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.

Hydroponic Lettuce Experiment - Week 2

Introduction

On May 5, 2013, I planted some lettuce seeds in my simple hydrogarden set-up in the hopes that something would grow. I have attempted similar experiments some months ago, but they were dismal failures. This experiment, on the other hand, appears to be at least somewhat successful thus far.

The purpose of this experiment is to gain some insight on how plants grow in a hydroponic environment. I need this information because I am not very familiar with growing plants without soil (or even with soil). Because of the philosophy of this experiment, it is not a true experiment, but rather an all-out test performed with some scientific principles.

It should be noted that no automated components are currently in use.

My hydroponics rig, as stated previously, is quite simple. It contains the following components:

• 473 mL plastic container
• Schell-Toogood v.1 nutrient solution
• Sponge (inert medium)
• Aquarium pump
• Lindenburg "Grand Rapids" lettuce seeds (Lactuca sativa).

You may have noticed the material called "Schell-Toogood v.1 nutrient solution." This solution was created by my chemistry teacher and I and it provides all nutrients necessary for plant growth. It is a slightly modified version of the PrometheusWiki's version of Hoagland Solution. If the solution is successful, I may write a more detailed explanation of what it is and how to create it.

For each day that the experiment is active, I will record the height of the plants and the length of the roots, the overall condition of the plants (especially any notable changes), and any alterations to the hydroponic system (e.g. replaced nutrient solution, turned off aeration pump, etc.).

Observations

Fig. 1 shows some pictures of the lettuce plants at various days throughout the experiment. The lettuce appears to be pale green in colour, but this may be due to the type of lettuce rather than resulting from any nutrient deficiencies. Additional observation and research are required to make any definite claim.

Fig. 1 - Lettuce plants on May 9, 15, and 18, respectively. Note the growth of additional leaves.

I also noticed a slight discolouration on one of the leaves (Fig. 2). Whilst it does not appear to be spreading, it does appear to be impeding the leaf's growth.

Fig. 2 - Lettuce leaf with discolouration on May 9 and 18, respectively.

Fig. 3 shows the growth of the lettuce plants in chart form. A trough in plant height occurs on May 17. My experiment journal claims that the plant appeared to be wilting on that day; as a result, the nutrient solution was replaced. However, it is unclear if the plant was indeed wilting or if it was spreading out to accommodate for new leaves.

Fig. 3 - A chart outlining the growth of both the lettuce plants and their roots over the past week.

Conclusion

Fig. 4 - A not-as-successful attempt at growing hydroponic lettuce.

This current attempt at growing plants hydroponically is much more successful than previous attempts have been (Fig. 4). In the last two weeks, lettuce plants have germinated and grown to a respectable height.

Several observations were made that require additional examination:

• Plants appear pale green, which is a sign of malnourishment, but this may simply be the nature of this particular type of lettuce.
• A discolouration was found on one of the leaves which should be kept in mind.
• A period of wilting may have occurred on May 17, although this may have been caused by leaves being spread out to allow new ones to grow instead.

I plan to do blog posts similar to this on a weekly basis every Sunday. Each post will contain my observations for the week and some analysis on it.

Control Program Roadmap

I want to get the program, garden, up as soon as possible as I hope plants will be growing soon. This post will act as a continuous roadmap for this piece of software.

garden

• Server-client programs
• Server
• Scheduling
• Access to hydrogarden components
• Client
• TUI interface
• dnc (Double-New Curses)
• Metrics and data
• Debug mode (?)
• Inter-process communication
• Sockets
• Conf file
• Set variable data
• Circuit pins
• X10 Firecracker information
• Set scheduling times
• X10 functions
• Lower-level
• Higher-level
• Daemon
• Init script
• Run as static user

The program will most likely be used before all of these features are complete, therefore it will be implemented gradually.

Additional TODO List

• Create new deployment diagrams for the software and communication
• Create new UML diagrams for server and client programs

Prototype Test - Take One

After months of research, design, and purchasing hardware, I finally have a working prototype of an automated hydrogarden. Having said that, it does not have everything that was planned; these items will be added in subsequent tests. Components not included in this test include water monitoring equipment, a camera, and a dedicated scheduling device (i.e. Raspberry Pi with a control program). More importantly, this prototype does include a water aeration system, lighting suitable for plant growth, and an automation program.

