Lesson 8
The Salty Solution
A study of the effects of salinization on
plant growth and development
Overview
In many areas of the world, including the United States, salinization of
the soil, or the accumulation of salts, is an important concern. A salinization problem can vary in magnitude from small, isolated cases, as
when road salt accumulates after snow melts, to larger, more serious
soil problems in regions where plants are heavily irrigated or ocean
tides salinize soils and groundwater.
This experiment investigates the effects of different salt solutions on
the germination and growth of brassica rapa seeds. Students can use
this experiment to study the effects of salt on seed germination, and, if
time permits, can continue looking at the growth and development of
plants in a saline environment.
Students will have an opportunity to generate alternative hypotheses,
and collect, record, compare and interpret quantitative data. After
completing this investigation, students will have a better understanding of how varying amounts of salt affect the growth and development
of plants.
Biological and Plant germination, growth and development
Osmosis
agricultural
Ecology
concepts
Water quality
Soil science
Scientific method
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Lesson 8
The
teachable
moment
Background
Teacher material
Both the biology and agriculture teacher can use this investigation to
illustrate a plant or crop science unit. The biology teacher may want to
use the material when addressing environmental issues or the affect of
an abiotic factor (salt) on a biotic system (plants). In the agriculture
classroom, the material can illustrate topics such as irrigation, landscape management and water quality.
Though all soils contain some level of soluble salts, soils containing
enough water-soluble salts to affect the germination and growth of
plants are considered saline or salty soils. Saline soil conditions reduce
the agricultural value and productivity of the land. More than onefourth of the irrigated farmland in the United States is affected to some
extent by soil salinity (Donahue et al. 1990).
Saline soils result when salts dissolved in soil moisture move to the
surface of the soil where they are left as a crust in high concentration
when the water evaporates. Repeated irrigation with low-salt water,
which often occurs in areas of the Southwest, can cause salinization of
the soil. Saline soils are also common in low-lying areas where drainage is poor and in areas where groundwater seeps into surface soil.
Salts accumulate at the soil surface as water evaporates or is used by
plants.
Saline soils also result when salty wastewater from oil or gas drilling
procedures dumped or any time soil is flooded with salty water. Soils
near an ocean can become saline from salty ocean sprays just as soils
near highways and roads become saline from road salt applied to melt
ice and snow.
High concentrations of salt in the soil cause problems for plants. Concentrated salt disrupts the balance of water (the physical process of
osmosis) in the soil and in the plant tissue, causing the plant to pump
water out of the cell and into the surrounding soil water. Less water is
available to the plant, which can cause the plant to wilt. In addition,
the sodium, carbonate and chloride ions found in saline soil are potentially toxic to plants.
In general, when salinization is a problem, a farmer will see uneven or
irregular plant growth in a field, and a whitish crust on the soil surface
from accumulated salt. Plants growing in a saline environment often
have a bluish-green appearance. In addition, soil salinity tends to
show up as more of a problem in dry years.
This investigation focuses on the effects of different salt solutions on
8-2
I
Salinization
Lesson 8
Teacher
Management
Preparation
Teacher material
plant germination, growth and development. Students hypothesize as
to how plants will be affected when grown in a salty environment and
test these ideas using bottle constructions.
Two hours for collection of materials and preparation of salt solutions.
You should make up appropriate amounts of 0.5,1.0, 2.5, and 5. percent
salt solutions according to the size of your class. Students should work
in groups of two or four. One liter of one of the salt solutions per
group will be more than adequate. Each group will test use a different
salt concentration and compare the results with a distilled water control. Each group makes two column-a control and an experimental.
Solution
5.0%
2.5%
1.0%
0.5%
Activity time
Grams of salt added to 1liter of water
50
25
10
5
Construction of bottle columns will take 1/2 to one full class period.
Setting up the activity will take one class period (this includes filling
columns with soil, planting seeds, watering, and setting up laboratory
sheets).
For Option A (germination only), watering, taking measurements, and
observing will take five to 15 minutes per class period for 5 days. An
additional class period will be needed to discuss individual group
results and any further extension experiments.
For Option B (growth and development), watering, taking measurements, and observing will take five to 15 minutes, three days/week
for five weeks. (See Activity Timetable, page 0-14.)
