Essay: An Investigation Into Seedling Development in Response to Vermiculite Concentration of Substrate

Exploration Research Question
Will increasing the concentration of vermiculite in the substrate increase seedling survival and growth of Phaseolus vulgaris seeds?
Background Information
I personally chose to investigate this topic because green beans are one of my favorite vegetables to eat, and I have tried to grow them several times with varying degrees of success. Because I was sometimes not able to grow the plants from seeds, I was interested in what variables could affect the seedlings’ growth, specifically soil amendments such as vermiculite or perlite. Because of this, I decided to investigate how the concentration of vermiculite in soil affects seedling survival of green bean, also known as Phaseolus vulgaris, seeds.
Before a seed begins to grow, it goes through a period of dormancy, where it is incapable of germinating, even under favorable conditions (Bentsink & Koornneef, 2008). In order to break this period of dormancy, the seed’s environment must contain optimal amounts of light, oxygen, temperature, and water, among other factors. (Seed and Seedling Biology, n.d.). In some cases, other germination-promoting factors such as light treatment, stratification, after-ripening, and applied chemicals can also cause seeds to overcome dormancy (Bentsink & Koornneef, 2008).
The process of germination begins with the stage of imbibition, where the seed begins to rapidly take up water, causing the outer seed coat to swell and soften (Seed and Seedling Biology, n.d.). Water uptake in the imbibition stage is triphasic, with the seed initially taking up water rapidly, then plateauing, then later further increasing its uptake (Bentsink & Koornneef, 2008). The next stage of germination is the interim or lag phase. In this stage, the seed initiates its internal processes, including cellular respiration, protein synthesis, and metabolization of food stores within the cell. (Seed and Seedling Biology, n.d.). Finally, the seed enters the third stage of germination, radicle and root emergence. In this stage, cells within the seed begin to elongate and divide, pushing the root and radicle out of the seed (Seed and Seedling Biology, n.d.).
After the process of germination, early seedling development begins. In dicots, or two-seed leaves, such as Phaseolus vulgaris, t he radicle attaches the plant to the ground and begins to absorb water from the substrate (Seed and Seedling Biology, n.d.). After this, the shoot emerges from the seed. The shoot is made up of 3 parts, the cotyledons, or seed leaves, the
 
hypocotyl, which is the section of shoot below the cotyledons, and the epicotyl, which is the section of shoot above the cotyledons (Seed and Seedling Biology, n.d.). In species of beans such as Phaseolus vulgaris, t he seed undergoes epigeal germination, in which the hypocotyl forms a hook which pulls the cotyledons and epicotyl to the surface of the soil. After this, the hypocotyl straightens, pulling the rest of the shoot into the air (Seed and Seedling Biology, n.d.).
(Seed Germination, n.d.)
In my investigation, I will be exploring the effect of vermiculite concentration within the substrate as it relates to seed germination, seedling growth, and survival. Vermiculite is a natural compound of the chemical formula (Mg,Fe++,Al)3(Al,Si)4O10(OH)2•4(H2O), and is mined across the United States and the rest of the world (Barthelmy, n.d.) Horticultural vermiculite is commonly used in agriculture, as it improves soil aeration while retaining necessary moisture and nutrients for plant growth (Horticultural Uses, n.d.). Vermiculite is particularly effective in seed germination, as it increases the availability of oxygen and water, two necessary components to germination, increasing germination rates when it is utilized (Horticultural uses, n.d.)
The relationship between vermiculite and seed growth has been previously investigated in some species. A 2015 study found that when Plukenetia volubilis L. seeds were grown either sand or vermiculite, the seedlings in vermiculite had a 98% survival rate, while while the survival rate of seedlings grown in sand was only 79%. (Cardoso, Obolari, Borges, Silva, & Rodrigues, 2015).
In my exploration, I will study the effect of vermiculite on Phaseolus vulgaris germination and seedling growth. Phaseolus Vulgaris, commonly known as a french bean, best grows in a sunny, warm position, in light, well drained soil, and prefers a ph between 5.5 and 6.5 (Phaseolus Vulgaris, n.d.).
Hypothesis/Explanation
 
