Bryan Curtin

2012

The Effect of Vibrational Energy on Seed Germination Rate

Abstract

What if it were possible to increase the rate of seed germination in the soil by using an

affordable method? This would greatly help any agricultural producer, such as a farmer or an

orchard tender, who’s only source of income is his or her cash crop. Also, in order to organically

keep weeds down and other pesky plants from competing with the crop, the farmer/orchard

tender needs an easily manageable, low laying cover crop that is rapidly growing. The motive for

this experiment was to speed up the germination time of Thymus serpyllum and potentially other

cover crops, or even the cash crops themselves, using an affordable method. There exist sound

wave transducers with frequencies of 1 to 5 MHz in an affordable price range and these can be

used to produce mechanical vibrations in the soil to attempt to stimulate seed germination.

The reasoning behind using vibrational energy was simple. If Thymus serpyllum seed is

exposed to mechanical vibrations of comparable scale to the seed size, then the germination time

of the seed will decrease due to enhanced moisture and/or nutrient fluxes across the seed wall

and chemical distribution within the seed.

To conduct experimentation, an affordable apparatus that consisted of three trays

mounted on a wooden table, one for each testing group: 1MHz, 3MHz and the control group was

constructed. Seeds were dispersed over the soil in each tray and each group was given a constant

amount of artificial sunlight, water and oxygen. The dependent variable, defined as Germination

Rate or the number of plants viewed at the surface after a period of 15 days, was tested.

Two factors were found to affect the germination rate of Thymus serpyllum. First, as

stated in the hypothesis, moisture, nutrient and chemical fluxes were possible factors.

Temperature also affected the germination rate of Creeping Thyme seeds. In a certain area the

temperature reached levels of 72°F as a consequence of the vibrational energy, and in this area

germination rate increased visibly. Unfortunately, the first factor that likely affects germination

rate (the possible fluxes in moisture and chemicals throughout the seed) needs to be further

exploited due to lack of affordable materials to study this information.

Introduction

Botany is a fascinating subject. The study of plant life has produced an array of scientific

principles ranging from seed growth and metabolism to the evolutionary relationships between

plants of this day and age and plants from long ago. The former topic includes how and why

seeds germinate after being in a dormant state for a period of time. This process has been studied

by scientists and involves a variety of chemicals and hormones in the seed that can be stimulated

by a range of factors, primarily heat or light, and water. Generally the process of seed

germination and emergence out of the soil can take a few weeks or longer depending on the seed.

But what if it were possible to increase the rate of seed germination in the soil by using an

affordable method? This would greatly help any agricultural producer, such as a farmer or an

orchard tender, who’s only source of income is his or her cash crop.

Also, in order to organically keep weeds down and other pesky plants from competing

with the crop, the farmer/orchard tender needs an easily manageable, low laying cover crop to

cover the rest of his field and therefore stop the growth of weeds where the cover crop has

already taken precedence. This cover crop must be fast growing, or at least faster growing than

the weed which the farmer is trying to prevent, and ideally perennial, in fields with permanent

plantings. Thymus serpyllum (creeping thyme), for example, would be an excellent cover crop

because of its low laying properties which rob any weeds of the space to begin growing.

However, creeping thyme is naturally slow to germinate.

The motive for this experiment was to speed up the germination time of Thymus

serpyllum and potentially other cover crops, or even the cash crops themselves, using an

affordable method to create mechanical vibrations in the soil. A major challenge was how to

find an affordable way to produce this effect. Due to clinical applications in physical therapy

(deep heat muscle stimulation), there exist sound wave transducers with frequencies of 1 to 5

MHz in an affordable price range and these were used to produce the needed mechanical

vibrations in the soil to attempt to stimulate seed germination.

There are several factors that need to be understood. First, what are the mechanisms

determining seed

germination and how are

they initiated? Also, what

is the sound speed in soil?

This is necessary to know

in order to derive the wavelength of the sound at various frequencies. Thirdly, are the

wavelengths of sound in the 1-3 MHz range on the same scale as the seed size? In order to

maximize the mechanical vibrations of the seed, the seed size and wavelength should be

comparable. Such vibrations would affect maximum displacement of the seed for a given

amplitude waveform (see figure). Two questions that the experimental design should answer are:

In exposing seed in soil to sound (elastic waves) with wavelength of comparable size to the seed,

can the effects of mechanical vibration (induced motion) and temperature change (energy

dissipation) be separated? And do mechanical vibration effects change the rate of seed

germination relative to a control sample not exposed to ultrasonic energy? Also, if a change in

germination rate is observed, what germination mechanism is the likely cause? Based on the

results, what practical applications can be derived and what future research is indicated? These

questions provided the basis for any research to be done.

