Problem: How does different amounts of salt affect the growth of a plant?
Research: A plant needs water in order to live and survive. Every week, a garden should get about an inch of water.
If a plant doesn’t have enough water, then it has the same symptoms as a plant that suffers from high salt salinity level in the soil where it is growing. During the process of germination and seedling in the growing cycle of a lot of plants is when they are most vulnerable to high soil salinity in the soil it’s growing in.
All most all of the water that a plant absorbs does not actually stay inside of the plant. Actually, 99% of the water that is absorbed by a plants roots moves to the surfaces of the leaves on the plant. From here, the water is taken into the atmosphere by the process of evaporation.
Plants can only take in water that is touching their roots. During the life of the plant, less water is taken from the lower part of the plants root zone than the higher part of the root zone.
When salt gets into the water that is absorbed by plants, then that becomes a problem that can end up being deadly for the plant.
Some plants can tolerate high salt levels. They can take in more salt than they can use. One example of one of these plants is a mangrove. Root hairs on most plants would get destroyed if they were exposed to salt concentrations as high as these plants tolerate. These highly tolerant plants survive because they have roots that adapt to these high concentrations of salt.
Salt water plants such as mangroves also have specialized cells. These cells pump the salt from the plant tissues to the surface of the leaf. Once the salt gets pumped to the outside of the leaf, then it is washed off by rain.
Salt can hurt some plants. The symptoms of these plants when they are hurt by salt are similar with the symptoms of drought. There is wilting and reduced growth in the plants. When the conditions get severe enough, the symptoms could become stunted plants and tissue death.
There are water soluble salts in all soils. Plants get nutrients which are necessary to their growth from soluble salts. Excessive accumulation of these salts can suppress the growth of the plant. The excessive accumulation of salts is called soil salinity. Soils with that are saline affected are found commonly in arid and semi-arid regions.
The osmotic effect is the affect that soil salinity generally has on plants. Osmotic effect means that the energy which holds water in the soil is increased by the salts. So, this means that in order to keep the same amount of water available to plants, the soil has to be wetter. If this happens then plants have to increase the energy that they use to get water from the soil.
A reduction in the plants growth happens when the soil salinity become greater than the plant can tolerate. Water becomes harder for the plant to get when salt concentrations increase. A plant actually could die in moist soil! This would happen if the salt concentrations become too high. So a plant could actually die from drought in moist soil!
Salts are nutrients. So, when there is too much salt in soil, then it interferes with some nutrients being taken up by plants. It actually upsets the nutrient balance in the soil where it is.
There are variations in the way that plants respond to soil salinity. Plants that are salt-tolerant are able to adapt internally to concentrations of high salt than plants that are less tolerant to high soil salinity. Plants that are salt-tolerant are able to better absorb water from saline soils than plants that aren’t very salt tolerant.
The
tolerances of a plant are influenced by the cultural practices, climate, and
soil conditions of where the plant is.
In cool weather, a plant doesn’t need to transpirate as much, so there
isn’t as much injury to plants from salt as in dry weather. Size and appearance are the best factors to
look at when you trying to find out a plant’s salt tolerance.
A good way to prevent an injury from salt to a plant is to water the plant more often. If there is no restricted drainage in the soil where you are planting your plant, then you can get salts out by leeching.
Plant growth can be effected by irrigation water. When soils that are in arid regions of the world get irrigated, then solutes that were in the irrigation water can end up collecting and get to levels so high that it would affect the plant growth of the plants in that soil. 10-35% of the agricultural land in the world is affected. Some places are now unusable. This is happening in farm fields.
Some wild plants live in saline environments. They live in estuaries, on the sea shore, and in saline deserts. Plants like this are called halophytes. In order to live in the environments where they do, they have adaptations.
Plants actually need salt to live. What’s bad is when there is too much salt. That’s when it becomes poisonous to the plant. One way that the salinity of soil becomes high is when it is flooded regularly with salt water. When there is too much salt in soil, then the plant takes too much of it up through it’s roots. There are chemical reactions in a plants cells that cause it to make food and grow. The salt interferes with these reactions and that obviously hurts the plant. The growth of the plant can be stunted, and it could die.
