineral elements due to their effects on it. These are:

Contenido

El cultivo sin suelo es justamente un conjunto de técnicas recomendables cuando no hay suelos con aptitudes agrícolas disponibles. El esquema consiste en: una fuente de agua que impulsa por bombeo agua a través del sistema, recipientes con soluciones madre —nutrientes concentrados—, cabezales de riego y canales construidos donde están los sustratos, las plantas, los conductos para aplicación del fertiriego y el recibidor del efluente.

El cansancio de los suelos por alta carga de patógenos tras cultivos repetidos o la acumulación de iones que conllevan alcalinidad o elevación del tenor de sodio ha empujado a muchos productores a realizar cultivos hidropónicos o sin suelo. En cultivos comerciales —en cuanto a su superficie— se hace obligatorio seguir normas ambientales amigables con el ambiente y emplear métodos de recirculación de las soluciones volviéndolas al cultivo tras equilibrarlas y desinfectarlas o buscándoles un lugar de descarga que evite la llegada de los nutrientes efluentes al suelo, cursos de agua y a los mantos acuíferos.

Ya existen métodos en sistemas abiertos que permiten un segundo cultivo, fijación por plantas que crecen en pequeñas lagunas de fondo impermeabilizado y otros ensayándose. Las recomendaciones de realizar cultivos hidropónicos o sin suelo solo por considerar su alta productividad y rendimiento económico, que no tengan en cuenta estos aspectos ambientales perniciosos, no son aconsejables. Los cultivos que son aptos para este método son el tomate, lechuga, repollo, pimiento "Chile (pimiento)"), pepino, espinaca, entre otros. Las temperaturas óptimas para cada uno son variadas: Mientras los que soportan temperaturas más bajas óptimas son el tomate, la lechuga o la calabaza, los que menos soportan temperaturas por debajo de los 18 grados son el pepino y el melón[7]​.

Investigating extreme crops in Antarctica

Germany's southernmost greenhouse is currently located in Antarctica and supplies researchers at the German Neumayer III station with kilos of fresh vegetables, something they normally lack in winter, without soil, sunlight or pesticides.

[8]​

[9]​

The hydroponic cultivation of vegetables is part of a project designed to supply food to human beings in extreme conditions or even in space.

The Neumayer III research station will soon have fresh peppers on its plates. However, the ten-man team will still be without strawberries, as team member Paul Zabel stated in a live video connection in January 2018.

Kilos of tomatoes, lettuce and cucumbers have already been harvested in the new greenhouse launched in February, although the strawberry plants are still not bearing fruit, he indicated. "The plants grow wonderfully and many flowers grow," he noted. But artificial pollination did not work. Why this is so still needs to be examined, said the space engineer.

But Paul Zabel, a researcher in the experiment starting in 2018, was able to show the first small green peppers on camera, although he acknowledged that the harvest was much smaller than expected.

Zabel has spent three quarters of a year sowing lettuce, pruning tomato plants and documenting growth for the German Aerospace Center (DLR). The project should not only enrich the crew's diet, but also provide information for future missions to the Moon and Mars.

In a well-insulated container with a growing area of ​​13 square meters, the plants grow at outdoor temperatures of up to -42 degrees Celsius without soil, daylight or pesticides. The necessary energy comes from the Neumayer III station, located 400 meters away.

A total of 183 kilograms of fresh vegetables have already been harvested. «There is fresh salad almost every day. In the case of cucumbers, the crew has already said: 'That's enough,'" reported project director Daniel Schubert.

Fresh vegetables are extremely important for the mood of the crew spending the winter, isolated in Antarctica for nine months, said Eberhard Kohlberg of the Alfred Wegener Institute (AWI) in Bremerhaven, who is responsible for local logistics.

For the future, Schubert, the project director, imagines that grapes or even apples could be grown in the greenhouse. "This is much more complex than growing lettuce."

Mineral solutions to provide the nutrients required for hydroponic crops were not developed until the 20th century. The gardens to cover parts of lakes of the Aztecs (chinampas) used earth. The Hanging Gardens of Babylon were gardens supposedly irrigated from the roof but there is no evidence that they used hydroponics.