The mechanisms for seed germination have been studied to some extent. The author of

several articles written in 1994 from an online plant physiology website, Ross E. Koning,

outlines the process in his words along with detailed diagrams of each step. He says initially that

dormant seeds with a thick seed coat need to go through a rather traumatizing situation, such as

gnawing by an animal or extreme temperature, called scarification in order for the germination

process to initialize. However, Thymus serpyllum seeds have a thin coat and therefore contain a

pigment called phytochrome positioned in the cotyledons of the embryo which reacts to sunlight

to start the metabolic process (Bryan D. Ness, 11/01/2002). Consequently, Creeping Thyme

Seed

Frequency 1MHz -3MHz

seeds use light in order to become biochemically active. As Koning says, “A thin seed coat is so

thin that it is no barrier to water. Some other kind of dormancy mechanism is needed. Knowing

that light can penetrate thin layers of plant tissue (leaves for example) should give you the idea

that light might be a signal.” (Ross E. Koning, 1994)

For the experiment, the plants are exposed to a constant stream of artificial sunlight and

so becoming active is not an issue. The primary motivation of the vibration is to act as a trigger

for protein synthesis so the plant can begin to grow; which factors allow the plants to take in

needed nutrients for germination and growth? “The first step in seed germination is imbibition.”

Koning explains. Imbibition is the uptake of water into the seed. “In this process, water

penetrates the seed coat and begins to soften the hard, dry tissues inside. The water begins to

activate the biochemistry of the dormant embryo.” The vibrations insonified into the soil speed

up the imbibition process as the seed is shaken around and exposed to a greater volume of water.

“The water coming into the seed and embryo dissolves a chemical made inside the embryo. This

chemical is called Gibberellic Acid (GA). It is a plant hormone, not too different from steroids.

The dissolved GA is transported with the water through the rest of the seed tissues until it arrives

at the aleurone layer.” The aleurone layer is a layer of cells containing protein in abundance

(Koning, ibid.). Russell L. Jones, an author from* the American Society of Plant Physiologists

concluded, “The aleurone layer was found to be the primary determinant of seed dormancy.” and

went on to describe how the gibberellic acid turns on certain genes in the aleurone cells which

facilitate protein synthesis so the plant can begin to grow. But before the gibberellic acid can turn

on these genes, it has to move through the seed to the aleurone layer and also pass through the

cytoplasm of the aleurone cells. The vibrations likely help move water containing the dissolved

GA through the seed. Additionally, the mechanical vibrations may allow for more rapid diffusion

of gibberellic into the water solvent

Next, the speed of sound in our soil is determined so that a corresponding wavelength can

be determined. In a report made by the Strategic Environmental Research and Development

Program, “Acoustical Characterization of Soil”, measurements in hundreds of soil samples with

different compositions and moisture contents indicate that the speed of sound ranges from 72 to

276 m/s. (For comparison, the speed of sound in air is 343.2 m/s and the speed of sound in water

is 1500 m/s.). For soil of the type and moisture content that was used in this experiment (sandy

loam, sample file number: sac311 based on SERDP report), the sound speed was estimated to be

approx. 139 m/s +/- 40 m/s.

Wavelengths within the 1-3MHz frequency range should be on the same scale as the seed

size based on the speed of sound in the sample of soil we are using. The formula required to

determine this is: wavelength = (sound speed)/frequency

So, using this formula: (139 m/s)/1 MHz = 139000 mm/1 MHz = 0.139 mm (139m/s)/3 MHz = 139000 mm/3 MHz = 0.0463 mm

Seeds were measured with a micrometer yielding an average diameter of 0.17 mm +/- 0.02 mm.

Thus, within experimental error, seed size is of the same order as the wavelength of 1 MHz

elastic waves in the soil type of interest. Based on these data and calculations, a physical

experiment is justified.

The purpose of this project was to determine whether optimized mechanical vibrations in

the soil could affect the rate of seed germination in a positive (or negative) way and therefore

also affect the net speed of plant growth overall. Would soil insonification at frequencies from 1-

3MHz affect the rate of seed germination in any way? In order to measure the dependant

variable, the germination rate (GR), I used: (number of plants observed at the surface after 15

day period).

Based on current literature, if Thymus serpyllum seed is exposed to mechanical

vibrations of comparable scale to the seed size, then the germination rate of the seed will

decrease due to enhanced moisture and/or nutrient fluxes across the seed wall and chemical

distribution within the seed. The causes of the possible decrease in germination time stated in the

hypothesis are outlined in the research section in the third paragraph.

