8/13/2019 Article ControlledEnvironmentAgriculture

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Co n t r o l l e d En v i r o n m e n t A g r i c u l t u r e A.J. Both, Ph.D., Controlled Environment Engineering Specialist

Controlled Environment Agriculture (CEA) crop production encompasses growingsystems for bedding plants, pot plants, cut flowers, plugs, and vegetables. CEAproduction incorporates some type of structure with related environmentalcontrol and plant growing systems. The structures range from simple shades tofully enclosed structures. The degree of environmental control ranges fromsimple (often manual and controlling a limited number of environmentalparameters) to highly sophisticated (computer control of all impactingenvironmental parameters). Similarly, the growing systems employed range fromentirely manual to totally automated. Often, the availability, affordability, andskill of the labor force significantly determine the necessary degree ofenvironmental control and growing system automation. CEA systems are

specifically designed to overcome the vagaries of outside weather conditions.

S t r u c t u r e s

Growing structures used for CEA crop production can be divided into two groups:single span and multi span (gutter connected) structures. These structuresgenerally have either curved or peaked roofs and can be glazed with a variety ofcladding materials such as plastic film (e.g., polyethylene), rigid plastic panels(e.g., polycarbonate or acrylic), or glass. Their foundations range from hollowposts driven into the ground to poured concrete foundations. Structuralcomponents can be wood (or similar materials such as bamboo), rigid plastic,aluminum, and steel (often treated: e.g., galvanized steel). All structures need tobe designed to withstand local weather conditions (wind, snow, hail, etc.), andstrong enough to support equipment (e.g., irrigation, supplemental lighting, andcurtain systems) and in some cases crops (e.g., hanging baskets or vegetablecrops supported by strings attached to the greenhouse structure). Multi spanstructures offer a clear advantage in terms of the heat energy required sincetheir exposed outside surface area per unit floor area is less compared to singlespan structures. Often, space utilization (ratio of the usable growing area andthe total production area) in multi span structures is higher compared to single

span structures. Many commercial designs rely on standardized dimensions (e.g.,distance between the posts, width of a bay, width of a roof section, length of abay, etc.) to reduce design and manufacturing costs.

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Gr o w i n g S y s t e m s

CEA crops can be grown on the floor (in the soil or sand, on top of gravel or aprotective fabric, or on concrete) or on benches (fixed or movable). Integrated inthe floor or the benches can be heating and irrigation systems (heated ebb and

flood floors and benches). The movement of plant material (if any) through thefacility can range from manual to fully automated with the movement of benches(tables) directed by a computer control system. For some crops (e.g., beddingplants), rolling benches are used to move the plant material outside during theday to harden off the crop. Overhead growing systems consist of stationary ormovable hanging baskets, and each system can be equipped with a dedicatedirrigation system. A specialized crop production system often associated with CEAsystems is hydroponics. In hydroponic systems, the rooting medium is ofteninorganic and limited to small volumes. Water and nutrients are provided to theplant roots continuously or at very regular intervals allowing for precise control ofplant growth and development. Obviously, these systems need to be designedwith redundancy and robustness since even short interruptions can causesignificant crop losses.