What is CEA?
A controlled environment can be simply described as any space or environment that is controlled. It can be a space for people, like a house, or a space for non-living objects, like a warehouse. In agriculture the space may be for the growth of plants, like a greenhouse, or a space for storage of harvested crops, such as a cold storage facility or refrigerator. Each space may have specific factors that are controlled, such as the

• air temperature and humidity
• sunlight intensity
• gasses in the air such as carbon dioxide [CO2] or ethylene [CH4]
• plant nutrients and water
• and even insects and diseases.

What specific factors are controlled, and to what value they are controlled to will depend on what 'product' is being produced within the controlled environment. Each type of product, for example, a growing green plant, or a cut, long-stem rose, or a frozen package of peas will require different factors to be controlled at different values.

CEA or Controlled Environment Agriculture is a high technology industry for the production of food crops, flowers, houseplants, and medicinals within greenhouses. The greenhouse is the controlled environment structure. It may have many shapes and sizes, but it will always be covered with a material transparent to sunlight. Sunlight is required by the plants to grow healthy, and to reach maturity to produce a nutritious edible product, or a beautiful, fragrant flower. The plants must also receive water and nutrients (fertilizer). One technology that can successfully provide water and nutrients is a hydroponic growing system.

What is Hydroponics?
Hydroponics may simply be described as growing plants with nutrients and water, and without soil. The water must be delivered to the plant root system. The root system may hang directly in the nutrient solution, be misted by it, or can be enclosed within a container or a trough which is filled with a substrate [a replacement for soil]. The substrate may consist of many different types of materials, such as perlite, sand, sawdust, wood chips, pebbles, or rockwool. All substrates must provide good water holding capacity, yet be porous for gas exchange. Between watering events, they become the storage location of water and nutrients for the plant root system. The roots grow within the substrate to secure the plant within the container, or trough.

There are many techniques to deliver water to the plant root zone. For container grown plants, each individual plant is provided an emitter for water from a drip irrigation system. Water may be channeled to a continuous row of plants within a trough, such as in the nutrient film technique system. A large tray of plants may be watered from below by filling the entire tray with water and then draining all excess water. This is called ebb and flood irrigation. Water is typically recycled within nutrient film technique and ebb and flood systems. It is more difficult to recycle in a drip irrigation systems and requires additional equipment such as water a sterilizer and fertilizer monitoring and adjustment equipment.
 
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