46 | Fine Focus

Effects of Vermicompost and Beneficial Microbes on 
Biomass and Nutrient Density in Purple Lady Bok Choy 

(Brassica rapa var. chinensis) in A Vertical Hydroponic Grow 
Tower System

Chelsea Pearson
(temperance@rocketmail.com)

Rochelle Gawel
(gawelrochelle@gmail.com)

Donna M. Maki
(donmaki@nmu.edu)

Department Of Biology, Northern Michigan University 
Marquette, MI



Vol 9 | 47

Abstract 
Indoor food production in vertical 
hydroponic systems can be done year-
round in any climate, has less negative 
environmental impacts compared to 
industrial agriculture and is a way of  
increasing the nutritional value of  crops. 
Indoor hydroponic systems make it easy 
to control the precision of  additives and 
amendments, such as fertilizers and 
vermicompost tea, to nutrient solution 
reservoirs. Vermicompost tea is known to 
contain beneficial microorganisms and 
can help increase the biomass, nutrient 
density, and overall health of  the plants. 
Microorganisms and plants have co-evolved 
and is an essential relationship that deserves 
recognition and further research. The goal 
of  the research presented in this paper was 
to better understand if  vermicompost tea 
and its associated microorganisms, such as 
bacteria, fungi, nematodes, and protozoa, 
would increase biomass and nutrient 
density of  Purple Lady Bok Choy (Brassica 
rapa var. chinensis) in vertical hydroponic 
systems. Statistical analyses were performed 
to compare the biomass and macro- and 
micronutrients of  three different treatments 
to one another and a control. There was 
a significant difference between the mean 
leaf  and root biomass among varying 
concentrations of  vermicompost tea 
solutions and added inorganic hydroponic 
fertilizer. The nutrient density for both 
macro- and micronutrients also differed 
significantly due to different concentrations 
of  vermicompost tea, suggesting that 
beneficial microbes may help plants uptake 
and absorb nutrients in a more efficient 
manner depending on the concentration of  
vermicompost tea and hydroponic fertilizer.



48 | Fine Focus

Introduction
Year-round growing of  crops in a variety of  
climates is not possible using conventional 
agricultural practices. Current industrial 
agricultural methods can also have a 
negative impact on the nutritional content 
of  food and the health of  the soil and 
the ecosphere (6). Moreover, interest in 
consumption of  locally grown food has 
risen with mounting evidence of  many 
associated benefits. Benefits of  locally grown 
food include but are not limited to; the 
reduction in overall production costs due to 
eliminated long-distance transportation and 
the need for long-term storage, increased 
nutrient density, taste profiles, texture, and 
freshness (8). Vertical hydroponic plant 
growth systems provide alternate means 
for food production and have potential 
to increase the amount of  locally grown 
food in many communities. Additionally, 
vertical hydroponic systems could easily be 
integrated into the average household and 
provide families in any climate with healthy 
food. Vertical hydroponic systems demand 
less space, input of  resources and are a more 
sustainable method of  agriculture compared 
to industrial agricultural practices that are 
dominant in the United States (3, 7, 13). 
Indoor agriculture and the use of  vertical 
hydroponic grow towers, which is soilless 
by nature, provides solutions to problems 
surrounding food production.

There are two fundamental systems 
for growing plants: in soil and soilless 
media. Plants in common horticulture/
agricultural systems are typically fed with 
either inorganic/synthetic nutrients or 
organic/biological nutrients. The goal of  
using both inorganic and organic nutrients 

in horticultural/agricultural systems is to 
grow healthy plants with the least amount 
of  input required and for as many months 
as possible. In systems in which biological 
nutrients are used, the nutrients are 
processed by living microorganisms which 
aids in the nutrient uptake by the plants (14). 
Plants and microorganisms have co-evolved 
and have formed an essential symbiotic 
relationship, whereby microbes increase 
mineral availability and uptake by the 
plants thus increasing the nutrient density. 
The beneficial symbiotic relationship 
between plants and microorganisms was the 
pinnacle of  the research presented, as living 
organisms were present in the vermicompost 
tea used for this research which had a variety 
of  beneficial fungi, bacteria, protozoa 
(flagellates, amoebae, and ciliates), and 
nematodes (Table 1). 

