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Science Fair experiment

 
Eli Jenkinson
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Hi, I am Eli

For my 6th grade science fair project I am grew 3 pea plants with 3 different colors of light, one red, one blue, and one green. Based on my research I thought the red light would make the plant grow fastest because it is the almost the opposite of the color of the plant. Because plants reflect green light I expected green to be slowest and red to be fastest. Somehow the green light made the plant grow fastest.

I tried the experiment again and this time I used I used a magenta light because Magenta is the opposite of green and plant growing light bulbs that are sold in stores are magenta, but Green still grew fastest. I am wondering if you can help explain why this happened.

The plants were in a black tent, the seeds were all planted and watered at the same time

I made a time lapse video. If you want to see the plants growing go to https://vimeo.com/65097813

Can anyone help to explain this?
 
John Polk
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I read an article about a year ago that might help explain why the 'green' plants won the race.

The study was using corn as the test plants.
As the seedling emerges, if it can sense green (growth) under it, it assumes that there will be competition for the sunlight.
It begins producing more growth hormones, as it needs that sunlight, and doesn't want to be shadowed out.

The conclusion was that the plants with green under them outgrew the others in height, but had smaller ears of corn.
The plants had used up so much of their energy getting 'tall', that they had little left for reproduction.

I doubt if I can find that article now, but if I do, I will post a link for you.

Another factor could have been the color temperature (in degrees Kelvin) of the various bulbs.
The closer you can get to the sun's color temperature, the better the seedlings should develop.



 
John Polk
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OK, this isn't the same article, but I believe it is based on the same study.

Ontario researcher says that corn’s negative reaction to weeds may have more to do with 'seeing' them than competition for nutrients, moisture and sunlight.


http://www.no-tillfarmer.com/pages/Feature-Articles---Corn-Doesnt-Like-The-Sight-Of-Weeds.php

Hope that this helps you in your quest for answers.

 
Eli Jenkinson
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Thank you Mr. Polk That is really interesting. MY dad is a photographer and helped me with setting up the experiment. He has special light meters to measure color temperature and we did find that the blue light was very close to natural daylight, and in the first expreiment blue was almost as fast as green. but we were still confused by the green being soooo fast. And in the second experinet blue was really slow. I'll look at the article you mentioned
 
Eli Jenkinson
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That article was interesting. I think it says that the color of light also cjhanges the root system of the plant, and when we looked carefully at the video it does appear like the while the red plant grows slower (up) it seems to grow roots faster and more comeplcated. Sorry the video got out of focus, but when we look at still picthers the red plant has thicker roots that go deeper than the green or blue
 
John Polk
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It stands to reason that if a plant is spending extra energy to get 'tall', it would have less energy to spend developing a strong root system. That would certainly effect the yield.

Will your experiment continue long enough to see how the different plants yield?

I do know a commercial grower who uses several blue panes in his greenhouse. (About 20%)
He says it gives better growth.

EDITed to add: A good experiment raises more questions than answers.


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