Materials
•
•
•
•
•
•
•
•
Four 1-liter labeled bottles per group of 4 students
Jiffy Mix or a 50/50 combination of peat moss and vermiculite
Liquid measuring devices, such as film canisters or beakers.
Twenty seeds per group. Fast Plants are recommended for
Option B, but almost any seed can be used for Option A.
Non-iodized pickling salt for making the saline solutions
One liter of each salt solution per group; 0.5, 1.0, 2.5, 5.0 percent.
Tap or distilled water
liquid fertilizer, such as Peter's (use standard 1T I gal)
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Lesson 8
Tips and Safety
Teacher material
If students are building bottle biology constructions for the first time,
allow extra class time for setting up the initial activity.
Two-liter bottles may be substituted for 1-liter bottles, but all quantities of water must be doubled.
For Option B, add wicks to the construction to make watering more
consistent and maintenance free.
Use salt that is pure NaCl (pickling salt). Do not use salt that has
aluminum silicate added to it.
Refer to the Wisconsin Fast Plants introductory section for growing
instructions.
Key terms
Leaching: when water passes through soil carrying soluble materials,
such as nutrients, along with it.
Osmosis: the movement of a fluid (like water) through a membrane
(like a cell wall) in order to create an equal concentration of dissolved
solids (like salt) on either side of the membrane.
Salinization: the accumulation of soluble salts in soil, which can adversely affect plant growth.
Soluble: capable of being dissolved in a liquid
References
Donahue, R.L., R.H. Follett, and R.W. Tolloch. Our Soils and Their
Management. Interstate Publishers, Inc. Danville, Illinois, 1990.
Harpstead, M.I., F. D. Hole and W.F. Bennett. Soil Science Simplified.
Ames, Iowa. Iowa State Univ. Press, 1988. pp. 118-9.
Hausenbuilder, R.L. Soil Science. Dubuque, Iowa: Wm. C. Brown,
1985. pp. 466-89.
8-4 I Salinization
Student material
Lesson 8
The Salty Solution
A study of the effects of salinization on plant
growth and development
Introduction
Just as humans can't survive by drinking salty ocean water, plants can't
grow well in the presence of too much salt either. How does soil get
too salty? And how much salt is too much?
Accumulation of salt in water or soil is called salinization. This is a
problem in many areas of the world, including the United States.
Saline soil conditions reduce the agricultural value and productivity of
the land. More than one-fourth of the irrigated farmland in the United
States is affected to some extent by soil salinity.
Saline soils result when salts dissolved in soil moisture move to the
surface of the soil, where they are left as a crust in high concentration
when the water evaporates. Repeated irrigation of plants with low-salt
water, which often occurs in areas of the Southwest from Texas to
California, can cause salinization of the soil. Saline soils also commonly occur in low-lying areas where water drainage is poor and in
areas where groundwater seeps into surface soil. Salts accumulate at
the soil surface as water evaporates or is used by plants.
Saline soils also result when salty wastewater from oil or gas drilling
procedures is dumped or any time soil is flooded with salty waters.
Soils along the ocean can become saline from salty ocean sprays just as
soils near highways and roads become saline from road salt applied to
melt ice and snow.
High concentrations of salt in the soil cause problems for plants. Concentrated salt disrupts the balance of water (the physical process of
osmosis) in the soil and in the plant tissue causing the plant to pump
water out of the plant cells and into the surrounding soil water. Less
water is available to the plant, which can cause the plant to wilt. In
addition, the sodium, carbonate and chloride ions found in saline soil
are potentially toxic to plants.
In this experiment, you will hypothesize about what concentration of
salt will affect a plant's growth. You will test your ideas using plastic
soda bottles, soil and seeds. If you live in an area where crops are
Salinization I
8-5
Lesson 8
Student material
irrigated, you may want to get try and obtain some of that water and
experiment with it.
Materials
Procedure
Option A
•
•
•
•
•
•
•
•
•
•
•
four 1-liter plastic bottles
a pair of scissors
soil or Jiffy mix
a marking pen
two film canisters
a plastic ruler
two beakers
tap or distilled water
20 seeds
forceps or tweezers
salt water (0.5, 1.0, 2.5 or 5.0 percent)
Option A investigates the effect of salt on plant germination only.
