Contrary to some modern sources, ancient peoples such as the Babylonians and Aztecs did not use hydroponics. The mineral nutrient solutions required for hydroponics were not developed until the 1800s. The so-called Floating Gardens of the Aztecs (chinampas) used soil. The Hanging Gardens of Babylon were supposedly irrigated roof gardens but there is no evidence they used hydroponics. The earliest published work on growing terrestrial plants without soil was the 1627 book, Sylva Sylvarum by Sir Francis Bacon. 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 for the culture of plants in water (from the Greek hydros, water, and ponos, labor). Reports of Gericke's work and his overzealous 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. They 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. [edit] 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 so represent 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. [edit] Advantages * No soil is required. * Soil borne diseases are virtually eliminated. * Weeds are virtually eliminated. * Fewer pesticides may be required because of the above two reasons. * 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 reuse of a solid medium. * Solution culture hydroponics allows greater control over the rootzone environment than soil culture. * Hydroponics is often the best crop production method in remote areas that lack suitable soil, such as Antarctica, and the deserts of the world.