Salt also keeps a plant from getting water. So plants that are in water that is salty can die from not getting enough water. The reason that this happens is because the salt interferes with the uptake of water of the plant. The salt actually sucks the water out of the plants cells, thus, soil with a high salinity keeps a plant from getting the water that it needs to survive.
There are indications that farmland has a high salinity level. In an area with high salinity the ground will be bear and there will a white crust type substance that is on the top of the row.
There are some indications that a plant has been affected by a high soil salinity problem. The leaves of the plant will be smaller and darker than they usually are. Once the problem becomes worse, then the leaves will turn to a yellow and will start browning. The outer edges of the leaves will also start to die. The plant will look like it has been affected by too much heat or drought.
There are some ways to try to prevent high salinity soils from destroying plants. One way is to use less salt water if it is possible. Another way is to lay put mulches on the top of the ground. You also would want to not use unnecessary irrigation water. Only use what you need.
These are some examples of when soil may have a high salinity level:
When a plant is watered with salt water, the salt absorbs a lot of the water in the area where the plants roots get their water. This leaves little water for the plants roots and this is the reason why plants can actually die from drought in a wet soil. If the water is salty, then the salt absorbs the water around the roots of the plant and then the plant can die from a lack of water.
There are two different types of soil salinity:
1. Dryland salinity- This is when there is high salinity on land where there is no irrigation.
2. Irrigated land salinity- This is when salinity occurs on land where there is irrigation.
A lot of Australia has a high salinity level naturally. Soil profile is the different layers of soil in the ground. There is salt in these profiles that is too deep to affect plants. When water tables rise, this brings the salt up to an area of the soil profile where it can affect the plants growth.
In western
Australia, the source that is believed to be supplying the soil profile with
salt is the ocean. Salt is deposited in
the soil by rain or dust. This process
has happened for millions of years in Australia, and now it has made the
Western Australia Wheat Belt.
Fertilizers are used to balance the nutrients in the soil in farming fields. These fertilizers have soluble salts in them. When the concentrations of these salts become too high, then the roots of the plant are injured. After the roots are injured, the top of the plant will eventually become affected also.
It is possible for plants to recover from injury caused by salt. If the concentration of salt in the saline soil lessens, then it is possible for the plant to recover. This could happen from irrigation water, or it could happen naturally from rain.
Some plants are more easily affected by soil salinity than others. Here are some examples: soybean, peanut, alfalfa, corn, vetch, timothy, and clovers.
When there is high soil salinity in the soil surrounding a plant, it actually makes the plant use more energy to get the water.
When salt is contained within soil that a plant is growing in, then the concentration of the soil solution becomes higher as the soil dries. This restricts the plant from getting as much water out the soil surrounding it’s roots.
There can be problems with water used for irrigation making a soil saline. When there is more water in a soil than there is water that is being evaporated, then the excess water in the soil can cause a problem for the plant. This leftover water gets into ground water and this causes water tables to rise.
When the water tables rise, then that means that the water from the water tables can get up to the top of the soil. When this water is evaporated, then it the water goes into the atmosphere, but the salt stays in the ground, this can cause the salinity of the soil to become higher.
So some salt is needed for plants to grow, but when it exceeds the needs of the plants, then it becomes bad and could end up being fatal for the plant in the surrounding soil.
Works Cited:
----. “20 Things to Know About the Impact of Salt Water on Agricultural Land in Aceh Province.” Retrieved March 7, 2006 from
Appleton, B., Greene, V., Smith, A., Hampton Roads AREC, French, S. “Trees and Shrubs that Tolerate Saline Soils and Salt Spray Drift.” January 2003. Retrieved March 7, 2006 from http://www.ext.vt.edu/pubs/trees/430-031/430-031.html
Averre, C., Bailey, J, Lilly, J. “High Soil Salts Injury to Field and Forage Crops.” Retrieved March 4, 2006 from http://www.ces.ncsu.edu/depts/pp/notes/oldnotes/gp2.htm
Blaylock, A. “Soil Salinity, Salt Tolerance, and Growth Potential of Horticultural and Landscape Plants.” February 1994. Retrieved March 17, 2006 from http://www.uwyo.edu/ces/PUBS/Wy988.pdf
----. “Effects of Abiotic Stress on Plants.” Retrieved March 17, 2006 from http://www.liv.ac.uk/~sd21/stress/salt.htm
Maurer, T. Growing Flowers. pp. 18, Vero Beach, Florida: The Rourke Book Company, Inc., 2001.
