Introduction: (Initial Observation)
Fertile land is limited and the demand for agricultural products is high. Farmers attempt to get the most from their land or in other words optimize their productivity.
Depending on the type of the plant, farmers follow certain rules for plant depth and spacing. For example tomato plants are often spaced about 12″ to 16″ from each other in a row and there is about 3 to 5 feet between rows. Farmers know that not enough space between seeds or transplants is known as crowding and has negative effects on plants.
Crowding is the condition that a large number of people, animals, or plants live together in a restricted area. Crowding is a cause of some environmental stress in many species and can affect their health.
Learning how crowding affect animals and plants can help us to distribute the population or resources more efficiently and reduce the harmful effects of crowding.
In this project I will study the effects of crowding on tomato plants. (Replace tomato with any other plant of your choice. If you don’t have enough time, select a fast growing plant such as radish or lima bean. See the germination table and Harvest table for estimated germination and harvest time of your subject plant.)
Information Gathering:
Choose one plant to be the subject of your research. Find the best conditions for the growth of the plant that you decide on. Read books, magazines, or ask professionals who might know in order to learn about the effects of crowding on your subject plant. Keep track of where you got your information from. The following are samples of information that you may find.
How to grow tomatoes.
1. Seeds can be started indoors 6-8 weeks before the last anticipated frost date in your growing area. Starting seeds directly outdoors will produce plants but your yield will be limited.
2. Obtain some seed starting mix at the local garden store. Kmart and WALMART have this available at reasonable prices. The mix should contain peat moss to help retain water during seed germination as the seeds should be kept moist for proper germination.
3. For seed growing trays, use 1/2 gallon cardboard milk/orange juice containers that are cut down their length with the ends stapled to hold them together.
4. In a old bowl, bucket, or other container, place some of starting mix and add water while mixing to moisten the mix.
5. Fill the trays with 1-1 1/2″ of the moistened seed starting mix and distribute seeds over surface. Cover seeds with 1/4″ of starting mix and gently firm the surface.
6. Check seed trays every 2-3 days to make sure they stay moist. Cover the trays with a loose fitting piece of plastic wrap to help retain water. Seeds will usually take 10-14 days to germinate (depending upon variety). Once the seeds have sprouted, they will need a light source. If you start your seedlings in a dark room or basement, you may use fluorescent grow lights which work very well. If you start the seeds on a window sill make sure you turn the seeds daily to keep them from bending toward the light. If started under a grow light, make sure the grow light is within 6″ of the seedlings or they will become tall and leggy. Seedlings need 12-16 hours of light a day. An inexpensive timer works well to control grow light time.
7. Once the seedlings begin showing a second set of leaves, it is time to transplant them from the starting tray to individual pots. We have found that the best pots are plastic as they retain more water. The peat pots work well if you make sure to keep them moist…they work great for transplanting as you do not disturb the root structure of the seedlings. Gently loosen the soil in the starting tray and separate individual plants. Fill the transplant pot loosely with moistened starter mix and use a pencil to make a hole in the starting mix. Insert the seedling into the hole up to the second set of leaves…this may require the slight twisting or bunching up of the plant’s root as they can get pretty long. Gently firm the soil around the seedling and moisten once you have finished transplanting.
8. If you start your seeds very early, you may need to transplant some of your biggest plants again as they will outgrow their pots. For our healthiest plants, we transplant them into 1/2 gallon milk containers that have been cut off about 6″ from the bottom…these work Great!!!
9. When it looks like it is time to plant your seedlings outside, you will need to harden off the plants. This is simply getting them adjusted to the changing conditions outdoors. When you begin this, make sure the plants are kept in the shade for the first few days of hardening so they don’t get sun-burned. Plants should be returned inside at night…this seems like a lot of work but it will yield stronger, healthier plants. Hardening off usually takes 7-10 days.
10. When planting your seedlings in the garden, make a shallow trench and lay the seedling in on its side. Bury the entire plant up to the first set of leaves, all of the stem up to these leaves is capable of producing roots. This will greatly improve your plants ability to obtain water and nutrients resulting in greater yields!!