Plants grown in hydroponic systems are 
typically isolated from their microbial 
partners, which would naturally be found in 
soil. Isolation from symbiotic microbes may 
be a decided disadvantage to plant growth 
and health. Results from animal studies have 
demonstrated the profound negative impact 
the absence of  symbiotic gut microbes can 
have on animal health and development (9). 
The Fraune and Bosch study (2010) reflects 
the fact that symbiotic organisms, such as 
plants and microbes, could be negatively 
impacted when deprived of  their symbiotic 
microbial partners. Additionally, microbes 
help plants by producing nutrients (e.g., 
nitrate), plant hormones, and behaving as 
biocontrol agents. Microbes are capable of  
chemically communicating with their plant 
host, stimulating the plant’s immune system, 
and aiding in the defense against pathogens 
(4, 5).



Vol 9 | 49

Numerous studies of  plants grown in 
soil demonstrate the positive impact 
microbes can have on influencing the 
plants’ physiology and health (12, 15, 18). 
“Vermicomposting” (worm composting) is 
defined as a process in which earthworms 
play a major role in conjunction with 
microbes in the conversion of  organic 
solid waste into a form of  a stabilized 
soil conditioner. Vermicompost is a 
nutrient-rich compost which has macro- 
and micronutrients and contains high 
populations of  diverse, beneficial microbes 
(1, 24). Vermicompost tea is a ‘brewed’ 
leaching process for extracting key nutrients 
and microbes in worm castings into a water 
solution. In a soil-based study done by 
Pant et al. (2009), they found the addition 
of  vermicompost tea increased macro- 
and micronutrient uptake, phenolics, and 
carotenoids in the plant’s tissue (20, 24). 
Furthermore, vermicompost is available 
commercially and would be relatively 
easy for the indoor-grow enthusiast to 
incorporate into their ‘gardening’ practices. 

Unfortunately, little evidence-based 
information exists regarding the addition of  
vermicompost tea and the associated benefits 
it may have on plant tissue in hydroponic 
systems.

 Studies assessing the addition of  beneficial 
microbes to hydroponic systems tend to 
focus on their use as biocontrol agents 
to combat plant pathogens (16). Could 
microbes be harnessed to provide benefits 
beyond reducing disease? The goal of  the 
research conducted for this study was to 
better understand whether vermicompost 
tea and its associated microorganisms would 
increase biomass and nutrient density of  
Purple Lady Bok Choy (Brassica rapa var. 
chinensis) in vertical hydroponic systems. The 
rationale for choosing vermicompost as 
the source of  beneficial microbes is due to 
its typically high populations and diversity 
of  microbes, which has shown to benefit 
plants in a myriad of  ways (1, 4, 15, 16, 20). 
Purple Lady Bok Choy was chosen due to its 
versatility, physiology, life cycle and stature. 

Vermicompost Detail Summary
Organism Result Units Desired 

Level
Flagellates 106,214.36 number/g >10,000
Amoebae 19,181.31 number/g >10,000
Ciliates 32.28 number/g >1254
Nematodes 28.31 number/g >10
Bacterial 28.31 number/g >10
Active Bacteria 109.54 µg/g >3
Total Bacteria 2,118.75 µg/g >300
Active Fungi 87.76 µg/g >3
Total Fungi 3,478.17 µg/g >300

Table 1: Vermicompost detail summary analyzed by Soil Foodweb New York, analyzed June 17, 2019.



50 | Fine Focus

It can be eaten fresh in salads, grilled, 
sautéed, fermented, or dehydrated. It is also 
known to have high levels of  Vitamins C, A, 
B6, calcium, iron, potassium, manganese, 
folate and is high in antioxidants due to an 
abundance of  anthocyanins (24, 25, 26). Not 
only are the anthocyanins responsible for 
the aesthetic purple coloration of  the Purple 
Lady Bok Choy variety, but the pigments 
are also linked to the reduction of  multiple 
diseases such as cardiovascular disease 
and cancer (24, 26). It has minimal heat 
and light requirements, was manageable 
within the given research space, has a quick 
germination rate and takes little time to 
reach full maturity, making this variety an 
ideal candidate for the indoor hydroponic 
research. The research tested and compared 
different concentrations and ratios of  
vermicompost teas and hydroponic fertilizer 
solutions. The prediction was that the 
addition of  the vermicompost tea would 
increase the nutrient density and overall 
biomass of  Bok Choy hydroponic systems. 

