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Growing plants in nutrient solution  

By Dr Adnan Younis & Atif Riaz

Hydroponics is the most intensive technology for growing plants in nutrient solutions (water containing fertilizers) with or without the use of an artificial medium to provide mechanical support. Food for plants are dissolved in water and fed directly to roots.

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 mineral nutrients in soil dissolve in water, plant roots are able to absorb them. When the required mineral nutrients are introduced into a plantís 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.

Hydroponics is also a standard technique in biology research and teaching and a popular hobby. There has been an increasing interest in the use of hydroponics or soilless techniques for the production of greenhouse horticultural crops but there is little commercial value because of it being more expensive than the traditional agriculture.

The two main types of hydroponics are solution culture and medium culture. Solution culture does not use a solid medium for 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 roots and is named for the type of medium, e.g., sand, gravel, or rockwool culture. There are two main variations for each medium, sub-irrigation and top irrigation. For all techniques, most hydroponics 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 nutrient solution.

The principle advantages of hydroponics include high-density planting, maximum crop yield, crop production where no suitable soil exists, freedom from the constraints of ambient temperatures and seasonality, more efficient use of water and fertilizers, minimal use of land area, and suitability for mechanized production and disease control.

A major advantage of hydroponics, as compared with culture of plants in soil, is the isolation of the crop from the underlying soil which may have problems associated with disease, salinity, or poor structure and drainage. The costly and time-consuming tasks of soil sterilization and cultivation are unnecessary in hydroponics systems, and a rapid turnover of crops is readily achieved.

In this system no soil is required and chances of soil borne diseases are virtually eliminated. The problems due to weeds are virtually eliminated with less or no use of pesticides.

Edible crops are not contaminated with soil. Water use can be substantially less than with outdoor irrigation of soil-grown crops. Solution culture hydroponics does not require disposal of a solid medium or sterilization and re-use of a solid medium. Solution culture hydroponics allows greater control over the root-zone environment than soil culture. In solution culture hydroponics, plant roots can be seen. This system is considered high-tech and futuristic and so appeals to many people. Hydroponics is excellent for plant teaching and research.

The principal disadvantage of hydroponics, relative to conventional open-field agriculture is the high cost of capital and energy inputs, especially if the structure is artificially heated and cooled by fan and pad systems.

A high degree of competence in plant science and engineering skills are required for successful operation. This system usually requires more and more frequent maintenance than geoponics. If timers or electric pumps fail, or the system clogs or springs a leak plants can die very quickly in hydroponics system.

Because of its significantly higher costs, successful applications of hydroponics technology are limited to crops of high economic value in specific regions and often at specific times of the year, when comparable open-field crops are not readily available.

A weakness in any number of technical or economic links snaps this complex chain. Deficiencies in practical management or scientific and engineering support results in low yields of nutrient-deficient and unattractive crops; plant diseases; insect infestation; summer overheating; winter chilling; under-capitalization; and indifferent cost accounting, all of which, separately or together, have caused hydroponics businesses to fail. There is no margin for poor management or mistakes.

Hydroponics has been exaggerated as miraculous. There are many widely held misconceptions regarding hydroponics, and the following facts should be noted:

Hydroponics will not always produce greater crop yields than with good quality soil; plants cannot be spaced closer together than soil-grown crops under the same environmental conditions; produce will not necessarily be more nutritious or delicious than soil-grown produce.

With hydroponics, capital costs are several orders of magnitude higher than those for open-field crops, and the types of food crops feasible for hydroponics are severely limited by potential economic return. Agronomic crops are totally inappropriate.

A decade ago, it was calculated that the highest market prices ever paid would have to increase by a factor of five for hydroponics agronomy to cover the cost. Since then, hydroponics costs have more than doubled, while crop commodity prices have remained constant. Repeated pricing studies have shown that only high-quality garden type vegetables like tomato, cucumber, potato, sweet peppers, melon, and specialty lettuce can cover costs or give a return in hydroponics systems.

As the consumer becomes increasingly aware of quality differences, especially the high quality of tomatoes, cucumbers, and leafy vegetables coming from hydroponics, the demand will increase. This, along with the increased emphasis on eating more vegetables for dietary and health reasons, will surely help the hydroponics industry.

Courtesy:  The Dawn

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