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Production Systems - Florida Greenhouse Vegetable Production Handbook, Vol 31
M. S. Sweat, G. J. Hochmuth2There are numerous production systems currently being utilized worldwide by commercial greenhouse vegetable producers. Among the more important include bag culture, trough culture, rockwool, nutrient film technique (NFT), and ground (in-soil) culture. Many modifications of these basic production systems are presently being utilized and most are appropriate for Florida, except ground culture.
There are also several minor production systems, including container culture, ring culture, straw bale, and aeroponics. Aeroponics is a relatively new production system which involves growing plants in a trough or container in which the roots are suspended and sprayed with a nutrient mist.
All greenhouse production systems require the use of similar environmental controls, shade structures, support wires, and general production practices. The major differences would be in the irrigation and nutrient delivery methods and controls.
Individual production systems are not necessarily crop specific. All of the major greenhouse vegetable crops can be grown successfully in most systems. No single system is superior to the others. The cost of each system is comparable and the production from all systems is high when the system is managed properly. Research studies have shown that there was no significant difference in tomato yield among rockwool, bag, and hydroponic NFT systems ( Fig.1 ). However, the study found that all of these systems produced higher yields than ground culture.
Figure 1. Several examples of media used to grow vegetables in soilless culture systems. Bag Culture
Bag culture is a production system where greenhouse vegetables are grown in a soilless mix contained in a polyethylene bag. The bag can be sealed around the mix or it can be an open bag. The closed bags are laid flat on the greenhouse floor with plants growing from planting holes in the sides of the bags. These are called "lay-flat" bags. The open top or "upright" bag system involves growing a single plant in a bag filled with mix. In either system, about 1/2 - 1/3 cubic feet of media mix should be made available for each plant.The upright bag system is used in some states, but has not been widely adopted in Florida. Media for the bags can be peat/vermiculite, sawdust, rockwool, rice hulls, pinebark, peanut hulls, or various mixtures. Bags can be purchased at greenhouse supply houses (most household garbage bags are not strong enough). The bags are filled with the desired sterile mix and placed in double rows in the house. Transplants are produced in a soilless mix, such as peat/vermiculite or rockwool and transplanted into the bags, usually one plant per bag. The soilless mix usually contains some fertilizer to start the plants.
Bags are irrigated and fertilized through a micro (drip) irrigation system in which a polyethylene pipe delivers water and fertilizer down the double-row of bags and each bag is irrigated from an emitter and piece of spaghetti tubing. Many types of emitters are available. One that will wet the entire bag of mix should be chosen. Fertilizer and water programs are available from other sections of this volume of the handbook.
Lay-flat bags contain the media, usually peat/vermiculite or rockwool mixes, in a totally closed bag. Growers can make their own bags, but most often these bags are purchased prepared. Bags are made of 4-mil ultra-violet-light stabilized polyethylene. Cost of new bags with mix would be approximately $3 each, depending on size and quantity purchased.
Bags are laid out in double-rows in the greenhouse and the drip irrigation lines installed. Depending on the size of bag and volume of mix, two to three tomato plants can be accommodated in each laybag. Plants are produced in peat/vermiculite mix or rockwool cubes and transplanted into the bags. An alternative is to grow transplants in "bottomless" or mesh-bottom pots, which are set into the bags.
Drainage slits are needed in the bottom edge of the bags so that excess solution can be removed. This is one problem with bag culture because methods are needed to collect excess fertilizer solution so that it does not leach into the soil under or around the greenhouse. Other production principles are those described under the specific crops elsewhere in this volume.
The main advantages of bag culture include ease of handling, sterilization of new media is unnecessary, reduction in the risk of spread of waterborne Pythium root rots in the house, and the capability of a "buffer" for water and fertilizer in case of power outages.
Trough Culture
Alternatives to straight ground culture include methods to grow plants in raised troughs or benches above the soil. The troughs are filled with the same types of soilless mixes as in the bag culture system. Trough culture is not common in Florida, however there are a few operators using peat-filled troughs for tomato culture.In the trough system, shallow wooden troughs contain the growing media. The troughs may vary from 6 to 8 inches deep and from 24 to 30 inches wide. The troughs can be plastic-lined to facilitate collection of excess nutrient solution. Troughs can be constructed on a slight sideways or lengthways angle, or have a "V"shaped center to facilitate drainage. Some growers might incorporate a perforated pipe buried in the center of the trench to collect the drainage solution and transport it to a central collection sump. Nutrient solution is not recirculated.