Materials & Methods
Seedling Preparation:

A total of  one hundred-twenty rockwool 
cubes with a two-inch diameter were used 
per treatment. In each cube a total of  three 
Purple Lady Bok Choy, Brassica rapa var. 
chinensis seeds were planted surrounded by 
Geolite (an irregularly shaped clay medium, 
Hydrofarm LLC), and nestled in two-inch 
net pots. The net pots were placed into trays, 
each tray associated with a specific tower, 
and covered with a clear plastic dome until 
the seeds were germinated. The Purple 
Lady variety of  Bok Choy is a cool weather 
species, is shade tolerant, germinates in 2-4 

days, grows 5-7” and can grow to maturity 
in 60 days. All the above factors made 
Purple Lady Bok Choy an ideal candidate 
for the indoor hydroponic research because 
it has minimal heat and light requirements, 
was manageable within the given research 
space, has a quick germination rate and 
takes little time to reach full maturity. 

For the first two weeks, the seedlings were 
watered with pH balanced tap water (pH 
6.0 - 6.5). After approximately three weeks 
of  growth, the seedlings were watered with 
a 1.25 grams per liter MaxiGro Hydroponic 
Nutrient solution (N-10, P-4, K-14). The 
germination took place under full spectrum 
LEDs on tiered “grow racks” on which the 
seedlings were grown for 30 days. After these 
30 days of  initial growth, the net pots were 
transferred to the vertical hydroponic grow 
towers (20 net pots per tower) and grew for 
an additional 30 days until they reached 
maturity and were ready to harvest.

Vermicompost Tea Preparation: The 
vermicompost used for the vermicompost 
tea was procured from Carney’s Crawlers 
LLC, Appleton, Wisconsin. The microbial 
composition of  the vermicompost was tested 
and verified by Soil Foodweb New York on 
June 17, 2019 (Sample # 03-12178) using 
direct count and the Differential Interface 
Contrast (DIC) microscopy technique 
(Table 1). DIC microscopy was also used 
to determine the probable number of  
protozoa using four replications of  a serial 
dilution of  10-1 to 10-6. The direct count of  
active bacteria and active fungal organisms 
was done using a fluorescein diacetate 
stain and counted under a fluorescent 
light. Nematodes were identified based 



Vol 9 | 51

on morphology and the population was 
determined by direct count method. The 
total bacterial count was determined using 
a fluorescein isothiocyanate stain and DIC 
technique. The living organisms in the 
organic matter/soil particles were stained 
using fluorescein isothiocyanate, strained 
through a syringe filter and directly counted.

The vermicompost tea solution 
was prepared by using 1.5 L of  the 
vermicompost which was “brewed” in 16 
L of  pH balanced water (pH 7), in 5-gallon 
food-grade buckets. A paint strainer 
was used as a “tea bag” to separate the 
vermicompost from the water. The solution 
was constantly aerated with large (4 inches 
long and 2 inches in diameter) air stones 
(Model ASC-100, Pawfly Co), which helped 
to oxygenate the water and encouraged 
the growth of  the beneficial bacteria and 
fungi. After the vermicompost tea brewed 
for 24 hours, two tablespoons of  unsulfured 
pure blackstrap molasses (‘Slow As’ brand) 
was added to feed the microorganisms that 
were extracted into the water from the 
vermicompost. The solution was aerated 
for an additional 24 hours before it was 
transferred to the vertical hydroponic towers.

Hydroponic Tower Design:

There were three modular units, each 
supporting two grow towers (made from 
PVC pipes and PVC fence posts), for a total 
of  six grow towers. Two of  the modules 
(with two towers each) were placed parallel 
to each other, while the third unit (with two 
towers) was placed perpendicular to the 
parallel modules which all together covered 
approximately 32 square feet (Figure 1). 

One grow tower housed 20 plants, for a total 
of  120 plants for all three modular units. 
The towers were equipped with a water 
pump (Bayite BYT-7AO15 DC 12V Solar 
Hot Water Heater Circulation Pump with 
DC Power Supply Adapter) that moved the 
solutions to the small reservoirs at the top 
of  the towers. The solutions trickled down 
via gravity feed and subsequently covered 
(‘showered’) the roots of  the plants in a 
consistent manner. PVC pipes were used 
as vertical support poles for each of  the 6 
LED strips (T8 LED Grow Lights, 4 feet, 
providing full-spectrum sunlight replacement 
at 400 nm - 800 nm, Monios-L Co.) and 
provided overall support for the units.