McGuinness, K. “Re: How does salt water affect the plants on land?” January 1997. Retrieved March 17, 2006 form http://www.madsci.org/posts/archives/mar97/853362106.Bt.r.html - 1.%20 How%20does%20(too%20much)%20ssalt%2
McWilliams, D. “Rio Grande Regional Soil and Water Series.” March 2003. Retrieved March 17, 2006 from http://www.cahe.nmsu.edu/pubs/_a/A-140.pdf
Miller, K. & Levine, J. Biology. pp. 644, Upper Saddle River, New Jersey: Prentice Hall, 2006.
Pearson, K., “The Basics of Sodicity Effects on Soil Physical Properties.” Retrieved March 5, 2006 from http://waterquality.montana.edu/docs/methane/basics_highlight.shtml - 1.%20%20The%20effects%20of%20salinity%200
----. “Salt, the Silent Killer!” Retrieved March 5, 2006 from http://wgscd.org/salt.html
Sarre, A. “Monitoring the white death- soil salinity.” November 1998. Retrieved March 4, 2006 from http://www.science.org.au/nova/032/032key.htm
Scherer, T., Seelig, B., Franzen, D. “Soil, Water, and Plant Characteristics Important to Irrigation.” February 1996. Retrieved March 17, 2006 from http://www.ext.nodak.edu/extpubs/ageng/irrigate/eb66w.htm - plants
Hypothesis: Plants that are given salt in their water will have less growth than the ones with regular water because high soil salinity causes reduced plant growth.
Materials:
2 pots
1 bag of planting soil
1 package of flower seeds
water
measuring cup
teaspoon measuring spoon
1 box of salt
Procedure:
1. Pour the planting soil into the two pots until it is about two inches from the top of the pot.
2. Wet the soil down and stir it around. Flatten the soil on the top.
3. Open the package of flower seeds. Sprinkle the same amount of seeds in both of the pots.
4. Pour ½ a liter of water into one of the pots. Try to spread the water out evenly over the soil.
5. Put one teaspoon of water into another ½ liter of water.
6. Pour this ½ liter of water into the other pot. Make sure to keep track of which pot is being watered with which type of water. It is important that you water the pots with the same type of water throughout the whole experiment.
7. Repeat steps 4, 5, and six once a day, every day, for 3 weeks. If the soil ever gets too damp, don’t water the flowers for a couple of days. Once the flowers sprout and start to grow, you may want to only water them every other day.
8. Record how the growth of the plants in the pot with regular water compares with the growth of the plants in the pot with salt water. Also record how the plants look in each of the pots. For example, do the flowers look yellow and wilted, or do they look green and healthy.
Prediction: If I water one pot of flower seeds with regular water and I water one pot of flower seeds with water that contains salt, then the flowers in the pot that is water with regular water will have more growth than the flowers that are in the pot with water containing salt because when I water the pot with water containing salt, then that makes the salinity of the soil in that pot become high and high salinity reduces plant growth.