Troughs are filled to the top with the chosen soilless mix and wetted. Some settling will occur and additional mix should be added. Additional mix will be needed between crops to replace that which oxidized or settled during the previous crop.
Cost to construct troughs is moderate since only lumber, polyethylene liners, and drainage pipes are needed and the useful life might be 15 to 20 years. Trough culture can be used in greenhouses with concrete or natural ground floors as long as the ground is covered with nursery cloth. Troughs spaced on 5-foot centers would accommodate the same number of plants per house as any other production system.
Transplants can be produced in the containerized tray method using peat/vermiculite mix or they can be grown in rockwool cubes. When ready, the plants are set in the troughs in twin rows to achieve the desired plant spacing for the specific crop.
Irrigation and fertilization in the trough culture system is by drip irrigation. Some fertilizer and lime can be mixed with the media when the troughs are filled or renewed between crops. In Florida, it is unlikely very much lime would be needed since the well water often contains high levels of calcium carbonate. Fertilizer should be supplied with the irrigation water using a nutrient solution formula for the specific crop. Media pH can be as low as 5.0 without danger since there should not be present high levels of toxic aluminum in an organic soilless mix.
Drip systems used should consist of one of the systems that applies solution directly to the media via a drip emitter or ring. Growers should avoid the spray-stake types since they can wet the leaves and stems promoting disease. When fertilizing, caution should be taken against excess buildup of soluble salts in the media. As fertilizer is applied, some salts can accumulate in the media as water is absorbed by the plants or is evaporated from the soil surface. An electrical conductivity of the solution in the media above 3.0 millimhos (mmhos) would be indicative of excess soluble salts and an application of water alone would be needed to flush excess salts from the media.
Media in trough culture systems can be reused for several years as long as it is sterilized between crops by steaming or fumigation. Irrigation systems and drainage systems will need cleaning and disinfesting between crops as well.
The major advantages of the trough system include ease of handling once the system is in place. Trough systems are flexible for various cropping decisions e.g., vegetables, cut flowers, etc. The system is relatively inexpensive to maintain from one crop season to another. The major disadvantage would be in disease control in a particular trough since an organism such as Pythium could spread the length of a trough. Care also is needed to avoid soluble salt buildup in the media during the season.
Perlite and Rockwool Culture
Rockwool production ( Fig.2 ) was developed in Holland around the mid 1970s and is currently experiencing widespread use among new or expanding greenhouse vegetable operations in Europe, Canada, and recently, the United States.
Figure 2. Young tomato plant growing in rockwool slab. Rockwool is an inert, porous, sterile growing medium made from rocks that are heated at high temperatures and formed into thin fibers. The actual composition is approximately 60% basalt, 20% limestone, and 20% coke.
The resulting fibers can be formed into slabs or bagged as a loose rockwool for bag culture. Small cubes of rockwool are used for starting transplants. Slabs for tomatoes are commonly 3 inches thick, 6 to 8 inches wide, and 36 inches long. Other sizes are available depending on crop. Slabs are packaged in white or white-on-black polyethylene sleeves. Depending on source and quantity, each slab costs about $2.50.
Perlite is a volcanic mineral that is expanded by heating at high temperature in a furnace. The resulting light-weight granular material makes a good media with high water-holding capacity. Layflat bags, about 0.5 cubic foot volume, are filled with perlite and can hold up to 3 tomato plants or two cucumber plants ( Fig. 3 ).
Figure 3. Young tomato plant growing in perlite-filled bag. Rockwool culture is similar to bag culture in greenhouse layout and operation. Slabs are laid in twin-rows and are irrigated by microirrigation with one emitter per plant. Transplants are started in small rockwool cubes and then the cubes are placed in larger transplant blocks, which are approximately 3 inches square. The blocks with the transplant are then placed in the greenhouse on the slabs where the plant will eventually root into the slab media. Two or three tomato plants can be grown per 36-inch slab. It is possible to achieve average populations of 2 ½ plants per slab by rooting plants over the end-to-end junction of two slabs. Half of the root system is in each slab. The latter population should be sufficient for most tomato cultivars in Florida.
Perlite bags are placed in the greenhouse like described above for rockwool. Seedlings can be started in rockwool cubes and then transplanted into the perlite bags.