The idea of ​​growing plants in environmentally controlled areas also existed in Rome. The Roman emperor Tiberius introduced the cultivation of cucumber[3]​ using hydroponic techniques.

The study of hydroponics dates back to 382 BC. C. but the first written information is from 1600, when the Belgian Jan van Helmont documented his experience that plants obtain nutritional substances from water. The first published work on the growth of terrestrial plants without soil was,

Sylva Sylvarum (1627) by Francis Bacon. After that, the water technique became popular in research. In 1699, John Woodward grew plants in water and found

that their growth was the result of certain substances in the water obtained from the soil, this when observing that the plants grew worse in distilled water than in sources of

not so purified water. With this he published his experiments of this technique with spearmint. In 1804, De Saussure expounded the principle that plants are composed

by chemical elements obtained from water, soil and air. The first to perfect mineral nutrient solutions for soilless cultivation were the German botanists Julius von Sachs.

and Wilhelm Knop") in the 1860s. The growth of terrestrial plants without soil in mineral solutions (solution culture) quickly became a standard research technique

and teaching and continues to be widely used. This technique is now considered a type of hydroponic farming.[4]​.

In 1928, Professor William Frederick Gericke of the University of California at Berkeley in California was the first to suggest that solution cultures be used for agricultural plant production. Gericke caused a sensation by growing tomatoes and other plants that reached remarkable sizes (larger than those grown in soil) in mineral solutions which led to his article entitled "Aquaculture: A Means of Producing Crops" (1929). By analogy with the term geoponics (meaning agriculture in ancient Greek) called this new branch hydroponics in 1937, although he claims that the term was suggested by Dr. W.A. Setchell of the University of California from hydros (water) and ponos (culture/cultivation).

Reports of this work and Gericke's fervent claims that hydroponics would revolutionize agriculture sparked a flurry of requests for additional information. Gericke refused to reveal his secrets, since he had done the studies at home and in his free time. This fact caused him to drop out of the University of California. In 1940, he wrote the book, Complete Guide to Soilless Gardening.

Two other plant nutrition specialists at the University of California were asked to investigate Gericke's claims. Dennis R. Hoagland and Daniel I. Arnon wrote the typical agriculture newsletter in 1938, debunking exaggerated claims made about hydroponics. Hoagland and Arnon concluded that hydroponic crops were no better than crops grown on good soil. Crops were limited by factors other than mineral nutrients, especially light. These investigations, however, overlooked the fact that hydroponics had other advantages including that the roots of the plant have constant access to oxygen and that the plant can have access to as much or as little water as it needs. This is one of the most common mistakes when the crop is over-irrigated or under-irrigated. Hydroponics is capable of preventing this from happening by draining or recirculating the water that is not absorbed by the plant. In crops on land, the farmer needs to have enough experience to know how much water he should water the plant with. The solution with which the roots will be in contact must be sufficiently oxygenated so that root metabolism is not impeded.

These two researchers developed several formulas for mineral nutrient solutions. Modified versions of Hoagland's solutions are still in use today.

One of the first successes of hydroponics occurred during World War II when American troops in the Pacific implemented large-scale hydroponic methods to provide fresh vegetables to troops at war with Japan on islands where land was not available and it was extremely expensive to transport them.

In the 1960s, Alen Cooper in England developed the Nutrient Film Technique. The Earth Pavilion at Disney's Epcot Center, opened in 1982, highlighted various hydroponic techniques. In recent decades, NASA has conducted extensive research for its CELSS (Controlled Ecological Life Support System).

Also in the 1980s, several companies began marketing hydroponic systems. Currently (2010) it is possible to purchase a kit to set up a small home hydroponic growing system for less than €200. Soilless cultivation (CSS) techniques are used on a large scale in commercial circuits for the production of tobacco plants, (floating) thus discarding the "Match (seedbed)") in soil that requires methyl bromide to disinfect the soil from weeds, pathogens and insects. Also in Holland and other countries with a high degree of development in intensive farming, CSS techniques have advanced, developing related industries and numerous technologies related to the development of new growing media such as perlite, rock wool, coconut fiber or cocopeat, toasted rice husk and other appropriate media.

