Name ___________________________________________
AP Environmental Science--Soil Salinization Design Lab (Adapted from Molnar by R. Geithner-Marron Jan. 2010)
Date ___________
Period _________
“Is This Water Too Salty for My Crops?” (Soil Salinization Lab)

Purpose:
o Develop a sound experimental design to investigate how salinization affects the germination of seeds
o Determine the highest salt concentration at which all seeds will still germinate ( the “threshold level of toxicity”)
o Determine the salt concentration that is considered to be the LD-50 (lethal dose for 50% of the seeds)
o Determine the salt concentration at which none of the seeds will germinate
o Make recommendations as to:

other “crop” seeds that might be more tolerant of salt
 how to remediate the soil if the salt concentration reaches toxic levels
 alternative irrigation methods that might be less likely to cause salinization

Background:
o Most of the fertile and easily farmed land in the world is either now under cultivation or is developed for other
purposes. This leaves less desirable land, such as arid land that will need irrigation, to be farmed in order to help
feed a growing global population. Soils in dry regions are generally rich in nutrients due to the fact that there is
little water to leach the nutrients below the root zone. These regions can be made “suitable” for growing crops
only through the irrigation of the land. Much of this water is pumped from underground aquifers that contain
dissolved mineral salts. As the water is sprayed onto the crops, some of it evaporates due to the low humidity of
the air in the region, and it leaves a thin layer of salts on top of the soil. In low concentrations, salt on the land is
not a problem. However, over time, the salts build up on the fields so that the soil is so salty that those salts
eventually interfere with the germination and growth of crops (by removing water from plant cells). Salts also
decrease the osmotic potential of the soil so that plants cannot take up water. Another way the salt interferes
with plant growth is by forming a crust on the soil that any seeds that do germinate have a hard time penetrating
and by impeding water infiltration.
o
Soil salinization is a serious threat to agriculture in arid regions where irrigation is necessary. These areas include
the central valley of California and other areas of the American west, the Middle East, central Siberia, and China.
In some areas, the summer irrigation effects are reduced by the winter snows, which wash the salts back down
below the root level. In other parts of the world, such as Saskatchewan, Canada, the water table is near the
surface and contains high concentrations of salt which move to the upper parts of the soil through capillary action.
During the summer in areas like this, the heat causes the water to evaporate out of the soil, leaving high levels of
salt behind. Salinization is also increased by poor soil drainage. Even though the effects of salinization may not be
immediate (and can actually take many seasons to be noticed), excessive salinity is currently costing billions of
dollars each year in the United States alone and has become “a cost of doing business”. In less developed
countries, it is often even a matter of life and death.
o
Many salt ions are involved in soil salinization, such as sodium, calcium, magnesium, potassium, carbonate,
chloride, and sulfate. The most common, by far are sodium and chloride. For convenience, your team will only be
studying the effects of sodium chloride (NaCl), ordinary table salt. An assumption will be made that the effect of
NaCl will be characteristic of all salts on the germinating seeds. Water is considered “fresh” if it has a salt
concentration (salinity) of 0.5% (0.5 g/100mL of water) or less. The salinity of water near the coasts of the United
States is about 3.5%, which is 3.5 g/100mL of water. Rarely does the salinity of the ocean reach 4.0% (or 4.0
g/100mL) of water. For your information, you will often see salinity written in “parts per thousand” (ppt) which
would be written as 350/00.
Name ___________________________________________
AP Environmental Science--Soil Salinization Design Lab (Adapted from Molnar by R. Geithner-Marron Jan. 2010)
Date ___________
Period _________

Problem: Your group is a team of consultants that have been hired by farmers in the community who are concerned about
how increasing salt concentrations in their soil will affect their crops. Your group’s job is to design a controlled experiment
to measure how increasing salt concentrations interfere with the germination of the crop seed they are growing. (In this
case they are growing _______________________).

Materials:
o Electronic balance
o Filter paper (or paper towels)
o NaCl
o scoopula
o Distilled water
o Beakers (___________ mL) (1 for each solution you are going to make)
o Stirring rods
o Potting soil
o Spoons/and or trowels
o Petri dishes (up to 8 per group)
o Seeds (_____________________)
o Forceps/tweezers
o Wax pencils/China markers
o Graduated cylinders or “medicine cups”
o Trays (to hold Petri dishes)

Pre-lab:
o Research… What type(s) of irrigation are most likely to result in soil salinization? Why?
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________
_____________________________________________________________________________________________

Procedure:
o Write your own procedure to test how the salt concentration of water affects the germination of plant seeds.
****I must approve your procedure before you start setting up your experiment.
 Indicate the following:
 Your independent variable: ________________________________________________________
 Your control: ____________________________________________________________________
 Your dependent variable: __________________________________________________________
 Your constants: __________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
Name ___________________________________________
AP Environmental Science--Soil Salinization Design Lab (Adapted from Molnar by R. Geithner-Marron Jan. 2010)







Date ___________
Period _________
Decide:
 Which concentrations of NaCl solution you will use. (Make the solutions using the mass/volume
method. For example: 4.0g NaCl/100 mL of distilled water to make a 4.0% NaCl solution.)
o You must use 0.0% and 4.0%. The other concentrations you use will be up to you,
however, keep in mind that some plants are very sensitive to salt.
o Do not use more than 8 different concentrations.
 List the concentrations of the salt solutions that you are using:
o 1. _____
2. _____
3. _____
4. _____
5. _____
6. _____
7. _____
8. _____
Formulate a hypothesis as to what you think is going to happen and explain why. (Use the “If, then,
because” format.)
 Hypothesis: _____________________________________________________________________
_______________________________________________________________________________
_______________________________________________________________________________
Design a table in which you will record your data, observations, and comments.
 Include the % of seeds that have germinated, not just a count of the seeds that have germinated.
Record your data, observations, and comments on your table over the course of the next week.
Construct two graphs of your final results. You must use the most appropriate graph type for each graph.
(If you are not sure which types are most appropriate, do some research to help you decide.)
 The first graph should compare the concentration of the salt solution with the number of seeds
that germinated.
 The second graph should compare the concentration of the salt solution with the % of seeds that
germinated.
Analyze your results and prepare your report (as outlined below) to be given to the farmers.
Report (conclusions):
o Your team will write a final report of your conclusions to be given to the farmers which must contain:
 A cover sheet with your experimental design, procedures, & equipment used.
 Be sure to identify your independent and dependent variables, your control, and your constants.
 Data tables.
 Graphs.
 Analysis of the graphs.
 Conclusions, based on your data, about how the crop grew under which conditions.
 Whether you accept or reject your hypothesis (and explain why).
 You must determine the salt concentration at which all seeds will still germinate (the “threshold
level of toxicity”), the salt concentration that is considered the LD-50 (lethal dose for 50% of the
seeds), and the salt concentration at which none of the seeds will germinate. (You may need to
do additional research to help you with defining some of the concepts.)
o Label these on your graph that compares the concentration of the salt solution with the
number of seeds that germinated.
 You must also make recommendations (which may involve additional research) as to:
o other “crops” that might be more tolerant of salt
o how to remediate the soil if the salt concentration reaches toxic levels
o alternative irrigation methods that might be less likely to cause salinization.
 Describe any errors that may have occurred and/or shortcomings in your design that would invalidate
your experiment. How might they be corrected?

Include citations for all outside sources you used during your research