Rockwool slabs and perlite bags are placed so that they rest on a slant toward a trench between the twin-rows of slabs. Twin-rows should be on 5-foot centers. Slits are made in the bottom edge of each bag so that leachate drains into the trench and can be removed from the greenhouse. New developments are being made to improve collection of the leachate so it does not seep into the greenhouse ground floor. A trough or channel ( Fig. 4 ) under the slabs is used to collect the leachate, which can then be used for other fertilization purposes (lawn, garden etc.). Leachate is not reused because of potential for re-introduction of disease organisms. It might be possible to treat the leachate by ultraviolet light or heat, and reuse it; however, this system is still experimental for Florida.
Figure 4. Construction of leachate collection system in a new greenhouse. Fertilization of rockwool and perlite is accomplished by fertigation through the drip irrigation system. Fertilizer is applied with each irrigation event. Irrigation scheduling is controlled by a "starter tray" ( Fig. 5 ). One slab and its plants are placed in the tray with the bottom of the polyethylene covering removed from the slab. The bare slab surface interfaces with a capillary mat in the bottom of the tray. A small reservoir collects a portion of the excess nutrient solution. A contact probe in the solution in this reservoir signals a start-up of the irrigation controller as soon as the probe breaks contact with the solution in the reservoir. The controller is preset for a timed irrigation event (e.g. 2 or 3 minutes) and it opens a solenoid valve to start the flow of water and fertilizers. In most systems, water is mixed with fertilizer stock solution in a 1:100 ratio before it is applied to the slabs. Simple proportioning pumps can do this task for most greenhouse operations without the need for complicated injectors. Growers need to be sure, however, that the proportioners used are accurate and resistant to fertilizers and acids.
Figure 5. NFT recirculation pump and sump tank (note raised-neck opening to sump tank). Irrigation frequencies may vary during the season depending on crop demand. Attention needs to be given to the control of soluble salt buildup in the slabs. Fertilizer programs and recipes are presented in the fertilizer section of this handbook. Samples of media solution should be tested regularly for soluble salt level. The soluble salt concentration should not vary more than plus or minus 1.0 mmhos of the applied solution conductivity.
Rockwool slabs and perlite can be reused for up to three seasons. In Florida, slabs should be sterilized between seasons and placed in new sleeves. Slabs that have been crushed or damaged should not be reused.
Rockwool or perlite culture has many advantages over other production systems. Among these are the ease of handling, installation, and media removal. Rockwool and perlite have a high water holding capacities and allow for more precise control of nutrients. Each medium is inert and sterile and offers predictable performance. The media has very high air pore space which provides for higher oxygen levels and thus better root growth than with the NFT tubes. However, the most important advantage of these systems is that they are not a recirculating system such as NFT.
Each slab or bag is "containerized" and nutrient solution does not flow from one slab or bag to another and back via a sump tank. This "closed" type of system reduces the risk of spreading a disease pathogen such as Pythium root rot. This culture also is considerably less labor intensive compared to NFT since the irrigation and fertilization are automatically managed by the starter tray and proportioners.
The major disadvantages of rockwool or perlite are the need for a leachate collection system and the need to replace the media every two to three seasons. However, these are small prices to pay by growers for peace-of-mind that root rot potential is substantially reduced, and that production can be more predictable.
Nutrient Film Technique
Nutrient film technique (NFT) is a type of a "water culture" system in which roots are continually bathed in a flowing nutrient solution. True NFT consists of growing plants in a shallow plastic-lined trough through which a nutrient solution is continually flowed. Roots spread out over the width of the 12-inch channels and are continually bathed in a thin film of flowing, oxygenated nutrient solution. Channels are on a slope to allow the nutrient solution to flow from one end of the channel to the other and be collected for return to the sump tank. Nutrient solution is pumped continually from the sump tank back to the channels ( Fig. 6 ). Nutrients are added to the solution as needed and the solution may be replaced periodically to reduce the buildup of salts and disease organisms.
