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Respiration
Respiration is the biochemical process by which oxygen and carbohydrates, or sugars, are assimilated in the plant.
The sugars produced by the plant during photosynthesis are incorporated into the growing plant at this
time. The process of respiration requires oxygen to act as an electron acceptor in the energy-producing processes.
This is known as aerobic respiration. Without the presence of oxygen, anaerobic respiration occurs. In many plants, anaerobic respiration takes the form of ethanol fermentation.
This can lead to the accumulation of ethanol reaching toxic levels.
Fertilizer Solution
Equal parts of Peter's HydroSol and Calcium Nitrate (CaNO3) are added
to RO water as a fertilizer solution. One component must be
dissolved in the RO water before the other component is added. If HydroSol and
CaNO3 are added at the same time, these components will react and form
a precipitate, resulting in an inadequate fertilizer solution. Approximately 170
g of both the HydroSol and CaNO3 are added to 300 L of RO water to
obtain an EC of 1200 microS cm-1.
Approximately
20 ml of 1N KOH is added to this solution to raise the pH
to 5.8. Larger volumes of fertilizer solution will require proportional increases
of HydroSol, CaNO3, and KOH.
RO Water
Reverse Osmosis (RO) water is de-ionized water containing very small amounts of nutrients or contaminants.
The RO water is used in order to obtain a solution with known concentrations of nutrients.
Tap water can be used to make the fertilizer solution; however, the nutrients in the tap water must be taken into consideration when adding the fertilizer.
Also, tap water may contain chlorine, which may cause problems for the growth of hydroponic lettuce.
Bicarbonates present in tap water can make pH adjustment of the nutrient solution difficult, as well.
The use of RO water bypasses this problem.
Lettuce Seed
Commercially available lettuce seed does not have to be specially treated
prior to seeding. The seed should be stored in a cool (4o C or 40o
F) dry location. The seed packets are usually hermetically sealed.
Once open,
the packets require special handling to keep the seed dry. Seed of varieties
specifically developed for greenhouse production should be used. The variety
shown in this handbook is 'Ostinata'. Lettuce production will be enhanced if
seeds of the best quality are purchased.
Seeding Machine
An automatic seeding machine, can be used for seeding of the lettuce seeds
in the plug trays. Automated seeding saves on seeding time and labor.
Other
seeding equipment would work well. See ding machines require special care.
They
are affected by relative humidity, and need to be maintained properly to ensure
precise seeding.
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