The Impact of Organic Soil on Growth Rate and Average Yield of Wisconsin Fast Plants
Sheena Forsberg and Christopher Thompson
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
Rapid Cycling Brassica rapa (AKA, Wisconsin Fast Plant) is a cruciferous plant, which is
known for its resilience and ability to adapt to various types of growth mediums as well as its
ability to complete its entire life cycle in a relatively short period of time. RC B.rapa is well
acclimated to grow in a laboratory environment in which it receives constant fluorescent light
and constant access to water. As such, it is an excellent candidate to test the effectiveness of
various growth mediums. The hypothesis being tested is that employing the use of organic soil
as a growth medium instead of conventional soil will result in a higher rate of germination, a
higher average flower yield, overall height, and cotyledon width. In this experiment all
measurements were obtained after the plants had grown for a period of two months in their
respective growth mediums: OSH potting soil mix and Edna’s Best Organic Potting Soil. The
conventional soil resulted in a germination rate of 97.2% with average height of 8.57cm, the
average flower yield being 4, and the mean cotyledon width as 1.72 cm. The organic soil had a
rate of 100% germination with the following results: (;) average height 7.87cm, average flower
yield 3 cm and the mean cotyledon width was 1.11cm. Results concluded that overall there was
no statistical difference between the two mediums with the exception of cotyledon width in the
conventional soil. According to the t-tests there was a significant difference between the
conventional soil and the organic soil with respect to cotyledon width (p= 3.26313E-20) as well
as number of flowers (p= 0.00045796).
Introduction
Rapid Cycling Brassica rapa is a member of the Cruciferous family of plants, and is therefore well
adapted to grow under many environmental conditions. One key growth factor is the RCBr’s ability to grow
under constant fluorescent light as opposed to sunlight which allows for greater flexibility in laboratory
studies. In addition to this RCBr has a rapid life-cycle which makes them an ideal test subject, as their lifecycle
completes in approximately 45 days after sowing (what’s this?) (Kelly 2004). Due to its rapid lifecycle, the
potential applications of RCBr to experimental plant biology are diverse (Kelly 2004; Musgrave 2000). RCBr
was used in this experiment to test which type of soil is best suited to produce the most positive results of
various plant growth factors of this member of the Crucifer family (Stephens and Kostewicz 2009). According
to Duke (who?) RCBr requires relatively low nitrogen levels (Duke 1978), and a high turnover margin requires
relatively low quality fertilizers as suggested by Wu (Wu 1972). Therefore it was believed that the organic soil
would prevail in producing the most favorable results. However according to a 21twenty-one- year study
conducted in central Europe, it was found that “nutrient input (N, P, K) in the organic systems to be 34 - 51%
lower than in the conventional systems, whereas mean crop yield was only 20% lower over a period of 21
years” (Maeder, et al. 2002). Additionally it was found that soil pH was slightly higher in the organic systems
(Maeder, et al. 2002), which is a factor believed to benefit RCBr (benefit how?) (Carolinalabs.com 2009).
This experiment was performed in order to determine whether there is a significant difference when growing
plants, in this case Rapid Cycle Brassica rapa (RCBr), in organic soil as opposed to conventional soil
containing chemical fertilizers. It is predicted that the RCBr grown in the organic soil will have more total
germinators, taller plants, wider cotyledon widths and more flowers per plant than those in the conventional
soil group.
Materials and Methods
Two bags of soil were purchased at Orchard Supply Hardware, a conventional potting soil (OSH
Fertilized Potting Soil) and one fully organic potting soil (E.B. Stone Edna’s Best Potting Soil). Seeds of
Brassica rapa were purchased online through Carolina Labs. Two growing trays and fluorescent lighting were
also obtained. 12 (2 Or 12?) wells (what are wells?) of each tray were lightly packed with damp soil, one tray
with conventional soil, the other with organic soil. Each well of each tray was then implanted with three B.
rapa seeds at a depth of .6 cm (Day 0, September 26th, 2009). The two wells were then placed under constant
fluorescent lighting, indoors, with constant temperature and humidity, and constant water in each tray. What
happened to the other wells? Observational were then taken each day until each group flowered. Upon
flowering, (Day 22, October 17th, 2009) measurements were taken using a centimeter ruler of;(don’t need
semicolon) height from soil to top of plant (n=35, n=39 (conventional, organic)), the average of two cotyledon
widths per plant (n=35, n=37), and the number of flowers on each plant (n=35, n=39). The average height,
average cotyledon width, and average number of flowers per plant per cell were then analyzed statistically
through an unpaired, one-tailed t-test.
Results
The mean height for RCBr in conventional soil is 8.574  0.345 cm ( S.E.M, n=35), while the mean
height for RCBr in organic soil is 7.87  0.317 cm (n=39, Figure 1); running an unpaired, one-tailed t-Test for
these data yields no significant difference between the two groups (p= 0.067662). The mean cotyledon width
for RCBr in conventional soil is 1.72  0.0371 cm (n=35), and the mean cotyledon width for RCBr in organic
soil is 1.11  0.0270 cm (n=37, Figure 2); Running an unpaired, one-tailed t-Test one these? data obtains a
significant difference between the two groups,; cotyledon width in conventional soil being greater than that of
those in organic soil (p= 3.26313E-20). The mean number of flowers for RCBr in conventional soil is 4.08 
0.423 flowers (n=35), while the mean number of flowers of RCBr in organic soil is 2.51  0.115 flowers
(n=39, Figure 3). Running an unpaired, one-tailed t-Test on these data obtains a significant difference between
the two groups, the number of flowers on plants grown in conventional soil greater than that of those grown in
organic soil (p= 0.00045796).