Figure 6. Irrigation starter tray for perlite or rockwool production systems. Various modifications of the basic NFT system have been tried. One popular system started for hobby greenhouses is to grow plants in a four-inch PVC tube instead of a wide channel. The PVC pipe system was popular among some commercial growers in north Florida. The PVC tube is extremely confining to the root system so that continual bathing of the root system is not possible because stoppage of water flow would occur and the root systems would flood. Therefore, the flow of nutrient solution is pulsed by a time clock. Programs and schedules for the irrigation events are presented in the irrigation section of this volume. Even with careful attention to irrigation scheduling so that flooding is minimized, many growers still have problems with oxygen availability to the roots. Pythium root rot then can attack the roots and presently, there is no legal chemical control Pythium in these systems. Many PVC growers have since switched to bag culture.
In all NFT or modified NFT systems, channels and plants are arranged in the greenhouse similar to bag or rockwool culture (twin-rows, plant spacing, etc.). Care needs to be given to proper channel slope and return system to the sump tank. Some systems call for 1 inch drop for every 100 inches of channel length. This is probably not enough slope for the NFT tubes. One inch rise for every 20 to 30 inches might be more appropriate.
NFT systems are expensive to install because of the channels, concrete greenhouse floor, return piping system, sump tank, and sump pumps. Installation might be slightly more expensive than rockwool or bag culture but the NFT materials represent basically a one-time expense. A high degree of management and expertise is required to optimally operate the system to ensure correct irrigation and fertilization and to prevent root flooding.
Transplants for NFT are usually started in rockwool or foam cubes and placed in the channels at proper spacings. In true NFT, the plastic liner is wrapped around the stems to prevent algae growth in the channel.
Crops adaptable to NFT include tomatoes, cucumbers, and lettuce. Lettuce is particularly adapted to NFT because it is a short-term crop and less subject to the damage from root rot.
Major advantages of NFT include the one-time expense for the basic system. The major problem with the NFT systems is the high probability that disease organisms such as Pythium could be recirculated quickly within the greenhouse. This limitation makes NFT systems questionable for large-scale commercial production in Florida. This problem is made worse because of the lack of labeled chemical pesticides for Pythium control. NFT systems also are extremely labor-intensive to manage the nutrient concentrations and pH of the solution, and there is no water-holding capacity in the event of a power failure.
Ground Culture
Ground culture of greenhouse vegetable crops involves growing crops directly in the natural soil under the greenhouse cover. Plants are oriented in double rows and irrigation is handled through the use of proportioners, injection pumps, or large nutrient storage tanks with sump pumps. Drip or ring emitters are placed at the base of each plant to provide water and nutrients to the plants.Ground culture production of greenhouse vegetable crops is not recommended for Florida conditions. Although many older greenhouse vegetable operations in the United States and Canada use ground production, most newly constructed houses utilize one of the more popular soilless production methods.
In Florida, the insect and disease pressures would prohibit ingreenhouse vegetable production for more than a year without extensive and costly fumigation. Northern operations have been successful with ground culture due to the use of large boilers and steam pipes for soil sterilization.
In addition, many areas of Florida have sandy soil profiles with fluctuating water tables. Excessive nutrient levels could leach into local ground water tables or accumulate in the soil surface. Another problem could be periodic flooding caused by a high water table.
Summary
As mentioned earlier, there is no single production system that is best for everyone. In comparing the most popular systems (bag, rockwool, and NFT), one would find that the installation cost of each system would be roughly comparable but rockwool and bags will need to be replaced periodically in those systems. The NFT systems are highly susceptible to root rot problems for which there are no chemical pesticide control measures. Low oxygen availability to roots in the NFT tube system makes this system risky.The total production of the three major systems can be extremely high depending on the level of management. This management level is higher for the NFT system as opposed to the bag or rockwool cultures. This is due primarily to the need for constant monitoring of the nutrient solution and the operating pumps and nutrient flow cycles to prevent flooding and subsequent root rot problems. In selecting a production system, a grower should weigh both the advantages and disadvantages as they relate to the individual's situation. Of particular concern, should be the relative sustainability of optimum production without resorting to the illegal use of unlabeled pesticides.