11. Once the tomato plants are in your garden they should be watered daily for the first week. They should be supported as they grow with wooden stakes or metal cages.
12. Tomatoes vary in how long they take to bear ripe fruit from the time they are transplanted into the garden. In general, most tomato varieties take 50 to 90 days to harvest.
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.
What happens when the plant population is too dense?
The purpose of this project is to see how crowding affects the growth and fruit production of a certain type of tomato plant. (Or any other plant that you choose)
Just remember there are many varieties or species of each plant, so we can not extend the results to all different varieties of our subject plant.
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.
Independent variable also known as manipulated variable is the plant spacing.
Dependent variables also known as responding variables are plant height, general health, leaves size, fruit size, fruit production.
Controlled variables are temperature, light, water, and nutrients.
Hypothesis:
Based on your gathered information, make an educated guess about what types of things affect the system you are working with. Identifying variables is necessary before you can make a hypothesis.
As plants get closer to each other (smaller plant spacing), the amount of nutrients and light available to each plant reduces and plants will not have their optimum growth and production.
Experiment Design:
Design an experiment to test each hypothesis. Make a step-by-step list of what you will do to answer each question. This list is called an experimental procedure. For an experiment to give answers you can trust, it must have a “control.” A control is an additional experimental trial or run. It is a separate experiment, done exactly like the others. The only difference is that no experimental variables are changed. A control is a neutral “reference point” for comparison that allows you to see what changing a variable does by comparing it to not changing anything. Dependable controls are sometimes very hard to develop. They can be the hardest part of a project. Without a control you cannot be sure that changing the variable causes your observations. A series of experiments that includes a control is called a “controlled experiment.”
Experiment 1:
Introduction:
Growing tomatos usually starts from planting seeds in wooden or plastic trays. Young plants will then be transplanted to the farm or individual pots.
Procedure:
1. Gather some plastic containers to be used as seed growing trays. You may use 1/2 gallon cardboard milk/orange juice containers that are cut down their length for growing seeds (staple the ends to hold them together).
2. Obtain some seed starting mix at the local garden store. Kmart and WALMART have this available at reasonable prices. The mix should contain peat moss to help retain water during seed germination as the seeds should be kept moist for proper germination.
3. In a old bowl, bucket, or other container, place some of starting mix and add water while mixing to moisten the mix.
4. Fill the trays with 1″ of the moistened seed starting mix and distribute seeds over surface. Cover seeds with 1/4″ of starting mix and gently firm the surface.
5. Check seed trays every 2-3 days to make sure they stay moist. Cover the trays with a loose fitting piece of plastic wrap to help retain water. Seeds will usually take 7-14 days to germinate (depending upon variety). Once the seeds have sprouted, they will need a light source. If you start your seedlings in a dark room or basement, you may use fluorescent grow lights as your light source. If you start the seeds on a window sill, make sure you turn the seeds daily to keep them from bending toward the light. If starting under a grow light, make sure the grow light is within 6″ of the seedlings or they will become tall and leggy. Seedlings need 12-16 hours of light a day. An inexpensive timer works well to control grow light time.
7. Once the seedlings are showing a second set of leaves (6 to 8 weeks), it is time to transplant them from the starting tray to the ground or individual pots.
Note that all pots have a hole at the bottom to discharge excess water. Plant roots need to access nitrogen from air and excess water can prevent accessing air by plant roots.
If you are transplanting into the ground, use cotton treads, wire or wooden sticks to divide the ground into 12 small 1′ x 1′ squares. If you are transplanting in to the pots, get 12 identical pots and measure the surface area of the exposed soil in each pot. You will later use this to determine the distribution rate or crowding rate.
Number the pots or squares from 1 to 12. These numbers also represent the number of plants in each pot or each square.