Increasing the concentration of vermiculite within the substrate will increase germination rate and seedling survival, but only until a certain point, at which the substrate will lack the necessary nutrients for plant growth normally supplied by soil, in turn decreasing seedling survival. This is because vermiculite increases aeration of the soil while also retaining water. Water retention is essential to germination and seedling development, as germination is started in the imbibition phase by rapid water absorption, and water is necessary for photosynthesis, the process by which plants convert sunlight into glucose. Soil aeration is also essential, as oxygen is necessary to overcome seed dormancy, as well as in cellular respiration, the process by which the plant’s cells convert glucose to usable energy in the form of ATP.
Independent Variable
Concentration of vermiculite in substrate (0%, 25%, 50%, 75%, 100%)
Dependent Variables
Germination Rate (%) Seedling Growth (cm)
Controls
Variable controlling
Why variable must be controlled
How variable will be controlled
Temperature (C)
Variation in temperature can affect whether seedlings will overcome dormancy and germinate.
Seedlings will be kept inside at room temperature, 25 °C.
Sunlight
Variation in sunlight affects plant photosynthesis and has an impact on overcoming dormancy.
Seedlings will be kept by window facing sun for approximately half of the day.
Ph
Ph of soil affects growth of Phaseolus Vulgaris, ideal ph is between 5.5 and 6.5.
Seedlings will be grown in Miracle Gro potting, which has an average ph of 6-6.8.
Water (ml)
Amount of water given to seeds affects rate of germination and photosynthesis.
Seedlings will be given 20 ml of water each day.
Oxygen
Amount of oxygen present can affect rate of germination and cellular respiration.
Seedlings will be kept inside a controlled indoor environment with a constant supply of oxygen.
 
Materials
● 5 gallon (18.92 liter) bucket of backyard soil
● 2 cu ft bag of Vigoro Vermiculite soil amendment
● NK pro-hex seed starting tray
● 15 liters tap water
● Bean Bush Blue Lake 47 ( Phaseolus vulgaris) Organic Seed packet X2
● Permanent marker
● 100 ml beaker (+/- 2 ml)
● Meter stick (+/- .05 cm)
● Measuring cup (+/- 1 oz or 30 ml)
Procedure
1. Measure 8 cups (1.893 liters) of soil and distribute evenly into 24 seed starter cells.
2. Label cells “0% vermiculite” with permanent marker.
3. Measure 6 cups (1.419 liters) soil and 2 cups (.473 liters) vermiculite and mix
thoroughly.
4. Divide mixture evenly into 24 seed starter cells.
5. Label cells “25% vermiculite” with permanent marker.
6. Measure 4 cups (.946 liters) soil and 4 cups (.946 liters) vermiculite and mix thoroughly.
7. Divide mixture evenly into 24 seed starter cells.
8. Label cells “50% vermiculite” with permanent marker.
9. Measure 2 cups (.473 liters) soil and 6 cups (1.419 liters) vermiculite and mix
thoroughly.
10. Divide mixture evenly into 24 seed starter cells.
11. Label cells “75% vermiculite” with permanent marker.
12. Measure 8 cups (1.893 liters) vermiculite and distribute evenly into 24 seed starter cells.
13. Label cells “100% vermiculite” with permanent marker.
14. Place trays by south-facing sunny window.
15. Use 100 ml beaker to add 15 ml of water to each cell.
16. Repeat water-adding process every 5 days.
17. After 14 days, record number of surviving seedlings for each concentration of vermiculite
and seedling heights using meter stick.
Risk assessment
Although almost entirely all modern vermiculite is safe to handle, some vermiculite can contain trace amounts of asbestos. For this reason, dampen vermiculite before handling and wear a mask when handling for prolonged periods of time.
Analysis Part I: Data
Data table 1: Height (cm) of Phaseolus vulgaris seedlings at vermiculite concentrations in substrate for 14 days
Height (cm +/- .05) at Vermiculite Concentration
Trial #
0%
25%
50%
75%
100%
1
28.5
31.9
33.7
26.0
0.0
2
36.4
39.1
13.6
31.1
1.1
3
24.3
37.6
37.3
0.0
1.3
4
0.0
30.0
33.1
24.3
3.7
5
35.7
36.0
34.8
0.0
0.0
6
30.3
35.3
31.4
11.5
0.5
7
24.3
28.2
34.7
20.5
0.0
8
28.5
0.0
38.5
6.8
0.7
9
18.4
37.5
32.2
24.4
0.4
10
33.0
40.1
33.4
0.0
0.0
11
0.0
34.9
29.6
35.6
0.0
12
34.6
28.5
36.7
0.0
0.6
13
0.0
41.2
0.0
33.0
0.0
14
0.0
36.5
38.3
32.2
5.2
15
30.5
33.8
34.7
31.9
0.0
16
35.4
33.6
28.9
30.2
4.7
17
30.5
31.7
34.6
26.1
0.8
18
0.0
31.3
21.4
25.2
12.2
19
24.7
33.2
36.7
24.5
0.0
20
0.0
33.7
35.4
33.1
14.9
21
0.5
36.0
37.1
6.8
4.9
 