More Information
For more information on greenhouse crop production, please visit our website at http://nfrec-sv.ifas.ufl.edu.For the other chapters in the Greenhouse Vegetable Production Handbook, see the documents listed below:
Florida Greenhouse Vegetable Production Handbook, Vol 1
Introduction, HS 766
Financial Considerations, HS767
Pre-Construction Considerations, HS768
Crop Production, HS769
Considerations for Managing Greenhouse Pests, HS770
Harvest and Handling Considerations, HS771
Marketing Considerations, HS772
Summary, HS773
Florida Greenhouse Vegetable Production Handbook, Vol 2
General Considerations, HS774
Site Selection, HS775
Physical Greenhouse Design Considerations, HS776
Production Systems, HS777
Greenhouse Environmental Design Considerations, HS778
Environmental Controls, HS779
Materials Handling, HS780
Other Design Information Resources, HS781
Florida Greenhouse Vegetable Production Handbook, Vol 3
Preface, HS783
General Aspects of Plant Growth, HS784
Production Systems, HS785
Irrigation of Greenhouse Vegetables, HS786
Fertilizer Management for Greenhouse Vegetables, HS787
Production of Greenhouse Tomatoes, HS788
Generalized Sequence of Operations for Tomato Culture, HS789
Greenhouse Cucumber Production, HS790
Alternative Greenhouse Crops, HS791
Operational Considerations for Harvest, HS792
Enterprise Budget and Cash Flow for Greenhouse Tomato Production, HS793
Vegetable Disease Recognition and Control, HS797
Vegetable Insect Identification and Control, HS798
Selected Readings
Bauerle, W. L. 1984. Bag culture production of greenhouse tomatoes. Ohio St. Univ. Special Circular 108, 7p.Cooper, A. 1982. Nutrient film technique. Grower Books, London.
Cooper, A. 1979. The ABC of NFT. Grower Books, London.
Hochmuth, G.J. (ed.). 1989. Design suggestions and greenhouse management for rockwool vegetable greenhouses in Florida Univ. Fla. Coop. Ext. Circ. SP110.
Johnson, H., G. Hochmuth, and D. Maynard. 1985. Soilless culture of greenhouse vegetables. Univ. Fla. Coop. Ext. Circ. 218.
Jones, J. B. 1983. A guide for the hydroponic and soilless culture grower. Timber Press, Portland, Oregon. 124p.
Judd, R. 1982. Bag culture. Amer Veg. Grower, p.42-44.
Ministry of Agric, Fisheries, and Food. 1984. Tomato production 6. Hydroponic growing systems. Grower Books, 50 Doughty St. London, WC1N 2LP.
Resh, H. M. 1978. Hydroponic food production. Woodbridge Publ. Co. PO Box 6189. Santa Barbara, CA 93160.
Savage, A. J. (ed.) 1985. Hydroponics worldwide: State of the art in soilless crop production. Int'l Center for Special Studies, 400 Hobron Lane, Suite 3502, Honolulu, HI 96815.
Sheldrake, R. 1982. Back to the bag. Amer. Veg. Grower, p. 36
Sheldrade, R. 1981. Money bags. Amer. Veg. Grower, p.15 and 34
Smith, D. 1987. Rockwool in horticulture. Grower Books, London.
Taylor, G. A., and R. L. Flannery. 1975. Growing greenhouse tomatoes in trough culture using a peat-vermiculite growing medium. Rutgers UnivCollege Coop. Ext. Serv. Veg. Crops Offset Series No.33.
Winsor, G. W., R. G. Hurd, and D. Price. 1979. Nutrient film technique. Growers Bulletin No.5. Glasshouse Crops Res. Inst. Littlehampton, England.
Wittwer, S. H. and S. Honma. 1979. Greenhouse tomatoes, lettuce, and cucumbers. Mich. St. Univ. Press, East Lansing, MI.
Footnotes
1. This document is HS785, one of a series of the Horticultural Sciences Department, Florida Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida. Original publication date December 1990. Revised February 2001. Reviewed February 2008. Visit the EDIS Web Site at http://edis.ifas.ufl.edu.2. M.S. Sweat, extension agent IV, Baker County, and G.J. Hochmuth, professor of Horticultural Sciences and Center Director, North Florida Research and Education Center, Institute of Food and Agricultural Sciences, University of Florida. The Florida Greenhouse Vegetable Production Handbook is edited by George Hochmuth, professor of Horticultural Sciences and Center Director, North Florida Research and Education Center - Quincy and Bob Hochmuth, extension agent IV, North Florida Research and Education Center - Suwannee Valley, Cooperative Extension Service, Institute of Food and Agricultural Sciences, University of Florida, Gainesville, FL 32611.
The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other extension publications, contact your county Cooperative Extension service.
U.S. Department of Agriculture, Cooperative Extension Service, University of Florida, IFAS, Florida A. & M. University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Larry Arrington, Dean.
Copyright Information
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