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Pond Area Stage
Environmental Set-Points
The environmental parameters during the pond area stage are adjusted to the following set-points:
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Day Temperature - 24o C (75F) (e.g., 08:00 - 18:00 hr)
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Night Temperature - 19o C (65F)
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pH - 5.8
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EC - 1200 microS cm-1
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DO - 4 ppm or greater
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Light - 17 moles/m-2d-1
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Nutrient Solution Temperature - 24o C (75o F)
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Relative Humidity - less than 70%
Growing conditions remain at these set-points during the entire pond area growth stage.
Day and night temperatures are based on the length of the daylight period.
Day 11
On Day 11, just after transplanting, the lettuce plants have sufficient exposure to light and enough space to expand for the next 10 days.
This photo shows the length of the lettuce roots on Day 11 at transplanting.
Day 18
By Day 18, the leaves have expanded to cover much of the Styrofoam floaters.
A head of lettuce weighs approximately 0.4 oz. (10.5 g) at this time.
The roots have grown extensively in the last seven days.
A view of the whole pond shows the lettuce covering much of the pond surface.
Compare this to the plant growth on Day
11.
Day 21 - Spacing
The leaves have now grown to a point where they are interfering with the growth of neighboring plants.
Respacing on Day 21 will allow adequate space for new growth.
The pond is now tightly packed with the quickly growing heads of lettuce. Heads now weigh approximately 0.75 oz.
(21.4 g).
The spacing is increased from 97 plants m-2 to 38 plants m-2 on Day 21.
The 38 plants m-2 spacing allows adequate space for the growth of lettuce plants until harvest on Day 35.
This photo shows how much extra space has been given for plant growth after increasing the spacing from 97 plants m-2 to 38 plants m-2.
This photo shows the increase in leaf and root growth on Day 21 (compare this
to Day 11.)
Day 25
On Day 25, an individual lettuce plant now weighs approximately 1.7oz. (47g).
Lettuce leaves are not yet blocking neighboring plants. Each plant has sufficient lighting and space for growth.
On Day 25, the pond appears to be completely covered. However, the plants do have adequate space.
The shadows seen on the pond are caused by the greenhouse construction elements.
Day 32
Heads now weigh approximately 4 oz. (114 g).
Day 35 - Harvest
At harvest, a head of lettuce weighs approximately 5 oz (150 g). The consistent growing conditions and proper production
scheduling for hydroponic lettuce production ensures the crop size will be uniform in size and quality.
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