Overview of Hydroponics

Consumption of tomatoes in the United States has reached 4.3 billion pounds each year. When consumers are willing to pay double or triple standard prices for a great tasting, blemish free product, buyers and sellers alike can smile at the possibilities. Repeated pricing studies have shown that only high-quality, garden vegetables, such as tomatoes, cucumbers, salad crops and culinary herbs, can provide break even or better revenues in hydroponic systems.

Hydroponics is a technology for growing plants in nutrient solutions (water and fertilizers) with or without the use of artificial medium (e.g., sand, gravel, vermiculite, rockwool, peat, coir, sawdust) to provide mechanical support. Liquid hydroponic systems have no other supporting medium for the plant roots: aggregate systems have a solid medium of support. Hydroponic systems are further categorized as open, where after the nutrient solution has been delivered to the plant roots, it is not reused; or closed where surplus solution is recovered, replenished, and recycled. The definition of hydroponics has been confined to liquid systems only, which blurs statistical data and leads to underestimation of the extent of the technology and its economic implications. All hydroponic systems in temperate regions of the world are enclosed in greenhouse-type structures to provide temperature control, reduce evaporative water loss, and to reduce disease and pest infestations.

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The principal advantages of hydroponic controlled environment agriculture (CEA) include high-density maximum crop yield, crop production where no suitable soil exists, a virtual indifference to ambient temperature and seasonality, more efficient use of water and fertilizers, minimal use of land area, and suitability for mechanization, disease and pest control. The major advantage of hydroponic (CEA) compared to field grown produce is the isolation of the crop from the soil, which often has problems of diseases, pests, salinity, poor structure and/or drainage.

The principal disadvantages of hydroponics, relative to conventional open-field agriculture, are the high costs of capital and energy inputs, and the high degree of management skills required for successful production. Capital costs may be especially excessive if the structures are artificially heated and cooled. This is why appropriate crops are limited to those with high economic value such as tomatoes.

The earliest food production in greenhouses was possibly the growing of off-season cucumbers under "transparent stone" for the Roman Emperor Tiberius during the first century. The technology was rarely employed, if at all, during the following 1500 years.

During the 1600's several techniques were used to protect horticultural crops against the cold. These included glass lanterns, bell jars, cold frames and hot beds covered with glass. In the seventeenth century, low portable wooden frames covered with an oiled translucent paper were used to warm the plant environment much as plastic row covers do today. In Japan, straw mats were used in combination with oil paper to protect crops from the severe natural environment. Greenhouses in France and England during the same century were heated by manure and covered with glass panes. The first glass house built in the 1700's, used glass on one side only as a sloping roof. Later in the century, glass was used on both sides. The glasshouse was used for fruit crops such as melons, grapes, peaches and strawberries and only rarely for vegetable production. The developers of this new technology kept market profitability in mind: they produced crops which appealed to the wealthy and privileged, the only people who could afford the luxury of fresh fruit produced out of season in greenhouses.

Greenhouse food production was not fully established until the introduction of polyethylene. In the U.S., the first use of polyethylene as a greenhouse cover was in 1948, when Professor Emery Myers Emmert at the University of Kentucky, used the less expensive material in place of more expensive glass. Professor Emmert is considered the father of plastics in the U.S. because he developed many principles of plastic technology for agricultural purposes through his research on greenhouses, plastic mulches and row covers.

The development of hydroponics has not been rapid. In the U.S., interest began to develop in the possible use of complete nutrient solutions about 1925. Greenhouse soils had to be replaced at frequent intervals or be maintained from year to year by adding large quantities of commercial fertilizers. As a result of these difficulties, research workers in certain U.S. agricultural experiment stations turned to nutrient solution culture methods as a means of replacing the natural soil system with either an aerated nutrient solution or an artificial soil composed of chemically inert aggregates moistened with nutrient solutions.

Photo by M. Jensen

Between 1925 and 1935, extensive development took place in modifying the methods of the plant physiologists to large scale crop production. Workers at the New Jersey Agricultural Experiment Station improved the sand culture method. The water and sand culture methods were used for large scale production by investigators at the California Agricultural Experiment Station. Each of these methods involved certain fundamental limitations for commercial crop production which were partially overcome with the introduction of the subirrigation system initiated in 1934 at the New Jersey and Indiana Agricultural Experiment Station. While there was commercial interest in the use of such systems, hydroponics was not widely accepted due to the high cost in construction of the concrete growing beds. In the post-W.W.II years, there was a bloom of interest in the Southwest US in gravel culture of tomatoes and cucumbers. However, the systems were not perfected and were eventually abandoned.

After a period of approximately 20 years, interest in hydroponics was renewed with the advent of plastics. Plastics were used not only in the glazing of greenhouses, but also in lining the growing beds rather than beds made of concrete. Plastics were also important in the introduction of drip irrigation. Again, numerous promotional schemes involving hydroponics became common with huge investments made in hydroponic growing systems. Escalating oil prices, starting in 1973, substantially increased the costs of CEA heating and cooling. This along with fewer chemicals registered for pest control caused many bankruptcies and a decreasing interest in hydroponics.

Almost another 20 years have passed since the last real interest in hydroponics, but growers are once again establishing CEA/hydroponic systems. This is especially true in regions where there are environmental concerns in controlling any pollution of groundwater with nutrient wastes or soil sterilants. Today growers appear to be much more critical in regard to site selection, structures, the growing system, pest control and markets.