¹Department of Bioresource Engineering
2Rutgers Agricultural Research and Extension Center
Cook College Rutgers University
New Brunswick, New Jersey USA

³University of Arizona
Tucson, Arizona

⁴University of New Hampshire
Durham, New Hampshire

Keywords: row crop plastic film mulch, tunnel, drip irrigation, plastic greenhouse, hydroponic crop production

The 23-year time period from the 7th International Agricultural Plastics Congress in San Diego, California in 1977 to the 15th in Hershey, Pennsylvania in 2000, has provided many fundamental applications of agricultural plastics within the greenhouse and intensive field production agricultural industry. The advancement of plastics technology and materials for the promotion of agricultural production has been recorded in the proceedings of these technical meetings held throughout the world. In 1977, San Diego County, California was the largest user of agricultural plastics in the US, with an estimated 80% of plastic products resulting from irrigation and water-related needs. Today plastic polymers for all forms of irrigation are prevalent throughout the United States and the world. However, drip irrigation was still described as a ‘new development’, and one-half of the papers in the 7th international proceedings were focused on news about drip irrigation. Since San Diego, the US Agricultural Plastics Association, renamed the American Society for Plasticulture has convened meetings in 15 locations from Florida to New Jersey and New Hampshire, and from Alabama to Arizona and Oregon, thereby helping to expand the influence of Plasticulture technology throughout the US, and advance the technology. The technological concerns of two decades ago were as basic as the reliability of polyethylene film and its potential failure due to stress cracks while in use. ‘Cross-linked’ PE was one solution introduced for eliminating stress cracks, allowing for reduced wall thickness, while adding longer life to the product. Many other additives to the plastic soon followed, suggesting that ‘designer’ films and rigid plastics could ultimately be accommodating to any situation and need envisioned. The efforts of Congress Co-chairman Bernarr J. Hall, San Diego County Farm Advisor, and Robert W. Grove, President Grove Products, Inc. brought more than 800 registrants from 31 countries and 37 US states to San Diego in 1977. There were 106 papers, and three tours that focused on plastic row covers and soil mulch; soil fumigation; greenhouse construction; mechanical application greenhouse glazing; drip irrigation on greenhouse and field crops, such as strawberries, tomatoes, kiwi, citrus, and flowers.

This review of Plasticulture technology development between the 7th and 15th International Agricultural Plastics Congresses will include: actively controlled environments, such as greenhouse systems; passive, modified environments, such as low and high tunnels; plastic film row crop mulches; drip, trickle, and fertigation irrigation systems; and greenhouse hydroponic crop production systems.

Design of Plastic Glazed Greenhouse Structures
William J. Roberts, Professor Emeritus Bioresource Engineering, Rutgers University

Plastic greenhouse structures in the U.S. were initially wooden frame buildings to which plastic film was attached to form an enclosure that controlled the environment around the plant and allowed PAR (Photosynthetically Active Radiation) to enter the structure for photosynthesis and crop production. Professor Emmert, of the University of Kentucky was an early pioneer in the development of plastic glazed growing structures. Many Universities and Experiment Stations in the 1950’s used these types of structures and were involved with applied research in this area.

Structures specifically designed for greenhouse production first appeared in the late 1950’s. Drs. Raymond Sheldrake of Cornell University and McNeil Marshall of VPI were actively involved with greenhouse research at that time. Curved steel frames were came into use at about this time, as well. Polyethylene (PE) film was the most popular glazing because it was available in wide widths. Polyvinylchloride (PVC) film was used less than PE because of its electrostatic properties, that enhanced adherence of dust. PVC was available only in narrow widths making glazing attachment difficult. Some rigid PVC panels were also tested but ultra-violet (UV) radiation from the sun adversely affected the panels causing excessive light transmission reduction. Rigid Fiberglass (FRP) panels with a longer life than PE were also available, but their cost limited wide spread use. These FRP panels were often surface treated to alleviate some of the damage caused by UV radiation. They are available today along with the new polycarbonate (PC) and acrylic (PMMA) panels for rigid structural glazing applications.