22
22.2
26.7
38.9
31.1
0.0
23
37.4
13.7
36.5
24.6
1.9
24
40.4
30.4
38.7
32.0
0.5
Data table 2: Qualitative observations
Vermiculite concentratio n
Observations
0%
Unable to support weight after 14 days, weaker stems, damp and dense soil
25%
Tall, sturdy stems, less damp, less dense substrate
50%
Tall, sturdy stems, best moisture and density in substrate
75%
Much shorter, lacking moisture in substrate
100%
Extremely short, little to no moisture in substrate
Part II: Data Processing
Overview
After recording all data, I decided that processing the average heights and standard deviations of the seedlings at each concentration, as well as processing the germination rates of the seeds at each concentration would best help to interpret the raw data. Through calculating the average height of the seedlings at each concentration by addition and division by the number of trials, I was able to come up with one value for height for each concentration that could be compared to that of others. By calculating the standard deviation of the data, I was also able to represent the variation within the data with 1 value for each concentration. Finally, in calculating the germination rate by dividing the number of seeds germinated over the total number of seeds, I was able to show the effect of the independent variable on seed germination.
Processed Data Tables
Date table 3: Average height (cm) of Phaseolus vulgaris s eedlings at vermiculite concentration (%) for 14 days (not including non-germinated seeds)
 
Average Height (cm +/- .05) at vermiculite concentration (% +/- 3.2)
Concentration
Average Height
Standard deviation
0%
30.3
6.1
25%
33.1
5.7
50%
33.5
5.9
75%
15.6
8.4
100%
3.6
4.4
Data Table 4: Germination Rate (%) of Phaseolus vulgaris seeds at vermiculite concentrations (%) in substrate
Germination Rate (%) at vermiculite concentration (% +/- 3.2)
Concentration
Germination Rate
0%
75.0%
25%
95.8%
50%
95.8%
75%
83.3%
100%
64.0%
Sample Calculation
Average height at 25% concentration (not including non-germinated seeds):
31.9+39.1+37.6+30.0+36.0+35.3+28.2+37.5+40.1+34.9+28.5+41.3+36.5+33.8+33.6+31.7+31.3 +33.2+33.7+36.0+26.7+13.7+30.4 = 760.9
760.9/23 = 33.1 cm
Standard deviation at 25% concentration (not including non-germinated seeds):
σ = √Σ|x−x| 2 n
|33.1 − 31.9|2 + |33.1 − 39.1| 2 + |33.1 − 37.6|2… = 713.82 713.82/23 = 31.04
√31.04 = 5.7
Germination rate at 25% concentration:
23 seeds germinated/24 total seeds = .958 = 95.8%
Data Presentation
 
In assessing the data shown, it is can be seen that the most effective concentration of vermiculite within the substrate for both seed germination and seedling survival is 50% vermiculite to 50% soil. This trend can be seen in the above graphs, as both germination rate and average seedling height increase from the 0% vermiculite trials to the 50% vermiculite trials, and then begin to drop off after this point. Seeds planted in the 50% vermiculite mixture grew to an average height of 31.7 cm after 14 days as compared to a height of 21.5 cm achieved by seeds planted in a 100% soil substrate. The germination rate of seeds planted in the 50/50 mixture was also substantially higher than that of the seeds planted in the control, at 95.8% as compared to 75%.
Statistical Tests
2 sample T test for μ1 − μ2 (Average heights at 0% and 50%):
s12 +s22 n1 n2
(x −x )−(μ −μ ) 1212
t=√
x1 = 30.3 , x2 = 33.5 s1 =6.1 s2 =5.9
n1 =24n2 =24
t =− 1.84
p = .071
2 sample z test for p1 − p2 (proportion of seeds germinated at 0% and 50%):
〈〈
(p −p )−(p −p ) z=√1 2 1 2
〈〈〈〈
pc(1−pc)+pc(1−pc) n1 n2
 
