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Hydroponics

Hydroponics


Hydroponics is the practice of growing plants in water as opposed to soil . It comes from the Greek hydro ("water") and ponos ("labor"), implying "water working." The essential macro- and micro- (trace) nutrients needed by the plants are supplied in the water.

Hydroponic methods have been used for more than 2,000 years, dating back to the Hanging Gardens of Babylon. More recently, it has been used by plant physiologists to discover which nutrients are essential for plant growth. Unlike soil, where nutrient levels are unknown and variable, precise amounts and kinds of minerals can be added to deionized water, and removed individually, to find out their role in plant growth and development. During World War II hydroponics was used to grow vegetable crops by U.S. troops stationed on some Pacific islands.

Today, hydroponics is becoming a more popular alternative to conventional agriculture in locations with low or inaccessible sources of water or where land available for farming is scarce. For example, islands and desert areas like the American Southwest and the Middle East are prime regions for hydroponics. Plants are typically grown in greenhouses to prevent water loss. Even in temperate areas where fresh water is readily available, hydroponics can be used to grow crops in greenhouses during the winter months.

Two methods are traditionally used in hydroponics. The original technique is the water method, where plants are supported from a wire mesh or similar framework so that the roots hang into troughs which receive continuous supplies of nutrients. A recent modification is a nutrient-film technique (NFT), also called the nutrient-flow method, where the trough is lined with plastic. Water flows continuously over the roots, decreasing the stagnant boundary layer surrounding each root, and thus enhances nutrient uptake. This provides a versatile, lightweight, and inexpensive system. In the second method, plants are supported in a growing medium such as sterile sand, gravel, crushed volcanic rock, vermiculite, perlite, sawdust, peatmoss, or rice hulls. The nutrient solution is supplied from overhead or underneath holding tanks either continuously or semi-continuously using a drip method. The nutrient solution is usually not reused.

On some Caribbean Islands like St. Croix, hydroponics is being used in conjunction with intensive fish farms (e.g., tilapia) which use recirculated water (a practice is more recently known as aquaponics). This is a "win-win" situation because the nitrogenous wastes, which are toxic to the fish, are passed through large greenhouses with hydroponically-grown plants like lettuce. The plants remove the nutrients and the water is returned to the fish tanks. There is a sensitive balance between stocking density of fish and lettuce production. Too high a ratio of lettuce plants to fish results in lower lettuce production due to nutrient limitation. Too low a ratio also results in low vegetable production, but this time as a result of the buildup of toxic chemicals . The optimum yield came from a ratio of 1.9 lettuce plants to 1 fish. One pound (0.45 kg) of feed per day was appropriate to feed 33 lb (15 kg) of tilapia fingerlings, which sustained 189 lettuce plants and produced nearly 3,300 heads of lettuce annually. When integrated systems (fish-hydroponic recirculating units) are compared to separate production systems, the results clearly favor the former. The combined costs and chemical requirements of the separate production systems was nearly two to three times greater than that of the recirculating system to produce the same amount of lettuce and fish. However, there are some drawbacks that must be considereddisease outbreaks in plants and/or fish; the need to critically maintain proper nutrient (especially trace element), plant, and fish levels; uncertainties in fish and market prices; and the need for highly-skilled labor. The integrated method can be adapted to grow other types of vegetables like strawberries, ornamental plants like roses, and other types of animals such as shellfish. Some teachers have even incorporated this technique into their classrooms to illustrate ecological as well as botanical and culture principles.

Some proponents of hydroponic gardening make fairly optimistic claims and state that a sophisticated unit is no more expensive than an equivalent parcel of farmed land. They also argue that hydroponic units (commonly called "hydroponicums") require less attention than terrestrial agriculture. Some examples of different types of "successful" hydroponicums are: a person in the desert area of southern California has used the NFT system for over 18 years and grows his plants void of substate in water contained in open cement troughs that cover 3 acres (7.5 ha); a hydroponicum in Orlando, Florida, utilizes the Japanese system of planting seedlings on styrofoam boards that float on the surface of a nutrient bath which is constantly aerated; an outfit in Queens, New York, uses the Israeli Ein-Gedi system which allows plant roots to hang free inside a tube which is sprayed regularly with a nutrient solution, yielding 150,000 lbs (68,000 kg) of tomatoes, 100,000 lb (45,500 kg) of cucumbers, and one million heads of lettuce per acre (0.4 ha) each year; and finally, a farmer in Blooming Prairie , Minnesota, uses the NFT system in a greenhouse to grow Bibb and leafy lettuce year-round so he can sell his produce to area hospitals, some supermarkets, and a few produce warehouses.

Most people involved in hydroponics agree that the main disadvantage is the high cost for labor, lighting, water, and energy. Root fungal infections can also be easily spread. Advantages include the ability to grow crops in arid regions or where land is at a premium; more controlled conditions, such as the ability to grow plants indoors, and thus minimize pests and weeds; greater planting densities; and constant supply of nutrients. Hydroponic gardening is becoming more popular for home gardeners. It may also be a viable option to growing crops in some developing countries. Overall, the future looks bright for hydroponics.

[John Korstad ]

RESOURCES

BOOKS

Resh, H. M. Hydroponic Food Production: A Definitive Guidebook for the Advanced Home Gardener and Commercial Hydroponci Grower, 5th ed. Santa Barbara: Woodbridge Press, 1995.

Saffell, H. L. How to Start on a Shoestring and Make a Profit with Hydroponics. Franklin, TN: Mayhill Press, 1994.

PERIODICALS

Nicol, E. "Hydroponics and Aquaculture in the High School Classroom." The American Biology Teacher 52 (1990): 1824.

Rakocy, J. E. "Hydroponic Lettuce Production in a Recirculating Fish Culture System." Island Perspectives 3 (198889): 510.

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