Materials and Methods

To conduct experimentation, an affordable apparatus that would effectively allow

transducers to have full contact with the soil, but also permit someone to easily access the

transducer functions was required. The device consisted of three trays mounted on a wooden

table, one for each testing group: 1MHz, 3MHz and the control group. Two 2” x 4” (referring to

width and height respectively) grooved lengths of wood gave room for the transducers and

provided human accessibility by supporting the trays above the table (see diagram 1 -appendix).

Each of these trays was filled with the same soil from the same source and Thymus serpyllum

seeds were evenly distributed over the soil.

One constant was the amount of light the plants/groups received. A Grow Light

purchased online was positioned above the three trays, suspended from the ceiling, and was

perpetually lit, powered by an electrical outlet (ibid.). Since light was provided, one of the

factors causing seed germination was in check. The other factor playing into seed germination,

water, was now necessary. For this, a spray bottle was filled with liquid and the trays were

periodically sprayed throughout the experiment.

In order to test whether transducers emitting vibrational energy into the soil would have

an effect on the germination rate of Thymus serpyllum seeds, pulses of vibrations from the

3MHz transducer and 1MHz transducer were released (10 minutes maximum at a time as the

transducers could not run for more than 10 minutes) for several times a day in the specified

areas. During the experiment, every occasion in which the transducers were allowed to pulse was

recorded and observations were documented. More specifically, any growth in any of the three

testing areas was noted (1 MHz, 3 MHz, and the control group) in a table on a notepad, based on

the amount of plants that had emerged that day in the specified group. The dependant variable

was Germination Rate = GR defined as: GR = (number of plants observed at surface after

15 days) since there was no affordable way of viewing the seed through the soil. Another factor

that was necessary to regulate was the temperature, which was achieved through a temperature

monitor previously purchased that recorded the temperature in the soil of the 1MHz transducer

every time the transducer pulsed, and the outside room temperature. The transducers were pulsed

for a period of fifteen days. After accomplishing experimentation, the quantity of plants that

germinated in each experimental sector (twelve sectors for every experimental group - see

diagrams 2,3, and 4 in appendix) were counted and a data table outlining this information was

constructed. A data table was also created to delineate the number of plants sprouted in relation

to the control from least to greatest number of plants germinated in each faction (see table 1A in

results). This data table also includes standard deviation for each group. An alternate graph

shows the fluctuations in temperature and how it may have affected the outcome of the

germination rate (see Graph 1C in results).

Data Collection and Analysis - Results

The data table on the following page shows the number of plants germinated after fifteen days

for both the 3MHz transducer and the 1MHz in relation to the control group. The mean number

of plants that sprouted for the 1MHz was about 1.62 plants for every 1 plant sprouted in the

control + or – 0.09 of a plant within a 95% confidence level. The 3MHz experimental group

fared even better, boasting 2.47 plants for every 1 plant germinated in the control group.

However, there was a little more variation and uncertainty in the 3MHz grouping, with the mean

value fluctuating 0.29 of a plant.

Table 1A

Graph 1B

This

Num

ber o

f Pla

nts

Ger

min

ated

0

10

20

30

40

50

60

70

1 2 3 4 5 6 7 8 9 10 11 12

1 MHz

3 MHz

Control

Sector Number

The above graph shows a comparison between the different experimental groups. As

shown, the 3 MHz group produced the greatest number of plants compared to the other two

groups, which supports the hypothesis. The 1 MHz compilation also showed significant

separation between the amounts of plants produced compared to the control group.

As stated previously, temperature had a role in plant germination as shown by the large graph

below. Where the temperature reached around levels of 72°F because of the vibrational energy

emitted by the transducers, the Thymus serpyllum seeds germinated/sprouted more frequently.

The plants affected by 1MHz and 3MHz sound waves, at the end of experimentation, reflect

where this band of healthy temperature lies (diagrams 2, 3, 4 –appendix and figure 1C below)

Figure 1C

66.0

71.0

76.0

81.0

86.0

91.0

21:58:0521:59:3522:01:0522:02:3522:04:0522:05:3522:07:05

66.0

71.0

76.0

81.0

86.0

91.0

22:08:11 22:09:41 22:11:11 22:12:41 22:14:11 22:15:41

Time (h:m:s)

Degrees (F)

A B C

1 MHz

3 MHz

Experimental soil tray (plan view)

Measurement locations

A: over transducer, no germination

B: maximum germination band

C: little germination

Transducer head (buried beneath soil)

A B C

Conclusion

The experimentation effectively tested whether vibrational energy in the soil could

benefit the germination rate of Thymus serpyllum. Thymus serpyllum, or Creeping Thyme, is a

low laying cover crop commonly used to organically restrict any weeds that might harm a

farmer’s cash crop. Unfortunately, Creeping Thyme is fairly slow growing and an effective cover

crop needs to exceed the speedy germination rate of any weeds that might sprout. The purpose of

the project was to accelerate the germination rate of Thymus serpyllum using an affordable

method so the cover crop could be more successful.