This soilless cultivation technique avoids the impediments or limitations that soil represents in conventional agriculture through the use of substrates, any solid material other than soil that is used for hydroponic planting as support for the plant and not for its nutrition. The use of substrates allows total control over factors that affect plant development, such as humidity, oxygenation and nutrition. They are soilless crops, in that they do not contain natural soil. Agricultural perlite, pumice stone, coconut fibers, peat[5]​ or rock wool, are substrates widely used in what are called hydroponic crops. The equivalent or most commonly used name became soilless crops -CSS or soilless (in English)- since the support medium for the plants became an inorganic substance such as perlite or organic such as peat or certain agricultural waste such as fruit peels -rice, almonds, etc.-. In the case of soilless crops, as they were developed by the industry or by hobbyists, they were not analyzed at first in terms of the impact that their use would have on the environment, as occurred with other developments that were commercially profitable. In the same way, hydroponic systems were from the beginning "open" as the environmental impact that the dumping of effluents after use would have was not considered. The development of "closed" methods that mean economy in terms of the possibility of reusing nutrients and avoiding the impact it has on the external environment, pouring a solution that carries a considerable amount of ions not used by the plants being grown, also, for example, lettuce, is grown in water depending on what type it is, it also depends on its size, it must be planted in a boat with water and if the root is large, only half of it should be submerged since if it all gets wet there may be oxygen problems.

Taking into account economics and possible environmental impact, closed or recirculating systems were developed. The management of these new systems requires more complex technology. As mentioned above, there are a series of developments in the field of substrates, in addition to certain automations developed to facilitate the control of solutions so that they do not vary their chemical parameters. Both hydroponics and fertigation") have given rise to the development of control instruments such as pH-meters and online conductivity meters, as well as processors that maintain control through solenoid or hydraulic valves, so that the solution can be balanced by computer programs that determine the addition of acids when the pH rises, the dilution when the electrical conductivity rises and other control processes that interact with the environment in which the plants are evolving in size and development.

Gericke originally defined hydroponics as growing crops in mineral solutions, without any solid medium for the roots. He opposed those who applied the term hydroponics to other types of soilless cultivation such as cultivation in sand or gravel. More recently, the most classic academic author of hydroponics is Howard Resh. The distinction between hydroponics and soilless growing has often been confusing. “Soilless growing” is a broader term than hydroponics; It only requires that there be no soils with clay or silt. Note that sand is a type of soil, although it is considered soilless cultivation. Hydroponics is always an agricultural soilless crop, but not all soilless crops are hydroponic. Many types of soilless crops do not use the mineral solutions required by hydroponics.

Very recently, the use of containers in hydroponic systems has been proposed. Along with "exponentially higher" yields, the use of containers in hydroponics ensures that all growing systems will also use 90% less water and 80% less fertilizer than those used in conventional agriculture. Hydroponics in these containers require ensuring that the water passes through the same place every 12 minutes of time interval.[6] Converting a shipping container into a "portable farm" is one of the challenges that those interested in hydroponics have, so that its reuse greatly pleases environmental movements.

A very conservative calculation using hydroponics suggests harvesting 4,000 to 6,000 units of vegetables per week (40-50 tons per year), equivalent to 80 times the number of units achieved in the same space using conventional planting and harvesting systems in agriculture.

The latest addition to the growing urban agriculture sector are abandoned shipping containers that make it possible to twin high-tech hydroponic cultivation and its monitoring system with one of the demands of the reuse movement, to make use of a "box farm" that can locally produce large quantities of fresh vegetables all year round.

In the United States, more and more shipping containers are used to grow gourmet strawberries, greens, lettuce, herbs and mushrooms.

The shipping containers hold 2,800 crop germination and development tanks in the 320 square feet (approximately 30 square meters), which can be equipped with artificial lighting, planting racks, an air conditioning and ventilation system, all the necessary hydroponic components (tank, pump, and monitoring and control system), and a complete set of 18 sensors to monitor almost any environmental condition inside the container.