1. Prior to setting up your lab, complete student worksheet,
Option A, numbers 1-4.
2. Take two one-liter bottles and remove the labels.
3. Cut the bottles eight em below the neck. (See directions for the
terraqua column in the Bottle Biology basic introductory section.)
4. Remove the bottle caps and punch a drainage hole in the center
of each cap. Replace the bottle caps.
5. Label one column with the percent salt solution that your group has
been assigned and the other column with "control." Write your
names on your columns.
6. Measure out 350 mls of soil into each beaker.
7. Dampen each portion of soil with 50 mls of water.
8. Place the damp soil into the upper unit of the column.
9. Pour 100 mls of the salt solution on the column you have labeled
as the salt column. Pour 100 ml of distilled water on the control
column.
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I Salinization
Lesson 8
Student material
10. Place 10 seeds on the surface of the soil in each column.
11. Cover the seeds with 30 mls of additional dry soil.
12. Water the column with distilled water until water begins to
drain into the lower reservoir.
13. Discard the water that has drained through and fill the bottom
reservoir with distilled water.
14. Place the columns under a light source (3 to 4 em from the light).
15. Water the columns with an additional30 mls of the appropriate
solution in two days.
16. Check for germinating seeds daily. Count the total number of
seedlings that are healthy and fully emerged from the soil for five
days.
17. In Table B, place a check mark for each seed that has germinated.
To determine the percentage of seeds that have germinated,
multiply the number of seedlings germinated by 10.
18. Be prepared to discuss your results in a class discussion and
complete Table C.
19. Complete the discussion questions.
Option B
In Option B you will witness a complete 40-day Fast Plant life cycle.
The rate at which your plants develop will vary depending on the
amount of light and the temperature of your classroom. We suggest
that you build your bottle columns on a Monday and plant your seeds
on Tuesday. (See timetable on page 8-15)
Prior to setting up the lab, complete student worksheet, Option B,
numbers 1 to 3.
1. Complete steps 1 through 16 as in Option A (preferably on Monday
and Tuesday), except add a Pelion wick running from the upper
reservoir into the lower chamber in the column.
2. On the third day after planting (Friday), count and record in
Table B the number of seedlings that are healthy and fully
emerged from the soil. Add 30 mls of salt solution to the salt
Salinization I 8-7
Lesson 8
Student material
column and 30 mls of distilled water to the control. Add 5 mls of
fertilizer to each column. Choose and number your three healthiest
plants and remove the other by cutting their stem right at the point
where they come out of the soil.
3. On day 6, record any additional plants that might have germinated.
Thin plants leaving three plants.
4. On day 8, measure plant height and fertilize each column with
12 mls fertilizer.
5. Measure the height of the plants on days 6, 8, 10, 13 and 15 (see data
sheet). Measure from the soil to where the new leaves are forming
(the apex of the plant). Calculate and record the average height of
your plants.
6. On days 15, 17, and 20 count and record the number of flowers that
are fully opened. Calculate and record the average number of
flowers on your three plants. Pollinate your flowers on each of these
days. On day 15 fertilize each column with 12 mls of fertilizer.
7. On day 20, punch off all new flower buds leaving the ones that you
pollinated. Continue to do this for the rest of the life cycle.
8. On days 27, 29 and 30, count and record the number of pods found
on your plants. Compute and record the average number of pods
per plant.
9. Remove your plants from water on day 36.
10. When pods are dry, around day 41, harvest them and count the
number of seeds produced by each plant. Compute and record the
average number of seeds per plant.
11. Be prepared to discuss your results with the class. You will record
the class results in Table C.
12. Answer the discussion questions.
8-8
I Salinization
Data sheets: Option A
Lesson 8
The Salty Solution
Date seeds were planted._ __
Salt solution used
%
1. What is your hypothesis?
2. Fill in Table A before setting up your experiment.
Table A - The same materials should go into each of your columns.
Record the following:
Amount of soil: _ _ _ _ _ _ __
Type of soil: _ _ _ _ _ _ __
Type of water: _ _ _ _ _ _ __
Amount of water: - - - - - - Number of seeds: _ _ _ _ _ _ __
3. What is the only difference between the designs of your control
and test?
