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The effect of excess salinity on plants

The effect of excess salinity on plants

Introduction: (Initial Observation)

The effectiveness of plant root systems to take up water and dissolved nutrients from the soil is dependent, in part, on the process of osmosis. Osmosis is the flow of one component of a solution through a membrane while the other components are blocked and unable to pass through the membrane.

The rate of osmosis (the movement of water across a cell membrane – in this case, a root hair cell) will be dependent on the evolutionary history of the plant and the adaptations it has to accommodate varying soil water salinities.


This project guide contains information that you need in order to start your project. If you have any questions or need more support about this project, click on the “Ask Question” button on the top of this page to send me a message.

If you are new in doing science project, click on “How to Start” in the main page. There you will find helpful links that describe different types of science projects, scientific method, variables, hypothesis, graph, abstract and all other general basics that you need to know.

Project advisor

Information Gathering:

Find out about plant biology and the growth mechanism. Read books, magazines or ask professionals who might know in order to learn about the effect of salt and other minerals on plants. Keep track of where you got your information from.

Following are samples of information you may find:

Osmosis is the movement of water molecules from an area of high concentration to an area of low concentration.

Cell membranes are completely permeable to water, therefore, the environment the cell is exposed to can have a dramatic effect on the cell.

Learn more about osmosis

Following are some useful links:

United States department of agriculture has a research laboratory specialized and focused on saltwater related studies. To visit their website click on http://www.ussl.ars.usda.gov/

or for information about Salinity in agriculture, click on http://www.ussl.ars.usda.gov/answers/salinity.htm

Although salty water is not suitable for most plants, there are a few plants that can live with salt water. For more information visit: http://mangrove.nus.edu.sg/guidebooks/text/1042.htm

These are some uses of osmosis:

Groceries spray vegetables by water so the vegetables will stay fresh.

Osmosis is used in dialysis machines to filter blood of diabetic patients.

Reverse osmosis is used to get fresh water from salt water.

When you eat salt you feel thirsty because salt sucks the water out of your body cells.

When you sprinkle salt on pilled eggplants or cucumbers, water drops will form on the surface. Salt sucks the water out of the cells. Cooks do this to increase the firmness of eggplants.

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 is the effect of Salt Water on a plant’s growth? We all know that plants get watered by fresh water, however, would salt water do the same job? Will the plants grow better or die because of the salt water?

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 (manipulated variable) is the salinity of water. You may use the percent of salt in water as the salinity of water.

Dependent variable (responding variable) is plant growth.

Constants are the type of plant, type of soil, amount of watering and experiment method.

Controlled variables are light and temperature


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.

This is a sample hypothesis:

Since the salinity of the water can cause the osmosis process to be thrown off course, the plant will probably be hurt from the salt water and will possibly die.

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: In this experiment germination of soybeans and growth of young soy plants are being tested under identical conditions, but various salinity waters.


  1. Get four pots and 12 soaked soybean seeds.
  2. Fill each pot about 2/3 full with potting soil.
  3. In each pot , plant 3 soybean seeds covering them loosely with about 1 cm. of soil (approximately the width of the seed).
  4. Label one pot with control.
  5. Label one pot with .5% salinity.
  6. Label one pot with 1% salinity.
  7. Label one pot with 3% salinity.
  8. Place all four pots in a tray and water them with tap water until plants reach a height of 18 to 20 cm. (This will take a week to 10 days.) Make and record observations of height and any other important observations.
  9. When all plants have reached a height of 18 to 20 cm. , transfer each of the potted plants to the correctly marked salinity tray.
  10. Water the plants with the correct salinity solution and continue to make observations for another week.
  11. Graph the observation of height to time (days).

How to make salt solutions with certain concentration?

To make a salt solution with a certain concentration, you need a scale. For example you may have a scale that can measure from one gram up to 500 grams. To make a 5% salt solution do the following.

Place an empty plastic container on the scale. Record the weight of the empty container. Then add salt to the container so the weight will increase 5 grams. Then add 95 grams water to the container. Remove the container from the scale and stir it until all salt is fully dissolved. This gives you a 5% salt solution. Essentially what you did was you mixed 5 grams of salt with 95 grams of water to make 100 grams of solution.

Often we have a scale that is not sensitive enough to show 5 grams. In this case we mix 50 grams of salt with 950 grams of water to make a 5% solution.

If you have a scale that does not show grams, you can mix 5 ounces of salt with 95 ounces of water. The result again is a 5% solution.

To make a 3% solution you mix 3 grams of salt with 97 grams of water.

To make a 1% solution, you mix 1 gram salt with 99 grams of water. Or if you have some extra 5% solution, mix one cup of that solution with 4 cups of water to make a 1% solution.

Materials and Equipment:

Following is a list of material used in our experiment.

  1. Soybean seeds (You cannot grow roasted or broken seeds)
  2. Small pots
  3. Distilled water
  4. 0.5% salt solution
  5. 1% salt solution
  6. 3% salt solution
  7. Potting soil
  8. Metric rulers
  9. Trays for plants
  10. Watering cans

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.


No calculations are required for this project.

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.


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.


Write a list of your references at this section. You will need to visit a local or school library and read some books about plants, irrigation, biology and osmosis. If you see any related material in these books, add them to your report or use them in your project.