Experimental Treatments:

Each treatment was executed consecutively 
through implementation of  all 6 towers at 
once. The utilization of  all six towers for 
each treatment at the same time helped 
maintain efficiency and consistency of  
said treatment. The number of  towers, 
6, provided the minimum number of  
repetitions necessary for proper statistical 
analysis. Each tower had a 16 L solution 
reservoir (5-gallon bucket). The control 
was prepared with 1.25 grams of  mineral 
solution (General Hydroponics, MaxiGro 
hydroponic nutrients) per liter of  water. 
Treatment one consisted of  0.625 grams 
of  mineral nutrients per liter and ~25% 
by volume vermicompost tea. Treatment 
two was made with 1.25 grams of  mineral 
nutrients per liter and ~25% by volume 
vermicompost tea solution. Treatment three 
was a solution composed of  0.625 grams 
of  mineral nutrients per liter and ~50% by 
volume vermicompost tea. The temperature 



52 | Fine Focus

Fig 1: Design layout of the three modular units which housed the six vertical grow towers that were 
surrounded by six strips of LEDs each. The photo was taken in Weston Hall, room 1208, at Northern 
Michigan University, in Marquette, Michigan, where the experiment was conducted from September 
2020 - March 2021.



Vol 9 | 53

of  the reservoir solutions was periodically 
measured and recorded. The solutions 
of  each treatment were added alternately 
when the reservoirs were approximately 
4-6 liters depleted. The reservoirs were
completely emptied and refilled with fresh
solutions approximately halfway through
each growth cycle, which was ~15 days,
except for treatment three. During treatment
three an experimental error occurred
where the reservoirs were refilled on day 28
rather than the 15-day time that had been
previously done in all the other treatments.
The pH was regularly checked and adjusted
to ~6.0-6.5 by using General Hydroponics
pH adjustment chemicals. The plants were
grown in the towers for 30 days, at which
point they were mature and harvested.
The plant biomass was dehydrated at
60°C (140°F) in dehydration ovens. The
dehydrated biomass was used to determine
the dry weights of  the leaves/petioles and
roots (the initial weight of  the rockwool
was deducted from the weight of  the roots)
which was used as a ‘dry weight method’
to perform proper statistical analysis. All
equipment was cleaned with hydrogen
peroxide solution (using ~2 tablespoons
of  3% hydrogen peroxide per 1 gallon of
water) and set up for the next treatment.

Plant Nutritional Analysis & 
Sample

Preparation:

Before the plants were harvested, six leaves 
were taken from each tower at random (as 
per the laboratory technician’s instructions) 
and immediately sent to A & L Great 
Lakes Laboratories (Fort Wayne, IN) where 

the nutritional density of  the plant tissue 
was analyzed. The samples were shipped 
via UPS, unrefrigerated. Once the plant 
tissue was received by the laboratory, the 
samples were dried overnight at 100-105°C. 
The dried tissue was ground with a Wiley 
Mill Grinder and sieved through 20 mesh 
screens. The plant tissue was tested for a 
variety of  macro- and micronutrients (Tables 
2 and 3). Total nitrogen was analyzed using 
the Dumas method (using an Elementar 
rapid-N cube), while mineral analysis was 
conducted using Inductively Coupled Argon 
Plasma (ICAP) run on a Thermo iCAP 
6500.

Environmental Measurements: The 
windowless room in which the research 
was conducted was on the campus of  
Northern Michigan University in Weston 
Hall, room 1208. A Govee Bluetooth 
hygrometer thermometer tracked the room 
humidity (14-42.5 g kg-1) and ambient 
room temperature (68.36-72.86°F). There 
were no significant changes in room and 
reservoir temperature or humidity while the 
research was being conducted. The average 
temperature of  the solutions in the tower 
reservoirs was 21-22°C (69.8-71.6°F) and 
was measured periodically with a submerged 
thermometer.

Statistical Analysis:

The variance among the towers was tested 
using a linear mixed model. The data was 
analyzed with R-studio using analysis of  
variance (one-way ANOVA). First, the data 
was checked for normality with histograms 
and a Shapiro-Wilk test. Homogeneity 
of  variance was tested with Levene’s test. 



54 | Fine Focus

Mean Macronutrients (%)
Nutrients: N S P K Ca Mg
Control 7.87 1.31 0.73 7.72 3.22 0.72
Treatment 1 6.27(-) 2.07(+) 0.95(+) 7.07 3.02 0.66
Treatment 2 7.02(-) 1.16 0.77 5.61(-) 2.71 0.39(-)
Treatment 3 5.85(-) 1.62(+) 0.93(+) 7.21 2.86(-) 0.53(-)

Table 2: Mean macronutrient (%) for the control and each treatment with a (+) or (-) indicating a 
statistically significant increase or decrease in mean nutrient density compared to the control. No 
symbol indicates no significant change (n= 6).