Hardware

Fig.1 - Preliminary hardware setup

I will begin by describing the hardware setup. The main load-bearing devices include an aquarium pump which aerates the water and an overhead light constructed specifically for plant growth. Both devices are attached to X10 appliance switches (see Fig.2), which allows them to be activated/deactivated from a computer; I will discuss this in more depth later. The water reservoir (see Fig.3) is ~500 mL in volume and has two holes in the top: one for the aeration tube and the other for the actual plant. The seeds are planted into a small sponge (the inert medium) which will provide the future plants with structural support. The reservoir is filled with Hoagland solution, which will be the topic of another blog post. The reservoir is placed in a heated dog dish as Canadian winters are quite cold, meaning that, during the night, the temperature of the seeds may drop below the 15°C needed for germination. The hardware design is very similar to that of the elaboration phase, albeit with a few exclusions.

Fig.2 - X10 switches and transceiver

Fig.3 - Close-up of the reservoir

Software

Now, onward to the software. Currently, I am using a program I call hydrocontrol to control automated aspects of DotSlashGarden. It is written in bash and is simply a wrapper for bottlerocket, a Linux-based command-line utility for controlling X10 Firecracker devices. It is extremely simply and I only created it because I can never remember the syntax for bottlerocket!

As an example, this would turn on the light:

# hydrocontrol -l on

hydrocontrol must be run as root as it requires access to serial devices (i.e. the X10 Firecracker module). Whilst this program is able to turn devices on or off, it is unable to do any type of scheduling; another program, such as cron, would be required to do such a task.

As you can see, this is much simpler to remember than:

# br -c A -n 1 -x /dev/ttyUSB0

If you would like to look at or use this program, it is available on my Dropbox. It should be noted that it is somewhat kludgey and it could easily be rewritten in 15 minutes; however, it does the job, and that is what is important.

Conclusion

With this test, I hope to identify some issues will the implementation so that they can be fixed as soon possible. I have already learned that small reservoirs are much easier to handle as 0.5 L of Hoagland solution is easier to make than 14 L. In order to move on to another prototype, the main control program (garden) needs to be integrated into the Raspberry Pi with features such as logging and serial control. Furthermore, the Raspberry Pi also needs to have networking support (something which has been eluding me as of late...).

At this moment, the seeds, which are of the lettuce variety, are germinating. In about a week or so, they should sprout and the real test of DotSlashGarden's growing abilities will commence.

Conditions for Germination

Before beginning a test of the current hydrogarden components, it is important to understand what a plant actually needs in order to grow. One area that I have not researched in this regard is germination.

There are many elements that a plant needs to begin germination. For this blog post, I will label them according to importance: required, preferable, and non-essential.

Required

• Water

Water is needed to soften the hard seed coat, which will allow a future sprout to grow. Water also allows the food reserve in the seed to be used. It should be noted that the seed only needs enough water to moisten it; it should not be submerged in water.

• Oxygen

As an aerobic organism, plants need oxygen to survive much like humans and various other organisms. Oxygen uptake may only occur after the seed coat has been softened, depending on the type of plant. Atmospheric oxygen should be sufficient, making aeration unnecessary.

• Heat

Most plants will germinate at temperatures in the range of 15 - 24°C.

Preferable

• Heat

For vegetables, the ideal temperature range is 24 - 32°C. As the first plant I will be growing is lettuce, this range is suitable.

Non-Essential

• Light

Most plants do not require a light source for germination to begin. The main types of plant that do are forest plants, which are not good candidates for hydroponics.

• Nutrients

Because a seed contains its own food supply, addition nutrients do not need to be added at this time.

Conclusion

When designing a testing procedure for the current hydrogarden, I will keep these elements in mind to ensure that the seeds will germinate. If the seeds do not germinate, I will look back at this list to check if the conditions are met.

The next blog post will outline the testing set-up, including the components and the implementation.