The battle between deicers and grass
Chris Dekker and Myrna Kelfkens
RSG Enkhuizen, The Netherlands
13 April 2011
Summary
Road salts are often spread during the winter to deice the roads. The principle of this process is that they lower the
freezing point of water. The downside of road salts are their harmful effects on many plants. The salts withdraw water
from the plants by osmosis, which leads to dehydration. Our inquiry question is: Which of the following deicers is the
least harmful for the growth of grasses: sodium chloride, magnesium chloride, calcium acetate or urea? Comparison of
the growth of grass treated with the aforementioned deicers showed that calcium acetate and magnesium chloride could
be a promising alternative for road salt. Further research is necessary before these salts could actually be used.
Introduction
When it freezes in the winter, people often spread salt on
the roads to prevent them from getting slippery. These
road salts mix with the snow and ice, which leads to a
lower freezing point.
Road salts have disadvantages. For example, it makes the
soil next to the road salty. This has negative effects on
many plants.
Most plants can’t tolerate high concentrations of salt. Salt
often causes reduced growth or even the death of the
plant. The cause of this is osmosis. Salt withdraws water
from the leaf and from the soil, which causes dehydration
of the plants.
There are many different types of deicers, such as sodium
chloride (NaCl), magnesium chloride (MgCl2), calcium
acetate (CaC4H6O4) and urea ((NH2)2CO). Sodium chloride
is used the most often, but this salt has negative effects on
plants. Calcium acetate and urea are said to be more
environmentally friendly.
Our inquiry question is: Which of the following deicers is
the least harmful for the growth of grasses: sodium
chloride, magnesium chloride, calcium acetate or urea?
Our hypothesis is that urea and calcium acetate are the
least harmful for the grass. Urea is a fertilizer and calcium
acetate is mentioned a lot as a more environmentally
friendly road salt, so we expect that these salts are less
damaging for plants.
Experimental design
Before we conducted the actual experiment, we did two
preliminary experiments.
The goal of our first preliminary experiment was to
determine which type of grass was the most suitable for
our research. We tested ordinary grass seeds, cat grass
that had already grown and cat grass seeds (not yet
germinated). The result of this experiment was that the cat
grass seeds were the most suitable, because they grew
very fast. This cat grass is barley, which is a type of grass.
The goal of our second preliminary experiment was to
determine a suitable concentration for the solutions of the
deicers. According to an internet source, grasses can grow
normally at a salt concentration of 2000 ppm. We decided
to choose a slightly higher concentration (3000 ppm),
which we tested on 5 cups with cat grass seeds. 3000 ppm
turned out to be not high enough (the grass could still grow
quite normally). This is why we chose a higher
concentration for the actual experiment.
For the main experiment we made solutions with a
concentration of 4000 ppm. We weighed 2 grams of every
substance and dissolved this amount in 500 ml water,
using volumetric flasks of 250 ml. We wanted to test
solutions of the 4 aforementioned substances and also a
cup with water, so for our experiment in triplicate, we
needed 15 cups, each filled with 20 grams of cat grass
seed.
We gave a different solution to every three cups:
1.
2.
3.
4.
5.
Water (H2O)
Sodium chloride (NaCl)
Magnesium chloride (MgCl2)
Calcium acetate (CaC4H6O4)
Urea ((NH2)2CO)
According to the packaging of the cat grass seeds, we had
to give each cup 65 ml of the corresponding solution on
the first day. We measured this with a measuring cylinder
of 100 ml. During 14 days, we gave each cup 10 ml of the
right solution every other day. We measured this with a
measuring cylinder of 10 ml. During the first four days, we
observed qualitative developments in germination. Starting
day 5, we measured the average height of the grass in
each cup. The cups were put in front of the window and
the tray was turned 180 degrees every day, so that every
cup would get an equal amount of light.
The independent variable of our experiment was the
substance that we dissolved (H2O, NaCl, MgCl2,
CaC4H6O4 or (NH2)2CO)). The dependent variable was the
height of the cat grass. The control variables were the
temperature, the amount of light and the amount of
solution that we gave the cups. We kept this variables
constant.
Results
During the first four days of our experiment, the grass
hadn’t grown yet. On these days, we observed qualitative
changes. On day 2, the growth of the roots began. The
grass which had been treated with water was the fastest
during this process and sodium chloride was the slowest.
On day 4, in all treatments the first leaf appeared, with
exception of the cup with sodium chloride. The leaves in
the cups with water and urea were further developed than
the other treatments.
