Introduction: (Initial Observation)
The first time that I heard about weed killer this question popped in my mind that How does a weed killer know which one is a good plant and which one is a weed? Actually what is the difference between weed and other plants? They are all plants (as far as I know).
So this project is a good opportunity for me to find out the difference between weeds and other plants. Also I will find out if weed killers can clearly distinguish between weeds and other plants, because if they don’t, other plants will also get hurt or killed by weed killers.
Information Gathering:
Find out about weed killers. Read books, magazines or ask professionals who might know in order to learn about the weed killers and how they work. Keep track of where you got your information from. Internet can be a good source of information about weed killers. Use a search engine such as yahoo for “Weed Keeler”. At this time you are only looking for general information about weed killers. You will find web sites of manufacturers such as Roundup and ORTHO and Finale that contains valuable information about how to protect trees, vegetables, lawn, walkway and flower beds from weeds. Among the search results I saw a page about The chemical, 2,4-dichlorophenoxyacetic acid or “2,4-D,” that is used as a weed killer and claims that this chemical may cause cancer in animals. This gave me the idea of searching for “Weed Killer Side effects”.
Also among the search results came the word “Herbicide”. What is that? So I quickly looked it up in dictionary.com and well! it is a scientific name for weed killer. It was defined as “A chemical substance used to destroy or inhibit the growth of plants, especially weeds”.
I searched for the meaning of weed in dictionary.com and these are the results:
Weed is a plant considered undesirable, unattractive, or troublesome, especially one growing where it is not wanted, as in a garden.
Other definition says weed is any plant that crowds out cultivated plants.
But these two does not tell me what is the difference between weeds and cultivated plants and more importantly how can weed killer differ between these two.
To find out, I searched for “weed killer side effects”.
Among the search results was many pages saying that “The weed killer will also kill your good plants.” and suggesting to ” Pull out weeds where you can”
Finally I searched for “difference between weed and plant”. Search result included a page from ASPS website with these information:
Plants which are intentionally grown in fields and gardens are called cultivated plants. All other plants which are not supposed to be there and grow unwanted, are called weeds. A weed is therefore a plant growing “in the wrong place”.
A plant which you might cultivate in your garden can become a weed if it escapes to a farmer’s field – don’t leave the flower-heads to set seed.
Some weeds cause harm:-
- Some are parasitic on crops.
- Some are poisonous to cattle and sheep.
- Some are unpalatable or even cause taints in milk or meat.
- Some can cause a problems to animals, e.g. by getting into sheep’s wool and be expensive to remove. Some thorns or spines can injure animals.
- Some interfere with farm machinery, getting tangled in the works.
- Some reduce the value of the crop (eg. deadly nightshade in peas, wild oats in cereals)
- Some are a host for pests and diseases.
- Some block drainage and irrigation channels.
- Some grow on non-agricultural land like roadsides and embankments and need cutting down.
I also found www.Gardenseeker.com with a very interesting article that I recommend you to read.
Before firing away with that ‘ready to kill’ weedkiller spray you have just bought, stop and think. For ‘weedkiller’ substitute the word ‘plant-killer’; for it can also kill, or seriously damage, many of your treasured garden plants that it comes into contact with. Now that’s o.k. with the larger plants (and weeds); you’re not an idiot; you can tell the difference: You only aim at the weeds – problem solved. But can you tell the difference between a weed and a garden plant when it is no larger than a half inch across?
By now I know what is weed and I know that weed killer can damage other plants too. So lets continue with the rest of project.
Question/ Purpose:
What do you want to find out? Write a statement that describes what you want to do. Use your observations and questions to write the statement.
The purpose of this project is to determine how does the strength of weed killer affect the plant growth. From the “Strength of weed killer” we mean the concentration of active chemicals in weed killer.
Identify Variables:
When you think you know what variables may be involved, think about ways to change one at a time. If you change more than one at a time, you will not know what variable is causing your observation. Sometimes variables are linked and work together to cause something. At first, try to choose variables that you think act independently of each other.
We change the Concentration of weed killer to see how does this affect the plant growth. So:
The independent variable (also known as manipulated variable) is the concentration of weed killer.
The dependent variable (also known as responding variable) is the plant growth.
Controlled variables are light and temperature. (Perform your plant experiments at the same time so all plants will be under the same light and temperature conditions)
Constants are the type, age and growth media of the plants.
Hypothesis:
My hypothesis is that as concentration increases, the plant growth rate will decrease. Each plant has a tolerance to weed killer that depends on the size of plant and type of plant. As a result small amount of weed killers with small concentration (strength) can not harm large trees.
Experiment Design:
In order to test the effect of weed killer strength on plant growth, we perform two different experiments. In one experiment we plant some seeds and test the strength of weed killer on seedlings or young plants.
In the other experiment we use larger plants such as inexpensive houseplants to test with weed killer.
Experiment 1:
You will need:
1. Five Styrofoam cups or small clay pots
2. dirt, potting soil etc.
3. 20 Bean seeds (4 for each cup or pot)
4. water
5. Journal
Directions:
- Fill the cups/pots with soil about half way. Plant the seeds. Cover with soil until the pots are about three-quarters full.
- Water and place all plant next to a window, where they can get enough light.
- Seeds will germinate in about 5 days.
- Prepare about 100 ml of a solution of a liquid weed killer with the concentration double the amount recommended by manufacturer. Label this with “Double Strength”.
