Soil Salinization Lab
Objectives
To be able to determine how salinization affects the germination of various species of crop seeds and at
what salt concentration seeds will no longer germinate.
Introduction
Salt build up is an existing or potential hazard on almost all of the 42 million acres of irrigated farmland in
the United States. Worldwide, much of the unused arable land is in arid or semiarid regions where
irrigation will be needed to make these lands productive farmland. Water contains small amounts of salts
and minerals dissolved in it, and over time this salt accumulates in the soil. A small amount of salt in the soil
will not affect the germination and growth of crops. However, as salt concentrations increase, negative
impacts occur. Eventually salt concentrations will effect the germination of seeds. Salt kills germinating
seedlings by removing the water from their cells (osmotic water loss). Excessive salinity is presently costing
the United States billions of dollars in lost food crops.
In the vast Wetlands Water District in Central California’s San Joaquin Valley, which provides irrigation
water to 600,000 acres of farmland in western Fresno and Kings Counties, as many as 190,000 acres have
salinity levels that limit the growers choice of crop species. This usually means growing lower value, but
more salt tolerant species, such as cotton and sugar beets, if they are able to grow anything at all.
In this investigation, your team will be investigating the effects of Sodium Chloride (NaCl) on germinating
seeds. NaCl has a maximum solubility of 35.7 grams per 100 ml of water. It is known that ocean water
averages 3.5% concentration (3.5 grams per 100 ml of H2O). Tapwater has an average concentration of
0.005% percent salt (0.005 grams per 100 ml of H2O). Distilled water should not contain any salts.
Materials
Petri dishes
Paper towels
Tweezers
Balances
Ziploc bags
NaCl
Tap water
Distilled water
Test tubes
Label tape / sharpies
Graduated cylinders
Flasks and beakers for
mixing solutions
* Other equipment may be
available by request
Procedure
Farmers in the central valley of California have become increasingly concerned about the buildup of
salt in the soil and water. Farmers know that small amounts of salts in the soil and water will not
adversely affect the germination of their crops. But as salt concentration increases, negative impacts
occur. They are afraid that salt concentrations may eventually become so great that the seeds of some
crops may not germinate, but they do not know what those levels of salt concentration are.
Farmers of various crop species have gotten together and hired your company (you and your lab
partner) to investigate this problem for them. They want your company to do the research and present
them with data and analysis of that data (written and graphical) that shows the effect of salt
concentration on several possible crop species. Specifically they need to know the relationship
between salt concentration and the percentage of seeds that will germinate.
Conduct an experiment(s) that will address these farmers questions and produce a report for the them,
telling them how increasing concentrations of salt will effect the germination of their seed crops and
make recommendations for them based on the data you collect regarding irrigation methods and
remediation plans for already salinized soils. Groups will have 7 days to conduct their investigations
and gather their data (this should provide ample time for seeds to germinate if they are going to
germinate at all under the experimental conditions they are exposed to. Your completed report should
be written in the format presented for formal lab write ups in APES. Be sure to state your objectives for
your experiment and your hypothesis. Make sure your procedure meets the requirements for a welldesigned, controlled experiment. Thoroughly analyze (graphically) and discuss your results and how
they relate to your experimental objectives and hypothesis, as well as what this means for your clients,
the farmers of the central valley.
General Procedure for Germinating Seeds:
1. Fold paper towels into squares; and place one in each petri dish
2. Place seeds of your selected crop variety onto the paper towels, place a second folded paper
towel on top of the seeds in the petri dishes.
3. Wet the paper towels in each of the petri dishes with a known volume of each of the different salt
solutions.
4. Cover the petri dish with a lid to avoid evaporation and label the concentration of salt used.
5. Monitor your seeds daily, looking for signs of germination and to insure that the paper towels
remain moist.
6. Record germination data in a data table similar to the one shown below.
[NaCl]
(gm/100
ml)
Volume of
Solution
Used (mL)
Total
Number of
Seeds Used
% Germination
Day
1
Day
2
Day
3
Day
4
Day
4
Day
5
Day
7
Day
6
0
0.25
0.50
0.75
1.0
1.5
2.0
3.0
Guidelines for Designing a Successful Lab Procedure
 Remember that germinating seeds need to remain moist to germinate, but they will not germinate if
submerged in water. The more solution you use the more salt is applied to the seeds even if the
concentration is lower.
 Seeds germinate underground. It is dark underground. Temperature triggers germination, not light.
 Making very dilute solutions of known concentration is difficult to do accurately because of limited
precision in measuring such small quantities of solute. Instead, start with the most concentrated
solution assigned to you and perform serial dilutions to obtain more diluted solutions.
 Use % to express the concentrations of solutions you make (1 g dry mass solute /100ml of solution =
1% solution)
 Be sure to control any variables other than the salt concentration of the solutions used for watering
that may affect the germination of your seeds.
 Make careful observations. Display this information clearly in a table(s) as well as in a graph(s).
 Thoroughly analyze your results and what they mean.