4. What do you think will be the major effect of salt on your plants?
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Lesson 8
Data sheets: Option A
Table B -Number of germinated plants
Salt Concentration (
Day
Date
control
experimental
3
control
experimental
6
Total
%)
# plants germinated
control
experimental
Table C- Class Data
Salt Concentration
Data
Total number
of seedlings
Results and
discussion
Option A
Day Control
0.5%
1.0%
2.5%
5.0%
1
2
3
4
5
1. What is the relationship between salt concentration and seed
germination?
2. At what concentration of salt do plants not germinate? Why do
you think this is?
3. Are there any salt concentrations, besides your control, that
seem to have no effect on seed germination?
4. Why is it important to compare your results to the control (0%
salt)?
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Salinization
Lesson 8
Data sheets: Option A
5. If your plants were allowed to grow and develop, what do you
think they would look like? How would the plants in the
control column compare to the plants growing in the salty
environment?
6a. Did groups experimenting with the same salt solution obtain
similar results?
b. If not, describe some variables that may have caused some of
these differences.
c. Choose one variable and describe how you could control this
"variable" in an experiment.
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8-11
Data sheets: Option B
Lesson 8
Data
sheets
Option B
1. What is your hypothesis?
2. Fill in Table A before setting up your experiment.
Table A- Experimental Design
Variables
Control
Test
amount of soil
type of soil
type of water
amount of water
number of seeds
3. What do you think will be the major effect of salt on your plants?
8-12 I Salinization
Lesson 8
Data sheets: Option B
Table B- Data
D ay
D ata
3
Number of
seeds germinated
3
Height: Plant 1
2
3
average
6
8
10
13
15
17
20
27
29
31
41
ContrlCl
oumn
o
(
S altCoumn
1
()
o/c)
Number of additional
seeds germinated
Height: Plant 1
2
3
average
Height: Plant 1
2
3
average
Height: Plant 1
2
3
average
Number of flowers:
Plant 1
2
3
average
Number of pods:
Plant 1
2
3
average
15
17
20
15
17
20
27
29
31
27
29
31
Number of seeds:
Plant 1
2
3
average
Salinization 1
8-13
Lesson 8
Data sheets: Option B
Table C- Class Data
Salt concentration
Data
Control
0.5%
1.0%
2.5%
5.0%
total%
germination
average height
average number
of flowers
average number
of pods
average number
of seeds
Results and
discussion
Option B
1. Describe the effects of higher salt concentrations on:
a. germination
b. plant height
c. flower and pod production
d. seed number
2. At what stage of development do plants seem to be the most
sensitive to high salt concentrations?
3. Are there any salt concentrations, besides your control, that seem to
have no effect on seed germination?
4. Why is it important to compare your results to the control (0% salt)?
Sa. Did all groups with the same salt solutions obtain similar results?
b. If not, describe some variables which may have caused some of the
differences.
c. Choose one variable and describe how you could control this
"variable" in an experiment.
8-14 I Salinization
Lesson 8
Data sheets: Option B
Activity Timetable - Option B
Monday
• build
columns
Tuesday
• plant seeds
• add 130 mls
salt sol'n
Wednsday
Dayl
Thursday
Friday
•
•
•
•
Day3
record germination
fertilize
add 30 rnls salt sol'n
thin to 3 plants
DaylO
• measure height
Day6
• record germination
DayS
• fertilize
• measure height
Day13
• measure height
DaylS
• measure height
• count and
pollinate flowers
Day17
• count and
pollinate flowers
• measure height
Day29
• count pods
Day31
• count pods
Day20
• count and
pollinate flowers
• terminate buds
Day27
• count pods
Day36
• remove plants
from water
Day41
• harvest seeds
Extensions
1. Does leaching the soil with tap water decrease the effects of
salinization?
2. Do different plants react to salty water the same?
3. How do other environmental factors affect the growth and
development of plants?
4. What effects do different salt solutions have on plant embryos?
5. What is the lowest level of salt that affects plant development?
6. How much salt actually enters the roots of plants grown in salty
water?
Salinization I 8-15