- Get 20 ml of double strength solution and add 20 ml water to that. That gives you 40 ml of standard weed killer with the concentration recommended by manufacturer. Label this “Standard”
- Get 20 ml of double strength solution and add 40 ml water to that. That gives you 60 ml of 50% weed killer. Label it “50% weed killer” because it’ concentration is 50% of recommended concentration.
- Get 20 ml of double strength solution and add 80 ml water to that. That gives you 100 ml of 25% weed killer. Label it “25% weed killer” because it’ concentration is 25% of recommended concentration.
- When you young plant is ready (this takes about 2 to 4 weeks depending on weather, light and water) then you can start your final stage of your experiment as follows.
- Label your plants with “Control”, “Double”, “Standard”, “50%” and “%25”. These labels represent the concentration of weed killer that you are going to use for that plant. You will use water instead of weed killer for control.
- Give one spoon of each weed killer to the plant reserved for it. Give one spoon water to the control plant.
- Observe the changes on plants every few hours and record the results.
- Repeat this if needed for up to 5 days or until your plants are all dead.
- Record the results in a table showing after how many hours each plant started to show the signs of weakness. After how many hours plant completely died.
- Continue watering the dead plants, but stop weed killer to see if any of dead plants will recover.
Enter your results in a table like this:
| Weed Killer Concentration | Experiment start date | Plant died on this date |
| Control (none) | ||
| Double | ||
| Standard | ||
| 50% | ||
| 25% |
Note: If the weed killer label is suggesting to spray the weed killer, then instead of using spoon as a measuring tool you must use spray bottles and pump twice on each plant. Twice or 3 times pumping with spray bottle will almost be equal to one spoon. Make sure to test and prepare the spray bottle away from the plants before each spray.
Control plant will be sprayed with water.
Experiment 2:
In this experiment we use well grown plants to test the effect of weed killer concentration.
Procedure:
- Find or purchase five same size green plants of any kind.
- Label your plants with “Control”, “Double”, “Standard”, “50%” and “%25”. These labels represent the concentration of weed killer that you are going to use for that plant. You will use water instead of weed killer for control.
- Give one spoon of each weed killer to the plant reserved for it. Give one spoon water to the control plant. (If your plants are not very small, use two spoon weed killer or more)
- Observe the changes on plants every few hours and record the results.
- Repeat this if needed for up to 5 days or until your plants are all dead.
- Record the results in a table showing after how many hours each plant started to show the signs of weakness. After how many hours plant completely died.
- Continue watering the dead plants, but stop weed killer to see if any of dead plants will recover.
In both experiments you stop daily watering of plant while you use weed killer.
Materials and Equipment:
List of materials extracted from the experiment 1:
- Five Styrofoam cups or small clay pots
- dirt, potting soil etc.
- 20 Bean seeds (4 for each cup or pot)
- water
- Journal
Results of Experiment (Observation):
Record the results of your experiment 1 in tables like this:
This table shows after how many hours did the plant show symptoms of weed killer effect and after how many hours did the plant die.
| HOURS | control | Double | Standard | 50% | 25% |
| Plant showed symptoms after | |||||
| Plant died after |
Questions :
1) Why did you need 5 plants to test 4 different concentration of weed killer? What conclusion could you draw if you had performed the experiment with only 4 cups?
2) What effect did the strength of weed killer have on the plant growth?
If you are performing experiment 2, make a similar table for the results of experiment 2.
| HOURS | control | Double | Standard | 50% | 25% |
| Plant showed symptoms after | |||||
| Plant died after |
Calculations:
You may need to do some calculation in order to make the recommended concentrations.
Summary of Results:
Summarize what happened. This can be in the form of a table of processed numerical data, or graphs. It could also be a written statement of what occurred during experiments.
It is from calculations using recorded data that tables and graphs are made. Studying tables and graphs, we can see trends that tell us how different variables cause our observations. Based on these trends, we can draw conclusions about the system under study. These conclusions help us confirm or deny our original hypothesis. Often, mathematical equations can be made from graphs. These equations allow us to predict how a change will affect the system without the need to do additional experiments. Advanced levels of experimental science rely heavily on graphical and mathematical analysis of data. At this level, science becomes even more interesting and powerful.
Conclusion:
Using the trends in your experimental data and your experimental observations, try to answer your original questions. Is your hypothesis correct? Now is the time to pull together what happened, and assess the experiments you did.
Related Questions & Answers:
What you have learned may allow you to answer other questions. Many questions are related. Several new questions may have occurred to you while doing experiments. You may now be able to understand or verify things that you discovered when gathering information for the project. Questions lead to more questions, which lead to additional hypothesis that need to be tested.
Possible Errors:
If you did not observe anything different than what happened with your control, the variable you changed may not affect the system you are investigating. If you did not observe a consistent, reproducible trend in your series of experimental runs there may be experimental errors affecting your results. The first thing to check is how you are making your measurements. Is the measurement method questionable or unreliable? Maybe you are reading a scale incorrectly, or maybe the measuring instrument is working erratically.
If you determine that experimental errors are influencing your results, carefully rethink the design of your experiments. Review each step of the procedure to find sources of potential errors. If possible, have a scientist review the procedure with you. Sometimes the designer of an experiment can miss the obvious.
References:
Find and review some books about plants, nutrients and fertilizers.
