Hydroponic Lettuce Experiment - Week 4

Introduction

The past two weeks presented a significant amount of changes to the lettuce plants:

• Two new generations of leaves have grown
• Plant roots have gained root hairs and begun to curl
• Nutrient solution was added
• Additional discolourations appeared on several leaves

Observations

Each lettuce plant has grown two new leaves. New leaves appear to be more wavy and curled than the previous generation. When leaves grow, they develop at the stem of the previous leaf. They eventually separate rolled into a cylinder. Over time, the leaf-coil unrolls into a proper leaf. Fig. 1 shows the growth of lettuce plants over time in photos.

Fig. 1 - Lettuce plants on various dates (from top to bottom, left to right: May 21, 22, 23, 26, 27, and 31.

Until recently, the roots have been growing relatively straight. Presently, they are slightly curved at the base. This likely results from the roots reaching the bottom of the hydrogarden reservoir and, therefore, is not considered to be an issue. Root hairs are also growing and measure 5 mm at the longest. Fig. 2 shows an image of the roots.

Fig. 2 - Lettuce roots on May 27. Note the end-curl and root hairs.

On May 26, 105 mL of stock nutrient solution (Schell-Toogood v.1) was added because a large quantity of it was used and/or evaporated. By knowing the original amount of solution and the number of days passed, one can produce this formula for nutrient solution evaporation:

, where V₀ is the volume of solution at t = 0.



In more understandable terms (or less, depending on how you see it), nutrient solution evaporates at a rate of 7.8 mL/day. It should be noted, however, that this assumes that evaporation is a linear process.

On May 19, discolourations on the tips of two leaves from the first generation were discovered. Eventually, similar discolourations began occurring on all first and second generation leaves. As of May 28, they did not appear to be progressing further. It is unknown whether it is a natural part of the growth of a lettuce plant or if it was caused by an environmental factor (e.g. lack of nutrients). Fig. 3 shows these discolourations.

Fig. 3 - Tip discolourations on some of the first generation leaves (Left: May 23, Right: May 26)

Fig. 4 shows the length of the lettuce plants and their roots over time. Data for May 21 and May 28-30 has been interpolated because measurements could not be made on these days. It appears that a plant height recession occurs before a new leaf separates from the main stem. After a recession, plant height increases to a greater height than before the recession.

Fig. 4 - Graph outlining the height of lettuce plants and roots over the past 4 weeks. Quick, what do lettuce plants and capitalism have in common?

Conclusion

Week 4 marks some significant growth and changes in the lettuce plants. Plants show signs of maturing, such as developing root hairs and general upward growth, as well as regression, as seen in leaf-tip discolourations.

Several observations require additional examination:

• The evaporation equation must be tested to ensure it is accurate in predicting the volume of nutrient solution.
• The spread and intensification of discolourations on first and second generation leaves must be monitored to ensure they do not result from a nutrient deficiency or other health issue.

In the coming weeks, I hope to gather enough data to find patterns that will give insight into the growth of lettuce plants.