Table 3: Mean micronutrients (ppm) for the control and each treatment with a (+) or (-) indicating 
a statistically significant increase or decrease compared to the control.

Mean Micronutrients (ppm)
Nutrients: Fe B Na Zn Cu Al Mn
Control 73.83 60.00 0.15 35.17 56.83 5.83 253.33
Treatment 1 72.50(+) 89.50(+) 0.14 18.00(-) 5.50 8.83 277.50
Treatment 2 85.50 59.50 0.08(-) 43.17(+) 5.17(-) 8.17 232.33
Treatment 3 73.83 82.17 0.11(-) 38.83 9.00(+) 4.33 287.33

The normality and variance assumptions 
were met, and the ANOVA was run. A 
post hoc Dunnett’s and Tukey’s test was 
used to determine if  the leaf  and root 
biomass of  the treatments were significantly 
different from the control and each other. 
The nutritional analysis from the labs was 
also tested for significance using one-way 
ANOVA and Dunnett’s test, examining 
the overall mean macro- and micro- 
nutrient densities compared to the control. 
Furthermore, each macro- and micro 
mean nutrient density was comparatively 
analyzed among each treatment via a one-
way ANOVA. Some macronutrients failed 
the Levene’s test of  homogeneity of  variance 
(P> 0.05), thus a Welch’s corrected one-way 
ANOVA was run for those nutrients.

Results
According to Soil Food Wed New York 
Lab, the vermicompost analysis resulted 
in above desired population levels for all 
organisms (Table 1). Importantly, the active 
bacterial and fungal populations were very 
high (109.54 µg/g, 87.76 µg/g respectfully). 
A linear mixed model showed that the 
variance among the towers was estimated 
at zero, meaning the growing conditions for 
each tower was the same. Treatment two 
had the highest mean leaf  biomass of  444 
grams, followed by the control (404.8 g), 
treatment one (300.1 g), and treatment three 
(197 g). Using a one-way ANOVA, the mean 
leaf  biomass was found to be significantly 



Vol 9 | 55

different among the treatments (F= 235.4; 
df= 6,21; P< 2e-16; Figure 2). In treatments 
one and three, the mean leaf  biomass was 
significantly less compared to the control 
(Dunnett’s: P= 0.0058 and P= 3.7e-06, 
respectively). Treatment two showed no 
significant difference in leaf  biomass 
compared to the control (P= 0.56). All 
treatments were significantly different from 
one another, excluding the control (Tukey’s: 
treat1-treat2 P= 0.0005; treat1-treat3 P= 
0.011; treat2-treat3 P= 3.0e-7). The mean 
root biomass was significantly increased in 
all treatments compared to the control (F= 
5.932; df= 3,20; P= 0.00458; Figure 3). 
The control had the lowest root biomass 
with a weight of  46 grams. Treatment three 
had the highest root biomass of  79 grams, 
followed by treatment one (73.3 g), and 
treatment two (71.7 g). Root mass did not 

differ significantly among treatments one, 
two and three (Tukey’s: P> 0.05).

The mean nutrient densities for micro- and 
macronutrients were tested separately with 
a one-way ANOVA and Dunnett’s post hoc 
test. These tests revealed that there were 
significant differences between nutrient 
levels among the treatments compared 
to the control for both macro- (F= 107.5; 
df= 5; P= 9.27e-13; Figure 4; Table 2) and 
micronutrients (F= 235.4; df= 6; P< 2.16e-
16: Figure 5; Table 3). The macronutrients 
that were significantly greater than the 
control occurred in treatments one and 
three, which included sulfur (trmt1 P= 
1.3e-08, trmt3 P= 0.002) and phosphorus 
(trmt1 P= 0.0007, trmt3 P= 0.002). The 
macronutrient, nitrogen, was significantly 
decreased compared to the control in all 

Fig 2: Results from ANOVA, Dunnett’s and Tukey’s tests of the mean leaf biomass showed a significant 
difference among treatments (F= 235.4; df= 6, 21; n= 6; P< 2e-16). Treatments one and three were 
significantly different from the control (Dunnett’s: P= 0.0058 and P= 3.7e-06, respectively) and from 
each other (Tukey’s: treat1-treat2 P= 0.0005; treat1-treat3 P= 0.011; treat2-treat3 P= 3.0e-7). Letters 
indicate significant differences. Bars indicate standard error.



