The effect of varied diets on the nitrate concentration of the castings of Eisenia fetida after
vermicomposting
Samantha Galang, Peter Garcia, Thomas Welsh
Department of Biological Sciences
Saddleback College
Mission Viejo, 92692
Vermicomposting is a commonly practiced form of fertilizing by using worms to recycle
food scraps and other organic materials into a valuable soil product. The nutrients
consumed by Eisenia fetida the ideal species used in vermicomposting, are integrated into
the compost produced by these worms, which is then used as fertilizer. In this experiment,
nitrate concentration was measured after feeding the worms three different diets including
dead leaves, which represented brown matter, broccoli stalks, which represented green
matter, and a no-nutrient diet, which was pure mulch. After one week of feeding the worms
these diets, a nitrate test was conducted to test the nitrate concentration of the castings of
the worms. The result showed that our hypothesis, a diet consisting of brown matter would
produce more nitrates, was, in fact, incorrect, and the diet consisting of green matter
proved to produce more nitrates.
Introduction
Eisenia fetida is a type of annelid presiding
primarily in North America. It commonly
feeds on vegetation in un-tilled areas like
meadows and woods (Boyle, 1997). Their
consistent movement through the soil
provides the soil with nutrients and allows
water and air to get into the soil. E. fetida
can feast on dead leaves, manure, and other
organic matter in the soil in which they live.
Additionally, these “red wigglers” consume
food by pulling leaves into the mouth of its
burrow in order to let the leaves decay
(Gruner, 1978).
Red wigglers’ castings are regarded as a topquality fertilizer because of the lack of
pesticides incorporated into the soil and fed
to the worms. The organic product of these
worms, as a result of worm composting or
vermicomposting, is coveted due to the rich
nutrient content. Earthworm farms are
heavily invested in producing organic
fertilizer through the use of night crawlers.
Materials and Methods
Three containers of both male and female
red wigglers in soil were purchased from
PetSmart in Tustin, CA on April 14th, 2014.
Each container held 50 to 55 worms for a
total of 165 worms. The worms were
divided into three groups with 55 worms per
diet. Fifteen separate plastic containers were
purchased from Smart ‘n’ Final to house the
worms. Holes were created in the lids of the
plastic containers for ventilation purposes.
The different diets for the worms consisted
of green matter, brown matter, and mulch,
which served as the control group. Each diet
would be fed to fifty worms, with a total of
150 worms being tested. The fifty worms
were divided into five containers, equaling
ten worms per container.
In order to produce create the mulch
bedding for the worms while they were in
the plastic containers, newspaper was
shredded into pieces, no more than one inchthick, and dampened with water. The green
matter was produced by blending broccoli
stalks with water to break up the broccoli
into small, moist pieces. The brown matter
was produced by crushing dead leaves and,
once again, dampening with water for a
softer consistency.
Approximately 17.30 g of mulch was placed
into each of the fifteen containers. A group
of ten worms was weighed, and placed into
one container of mulch. This served as the
first control group (Group C1). Four more
groups of ten worms were weighed and
placed into containers, which resulted in the
remainder of the control groups (Groups C2
to C5). Approximately two to three grams of
green matter was placed into five more
containers with mulch. These groups were
titled Group V1 to V5. Approximately three
to four grams of brown matter was placed
into another five containers. Once again, the
mass of each group of ten worms was
obtained before placing them into the
containers. A sample of each diet, mulch +
green matter, mulch + brown matter, just
mulch, were obtained. Once all the
containers of worms were prepared, they
were left indoors to retain constant
temperature.
The castings of each group were obtained
for each group, and placed into their own
centrifuge tubes. For every gram of castings,
5 mL of 1M KCl was dispensed into the
centrifuge tube of castings. The tubes were
shaken at 100 rpm for ninety minutes, then
centrifuged for fifteen minutes at 3200 g.
Afterwards, the sample was decanted into a
10 mL test tube. Each sample was then
tested for nitrates using the LaMotte’s
testing kit. Using the color scale provided by
the nitrate test, each sample was interpreted
in terms of nitrate concentration (ppm).
Results
Using the LaMotte’s Nitrate test kit it was
shown that the level of nitrates was highest
in the green matter, followed by brown
matter, and the control held the least amount
of nitrates.
Diet
Control
Group
Brown
Matter
Green
Matter
Tube 1
0
Tube 2
0
Tube 3
0
Tube 4
0
Tube 5
0
1
1
1
2
1
2
2
2
1
1
Table 1. Comparison between three dietary
groups in parts per million (ppm). Green
matter yielded the most nitrates in the tubes,
while the control group yielded the least
amount of nitrates. La Motte’s Nitrate test
kit was used to make a comparison between
the three dietary groups.
We had expected that the Eisenia fetida
which were fed a diet of brown matter
would have castings that were more nitrate
rich.
We hypothesized this outcome
because the habitat of E. fetida generally
consists of the decaying vegetation which
exists in the upper soil levels (Paradise
2001). The results indicate that the castings
from the E. fetida that were fed the green
matter had a higher nitrate concentration.
We found that the casting in the green
matter had a higher average concentration of
nitrates than the brown matter castings by
0.4 ppm.
