NFT Area
Concepts involved in the Nutrient Film Technology (NFT) area are:
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NFT Area Size
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Nutrient Solution
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Construction
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Lighting
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Turbulator Fan
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Aspirated Box
NFT Area Size
The production of 1000 plants/day requires a NFT trough area of approximately 5200
ft2 (490 m2). If NFT rolling benches 12.5 ft in length (4 m) are used, about 440 lineal feet of rolling bench will be required. Assuming 3 feet wide (1 m) aisles are used between rows of benches and around benches, evaluation of several configuations indicate 6300 to 7200 ft2 (600 to 670 m2) will be required for aisles. The total glasshouse space required will be approximately 12,000 ft2 (1100 m2).
Spinach plants are initally transplanted at a spacing of 7 * 3 inches (17.8 * 7.6 cm). This is a density of 6.9 plants/ft2 (74 plants/m2). The spinach plants are grown at this spacing in the NFT area greenhouse for 14 days. On day 22 after seeding, the spacing is doubled by increasing the distance between each NFT trough by three inches (7.6cm). The plants remain at this spacing for an additional 11 days. Final harvest takes place 33 days after seeding.
Nutrient Solution
Set points for the macro and micro-nutrients in the nutrient solution for hydroponic spinach grown in NFT are:<
| Macro-nutrients: | Micro-nutrients: | ||||
|---|---|---|---|---|---|
| N | 8.9 | millimol l-1 (125 ppm) | Fe | 16.8 | micromol l-1 (0.94 ppm) |
| P | 1.0 | millimol l-1 (31 ppm) | Mn | 2.5 | micromol l-1 (0.14 ppm) |
| K | 5.5 | millimol l-1 (215 ppm) | B | 15.0 | micromol l-1 (0.16 ppm) |
| Ca | 2.1 | millimol l-1 (84 ppm) | Cu | 0.4 | micromol l-1 (0.03 ppm) |
| Mg | 1.0 | millimol l-1 (24 ppm) | Zn | 2.0 | micromol l-1 (0.13 ppm) |
| S | 1.1 | millimol l-1 (35 ppm) | Mo | 0.3 | micromol l-1 (0.03 ppm) |
The desired Electrical Conductivity (EC) and pH of the nutrient solution are 1.2 mS/cm and 5.8, respectively. The EC can be adjusted by adding more concentrated nutrient solution or RO water. The first will increase the EC and the latter decrease it. The pH is maintained by adding an acid (1 N nitric acid) or a base (1 N potassium hydroxide). A concentrated nutrient solution formulation is shown in Stock Solutions A and B.
Construction
Some of the details of the NFT troughs placed on rolling benches. Typically the troughs are 12 feet long. The bench is a few inches longer to acommodate plumbing and 5 feet wide. This makes it possible for most people to work of the center of the bench.
Lighting
Uniform light distribution is required
in the NFT Growing Area. Supplemental lighting is added to achieve approximately
200 micromol m-2s-1 at the plant level is recommended.
High pressure sodium (HPS) lamps are used to supply supplemental light. These
lamps are the most efficient, have a long life, and have only limited decay
in output over time. Independent lighting consultants (architects and some CEA
specialists, for example) have specialized software to determine proper number
and placement of lamps needed for a specific and uniform light intensity. It
is critical to have the correct lighting system installation that has both a
high level of uniformity over the growing area.
Because the CEA spinach program is production-intensive, lighting and electrical power usage is high. Local utility companies have information on special rates and rebate programs for new industries and Controlled Environment Agriculture facilities.
Turbulator Fan
It is necessary to provide adequate air flow into the spinach leaf canopy. The airflow is needed to increase plant transpiration. This increases the transport of nutrients from the roots to the young, fast-growing spinach leaves. The greater rate of nutrient transport provides sufficient amounts of calcium to the leaves and, therefore, prevents tipburn.
Without this airflow, spinach must be grown under reduced light levels, which slows the rate of growth. One method to achieve this is to blow air vertically down onto the spinach plants by means of a Turbulator Fan. An alternative approach is to provide horizontal air flow with some method to force the air through the plant canopy. Two opposing air streams will create enough turbulence to provide this effect. Careful sizing and placement of the fans and measurement of the air velocity and turbulence is necessary if tipburn is to be avoided.
Aspirated Box
The aspirated box is located in the growing area and has the same function
as the aspirated box in the germination
area.