Aart Van Wingerden, a leader in commercial controlled environment plant production agriculture, built low-cost wooden structures designed for application of two layers of greenhouse film. The primary purpose was to reduce energy costs by 30% and reduce condensation dripping from the glazing onto the plants. Van Wingerden’s design included for a 2 by 4 inch (5 by 10 cm) wooden rafter spaced on 4 foot (1.2 m) centers. After one layer of film was applied, a 2 by 2 inch (2.5 by 2.5 cm) wooden spacer was placed over the first layer of film on the rafter and a second layer of film was applied. The second layer of film was secured to the spacer with a 1 by 2 inch (2.5 by 5 cm) wooden spacer. This concept was adapted for many wooden frame greenhouses, including the slant-leg, rigid-frame design developed by Professor W. J. Roberts at Rutgers University in 1963. Steel pipe frame structures were more difficult to glaze with two layers. Dr. Norman J. Smith of Rutgers University used plastic rope laced over the greenhouse between the steel bows to hold the inner layer securely. An outer layer of film was then installed. The two plastic film layers were separated apart by drawing the inner layer tightly down with the plastic rope.

Each design for double-glazing required that the plastic film would have to be replaced each year, and if a newly developed UV resistant film was used, possibly every two years. In 1964, Roberts developed the air-inflated system of double-glazing using air pressure to separate the two layers of film. Two layers of film were applied together to the structure, whether wooden or steel frame. After the plastic glazing was secured air was forced between the two layers causing them to separate and form a thermal barrier, as well as, providing rigidity and added strength to the film glazing. By constraining the movement of the plastic film, the failure caused by fatigue was nearly eliminated, and the useful life of the film was extended. This glazing system along with the magnificent improvements made in the formulation and subsequent properties of the film by the manufacturers has increased the life and made polyethylene film with the air inflation glazing system the choice of many growers. Over 65% of all the greenhouses in the USA are glazed in this way. Current four-year films that include heat retention and anti-drip properties has been a great advancement from the 1960’s when the film would last 8 months if the greenhouse were covered in September, or only 5 months if covered in March.

Rapid growth in the industry came with the next innovation of multi-bay greenhouses that led to large, continuous greenhouse ranges. The benefits of more efficient materials handling equipment, energy conservation with reduced surface area of the exposed glazing, and opportunities for better production systems, all contributed in the rapid expansion of the plastic greenhouse industry.

Plastic Greenhouse Energy Conservation
David R. Mears, Bioresource Engineering, Rutgers University

The importance of energy management and cost in greenhouse operations has varied widely relative to other greenhouse issues over the past 40 years. In the early ‘60’s most commercial greenhouse operations were in glass structures, and they were almost always single span units. Some low-cost polyethylene structures were appearing, which were usually considered temporary units, and mostly used to produce seedlings in the short spring season. A significant problem with single-covered plastic units was condensation drip so methods of applying two layers of plastic film were developed so that the inner layer would be relatively warmer and produce less drip. A consequence of the double layering was a significant reduction in fuel requirements, and generally to about two-thirds of what would be required for a single glazing of glass.

Another important trend in commercial greenhouse construction was the shift from freestanding, single-span units to large, contiguous blocks of gutter-connected structures. This reduced the total glazed area relative to floor area, particularly for tall greenhouses, thereby reducing heat loss for a given crop. The columns ‘a’ and ‘b’ in the graph below compare the annual energy requirement per unit growing area for these two types of structures. All the values in the figure are based on the same total annual degree-day heating requirement. Column ‘c’ includes the reduction in energy requirement resulting from the use of a double layer of air-inflated polyethylene film as the glazing.

The energy crisis of the ‘70’s and particularly the oil embargo of 1973 stimulated a flurry of research and development on methods to reduce requirements for fossil fuel to heat commercial greenhouses. Although the application of freestanding solar collectors has not become widespread, the solar energy projects at Rutgers and other universities facilitated the development and adoption of technologies that achieved great reduction in energy use. It was quickly realized that the greenhouse floor was a convenient place to store heat (derived from fossil fuel, or from waste heat sources), and that the warm floor served as an effective primary heat exchange surface to the greenhouse crop. Experience with a variety of crops demonstrated that independent control of root zone temperature was an important crop management tool, so root zone heating was widely adopted, even when fossil fuel was required to provide the energy. For many crops, air canopy temperatures were reduced without affecting plant development, if there was an independent root-zone heating system. Column ‘d’ of the graph below, includes the savings in energy that resulted from reducing night air temperature for crops responding positively to that reduced air temperature management strategy. The addition of a movable heat curtain system reduced heat loss nearly 40%. Column ‘e’ reflects the potential savings of the most effective heat curtain insulation systems alone, and column ‘f’ includes the savings resulting from the combined use of floor heating and highly reflective heat curtain insulation. Column ‘g’ includes the influence of the natural solar gain on the heat energy reduction, compared to column ‘f’.