Fill up all the pots with potting soil. Transplant one plant in pot number 1, two plants in pot number 2, three plants in pot number 3 and continue with the same order until you transplant 12 plants in pot number 12. (The following diagram shows how you may divide the soil into 1′ x 1′ squares. Optionally you may leave some extra space between squares to ensure your test groups will not affect each other. You may also keep all 12 squares in one row.)
For each transplant gently loosen the soil in the starting tray and separate individual plants. Fill the transplant pot loosely with moistened starter mix and use a pencil to make a hole in the starting mix. Insert the seedling into the hole up to the second set of leaves…this may require the slight twisting or bunching up of the plant’s root as they can get pretty long. Gently firm the soil around the seedling and moisten once you have finished transplanting.
8. Make daily observation and water the plants if needed. Only water the soil and make sure that the soil remains moist. Also make sure that all plants get the same amount of light. Record your daily observation in a journal. After about 6 weeks your plants must have fruit. At this time make your final observation and record your observations in a data table like this:
Growth and production of tomato plant at different crowding rates
Values are averages for each group, sqf= Square foot, Lbs= pounds
| Crowding | Plant height | Number of leaves | Size of leaves | Total fruit Lbs/sqf |
Fruit size |
| 1 plant/ sqf | |||||
| 2 plant/ sqf | |||||
| 3 plant/ sqf | |||||
| 4 plant/ sqf | |||||
| 5 plant/ sqf | |||||
| 6 plant/ sqf | |||||
| 7 plant/ sqf | |||||
| 8 plant/ sqf | |||||
| 9 plant/ sqf | |||||
| 10 plant/ sqf | |||||
| 11 plant/ sqf | |||||
| 12 plant/ sqf |
To prevent physical damage to plants, many measurements can be estimated or sampled. In other words you will measure the size of a few leaves instead of measuring all leaves in each group.
You may modify the above data table by eliminating some columns and including other information such as general plant health and color of leaves and color of fruits.
Since the production of fruit is the main purpose of planting tomatos, you may simply measure and record the weight of produced fruit. To do that you may measure and report the total weight of fruit in each group or you may only measure the weight of good quality and marketable fruit.
Use the above table to draw a bar chart to show the relation between the rate of crowding and the rate of fruit production.
Experiment 2:
Introduction:
In order to see the effect of crowding on plants, you may choose a fast growing plant such as radish. Following is a sample procedure.
Procedure:
- Cut off the top of two empty orange juice cartons so they can be used as pots. Punch three small holes into the bottom of each carton.
- Use the marker to label the cartons “A” and “B”.
- Fill each carton 3/4 full with garden soil. Do not pack in the soil.
- In carton “A”, plant three radish seeds about three centimeter apart. In carton “B”, plant 20 radish seeds about 1/2 centimeter apart. To plant each seed, insert it about 1 cm in the soil.
- Place both cartons in the pie pan. Water each carton with about 1/4 cup of water. Water each carton every 3-4 days. Keep the soil damp, but not soaked.
- Observe and measure all the plants in each carton after one week and again a week later. Keep a record of the plant growth.
Materials and Equipment:
List of material can be extracted from the experiment section.
Results of Experiment (Observation):
Experiments are often done in series. A series of experiments can be done by changing one variable a different amount each time. A series of experiments is made up of separate experimental “runs.” During each run you make a measurement of how much the variable affected the system under study. For each run, a different amount of change in the variable is used. This produces a different amount of response in the system. You measure this response, or record data, in a table for this purpose. This is considered “raw data” since it has not been processed or interpreted yet. When raw data gets processed mathematically, for example, it becomes results.
Place your results table and the graph in this section of your report.
Calculations:
You may need to calculate the average plant height or leaves size (surface area).
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.
1. In which rate of crowding were the plants taller?
2. In which rate of crowding were the plants fuller?
3. What might have caused the difference in the way the plants grew?
4. What might happen to the soil when the plant population becomes too dense?
5. Do you think overcrowding might cause similar problems in other plants or animals?
6. What problems can you think of that might happen in an overcrowded human population?
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.
