Stephen Herr
AP Environmental Science
Section 1
stephen_herr@verizon.net
Lab 5 Effects of Soil Salinity on
Seed Germination
February, 2005
Data Worksheet - Lab 5
Effects of Soil Salinity on Seed Germination
Trial 1
salt concentration
0%
0.22%
0.44%
0.88%
1.75%
3.50%
number of mung bean seeds germinated
1 day
2 days
3 days
4 days
10
14
18
19
0
12
18
18
0
12
16
19
0
2
10
12
0
0
14
14
0
0
0
0
Cookie Mining - Lab 3
Stephen Herr
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LAB REPORT/ ANALYSIS QUESTIONS
questions using complete sentences.
Provide answers to the following
1. What can be the effect of salinized agricultural land on developing crops?
In the lab I conducted, high salt concentrations inhibited both the germination and growth
rate of plants. The same thing probably happens with other crops.
2. What are the sources of the salts on the salinized land?
Salinity refers to the build up the following minerals that are deposited by evaporating
water: Na+, K+, Ca2+, Mg2+, Cl-, HCO3- and SO24-. Over irrigation and excessive
evaporation worsen this problem.
3. Why was it necessary to keep the beakers covered with plastic wrap in the
experiment?
Water would evaporate and the percent salinity would change if the Petri dishes were not
covered during the experiment. This would affect the results of the experiment.
4. Why was it necessary to stir the solutions very well when making the serial
dilutions in the experiment?
Stirring the solutions very well ensured that the salt was completely dissolved and evenly
distributed throughout the solution. This made the serial dilutions more accurate.
5. Why was it necessary in the experimental design to have some seeds germinating
in pure distilled water (0%)?
The seeds growing in the distilled water served as a control in the experiment. The data
collected from plants growing in other concentrations of salt water can be compared to
this.
6. Make a graph showing the relationship (for each solution) between the number
of mung seeds germinated and the salt concentration. Be accurate and label your
axes.
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Stephen Herr
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Germination vs. Salinity
20
18
number germinated
16
14
0%
0.22%
0.44%
0.88%
1.75%
3.50%
12
10
8
6
4
2
0
1 day
2 days
3 days
4 days
Days
7. Using your data and the graph, fully discuss the results of your experiment. A
complete discussion includes an analysis of the data.
I decided to define germination as the cracking of the mung bean seed coat. I did this
because this was the easiest way to observe. The graph and data shown above seem to
indicate that increasing the salinity decreases the germination rate of mung beans. In
addition to germination rate, the salinity also seemed to affect the rate at which the roots
of the mung beans grew. The germination rates were identical for 0%, 0.22%, and 0.44%
were nearly identical after four days, but the growth rates were considerably different
with the greatest growth in the purest water.
8. What are possible sources of error in this experiment?
One potential source of error was the variability in the health of beans used in the
experiment. The experiment originally called for five mung beans to be used in each
trial, but I increased that number to twenty in order to attempt to reduce potential
sampling error. Different environmental conditions such as light, temperature, humidity
could have also contributed to errors in this experiment. I attempted to keep these factors
the same throughout the experiment to reduce the error.
9. In addition to determining the number of germinations, what other data could
have been collected to determine the effect of soil salinity on plant growth?
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The following data could have been collected to determine the effect of salinity on plant
growth: plant biomass, growth rate, root length, crop yield, flowering rate, plant
appearance, reproduction rate, and photosynthetic rate.
10. Discuss three specific ways that farmers can remediate the salinization of their
cropland.
Salt can be leached from the soil by watering the crop with more water than it needs.
This washes the salt away from the crops roots. Farms also use a method that uses
artificial drainage in combination with leaching. A third process that is used is known as
managed accumulation through double-row bed systems. Using this system, salt is
moved away from plant roots into furrows, which do not receive water.
11. Looking at your answers to number 10, give one negative aspect to each of the
remediation techniques listed above.
The first method described in question number 10 uses a lot of water. This excess can
damage the crop. The second method is very expensive and typically is not economically
viable. The third method requires extremely precise rows and is hard to implement in
uneven fields. It also does not remove the salt from the field. Instead it redistributes it.
12. Write a comprehensive summary and conclusion of your lab results.
In this laboratory I examined the influence of salinity upon the germination of mung
beans by placing mung beans in Petri dishes containing filter paper saturated with
solutions ranging from 0% to 3.5% salinity. Germination was defined as breakage of the
seed coat. The graph shows that the germination rate of the mung beans is dependent
upon the time of exposure to the solution and the salinity of the solution. The highest
germination rate was observed in those beans exposed to distilled water (50% after one
day, and 95% after 4 days), while the lowest germination rate was for those exposed to
3.5% salinity (0% after 4 days). The germination rates of the beans in the intermediate
solutions varied with the date of observation, but less than the rate in distilled water, and
more than the rate in 3.5% salt solution.
After two weeks in solution, the effects were more pronounced, with greatest growth in
the pure water (0% salt) and diminishing growth with increasing salt concentration.
Those seeds placed in 3.5% solution never showed any growth and were soon covered
with mold.
My research has shown that increasing concentrations of salts causes a reduction in the
germination rate of mung beans. If other crops behave similarly to mung beans when
exposed to high salt concentrations, then salinization of farmland poses a dire threat to
agriculture. Careful attention should be given to techniques of irrigation to minimize salt
build-up and maximize growth potential.
Cookie Mining - Lab 3
Stephen Herr
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Cookie Mining - Lab 3
Stephen Herr
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