56 | Fine Focus

treatments (trmt1 P= 1.2e-07, trmt2 P= 
0.0004, trmt3 P= 6.0e-12). Treatment 
two had significantly decreased levels 
of  potassium (P= 1.6e-07), calcium (P= 
0.0008) and magnesium (P= 2.9e-11) 
compared to the control. Treatment three 
had significantly decreased levels of  calcium 
(P= 0.016) and magnesium (P= 3.0e-05) 
compared to the control. On the other hand, 
the micronutrients that were significantly 
greater than those in the control occurred 
in treatment one with boron (P= 4.7e-06), 
treatment two with iron (P= 0. 016), and 
zinc (P= 0.014), and treatment three with 
copper (P= 0.0018). The micronutrients 
which were significantly lower than the 
control occurred in treatment one with zinc 
(P= 5.8e-06), treatment two with sodium 

(P= 2.3e-08) and copper (P= 0.014), and 
treatment three with sodium (P= 0.0009).

Moreover, each individual nutrient 
underwent a one-way ANOVA test, 
comparing the mean nutrient density of  
each treatment among the same nutrient 
in different treatments. Macronutrients 
nitrogen, phosphorus, and magnesium 
failed the Levene’s test for homogeneity 
of  variance (P< 0.05), thus these 
macronutrients underwent a Welch’s 
corrected ANOVA instead, which doesn’t 
assume equal variances. The ANOVAs 
resulted in all nutrients, both macro and 
micro, amidst each treatment to have a 
significant difference in mean nutrient 
density (P< 0.05; Table 4; Table 5).

Fig 3: Results from ANOVA, Dunnett’s, and Tukey’s tests of the mean root biomass showed a significant 
difference among the treatments (F= 5.932; df= 3, 20; n= 6; P= 0.00458). The three treatments were 
significantly increased compared to the control (Dunnett’s: treat1 P= 0.023, treat2 P= 0.035, treat3 P= 
0.004), but did not significantly differ among one another (Tukey’s: P> 0.05).  Letters indicate significant 
differences. Bars indicate standard error.



Vol 9 | 57

Fig 5: The mean micronutrient (ppm) per treatment was significantly different compared to the control 
(F= 235.4; df= 6; n= 6; P< 2.16e-16). Letters indicate significant differences. Bars indicate standard error.

Fig 4: The mean macronutrient (%) per treatment was significantly different compared to the control 
(F= 107.5; df= 5; n= 6; P= 9.27e-13). Letters indicate significant differences. Bars indicate standard error.



58 | Fine Focus

Discussion
In the presented research, treatment two 
(1.25 grams of  mineral nutrients per liter 
and ~25% by volume vermicompost tea) 
had the highest leaf  biomass (Figure 2), the 
second highest root biomass (Figure 3) and 
increased concentrations of  micronutrients 
iron and zinc compared to the control 
(Table 3). These two micronutrients are 
very important to human health yet are 
recognized to be deficient in many crop 
species and are part of  the phenomenon 
of  ‘hidden hunger’ that impacts significant 
portions of  the human population (11, 
21, 23). In contrast, treatment two had 
the greatest decrease in macronutrients 
compared to the other treatments, but 
the lab nutrient analysis showed that 
this decrease was not enough to drop 
the macronutrients into an unacceptable 
nutrient density level. There was no 
uniform gain or loss of  nutrients among 
the treatments, although the lab analysis 
of  leaf  nutrient density showed that the 
control and all treatments were deficient in 
the micronutrient zinc except for treatment 
two, which had the highest level recorded. 
This may suggest that the concentrations 
of  nutrient mineral solution and beneficial 
microbes in the vermicompost tea used in 
this treatment were the most effective in 
increasing overall health and biomass of  Bok 
Choy (B. rapa var. chinensis). In Abul-Soud’s 
et al. study (2015), they found that optimal 
plant growth responses occurred with the 
addition of  10 - 20% vermicompost by 
volume, along with the addition of  mineral 
nutrients (for the majority of  crops in their 
research) (1).

