Agriculture Reference
In-Depth Information
If the flow rate is too slow or the film very deep (no longer a film), oxy-
gen demand of the plant roots will not be met and the roots will start
to die. Ideally, the upper portion of the root mat that forms in an NFT
channel should be above the water level and exposed to air at 100% rela-
t ive hu m id it y.
Both the slope and flow rate of the solution affect the dissolved oxygen
content of the nutrient solution. As a root mat forms in the NFT channel
a “damming” effect of the root mat can lead to stagnation of the nutrient
solution with regions of low dissolved oxygen. To keep the low of solution
from getting stagnant use a slope of at least 1 in 50 (2%) or up to 3% to 4%
with the NFT channels. It has also been found that flow rates of 2 to 3 liters
per minute or slightly greater increase oxygenation. The height of free fall
of the solution back to the nutrient reservoir is important in aeration of the
solution. More height causes a finer break up of the solution and introduces
air bubbles into the tank.
You can also use an air pump with air stones in your nutrient tank
to enhance the dissolved oxygen level of the solution. These factors are
important in the design or choice of an NFT system whether you build it
yourself or purchase a complete ready-to-go system.
CHOOSING THE SYSTEM
The correct choice of system will improve your success in growing. Ask
yourself some of these questions. What crops do I want to grow? How
many plants of each crop do I wish to grow? What available floor area do
I wish to use? Remember the spacing needs of plants discussed earlier in
Chapter 3. You must base the number of plants on the total floor area you
have available. Do you want a large system or a series of smaller ones? As
pointed out earlier do not grow lettuce together with vine crops, as it will
get insufficient light. Keep low profile plants in separate systems from the
vine crops. Do you want to utilize your hydroponic units most effectively
by starting your seedlings in another system of trays with rockwool cubes
and blocks? This gives you a head start on the growing cycle by transplant-
ing older plants.
To help you answer some of these questions consider this. Determine
how much salad crops you need for your family. How many heads of
lettuce a week, and how many pounds of cucumbers, tomatoes, and pep-
pers do you consume weekly? Once you have these numbers and types
of crops you eat weekly, you can calculate the total number needed of
each. Remember that you need to sow lettuce at least two to three times
a week and the time for them to mature may take up to 40 days in the
hydroponic system.