As for the nutrient solution, the aim is to provide the plant with the 13 main mineral elements due to their effects on it. These are:

Contenido

El cultivo sin suelo es justamente un conjunto de técnicas recomendables cuando no hay suelos con aptitudes agrícolas disponibles. El esquema consiste en: una fuente de agua que impulsa por bombeo agua a través del sistema, recipientes con soluciones madre —nutrientes concentrados—, cabezales de riego y canales construidos donde están los sustratos, las plantas, los conductos para aplicación del fertiriego y el recibidor del efluente.

El cansancio de los suelos por alta carga de patógenos tras cultivos repetidos o la acumulación de iones que conllevan alcalinidad o elevación del tenor de sodio ha empujado a muchos productores a realizar cultivos hidropónicos o sin suelo. En cultivos comerciales —en cuanto a su superficie— se hace obligatorio seguir normas ambientales amigables con el ambiente y emplear métodos de recirculación de las soluciones volviéndolas al cultivo tras equilibrarlas y desinfectarlas o buscándoles un lugar de descarga que evite la llegada de los nutrientes efluentes al suelo, cursos de agua y a los mantos acuíferos.

Ya existen métodos en sistemas abiertos que permiten un segundo cultivo, fijación por plantas que crecen en pequeñas lagunas de fondo impermeabilizado y otros ensayándose. Las recomendaciones de realizar cultivos hidropónicos o sin suelo solo por considerar su alta productividad y rendimiento económico, que no tengan en cuenta estos aspectos ambientales perniciosos, no son aconsejables. Los cultivos que son aptos para este método son el tomate, lechuga, repollo, pimiento "Chile (pimiento)"), pepino, espinaca, entre otros. Las temperaturas óptimas para cada uno son variadas: Mientras los que soportan temperaturas más bajas óptimas son el tomate, la lechuga o la calabaza, los que menos soportan temperaturas por debajo de los 18 grados son el pepino y el melón[7]​.

Investigating extreme crops in Antarctica

Germany's southernmost greenhouse is currently located in Antarctica and supplies researchers at the German Neumayer III station with kilos of fresh vegetables, something they normally lack in winter, without soil, sunlight or pesticides.

[8]​

[9]​

The hydroponic cultivation of vegetables is part of a project designed to supply food to human beings in extreme conditions or even in space.

The Neumayer III research station will soon have fresh peppers on its plates. However, the ten-man team will still be without strawberries, as team member Paul Zabel stated in a live video connection in January 2018.

Kilos of tomatoes, lettuce and cucumbers have already been harvested in the new greenhouse launched in February, although the strawberry plants are still not bearing fruit, he indicated. "The plants grow wonderfully and many flowers grow," he noted. But artificial pollination did not work. Why this is so still needs to be examined, said the space engineer.

But Paul Zabel, a researcher in the experiment starting in 2018, was able to show the first small green peppers on camera, although he acknowledged that the harvest was much smaller than expected.

Zabel has spent three quarters of a year sowing lettuce, pruning tomato plants and documenting growth for the German Aerospace Center (DLR). The project should not only enrich the crew's diet, but also provide information for future missions to the Moon and Mars.

In a well-insulated container with a growing area of ​​13 square meters, the plants grow at outdoor temperatures of up to -42 degrees Celsius without soil, daylight or pesticides. The necessary energy comes from the Neumayer III station, located 400 meters away.

A total of 183 kilograms of fresh vegetables have already been harvested. «There is fresh salad almost every day. In the case of cucumbers, the crew has already said: 'That's enough,'" reported project director Daniel Schubert.

Fresh vegetables are extremely important for the mood of the crew spending the winter, isolated in Antarctica for nine months, said Eberhard Kohlberg of the Alfred Wegener Institute (AWI) in Bremerhaven, who is responsible for local logistics.

For the future, Schubert, the project director, imagines that grapes or even apples could be grown in the greenhouse. "This is much more complex than growing lettuce."