Plants need nutrients to maximize their 
biomass in the form of  ions (a positively 
or negatively charged compound), 
regardless of  whether a system is synthetic 
or biological. The use of  artificially based 
nutrients (inorganic salts/minerals) does not 
typically include living microorganisms, is 
unsustainable and is an attempt to mimic 
what natural biological systems have been 
successfully performing over eons of  time 
(14). Treatment one and three experienced 
a significant decrease in the mean leaf  
biomass compared to the control. These 
two treatments also had the least amount 
of  mineral nutrient additives (0.625 grams 
per liter), which could have led to nutrient 
stress, reducing leaf  biomass. In a similar 
study by Aini et al. (2019), they found 
that the reduced nutrient content added 
to their hydroponic system led to smaller 
plants that took two weeks longer to reach 
maturity and had significantly less biomass 
due to nutrient stress (2). While treatment 
three did have the least amount of  leaf  
biomass, it had the highest amount of  root 
biomass. Additionally, treatment three’s 
reservoirs were not emptied and refreshed 
with new solutions halfway through the 
growing process, which could have increased 
the bacterial concentration even further. 
The increase in root biomass and not leaf  
biomass may be due to a stress response 
caused by an overgrowth of  microbes on the 
roots, resulting in an increase of  root growth 
but limiting nutrient uptake to the rest of  
the plant (17). No visual evidence of  plant 
disease was present in this treatment (or any 
of  the other treatments). Similar results were 
found in a study by Li et al. (2018) where 
shoot growth was limited while root growth 
increased due to the lack of  water micro 



Vol 9 | 59

droplets and nutrient availability caused by 
aeroponic misting intervals and droplet size 
(17). Comparatively, the increase in root 
growth found in treatment three and the Li 
et al. research could reflect a stress response 
due to a lack of  nutrients. The effects of  
treatment three may coincide with the study 
conducted by Abul-Soud et al. (2015), using 
vermicompost in soilless culture wherein 
they found increasing the vermicompost 
concentration to 15% was the plateau at 
which the plants received positive effects 
(1). Beyond this limit, significant negative 
effects in yield, quality and nutrient density 
occurred with certain crops.

Though treatment three in the presented 
research had the greatest root biomass, the 
exact mechanisms for this result are not 
clear; it may be worth further investigation 

for applications when an increased root 
biomass is desired. Increased root biomass 
in medicinal root crops cultivated in 
a greenhouse, using an aeroponic or 
hydroponic system, could make medicinal 
roots more readily available to the public 
(17, 19). According to a study conducted 
by Pagliarulo et al. (2004), there is a 
multibillion-dollar market for medicinal 
botanical products, such as purple 
coneflower (Echinacea purpurea), burdock 
(Arctium lappa), ginseng (Panax ginseng) and 
St. John’s wort (Hypericum perforatum) (19). 
In their study, they found that E. purpurea 
had a significantly greater root biomass 
when grown in an aeroponic setting versus 
in soil (19). This suggests the use of  indoor 
aeroponic systems can be very advantageous 
when operated properly. Aeroponic and 
hydroponic systems function similarly 

One-Way ANOVA Summary for Macronutrients
Nutrients: N S P K Ca Mg
df 3, 9.55* 3, 20 3, 10.17* 3, 20 3, 20 3, 8.72*
F-value 57.56 55.78 42.43 23.38 7.10 89.17
p-value p<0.001 p<0.001 p<0.001 p<0.001 0.002 p<0.001

Table 4: One-way ANOVA summary outputs for macronutrients when assessed individually, resulting 
in all nutrients having significantly different mean nutrient densities among each treatment (P< 0.05, n 
=6). Welch’s corrected ANOVA was run on nutrients N, P, and Mg due to unequal variances, hence the 
changes in the denominator df (*). 

Table 5: One-way ANOVA summary outputs for micronutrients when assessed individually, resulting in 
all nutrients having significantly different mean nutrient densities among each treatment (P< 0.05, n= 6).

One-Way ANOVA Summary for Micronutrients
Nutrients: Fe B Na Zn Cu Al Mn
df 3, 20 3, 20 3, 20 3, 20 3, 20 3, 20 3, 20
F-value 5.13 25.36 30.32 37.32 21.15 5.32 3.68
p-value 0.009 p<0.001 p<0.001 p<0.001 p<0.001 0.007 0.029



60 | Fine Focus

and may have some of  the same benefits. 
The experimental results of  the research 
conducted for this paper showed that 
adding microorganisms via compost tea 
increased the root biomass of  Bok Choy 
in a hydroponic system. The addition of  
beneficial microbes to indoor cultivation 
systems has great potential to increase 
biomass and reduce the need for synthetic 
fertilizers and pesticides conventionally used 
for crop production.

