Abstract

Objective

Introduction

You probably know that just as we get our nutrients from food, plants get their nutrients from the soil. To thrive, plants need both macronutrients (like carbon, nitrogen, and phosphorus) and micronutrients (like iron, sodium, and zinc). Soil can contain all of these.

Plants also need water and use it in many ways. First, water acts as a solvent and helps to transport nutrients from the soil throughout the plant. Second, water-filled cells help support various biochemical reactions in the plant. A biochemical reaction is a reaction that occurs between chemicals inside the plants' cells to keep it alive. A plant biochemical reaction that you may have heard of is photosynthesis. Photosynthesis, a reaction involving sunlight, the chlorophyll in plant cells, water, and carbon dioxide, produces sugar for the plant to use as food. When a plant doesn't receive water, photosynthesis and other biochemical reactions stop, the plant begins to turn yellow, dries up, and then dies.

So is soil really necessary for a plant to survive, or can plants survive in just water? What if the water had all of the nutrients in it that soil does? The answer to this question is yes. Plants can survive without being planted in soil. The science of growing plants in nutrient-rich water is hydroponics. The word hydroponics means "working water" and comes from the Latin words hydro, meaning "water," and ponos, meaning "work." In hydroponics, the nutrients are available at the plant's roots. So, without any work, the plant gets its food and nutrition. A plant with roots in soil has to work hard to extract its nutrition from the soil, and it can waste a lot of energy doing that. But a plant in nutrient-rich water can spend its energy growing bigger leaves, fruits, and flowers in a shorter amount of time. One benefit of growing plants hydroponically is that the nutrients in the water can be completely controlled, and the plant can receive exactly the right amount of nutrients at exactly the right time. Another benefit of hydroponics is that it works in areas where the soils are not arable (not suitable for farming) and in areas where there is no soil. Figure 1 shows a NASA scientist examining hydroponically-grown plants.

Figure 1. A NASA plant physiologist at Kennedy Space Center examining his hydroponically-grown plants. (NASA, 2004.)

There are six basic types of hydroponic systems: wick system, water culture system, ebb-and-flow system, drip system, nutrient-film technique, and the aeroponics system. Each system has its advantages and disadvantages. In this plant biology science project, you will experiment with the water culture system and perform your own hydroponics experiment. You will compare the growth rate of lettuce seeds grown in potting soil with those grown hydroponically. Which method will produce seedlings the fastest? Will there be a difference in root growth between the two methods? At the end of this science project, instead of having a "green thumb," you might have a "blue thumb"!

Terms, Concepts, and Questions to Start Background Research

• Macronutrient
• Micronutrient
• Solvent
• Cell
• Biochemical reaction
• Photosynthesis
• Chlorophyll
• Hydroponics
• Arable
• Physiologist
• Water culture system
• Aerate
• Area
• Ellipse

Questions

• What are the differences between a macronutrient and a micronutrient?
• You might think that hydroponics is a new way of growing plants, but it isn't. What ancient cultures reportedly used or mentioned hydroponics? How old is the science of hydroponics?
• Why is NASA interested in hydroponics? What kinds of hydroponics experiments do NASA scientists perform?
• What are the differences between the six basic types of hydroponic systems? What are the advantages and disadvantages of each?

Bibliography

• Helney, A. (2007, November 27). Farming for the Future. Retrieved June 15, 2010, from www.nasa.gov/missions/science/biofarming.html
• Information. Green Coast Hydroponics. (2006). Retrieved June 15, 2010, from www.gchydro.com/information_introhydro.asp#History
• Simply Hydro. (2008). Simply Hydroponics and Organics. Retrieved June 10, 2010, from www.simplyhydro.com/whatis.htm

The following website shows how to calculate the area of common shapes. You can learn some interesting information about the shapes by clicking on the name.