Data/Results:
|
Day |
Observation |
Taller Plants |
|
Day 1 |
Today I planted the seeds and watered the pots for the first time. |
No flowers |
|
Day 2 |
I watered the pots of flowers again. Nothing has started to sprout yet. In the bowl with salt water, there are a few clumps of white that I think are salt clumps. |
No flowers |
|
Day3 |
I watered the flowers today. Nothing new has happened except that the white clumps of salt are no longer in the salt pot. |
No flowers |
|
Day 4 |
I watered the plants again today. Nothing has started to sprout yet. It’s dark and cloudy today. It doesn’t look like all of the water from yesterday has even dried yet. |
No flowers |
|
Day 5 |
I watered the plants again. No new developments |
No flowers |
|
Day 6 |
No new developments. |
No flowers |
|
Day 7 |
No new developments. |
No flowers |
|
Day 8 |
No new developments. |
No flowers |
|
Day 9 |
There seems to be some white buildup on the top of the soil in the salt pot. This could be salt. |
No flowers |
|
Day 10 |
No new developments |
No flowers |
|
Day 11 |
No new developments |
No flowers |
|
Day 12 |
No new developments |
No flowers |
|
Day 13 |
No new developments |
No flowers |
|
Day 14 |
The flowers in the pot being watered with regular water are sprouting. |
No flowers |
|
Day 15 |
The salt water plants still haven’t sprouted. There seems to be a lot of the sprout from the regular water pot that are all on one side of the pot where it is shady. |
Regular Water |
|
Day 16 |
The sprouts seem to be grouped in the shaded part of the pot |
Regular Water |
|
Day 17 |
The sprouts are all over the pot, but the salt water flowers still haven’t even sprouted yet. |
Regular Water |
|
Day 18 |
I had to stop watering the plants for the weekend because they are getting too wet. |
Regular Water |
|
Day 19 |
I didn’t water the plants today. |
Regular Water |
|
Day 20 |
I watered the plants again today, the salt water pot flowers till haven’t sprouted. |
Regular Water |
|
Day 21 |
There still is no growth in the salt water pot. The sprouts have been sprouting for about a week now. |
Regular Water |
|
Day 22 |
I didn’t water the plants today |
Regular Water |
|
Day 23 |
The pots seem like they may still be getting too much water. The soil looks damp and dark. The sprouts in the regular water pot are green. |
Regular Water |
|
Day 24 |
I didn’t water the plants today. The middle of the regular water pot seems to be dry, so that is a good sign for my watering. |
Regular Water |
|
Day 25 |
It rained last night and all day today, so I didn’t water the plants today. |
Regular Water |
|
Day 26 |
I’m not going to water the plants for the rest of the experiment because they received so much water from the rain that we got on Friday night and Saturday. |
Regular Water |
|
Day 27 |
I didn’t water the plants |
Regular Water |
|
Day 28 |
I didn’t water the plants |
Regular Water |
|
Day 29 |
I didn’t water the plants, some of the regular water sprouts seem to be getting bigger. The sprouts are a kind of light green color. |
Regular Water |
|
Day 30 |
The salt water plants still have not sprouted. The flowers in the regular water pot range in height. |
Regular Water |
Data Analysis: The flowers in the salt water pot never grew or sprouted, while the flowers that were in the regular water pot sprouted and grew for about two weeks at the end of the experiment. This supports my hypothesis because the plants in the regular water pot grew and the plants in the salt-water pot didn’t grow at all. The flowers inside the salt-water pot never even sprouted or showed any signs of growing. The regular water plants grew for 17 days before the end of the experiment and the salt-water plants still did not sprout. One other thing that supports my hypothesis is that after the experiment was over, the salt water flowers started to get watered with fresh water. Once this happened, the salt water seeds began to sprout!
I might have been watering the plants in the wrong way at the beginning of the experiment. I wasn’t sprinkling the water on, it was more like the dumping the water on. I also may have been watering the plants too frequently. I had to stop watering them on the last weekend before the end of the experiment because they were getting too much water. There were also a few days were it was overcast, and one time it rained one night and then all day the next day, so that may have affected the flowers photosynthesis.
If I would have watered the plants by sprinkling the water onto then the whole time, then the flowers may have sprouted sooner. If I would have taken breaks in my watering, then the plants might have had a more rapid rate of growth. If it would have been sunny all of the days during the experiment, then the plants may have grown faster because there would have been more sunlight for photosynthesis to occur.
Conclusion: It can be concluded from this experiment that plants grow better in regular water than they do in salt water. This would explain why plants that are grown in saline soil die or have stunted growth. It could be what salt does to the inside of the plant, not what it does to the soil. There would need to be further experiments done to conclude if this is the case or not.