The combination of strategies discussed above has provided the potential to reduce fossil fuel consumption from over two and a half gallons of fuel oil per square foot to about one third of a gallon, nearly an eight-fold reduction. Another project started in the early ‘80’s at Rutgers University, demonstrated that when industrial waste heat was available the fossil fuel back up requirement could be reduced dramatically. Column ‘h’ on the chart shows the annual fuel requirement determined from a 1.1 hectare (3 acre) commercial greenhouse utilizing waste heat from an electrical generating station. The floor heating system was the primary means of delivering the waste heat to the greenhouse with some additional heat transfer capability provided by warm water to air heat exchangers. Some fossil fuel was required for touch up heat under the most extreme weather conditions and to provide backup when the power plant shut down.
(a) Single Span/Single Glazing; (b) Multiple Span/Single Glazing; (c) Multiple S/Double Film; (d) MS/DF w/floor heat; (e) MS/DF w/heat curtain; (f) MS/DF w/FH + HC; (g) MS/DF w/FH + HC + solar; (h) MS/DF w/FH + HC + power plant waste heat.

Low and High Tunnels – Passive, Modified Environmental Control
Otho S. Wells, Professor Emeritus, University of New Hampshire

It was April, 1977 in San Diego, California. In a near perfect climate, hundreds of agricultural plastics delegates from around the world had assembled for open information exchange and a co-mingling of innovative ideas. The world leaders in agricultural plastics technology were at this 7th International Plastics Congress; and personally, I was very pleased to be there to meet some of the “giants” of plastics.

To say the least, this Congress was skewed heavily toward drip irrigation, a topic that attracted almost half of the papers. A close second in popularity was greenhouses. The remaining papers were a wide variety of other uses of plastics. At that time, one of my primary interests was plastic row covers (low tunnels), but out of 98 contributed papers only four related to row covers and none to high tunnels.

One thing was certain, however. There might have been a paucity of row cover papers, but there was no lack of interest on the part of Congress Co-Chairmen Bernarr Hall and Bob Grove. On one of the tours, Bernarr led us right down into the southwest corner of the United States. With a westward look toward the Pacific, the hills of Tijuana were looming on our left.

Nestled in that corner of the country were fields of thousands of tomato and cucumber plants, all carefully protected by an intricate system of plastic row covers. Bernarr Hall had devoted years working with growers on what he called “ Unique Plastic Row Covers Developed for Vegetables in San Diego County.” And now he had the opportunity to share with the world his accomplishments on behalf of a healthy California vegetable industry. Rightly so, he was proud of what he was showing us. Those were stimulating moments.

These were the defining days of row cover research in the United States. From the meeting in 1977 came the impetus for many researchers across the country to look more carefully at passive environmental control techniques, during the next two decades, and especially in northern states where the growing season is relatively short.

Although the principle of row cover plant protection is a constant, the variation on the theme is diverse. The original row covers that Bernarr Hall conceived consisted of two, 3 foot (0.92 m) wide pieces perforated polyethylene plastic, supported by metal wire hoops, with one edge buried in the soil. They were opened at the top each morning to provide daytime ventilation during the day and to form a windbreak on either side of the row. They were secured at night by re-joining the pieces together with sturdy clothespins, which incidentally came from all the way across the country from the state of Maine. From this rather labor-intensive system came the one-piece, 5 foot (1.5 m) wide slitted row covers that were constructed of plastic film with a doubled row of slits. This idea was a spin-off of an idea developed in New Jersey by long-time plastic researcher, Dr. Norman J. Smith.

Subsequent row cover modifications included various perforation configurations and experimentation with row cover materials developed in Europe. One of the first was an expandable, self-ventilating plastic film, known as Xiro, from Switzerland. It was wide enough to cover multiple rows, and of such light weight that the cover lay directly over the crops. There was no need for daily opening and closing of the cover.

Soon came spunbonded polyester, followed by spunbonded polypropylene, both of which were called floating row cover because of their extreme lightweight. Similar row cover materials were already being used in Europe but had not made its way to the U.S. These covers came in multiple widths from 6 feet (1.8 m) up to 50 feet (15 m) wide, and in a great variety of lengths. There were two major advantages: reduced labor for installation and no manual ventilation necessary. Also, these materials could be used on many different crops – vegetables, fruits, and flowers. Insect protection was another big advantage of the spunbonded covers.