• MathIsFun.com. (2010). Area Calculation Tool. Retrieved March 15, 2011, from www.mathsisfun.com/area-calculation-tool.html

For help creating graphs, try this website:

• National Center for Education Statistics. (n.d.). Create a Graph. Retrieved June 2, 2009, from http://nces.ed.gov/nceskids/CreateAGraph/default.aspx

Materials and Equipment

• Hydroponics experiment kit (1); available from Edmund Scientific, www.scientificsonline.com, SKU 3152199. This kit comes with a dome terrarium, rack, manual hydro-pump, net pots, rock-wool cubes, scoop, instruction booklet, two packets of nutrients, and a packet of lettuce seeds.
  1. Check to see if there is a packet of lettuce seeds that came with the kit. If you didn't receive lettuce seeds, then go to your local gardening store or plant nursery and purchase a packet of lettuce seeds.
• Filtered water. You can use a water filter pitcher to make filtered water, or you can purchase bottled filtered water.
• Measuring cup, 2-cup
• Microwave or stove top with pot
• Disposable gloves; available at your local drug store or pharmacy
• Small table
• Grow lamp (optional)
• Seedling mix; special kind of soil potting mix available at gardening stores and plant nurseries
• Terra cotta pots, 3-inch (4)
• Hand trowel
• Watering can
• Lab notebook
• Ruler with millimeter markings
• Digital scale, such as the Fast Weigh MS-500-BLK Digital Pocket Scale, 500 by 0.1 G, available from Amazon.com
• Paper towels (1 roll)

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Experimental Procedure

Setting Up the Hydroponic Experiment

1. Read the entire instruction booklet that comes with the hydroponics kit.
2. Break the rock wool carefully into four equal pieces (cubes). Notice that each cube has an indent in it.
3. Soak all four rock wool cubes in filtered water in the bottom of the terrarium for 24-36 hours.
4. After the time has elapsed, place each rock wool cube into a net pot. Don't wring the rock wool dry. Make sure that the indent in each rock wool cube is facing up.
5. Place three lettuce seeds in the indent in each of the rock wool cubes.
6. Snap the rack into the bottom part of the terrarium. Then, place a net pot into each of the openings in the rack. Shut the terrarium with the clear dome so that the tabs on the dome and the bottom are side by side.
7. Put the terrarium on the table in a south-facing or west-facing window that gets plenty of light. If direct sunlight is unavailable, use a grow lamp to provide light for the seeds. Figure 2 shows the completed hydroponic terrarium.

Figure 2. The completed hydroponic terrarium.

8. Record the date that you set up the hydroponic terrarium in your lab notebook.

Setting Up the Soil Experiment

1. Now plant the lettuce seeds in the four pots. Using the hand trowel, place some seedling mix into each of the pots. Place three lettuce seeds into each of the pots, and lightly cover them with a thin layer of soil.
2. Over a sink, water each pot carefully so that a little bit of water comes through the hole at the bottom of the pot. Do not over water the seeds.
3. Place the four pots at the same location as the hydroponic terrarium. Numerically label each pot and note the labels in your lab notebook.
4. In your lab notebook, record when you started growing the lettuce seeds in the pot, the depth at which the seeds were planted, and the brand of seedling mix that you used.

Growing and Feeding Instructions

1. Monitor the hydroponics terrarium to see when the seeds start to sprout. Once they do, wait one more day to make sure that as many seeds sprout as possible.
2. Once all of the seeds have sprouted, remove the rack of net pots, follow the instructions, and mix the nutrient solution in the bottom of the hydroponics terrarium. You will need to warm four to five cups of water to make the nutrient solution. You can warm the water in the microwave or on a cooktop in a pot. The water should be lukewarm, or cool enough for you to put your hand in comfortably.
3. Place the rack of net pots back into the terrarium, and re-cover it with the clear dome. Put it back in the window.
4. Check the soil of the lettuce seeds in the pots every day. Do not let it get dry, but it should not be too wet either. If the soil is dry, use the watering can and water the pot(s). Water each pot until a few drops of water come out from the bottom.
5. Check both the sprouts in the hydroponics terrarium and the pots every day at about the same time. Check to see how the sprouts look in the hydroponics terrarium. Note the date each seed in the terrarium and the pots sprouted. Every seventh day after each individual seed in the terrarium and the pots sprouts, count how many leaves it has. Use the ruler to measure the length and width, in millimeters (mm), of the largest leaf on each sprout.