E. fetida are commonly used to help
break down dead organic organisms in a
process referred to as Vermicomposting.
The worms help to aerate the substrate and
their castings provide a nutrient rich
fertilizer of sorts. E. fetida are also known
to decrease microbial bacteria populations
while possibly increasing the efficiency of
microbial resource utilization (Scheu 2002).
Vermicomposting is a faster and safer
alternative to regular composting, which can
reach high temperatures. The fact that E.
fetida more efficiently recycles green matter
can allow for more efficient composting
through
the
implementation
of
vermicomposting.
Conversely,
these
findings could be used to try to mitigate
nitrate pollution by decreasing the nitrate
levels in the soil by removing the green
matter from the area. This finding could
also be used to artificially boost population
activity in microbial bacterial colonies.
As a supplement to this experiment it would
be interesting to isolate the species of
microbial bacteria that E. fetida affects, and
test how this species effects the nutrient
concentrations found in the soil.
Literature Cited
Boyle, K. E., Curry, J. P., & Farrell, E. P.
(1997). Influence of earthworms on soil
properties and grass production in reclaimed
cutover peat. Biology and fertility of
soils, 25(1), 20-26.
Gruner, B., & Zebe, E. (1978). Studies on
the
anaerobic
metabolism
of
earthworms. Comparative Biochemistry and
Physiology
Part
B:
Comparative
Biochemistry, 60(4), 441-445.
Paradise, C., 2001, A Standardized Soil
Ecotoxicological Test Using Red Worms
(Eisenia fetida), The American Biology
Teacher, v. 63(9), p. 662-668.
Scheu, S., Schlitt, N., Tiunov, A.,
Newington, J., and Jones, T., 2002, Effects
of
the
Presence
and
Community
Composition
of
Earthworms
on
MicrobialCommunity
Functioning,
Oecologia, v. 133(2), p. 254-260
Review Form
Department of Biological Sciences
Saddleback College, Mission Viejo, CA 92692
Author (s):
Samantha Galang, Peter Garcia, Thomas Welsh
.
Title: The Effect of Varied Diets on the Nitrate Concentration of the Castings of Eisenia fetida
After Vermicomposting
Summary
Summarize the paper succinctly and dispassionately. Do not criticize here, just show that you understood the paper.
Vermicomposting is a form of fertilizing utilizing worms because worms are able to recycle food scraps
and other organic materials into soil products. Eisenia fetida was used because their castings lack
pesticides, making it the ideal species that is used in vermicomposting. Investigators hypothesized that
the brown matter diet would yield a higher concentration of nitrates due to the resemblance in the
natural habitat of decaying vegetation. Investigators used three different diets to test for nitrate
concentrations; dead leaves blended with water, broccoli stalks blended with water, and mulch, each
representing brown matter, green matter and a no nutrient diet, respectively. 55 worms were assigned
to one of the three diets, but only 50 worms were fed from each group. The 50 worms for each diet type
were divided up into 5 different containers, with each container housing 10 worms and their respective
diets. Green matter diet consisted of ~17.30 g of mulch and 2-3 g of the green matter blend, the brown
matter diet consisted of ~17.30 g of mulch and 3-4 g of the brown matter blend, and the no nutrient diet
only consisted of mulch. Castings in each sample were obtained and were analyzed for their nitrate
concentrations. Nitrate levels for each sample were tested for using LaMotte’s testing kit. Green matter
diets produced higher concentrations of nitrates, which did not support the investigators hypothesis.
The results of this study indicate vermicomposting as an efficient composting method, and could be
used to decrease nitrate pollution by reducing the amounts of green matter in areas.
General Comments
Generally explain the paper’s strengths and weaknesses and whether they are serious, or important to our current
state of knowledge.
Strengths: Materials and methods are easy to follow and easy to comprehend. Investigators
also provided a lot of details in the procedure. Overall the paper is organized, easily understood
and flows well.
Weaknesses: The paper has some minor grammatical and formatting errors.
*Overall a good paper! Could expand in certain areas like the introduction and discussion.
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
Section
Title
Abstract
Introduction
Materials
and
Methods
Results
Discussion
Other
Formatting
This paper was a rough draft
Issue
Capitalize the title, besides prepositions like of, the, etc.
Italicize Eisenia fetida.
Could be lengthened, introduction is missing information like:
 Previous studies, previous findings
 Why are you testing for this?
 What is the hypothesis?
Date formatting: Day, Month, Year
Paragraph 2, Sentence 1 is not easy to follow
“In order to produce create the mulch … “
Table caption should be above the table with a smaller sized font than the text in
the actual journal.
Provide the means of nitrate concentrations from each group to show the
difference of 0.4 ppm. (I had to calculate it myself to see that brown matter had
an average of 1.2 ppm and green matter had an average of 1.6 ppm)
No distinguished discussion section, Paper is missing the discussion heading
Headings should be bold
No columns according to peer review page
Single space between names and department information
Literature
Cited
In text citations (Introduction, Discussion) should include all authors involved in
the literature
Need 6 more references for the minimum of 10 citations.
Recommendation
 This paper should be published as is
 This paper should be published with revision
 This paper should not be published