Figure 1. Mean height of RCBr grown in conventional soil (8.574  .345 cm ( S.E.M, n=35) and organic soil
(7.87  .317 cm (n=39). (p= .067662).Is there a difference? What is the graph saying? What is the x axis?
Figure 2. Mean cotyledon width of RCBr grown in conventional soil (1.72  .0371 cm (n=35) and organic soil
(1.11  .0270 cm (n=37). (p= 3.26313E-20). I still don’t know what this graph is telling me…loose the 1 under
the x axis. What is the x axis?
Figure 3. Mean number of flowers of RCBr grown in conventional soil (4.08  .423 flowers (n=35) and
organic soil (2.51  .115 flowers (n=39). (p= .00045796).remove the 1 under the x axis, what is it?
Discussion
The data and results show that there is a difference in all categories tested between the two groups,
organic soil germinating in 100% of seeds planted, while conventional only 97.2%, and conventional soil
yielding plants with greater averages in the other three categories. (run-on/confusing sentence) However,
regarding height and ability to germinate, there was no significant, statistical difference between the two
groups, therefore, in the two categories with statistical differences, conventional soil proves to be the better
growth medium. The RCBr grown in conventional soil had cotyledons which excessively outsized those grown
in organic soil, and the number of flowers in the conventional soil group also outnumbered those in the organic
soil group. In the case of this experiment, the hypothesis being tested was incorrect, and proved wrong (don’t
need this). The conventional soil is made specifically for this reason, to be a better substitute for organic soil.
Even in B. rapa, which requires low nutrient levels and is easily sustainable, the conventional soil allowed for
better growth. Other than the growth medium, all variables in this experiment were kept equal (consistent?)
except for one; the pH content of each soil. Because B. rapa is assumed to grow better in a higher pH
environment (Carolinalabs.com 2009), the greater pH of the organic soil did not affect the hypothesis. If this
experiment were to be expanded on, however, soil pH should be equal and the null hypothesis assumed.
Literature Cited
CarolinaLabs.com. “Wisconsin Fast Plants.” Carolina Biological Supply Company. 2009.
Duke, J.A. 1979. “Ecosystematic data on economic plants.” Quart. J. Crude Drug Res. 17(3-4):91-110
Kelly, Martin G. “Education Resources Information Center.” Demonstrated Ways to Use Rapid Cycling
“Brassica rapa” in Ecology Instruction and Research. 11 2004.
Stephens, J.M., and S.R. Kostewicz. Producing Garden Vegetables with Organic Soil Amendments. July 2009.
Wu Leung, Woot-Tseun, Butrum, R.R. and Chang, F.H. Part I. Proximate Composition Mineral and Vitamin
Contents of East Asian Foods. Oxford University Press 1972.
Review Form
Author (s):_ Sheena Forsberg and Christopher Thompson _____
Title:_ The Impact of Organic Soil on Growth Rate and Average Yield of Wisconsin Fast Plants_________
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
The idea of the experiment was to find if there was a difference in growth, flowering, and germination of
the RCBr plants when in contact with either organic soil or the conventional soil. Because this plant was
able to thrive off of various kinds of earth, the investigators thought it was a good choice to experiment
with. This particular plant also made it easy on the investigators because of its ability to live under
constant fluorescent light indoors. The background information provided the reader with knowledge
about how conventional soil was made up of a great deal more nutrient percentage than organic soil.
The investigators hypothesized that there would be a significant statistical difference in the height and
width growth of the RCBr’s, as well as the number of flowers. The plant seeds were planted in wells
(don’t know what those are) and left to grow. Four plants were tested, two in the conventional soil and
two in the organic. They were then allowed a two-month growth/reaction period before results were
observed and then recorded. It was then found that there was no significant difference in the growth
values statistically. But the difference that was there told the authors that the conventional soiled plants
were more successful in the height, width and flower growth. The original hypothesis was claimed to be
incorrect. The germination percentage was also higher for the conventional soil.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current
state of knowledge.
The paper was pretty good at explaining what they did, how and what their results were. But I got the
sense that the investigators themselves were a little confused as to how to use certain punctuation.
Semicolons were used inappropriately and were completely missing when needed. I found no spelling
errors but did get confused when the wording dragged on or sometimes just didn’t make sense. It was
as if the authors were trying to make their sentences longer and just thought to break them up with a
“however…” here and there. Other times, the authors just added a rewording at the end of the
sentence. A few sentences were just too long and wordy to understand. When referencing, the authors
used the reference’s name in the sentence, and then at the end of the sentence put the year of the
source in parenthesis. The sources in the works cited page were fine. The figures didn’t have any title
for the x axis, and the figure captions explained very little for the reader to understand. All of the
background information was clear and easy to understand. But there was a difference in the hypothesis
mentioned in the abstract and the information section, whether it was meant to be different or was just
worded differently I couldn’t tell.
Technical Criticism
Review technical issues, organization and clarity. Provide a table of typographical errors, grammatical errors, and
minor textual problems. It's not the reviewer's job to copy Edit the paper, mark the manuscript.
This paper was a final version
This paper was a rough draft
Several run-on sentences provided confusion for the reader. Other words noted in red were either
misused or not needed. Every other correction in red is explained in parenthesis.