During the further growth of the grass, we saw that the
cups with urea began to fall behind compared to the rest of
the cups. There was also water on the bottom of those
cups and there was a rotting smell.
On day 5, we started measuring quantitative changes. The
subjoined table shows the average height of the grass in
the cups (with mean deviations). The zeros on day 4
indicate that the seeds hadn’t germinated measurably yet.
Day
number
Day 4
Day 5
Day 6
Day 7
Day 8
Day 9
Day 10
Day 11
Day 12
Day 13
Day 14
H2O
0
2,17 ±0,223
3,30 ±0,267
5,70 ±0,267
7,20 ±0,533
7,70 ±0,467
9,87 ±0,690
10,2 ±0,533
11,0 ±0,767
11,5 ±0,833
11,8 ±1,07
NaCl
0
1,57 ±0,290
2,33 ±0,110
4,83 ±0,510
5,83 ±0,177
6,50 ±0,267
9,23 ±0,423
9,67 ±0,377
10,3 ±0,500
10,8 ±0,500
11,2 ±0,367
Average height (cm)
MgCl2
CaC4H6O4
0
0
2,30 ±0,133
1,23 ±0,043
2,87 ±0,090
2,50 ±0
5,90 ±0,133
5,37 ±0,510
7,70 ±0,200
6,77 ±0,777
9,40 ±0,800
8,77 ±0,777
10,6 ±0,100
10,1 ±0,667
11,1 ±0,100
10,5 ±0,633
11,7 ±0,233
11,3 ±0,700
12,1 ±0,367
11,7 ±0,900
12,5 ±0,367
12,0 ±0,967
Average height (cm)
The average height of the grass in the cups is also
presented in the following graph. We left out the first 3
days, because the seeds hadn’t germinated yet during
those days.
Starting day 10, the differences between the treatments
remained the same. The order of the leaf height was (from
low to high): urea, sodium chloride, water, calcium acetate
and magnesium chloride.
13
12
11
10
9
8
7
6
5
4
3
2
1
0
H2O
NaCl
MgCl2
CaC4H6O4
(NH2)2CO
4 5 6 7 8 9 10 11 12 13 14
Day number
Discussion and conclusion
We observed a difference in the effects of the solutions
between the first and second phase of germination.
In the first phase (the appearance of roots), the salts
slowed down the germination. The best results were
obtained with water and sodium chloride retarded
germination the most. Because water, light, oxygen and an
appropriate temperature are the only requirements for
germination, it is likely that salt affects the water uptake
and slows down germination. We only observed qualitative
changes. Quantitative measurements of the germination
may confirm these results.
In the second phase (the leaf growth), the best results
were obtained with magnesium chloride, calcium acetate
and water. Magnesium chloride seems to give the best
result. An explanation for this could be that magnesium is
an important fertilizer. There doesn’t seem to be a
significant difference between calcium acetate and water.
Magnesium chloride and calcium acetate are therefore
(NH2)2CO
0
2,07 ±0,180
2,43 ±0,377
4,37 ±0,790
5,73 ±1,31
6,73 ±1,31
7,73 ±1,31
8,40 ±1,20
9,13 ±1,04
9,57 ±1,11
10,2 ±1,23
promising alternatives for road salt.
The effect of sodium chloride is as expected: compared to
water, it reduces the growth of the grass. The growth with
urea is clearly the most retarded. It seems like urea slows
down the water uptake. An explanation for this could be
that urea can immediately be used to produce proteins, so
the plant doesn’t have to uptake extra water to correct the
osmotic pressure. Therefore, there was water on the
bottom of the cups. This caused rotting, which affected the
growth even more. Although urea can be used as a
fertilizer, it is known that the concentration can easily get
too high. This is confirmed by preliminary experiment 2,
where we used a lower concentration (3000 ppm), and in
which urea did best. Since the concentration of urea can
easily get too high, urea isn’t very suitable as a deicer.
Our hypothesis was that urea and calcium acetate would
be the least harmful for the grass. The results show that
urea isn’t a good alternative for road salt. Calcium acetate
could be a promising alternative. Further research has to
show what the effect of other concentrations of calcium
acetate is, before this salt could be used as an alternative
for road salt.
Evaluation
For a more valid conclusion, more repetitions of the
experiment are needed. The control variables should also
be kept even more constant by using an incubator and a
lamp instead of sunlight.
Further inquiry questions could be: What is the salt
tolerance of different plant species?, What is the influence
of the deicers: sodium chloride, magnesium chloride,
calcium acetate and urea on only the germination of the
plants?, In which concentration is urea not damaging for
plants and good enough to melt ice?
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