Science Buddies: "Ask an Expert"

My 6th grade son has decided to experiment with the dosage of glysophate that affects plants. He chose this topic because we farm so he is familiar with Round Up and how we use it on our crops. My question is: What type of plant, that may be available in West Texas nurseries at this time, would you suggest he use for this experiment?
His project is due Dec. 5th.

Hi! This is a great idea for a project, especially since it's so applicable to your son's daily life. I'd say the best advice I could give is to visit local nurseries and find out which plants are available right now and grow best in winter. After that, you could note the plants' species and research on their characteristics and how glysophate might affect them. Please post back if you have any questions!

In addition to the feedback scibuddyAK gave you, I wanted to point out this Science Buddies project:

Weeds Be Gone! Experiment with Factors that Affect Roundup® Weed Killer
https://www.sciencebuddies.org/science- ... ml#summary

Maybe you are already using this. But just in case, I wanted to mention it since it has a procedure that might be helpful for your son to see.

The materials list for the project doesn't specify what kind of plant, but it does offer some notes about choosing plants with well-defined leaves since in that procedure, part of the test will involve testing per leaf.

Amy
Science Buddies

Hi,
Almost every plant can be killed by glyphosate [tech note: the correct spelling is glyPHOsate, not glySOphate], that's why Monsanto had to genetically modify crops plants to be resistant to the herbicide.

In order to measure the effect of various doses of RoundUp, you will need to have some endpoint that you can use consistently and scientifically. Since the chemical is absorbed through the leaves, selecting a broad-leaved plant would be a good idea and you would want them all about the same age and size with no flowers or fruit.

Vegetables like cabbage, broccoli or kale don't mind a little cold weather and you can buy a flat of those all about the same size. You need to get enough to be able to use 3 or 4 plants for each dose in order to get a statistical average. Use the same soil, the same pot size and the same amount of soil per pot to be consistent. They should all have the same amount of sun and water also. And be sure to label the pots carefully and put them some place where critters [squirrels, cats, birds, etc] can't bother them.

I don't know how you plan to apply the RoundUp dose, but you need to be as careful as possible to get the same amount on each plant. That's why you need to treat at least three separate plants with each dose, to get an average.

Now what exactly are you going to measure as the 'effect' of the herbicide? How long does it take for the effects of RoundUp to be seen on, for example, a young cabbage plant? Let me also remind you at this point to take sequential pictures of your plants to document the changes.

As i understand the way glyphosate works, it inhibits an enzyme that is essential for plant growth so I would expect the plants to stop growing and then eventually die. If you read the scibuddies project procedure in Amy's post it says to rate the health of the plants on a scale of 1 to 5, take pictures of them every day or so and record the time it takes for them to die. While i agree with this mostly, I think 'time to die' might be a bit hard to decide. I like to have a good weight measurement in an experiment, so what i would suggest is to spray the plants, record the changes on the health scale with photos to show the differences, then at some point before the plants treated with the highest dose of RoundUp turn completely brown, take one last photo, pull up all the plants, shake off the soil and weigh them using an accurate digital scale.

The plants you sprayed with only water will have grown into nice healthy cabbages and will weigh a lot more than those sprayed with RoundUp. You will be able to graph the weight on the y-axis against the dose of RoundUp on the x-axis and show a nice decrease in weight because of the herbicide. You could also do some treatments where you measure the time to die, but you will have to define it some way--after the plant stops growing? After the leaves start to shrivel? After they turn brown? See what I mean. You can tell when a plant is dying, but how do you say when it is totally dead?

Good luck with your project, and keep us posted on your progress, and if you have more questions.

Regards,

Sybee

Thank you for all your replies and the great advice!