The row covers had a limited amount of environmental control, while heated greenhouses were too expensive in many applications, therefore something between those two choices was needed. The answer came in the form of high tunnels, which are walk-in, unheated greenhouses covered with a single layer of plastic. They are ventilated daily by manually opening and closing the sides, generally with a roll-up mechanism.

Plastic Film Mulches on Soils
Dr. Stephen A. Garrison, Rutgers University Agricultural Research and Extension Center

Many significant developments in both film materials and techniques for using plastic mulches have occurred since the 13th NAPA Congress in 1977. These include: degradable mulches, solarization techniques, colored and reflective mulches, wavelength-selective mulches, and refinement of plastic culture techniques.

A potential limitation for the wide scale use of plastic mulches for crop production has been the requirement to remove and dispose of the used plastic (1) (2). Concern about the impact of plastics on the environment and the costs and restrictions for disposal also provided impetus for the development of degradable mulches (3). Early work on photo-initiated degradation was conducted at Princeton Chemical Company by Reich and others who produced a number of experimental films that were tested by B.L. Pollack, and others at Rutgers University (1) (5). Carnell (4) reported on a photodegradable polyethylene film containing UV sensitive carbonyl groups. Ecolyte ®, a commercial film, based on this principle was subsequently introduced. The work of Gilead and Scott led to Plastigone ®, a polyethylene based plastic that degraded in response to exposure to specific quantities of solar radiation (3).

Factors that controlled and altered the rate of breakdown of photo-degradable mulch films included: formulation and quality control in film production, seasons of use (9), geographical region of use as it affects film temperature, quantity, and quality (especially UV) of solar radiation related to day length, cloud cover, sun angle, etc. (7) (8). The interval between mulch application and planting, crop canopy development, time of crop removal, and exposure of film to solar radiation after crop removal, also alter the time and rate of film degradation.

Degradable mulches including Ecolyte ®, Plastigone ®, and Biolan ® (16) achieved commercial use in the late 1970’s and 1980’s. By 1992 the use of photodegradable mulch was estimated to be 3 million pounds out of a total annual use of 60 million pounds of plastic for mulch (6). Since the early 1990’s, commercial use of degradable mulch declined dramatically in the USA. The 15 to 50% increase in purchase price over standard PE, the lack of predictability of its breakdown, increased costs of weed control, pick up and removal costs associated with premature breakdown, or the persistence of mulch in the field are the reasons.

Solarization, using plastic film mulch to achieve soil temperatures sufficiently high to destroy pathogens, weeds and nematodes, was conducted in Israel just before the 13th NAPA Congress (10). Solarization was well adapted to arid regions with extended periods of high solar radiation, such as California, Texas, and Florida. The team of Stevens, Khan, and Wilson at Tuskeegee University and Brown at Auburn University has improved techniques for solarization in the warm, humid areas such as the southern USA. Solarization reduced Southern Blight in peppers (12), controlled a wide range of weeds (13), and increased the yield of strawberries over a non-fumigated control (14). Solarization has destroyed sclerotia (22), decreased early blight of tomato, Alternaria leaf spot and anthracnose of watermelon (31), Pythium ultimum and galling of lettuce roots by root knot nematodes (28).

The use of IR-barrier clear mulch was more effective in increasing the soil temperature and the number of solarization days above 43o C compared to standard clear polyethylene (25). Fumigation with methyl bromide is usually more effective in decreasing soil pests and increasing plant vigor and yield than solarization (33) (32). The phasing out of methyl bromide for soil fumigation has made the identification of alternative techniques for controlling soil borne pathogens and weeds even more urgent.

Early work on the use of plastic soil mulches often compared the temperature and crop response to black, clear or white films. The use of reflecting films to reduce the population of aphids and vectors of virus diseases of many crops, especially the cucurbits was already established before the 13th NAPA congress.

Decoteau and his colleagues at Clemson University and the USDA compared the response of tomatoes and other crops to several colored mulch films (17). They suggested that morphological changes and increases in early growth and yields of tomatoes grown on red mulch were due to the reflection of light to the plant altering the quantity and quality, especially the Red:Far Red light received by the plant (17). Previous research indicated that plastic mulches modified plant responses by altering soil temperatures and retaining soil moisture and nutrients, for optimum root growth. Work by Loy and others (24) suggested that the early growth response of tomatoes grown on red plastic mulch was due primarily to the increased reflection of PAR into the plant canopy, increased photosynthesis and biomass accumulation. Several researchers have emphasized the importance of accurately measuring the reflectance with a spectroradiometer and including a better definition of the conditions during testing. (23) (27). The commercial efficacy of colored mulches other than black, white and reflective still remains to be established.

