NFT Area
Concepts involved in the Nutrient Film Technology (NFT) area are:
-
NFT Area Size
-
Nutrient Solution
-
Construction
-
Lighting
-
Turbulator Fan
-
Aspirated Box
NFT Area Size
The production of 1000 plants/day requires a NFT trough area of approximately
10,400 ft2 (980 m2).
If NFT rolling benches 12.5 ft in length (4 m) are used, about 880 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 12,600 to 14,400 ft2 (1,200 to 1,340 m2) will be required for aisles. The total glasshouse
space required will be approximately 24,000 ft2 (2,200 m2). Pak choi plants are initally
transplanted at a spacing of 14 * 3 inches (35.6 * 7.6 cm). This is a density
of 13.8 plants/ft2 (37 plants/m2). The pak choi plants are grown at this spacing
in the NFT area greenhouse for 10 days. On day 21 after seeding, the spacing
is doubled by increasing the distance between each NFT trough by three inches
(7.6 cm). The plants remain at this spacing for an additional 14 days. Final
harvest takes place 35 days after seeding.
Nutrient Solution
Set points for the macro and micro-nutrients in the nutrient solution
for hydroponic pak choi 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 pak choi 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 pak choi leaf canopy. The airflow is needed to increase plant transpiration. This increases the transport of nutrients from the roots to the young, fast-growing pak choi leaves. The greater rate of nutrient transport provides sufficient amounts of calcium to the leaves and, therefore, prevents tipburn.
Without this airflow, pak choi 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 pak choi 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.