6. At the same time that you check the sprouts in the hydroponics dome and pots, make sure to aerate the nutrient solution in the terrarium. A plant's roots need oxygen in order to grow. Follow the instructions to learn how to use the manual hydro-pump to do this. You should aerate the solution twice a day.
7. Replace the nutrient solution in the hydroponics terrarium every week. Once you can see the roots stick out from the rock wool, strengthen the nutrient solution as directed in the instructions.
8. Keep monitoring, measuring, feeding, and watering your plants for a month.

Analyzing Your Data

1. After six weeks, gently uproot the plants from each group and carefully remove and wash the soil from the roots. Carefully dry the plants with paper towels. Keep the hydroponically-grown plants separate from the soil-grown plants.
2. Using the digital scale, weigh the uprooted plants, and record the data in your lab notebook.
   1. Observe the color of the roots for the plants in each group. Are they white, yellow, or brown?
   2. Record the number of hairs that you see on the roots for each plant. Root hairs enable a plant to take in nutrients.
3. Compare the growth of the hydroponically-grown plants and the plants grown in soil. Review the data that you collected. Calculate the area of the largest leaf for each plant in both groups on each day that you made measurements. You may have to make an estimation about the shape of the leaf. Separate the shape of the leaf into two shapes, like an ellipse, or oval, and a triangle, as shown in Figure 3. You can estimate the area of the leaf by calculating the area of the oval and adding the value to the area of the triangle. If you would like some additional information on calculating the area of common shapes, refer to the Bibliography. Record your data in a table (like Table 3 and Table 4) in your lab notebook.

Figure 3. This image gives an idea of how to estimate the area of a leaf using an ellipse (oval) and a triangle.

4. Average the area data by group and day. First, separate all the hydroponic plant data from the soil-grown plant data. Then, for each group, average the data for each day (day 7, day 14, day 21, etc.). Record the data in a table (like Table 5) in your lab notebook. Average the number of leaves on the plants by group and by day.

5. Average the number of root hairs for each group of plants. Record the data in a table (Table 6) in your lab notebook.

6. Plot the average area data. Label the x-axis Day and the y-axis Average Area. Use different colors for hydroponic data and soil-grown data in order to show the difference between them. Make your plots by hand or online. For help creating plots online, try the CreateAGraph website.
7. Plot the leaf area data points for both groups by day. Again, use one color for all of the hydroponically-grown plants and another color for all of the soil-grown plants. This graph will show you the range of the data.
8. Plot the average number of leaves for both groups by day. Label the x-axis Day and the y-axis Average Number of Leaves. Use different colors on the plot for hydroponically-grown plants and soil-grown plants.
9. Is there a difference in the average growth between the plants grown hydroponically and the plants grown in soil? Is there a difference in the weight and in the number of root hairs between the two groups? Does the range of the data between the two groups vary? Does the average number of leaves by group vary? Do you think that growing plants hydroponically is a good choice? Is it better than using soil?

Variations

• Grow different varieties of lettuce hydroponically. Do all varieties grow better hydroponically, or does growth depend on the variety?
• Instead of growing lettuce, try growing different seeds hydroponically. Grow tomatoes, both hydroponically and in soil. Is there a difference between the hydroponically-grown tomatoes and soil-grown tomatoes? Do all plants grow equally well using both methods, or do some seeds grow better in either soil or a hydroponic system?
• What happens if you don't have a balanced nutrient-water solution to grow plants hydroponically? Follow the directions given in the instruction booklet, and vary the amounts of nutrients in the nutrient solution to see how it affects the growth of the plants.

• For more science project ideas in this area of science, see Plant Biology Project Ideas.

Credits

Michelle Maranowski, PhD, Science Buddies