Wavelength selective films were initially developed for greenhouses (11) or row covers (15). These films, described as thermic or infra-red (IR) films, transmit PAR and near infrared wavelengths and absorb or block the transmission of longer wavelengths, thus enhancing the “greenhouse effect” or heat retention capability of clear films. (11).

Loy and others (18), have made a significant contributions to mulch film technology by designing a mulch film known as IR-T ® that transmits short wave infra-red solar radiation and contains pigments that block the transmission of solar radiation in the red and blue regions of the spectrum. The IR-T film increased soil temperature more than opaque black polyethylene, reduced weed growth (20) (19) by decreasing light in both the red spectrum region required for seed germination, and the red and blue regions required for photosynthesis (18). Early and total yield increases in response to IR-T films compared with black polyethylene have been greatest with vine crops that require higher soil temperatures (21) (30), crops planted early in the growing season when soil temperatures are sub-optimum (26), and in areas with a short growing season (29). IR-T ® film is currently used in the production of vine crops and other warm season crops, especially in areas with a short growing season.

Numerous useful concepts, and materials and applications of plasticulture have been reported in the NAPA and ASP proceedings since 1977. Only a sampling is listed here. Double cropping on established plastic-covered drip-irrigated beds, after a fall or early spring crop has reduced input costs. A high-density thin gauge polyethylene mulch film with high tensile strength with increased value for recycling has been developed and marketed by Sonoco®. A new metalized process for polyethylene has produced highly reflective films that can be used to reduce soil temperature and repel aphids. Reflective films have also been used in strips between trees in orchards, resulting in increased color development in apples. The Plasticulture technique for strawberry production used in California has been adapted to the northeast. Many papers have been devoted to the effects of mulch type, alone or in combination with row covers on crop productivity as related to the control of insects, nematodes, and soil borne diseases. Improved fumigation barrier films have been developed that allow 33 to 50% reduction in the usual rates of methyl bromide compared to low density linear polyethylene (LDPE). Improved hindered amine light stabilizers promise to provide greater resistance of mulch films to degradation in the field.

Drip/Trickle Fertilization
James W. Paterson, Professor Emeritus, Rutgers University

Applying plant nutrients through a drip/trickle irrigation system under plastic mulch in the Northeast was initiated in the late 1960's. Nitrogen-rich fertilizer was pumped through a drip/trickle tubing periodically under clear plastic mulch for vegetable production. Earlier fertilizer investigations using this system involved broadcasting and incorporating all the needed plant nutrients into the soil prior to laying the tubing and mulch and then applying just water through the drip/trickle system. If the amount of fertilizer applied at preplant was inadequate, there was little opportunity to apply additional nutrients later in the growing season. Side dressing fertilizers at the edge of the mulch during the growing season was attempted and found to be inefficient and unsatisfactory.

After noting that applying nitrogen-rich fertilizer periodically through the drip/trickle system was no more effective than applying all the needed nitrogen preplant, fertilizers carrying multiple plant nutrients were applied through the tubing with much better results. Fertilizers carrying nitrogen (N), phosphate (P2O5) and potassium (K2O) consistently produced better results than the fertilizers which carried only one or two of the major plant nutrients. It was also noted that a 1-1-1 ration of N- P2O5 - K2O fertilizer was consistently better than varying the rates of these applied nutrients which the soil test results would suggest. One of the major objectives of these studies was to closely relate this newer system of fertilization to the standard soil test program. To date this has not been satisfactorily accomplished.

It was noted early in the investigations that some preplant fertilization was needed along with the nutrients which were to be applied through the drip/trickle system. Applying some of the total needed plant nutrients (NPK) to the soil prior to laying the tubing and the mulch consistently produced better results than not applying any preplant fertilizer. The remainder of the total needed major plant nutrients was split into periodic applications throughout the growing season. The number of drip/trickle applications was mainly determined by crop, length of growing season, and nutrient holding capacity of the soil (cation exchange capacity, CEC).