After accomplishing the experimental design, the results showed significant trends

among both the 1MHz and 3MHz trial groups and the control. The mean values for all trials (12

factions in each group) were calculated (Results - table 1A) showing the 3MHz group to produce

over two times as many plants as the control and the 1MHz set causing almost twice as many

plants to germinate as in the control. The hypothesis states that the transducers would affect the

germination rate positively, which goes to say that the transducers would reduce germination

time. Therefore, the data supports this hypothesis since the trial groups caused more plants to

germinate than the control group in the same amount of time.

Based on an online article by Bryan D. Ness, “Seeds germinate within a restricted range

of temperatures, moisture, oxygen, light, and freedom from chemical inhibitors.” (Ness 2002).

Since both the amount of water provided and the quantity of light and oxygen supplied were held

constant, there were two evident factors that were plausible reasons for this decrease in

germination time. First, the sound waves, which were roughly comparable to the size of the seed

to allow for maximum vibration, must have enhanced moisture and nutrient fluctuations within

the seed and across the seed coat. In other words, the mechanical vibrations sped up the

absorption of water into the seed causing the dry tissues in the seed to soften up for activity. The

vibrations also likely enhanced the process of dissolving the hormone gibberellic acid and

dispersing it throughout the seed to start the process of protein synthesis. This explanation is

supported by the hypothesis. The only other factor affecting germination rate, since the chemical

components are explained, is temperature. Temperature had a large impact on the positioning of

germinated plants and the rate at which they germinated. However, the temperature range that

was beneficial to the plants was only attainable because of the transducers. The transducers

emitted vibrations that decreased in strength as they emanated outward (see figure at right).

Within the central rings (the middle of the vibrational pattern) the temperature reached around

72°F which was an ideal temperature for germination based on

the number of plants that germinated in these central rings (see

figure 1C in results and pictures 2,3,and 4 in appendix). The

hypothesis does not directly promote the idea that temperature

would have an impact on germination rate, but since the

temperature was enhanced by the transducers and the hypothesis

states that the transducers would have an effect on speed of

germination, this component does support the hypothesis.

Due to lack of an affordable method to view and

determine whether dispersion of water and chemicals was actually a possible factor on the rate of

seed germination, further research and experimentation will need to be conducted. Future

experimentation will need to focus on whether mechanical vibrations have an effect on diffusion

of chemicals and moisture throughout the seed.

Literature Cited

- Ness, Bryan D. “Germination and seedling Development” Magill's Encyclopedia of Science: Plant Life 11-01-2002

- Paul C. Bethke, Igor G.L. Libourel, Natsuyo Aoyama, Yong-Yoon Chung, David W. Still and Russell L. Jones “Journal of Plant Physiology” American Society of Plant Physiologists, January 12, 2007. www.plantphysiol.org/cgi/doi/10.1104/pp.106.093435

- Koning, Ross E. "Seeds and Seed Germination". Plant Physiology Website. 1994. http://koning.ecsu.ctstateu.edu/plants_human/seedgerm.html

http://12knights.pbworks.com/w/page/25610401/935%20Outline%20the%20metabolic%20processes http://web1.uct.usm.maine.edu/~champlin/Courses%20F%2708/Handouts/seed%20germination.htm http://www.biologie.uni-hamburg.de/b-online/ibc99/koning/seedgerm.html

-Reference: SERDP Final Report “Acoustical Characterization of Soil”, February 2000

Appendix

1) Experimentation Apparatus

2) 3MHz (After Experimental Design)

3) 1MHz (After Experimental Design)

4) Raw Data

5) Control Group (After Experimental Design)

Plants Germinated (After 15 Days)

Faction Number 1 MHz 3 MHz Control1 20 11 122 26 30 213 23 41 94 32 44 55 15 43 106 10 41 187 15 43 218 39 49 169 35 47 29

10 36 59 2811 46 50 2412 33 29 16

Mean Value = 27.5 40.6 17.4

Total Plants = 330 487 209

6) Transducers and Temperature Logger

3 MHz transducer

1 MHz transducer

Temperature Data Logger

Bottom View Top View

7) Documentation

8) Thymus serpyllum Seeds