A study done by Giurgiu et. al (2018), 
showed that certain medicinal plants 
(Hypericum perforatum) treated with Trichoderma 
spp., (a known beneficial fungus) in rockwool 
substrate in a hydroponic system had a two-
fold increase in foliar biomass and enhanced 
root development compared to plants 
treated with a pathogenic microbe (10). 
Their research highlights the complexity 
of  plant-microbe interactions regarding 
the impact on plant growth and nutrient 
levels. The research conducted in this paper 
demonstrated variable plant responses with 
the different levels of  inorganic fertilizer and 
vermicompost tea solutions.

Overall, research results indicate there 
may be no “one size fits all” when it comes 
to the implementation of  amendments 
to hydroponic systems to reach the goals 
of  improvements in plant biomass and 
nutrient profiles. Similarly, Sheridan et. 
al. (2017), investigated how plant growth 
promoting microorganisms (PGPMs) affect 
the root zone microbiome of  four common 
food crops (durum, potato, bread wheat 
and soybean) in recirculating hydroponic 
cultivation systems for the whole life cycle 
of  each plant (22). They concluded crops 

inoculated with a mixture of  commercial 
PGPMs (with a composition of  microbial 
communities associated with root 
rhizosphere, rhizoplane, and endosphere 
with a recirculating nutrient solution) were 
more stable in a plant based biological life 
support system over time, depending on the 
specific crop (22). However, more research 
is needed to better understand this dynamic 
and to fine tune experimental protocols to 
achieve desired results.

Vermicompost is a PGPM, is available 
commercially and would be relatively 
easy for the indoor-grow enthusiast to 
incorporate into ‘gardening’ practices. 
Based on the results of  the experimental 
study, the addition of  vermicompost tea 
in a hydroponic system can result in an 
enhancement to the plant biomass and 
nutrient density of  Bok Choy when applied 
at specific concentrations. A thorough 
analysis of  the microorganism species 
which were present, persisted, or died off, 
on plant roots at the beginning and end 
of  the experiment would provide more 
insight as to how the species of  plants, 
amendments and microorganisms interacted 
and would enhance the continuation of  the 
presented research. Modifying the current 
experiment to include a second control 
consisting of  0.625 g of  mineral nutrients 
in future studies may give further insight to 
how the beneficial microorganisms in the 
vermicompost tea influences the growth and 
nutrient density of  Bok Choy. Investigating 
the specific species of  microbes’ and 
deciphering their impact on plant growth, 
biological and chemical properties, such 
as antioxidants and polyphenols, would be 
valuable. Research conducted by Chandra et 



Vol 9 | 61

al. (2014) suggested that aeroponically grown 
crops may provide an environment in which 
plants produce higher levels of  antioxidant 
activity (10). Moreover, hydroponic systems 
might offer a higher level of  reproducibility 
for influencing the concentrations of  
vitamins and phenolic compounds within a 
crop (10). These findings should be studied 
further using larger data sets and total 
environmental and nutrient input controls. 
With a greater understanding of  the specific 
microbes and their impacts on plants, it 
would provide better insight as to how to 
adjust and fine-tune the percent solutions 
to achieve the specific desired results for 
certain plant species. The incorporation of  
beneficial microbes into hydroponic systems 
holds promise for improving plant growth 
and nutritional characteristics and could 
play an important role in the transition 
from conventional agriculture to indoor 
hydroponic systems which may lead to 
significant advancements in the future of  
farming.

Acknowledgements

We would like to extend our sincerest 
gratitude to Dr. Donna Maki for her 
unrelenting support and help with the 
overall execution of  this research. We would 
also like to thank Dr. Alan Rebertus for 
his generosity and abundant knowledge 
regarding R-studio and statistical analysis. 
Much thanks to Regan Doran for his 
expertise and build of  the vertical towers. 
Additionally, we would like to thank 
Sarah Kunister for her help throughout 
the research and Michael Fishman for 
his assistance with the initial installation 
of  the modular units. We would also 

like to extend our gratitude to Mrs. 
Marilyn Scheidemantel, as our research 
was supported in part by a grant from 
the Scheidemantel Research Fund for 
undergraduate students.



62 | Fine Focus

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Publisher Corrections:

Table 3: An incorrect title and description for Table 3 were originally published with 
the article, due to a publisher error. The corrected title and description were 
published on 12/4/2023.

Figure 2: The incorrect image for Figure 2 was originally published with the article, 
due to a publisher error. The corrected figure was published on 12/4/2023.