x1 =17×2 =23 n1 =24n2 =24 z = 2.32
p = .02
Evaluation
The above data support the hypothesis that increased vermiculite concentration within the substrate, to an extent, increases seedling growth and germination rate in Phaseolus vulgaris seedlings, with the most effective concentration being 50% vermiculite to 50% soil. In the experiment, seeds planted in the 50% vermiculite mixture grew to an average height of 31.7 cm after 14 days as compared to an average height of 21.5 cm achieved by seeds planted in a 100% soil substrate. Seeds planted in the 50% mixture also demonstrated higher germination rates in than seeds planted in only soil, 95.8% in the optimal mixture as compared to 75% without any vermiculite added. With concentrations higher than 50% vermiculite, seedling growth did suffer dramatically, with the worst performing seedlings in the 75% and 100% vermiculite ranges. The differences in seedling height and germination rate are also statistically significant, as the 2 sample T test yielded a p value of .07 when comparing the average heights of the seedlings planted in 0% and 50% vermiculite substrates, and the 2 sample Z test yielded a p value of .02 when comparing germination rates at the same concentrations. Both p values point to a statistically significant difference at the 90% confidence interval, and the .02 value for germination rates remains significant at the 95% confidence interval.
Based on previous research, the results of the experiment reflect the scientific basis upon which the hypothesis that plant growth would improve, to an extent, with increased vermiculite within the substrate. This hypothesis was based on the fact that vermiculite increases aeration of the soil while also retaining water (Horticultural Uses, n.d.). Water retention is essential to germination and seedling development, as germination is started in the imbibition phase by rapid water absorption, and water is necessary for photosynthesis, the process by which plants convert sunlight into glucose (Seed and Seedling Biology, n.d.) . Soil aeration is also essential, as oxygen
is necessary to overcome seed dormancy, as well as in cellular respiration, the process by which the plant’s cells convert glucose to usable energy in the form of ATP (Seed and Seedling Biology, n.d.) .
Despite producing relatively consistent data, the experimental design of the investigation did have some flaws. First, the only measurement of seedling growth used was height, while other factors such as mass, stem thickness, and more could have been used to measure the growth of the seedlings. Also, as in any experiment, more trials could have been performed in order to increase the accuracy of the results. Finally, the investigation only addressed 5 concentrations of vermiculite within the substrate, meaning that the ideal concentration of vermiculite for Phaseolus vulgaris s eedling growth could not have been tested in the experiment.
In a future version of the investigation several changes could be made. First, after the 2 weeks of growth, plants could be removed from the substrate and weighed to measure growth. Root lengths could also be measured in order to better measure seedling development. Again, more seedlings could also be grown in order to produce more accurate results. After analyzing the results of the investigation, additional research questions can be proposed. One such question related to the experiment would be to analyze the differences in seedling growth in different soil amendments, including lime, fertilizers, vermiculite, gypsum, and clay. While the previous investigation only addressed the effects of vermiculite on seedling development, this investigation would compare the effects of different amendments and blends in order to determine the most efficient substrate composition.
 
Works Cited
Barthelmy, D. (n.d.). Vermiculite Mineral Data. Retrieved September 14, 2018, from
http://webmineral.com/data/Vermiculite.shtml#.W5vFl2hKjrc
Bentsink, L., & Koornneef, M. (2008, December 30). Seed Dormancy and Germination. Retrieved September 13, 2018, from https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3243337/
Cardoso, A., Obolari, A., Borges, E., Silva, C., & Rodrigues, H. (2015, June). Environmental factors on seed germination, seedling survival and initial growth of sacha inchi (Plukenetia volubilis L.). Retrieved September 13, 2018, from http://www.scielo.br/scielo.php?script=sci_arttext&pid=S2317-15372015000200111
Horticultural Uses of Perlite and Vermiculite. (n.d.) Retrieved October 4, 2018, from
http://www.schundler.com/hort.htm
Phaseolus vulgaris – L. (n.d.). Retrieved September 13, 2018, from https://pfaf.org/user/plant.aspx?LatinName=Phaseolus vulgaris
Seed and Seedling Biology. (n.d.). Retrieved October 4, 2018, from
https://extension.psu.edu/seed-and-seedling-biology
Seed Germination. (n.d.) Retrieved October 4, 2018, from
https://staff.guilan.ac.ir/staff/users/jolfati/fckeditor_repo/file/%D9%81%DB%8C%D8% B2%DB%8C%D9%88%D9%84%D9%88%DA%98%DB%8C%20%D8%B3%D8%A8
 
%D8%B2%DB%8C%D9%87%D8%A7/SEED%20GERMINATION_ppt%20%5bComp atibility%20Mode%5d.pdf