Over the years new slow release fertilizers have been developed which have a nutrient release pattern more conducive for growing field produced row crops. Applying some of these various types of slow release fertilizers in bands or placing them directly under the transplant on unmulched soils produced some encouraging results. Later studies showed that strategically placing these slow release fertilizers in mulched row crops also produced very good results. For the last several years, work has been done on preplant fertilizing mulched row crops with slow release fertilizers which are to be drip/trickle fertilized. Most of the research was done by hand placing slow released fertilizers directly into the transplant hole just prior to planting. Since this technique was very laborious and time consuming, a machine was needed which could strategically place the slow release fertilizers in the soil of the mulch-drip/trickle grown crop. The machine used for this purpose banded the slow release fertilizers in the middle of the plant bed or placed a band close to each plant row in a double row planting before the drip tube and mulch was laid.

Hydroponic Crop Production Systems
Merle H. Jensen, Department of Plant Science, University of Arizona

Although the first use of controlled environment agriculture (CEA) was for growing off-season cucumbers under “transparent store” for the Roman Emperor Tiberius during the first century, the technology is believed to have been used little, if at all, for the following 1500 years. Greenhouses (and experimental hydroponics) appeared in France and England during the seventeenth century. Woodward grew mint plants without soil in England in the year 1699. The basic laboratory techniques of nutrient solution culture were developed (independently) by Sachs and Knap in Germany in 1860 (34).

In the United States interest began to develop in the possible use of complete nutrient solutions for large-scale crop production about 1925. 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 (35). The water and sand culture methods were used for large-scale production by investigators at the California Agricultural Experiment Station (34). Each of these two methods involved certain fundamental limitations for commercial crop production, which partially were overcome with the introduction of the subirrigation system initiated in 1934 at the New Jersey and Indiana Agricultural Experiment Stations (36). Gericke (37) published a description of a quasi-commercial use of the liquid technique and apparently coined the word hydroponics in passing. The technology was used in a few limited applications on Pacific islands during World War II. After the war, Purdue University popularized hydroponics (called nutriculture) (36). While there was commercial interest in the use of such systems, hydroponics or nutriculture was not widely accepted because of the high cost in construction of the concrete growing beds.

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 place of concrete in lining the growing beds. Plastics were also important in the introduction of drip irrigation. Numerous promotional developments involving hydroponics became common with huge financial investments made in growing systems. Greenhouse areas began to expand significantly in Europe and Asia during the 1950s and 1960s, and large hydroponic systems were developed in the deserts of California, Arizona, Abu Dhabi and Iran, as early as 1970 (38, 39).

Unfortunately, escalating oil prices, starting in 1973, substantially increased the costs of CEA heating and cooling by one or two orders of magnitude. This, along with fewer chemicals registered for pest control, caused many bankruptcies and a decreasing interest in hydroponics, in the US.
Since the inception of hydroponics, research to refine the methodology continued. In the late 1960s researchers at the Glasshouse Crops Research Institute (GCRI), Littlehampton, England, developed the nutrient film technique along with a number of subsequent refinements (40). This research gave rise to the hydroponic systems used today.

Almost 20 years have passed since the last real commercial interest in hydroponics, but today there is renewed interest by growers establishing CEA/hydroponic systems. This is especially true in regions where there is concern about controlling pollution of groundwater with nutrient wastes or soil sterilants. Today growers are much more critical in regard to site selection, structures, the growing system, pest control and markets. There are many types of controlled environment/ hydroponic systems. Each component of CEA is of equal importance, whether it be the structural design, the environmental control or the growing system. Facilities range in size from a few hundred square meters to many hectares, with new facilities being constructed in Colorado, Arizona, Mississippi, New York and Pennsylvania. Current production area in the U.S. is estimated at 300 acres of commercial hydroponic production of tomatoes, which is the most common crop grown. Tomatoes represent one-half of the total production of hydroponically grown greenhouse vegetable crops.

Extensive research and development programs in Europe have vastly improved hydroponic production systems. These new technologies are today being successfully transferred to the United States, proving that hydroponics is a technical reality in the high light regions of the desert southwest. The technology of hydroponic systems is changing rapidly with systems today producing yields never before realized. The future for hydroponics appears more positive today than any time over the last 50 years.

Acknowledgments

NJAES Paper Number P-03130-20-00 Supported by State and Hatch Act funds.
Much appreciation is due the co-authors of this manuscript for their interest and cooperation toward its completion. It has always been a pleasure and an honor to have known and worked with these ‘pioneers’ of Plasticulture. GAG

References