A Little Bit More
How often have you heard people refer to fertilizer as plant food? While fertilizer can add valuable nutrients to the soil, it makes more sense to think of fertilizer as a vitamin pill. All of a plant’s food comes from a chemical reaction involving sunlight. In fact, almost all of our world’s energy can be traced to the sun (all except radioactive materials). In a process we call photosynthesis, green plants trap this fleeting energy source and transform it into potential chemical energy in carbohydrate molecules (sugars and starches) that can be stored indefinitely. Once stored, the food is available for both plant and animal needs, making life as we know it, possible on our planet.
Photosynthesis is literally, light putting-together. In the presence of light, carbon dioxide, water, and chlorophyll, most plants produce carbohydrates and oxygen. These plants include the unicellular and multicellular algae, blue-green algae, and our familiar green land and water plants. Photosynthesis that took place in prehistoric times provide us with the oil and coal we use today. The gas in our car and the coal that powers our lights had its origin in sunlight that fell on the earth millions of years before humans even existed.
Activities
Science – Feed It, whoops, Fertilize It!
Objectives: See effects of fertilizer on plants
Materials: Minimum of 2 similar potted plants, small amount of a houseplant fertilizer, (optional – digital camera)
It’s interesting to note that although all of the companies that make fertilizers for home and garden use, know that their product is NOT plant “food”, their labels often include this misnomer anyway: I guess it’s called marketing. It’s no wonder the public isn’t entirely clear on this subject.
This is not an immediate-results project but one that will take at least 4-6 weeks to complete, but it’s well worth doing.
Almost every school, if not classroom, has an assortment of house plants that are cared for within the building so I trust you’ll have material to work with. If not, a local nursery, once they know you’re doing an experiment with students, will be happy to provide a few plants for your activity. You can also start this project from seed, if you wish. (If you can’t do this inside, maybe you can work with two plots of ground outside)
1. Obtain a minimum of two plants that are as similar as you can find and bring them into your area (species, size, pot size, soil, etc). Your plant selection will work best if you have faster-growing plants, ie. don’t use slow-growing cacti for this exercise..
2. Place the plants next to each other and label half of the Plants “A” and the other half of the Plants “B”
3. Decide where your two (or more) plants will be located, keeping in mind their need for adequate sunlight. Some plants will require full sun while others may do just fine with less light.
4. Establish a watering procedure that you or your students can use over the next 4 to 6 weeks. This watering will be exactly the same for ALL of the plants. Your plants should not be soaking wet all the time but will do best if watered and then allowed to dry out a bit (not bone dry, but moist).
5. Although the watering procedure will be identical for all plants, there will be one difference in the procedure – this is what our experiment is testing for. One group of your plants (note which group this will be) will receive water alone while the other group of plants will receive the same water but water that contains the recommended amount of fertilizer (see package for instructions). Once a week or once every other week is probably going to be about right for fertilizer if it isn’t too concentrated.
6. It will be interesting for the students if they do NOT know which group of plants is receiving the fertilizer! You can tell them that they’re taking part in a “blind study” in which those analyzing the results do not know which is the experimental group of plants. This should also add to their intrigue.
7. If you have access to a digital camera, take pictures of the plants BEFORE the experiment begins. You can then take a weekly photo making sure it’s obvious which plants are the “A” plants and which are the “B” plants.
8. Each week students should examine Group A and Group B plants to see if there are any obvious differences/changes. Students can look for new growth, greener color, more “sturdy” looking leaves, flowers, etc and write this down in a notebook for later reference.
9. By the end of 6 weeks, it should be obvious that one group is “different” from the other. Their final observations can be documented in their notebook. Up until this point they shouldn’t know which are the fertilized and non-fertilized plants. Once all have written in their notebooks what they feel are the differences, if any, the students can be informed which group was the fertilized group.
10. Once the students know which is which, it will be interesting to know whether their notebook observations concur. This should spark some discussion about fertilizers, observation techniques, and the value of taking notes.
Be sure to emphasize to the students that in our mini-experiment, the fertilized group of plants was our experimental group (group to which we’re making a change) while the non-fertilized group (group to which no changes are made) of plants was our control group. To make our experiment meaningful, every effort was made to keep everything as uniform as possible with only one exception – use of fertilizer. Thus, we can look at the results we obtained and infer that the use of fertilizer did or did not make a difference to the plants in our study.
Once the results are in, you may want to ask your students why we only changed one variable (fertilizer or no fertilizer) in our experiment? By keeping everything as much the same as possible between the plants used, by changing only one variable we were able to determine that the one difference did or did not make a difference. If we had many different variables, we wouldn’t know for sure which one(s) made the difference. This approach to experimental setups is always crucial if one is to make any sense out of the outcome and is important for students to understand.
Key Concepts
Scientific Method/Approach, Growth and Development
Questions
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