The Development of a Novel Sodium Polyacrylate Seed Treatment

Kira Elizabeth Powell

Odessa High School, 204 East 4th

Avenue

Odessa, Washington 99159

March 7, 2012

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ACKNOWLEDGEMENTS

I would like to first acknowledge the Odessa School District for all their support and

encouragement. I would also like to thank Mr. Jeffery Wehr, my teacher and mentor for his wise

guidance and ever present inspiration. Gratitude is also due to Dr. Sylvia Oliver for general

chemistry advice as well as the use of her lab on the Washington State University, Spokane

Extension, Campus.

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I.INTRODUCTION

In the world today, agriculture is growing ever more important. As the world population

grows 1.14% each year, the need for food also increases (Rosenberg, 2011). Finding ways to

make agricultural production more efficient is of utmost importance. Seed treatments,

specifically in grains, have been traditionally used in preventive capacity against pre-planting

and early stage afflictions such as protection against the soil fungi Rhizoctonia solani, but now

are being regarded as a tool to increase both the quantity and quality of yields (Taylor, 1990).

For example, IntelliCoat produced by LANDEC Ag Inc., contains temperature sensitive switches

that are useful in controlling germination (LANDEC, 2007). Worth an estimated $2.25 billion,

the seed treatment industry is currently the fastest growing segment of crop production, projected

to increase at a rate of 13.5% between 2011 and 2016. North and South America account for

over 80% of that market. It is an industry driven by innovators, evidenced by the success of

companies like Bayer CropScience and NuFarm that produce their exclusive “treats”

(MarketsandMarkets, 2012). Developing a new treatment that has a tangible benefit could have a

great impact on agriculture production.

Previous research has been done with regards to a certain polymer, sodium polyacrylate,

which showed potential as a moisture retaining soil additive. Sodium polyacrylate (C3H3NaO2)n

is a mixture of sodium acrylate and acrylic acid. It has a high absorbency capacity and is

classified as a hydrogel, a colloidal gel in which water is the dispersion medium. Sodium

polyacrylate exists in randomly coiled chains, with an absence of Na+ ions. The negative charges

on the coils repel each other causing them to unwind. Water is then attracted to the negative ions

and attaches with hydrogen bonds until all negative ions are linked to water (FIG 1). This

phenomenon allows 500 times the polymers weight in pure water to be absorbed (France, 2008).

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This chemical showed promise in previous research by increasing crop production by 22% in

dry-land wheat (Powell, 2011). The principle being that the sodium polyacrylate acts as a

miniature reservoir in the soil, capturing and holding moisture available through rainfall for the

plant to access when it needs it. The presence of the sodium polyacrylate allows for efficient use

of water, because it lessens the amount of moisture lost through evaporation and percolation.

This quality of efficient water use could be beneficial in drought areas, where the amount of

water received is already reduced and any moisture must be used effectively. Water availability

is directly linked to crop production, thus more water, increased crop growth. However, a

problem was observed with the application method during the planting stage.

In the planting process, seeds are poured in large hoppers connected to tubes down which the

seeds travel when being implanted in the soil. The tubes can be set at specific distances to allow

for optimal growth. When the sodium polyacrylate was mixed with the wheat, due to its fine

consistency, it fell to the bottom; there was not equal distribution. Moisture had to be applied to

temporarily fix the problem which made the planting process more labor intensive and did not

uniformly deposit the chemical around the seed. Uniformity of the chemical application in the

seeding allows for more reliable results, which the soil application lacked and could potentially

FIG. 1 A model of dry coiled sodium polyacrylate,

and an uncoiled strand bonded with water (Richer,

2007).

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be achieved using a seed treatment (Bergstrom, 2007). Without it, the crop could potentially not

experience the benefit from the added sodium polyacrylate. It was theorized that this problem

could be eliminated by incorporating sodium polyacrylate into a seed treatment, thereby

facilitating the even coverage of the chemical, more accurate application ratios and ease of

application.

The goal of the project was to engineer a seed treatment incorporating sodium polyacrylate in

order to streamline the application process of the chemical and maximizing the efficient use. The

application rates per kernel were calculated from previous research involving sodium

polyacrylate using the individual kernel data (Powell, 2011). For the 2.5% application rate there

was theoretically 0.7480 mg of sodium polyacrylate per wheat kernel and 1.496 g of sodium

polyacrylate per wheat kernel for the 5.0% application rate. These figures served as a per kernel

sodium polyacrylate mass goal for the individual kernel data. The adhesive component of the

treatment developed to accomplish this would need to be non-toxic (seed and consumer), and an

adhesive liquid thin enough to apply in a spray and ultimately successful in adhering the

chemical to the seed. If the seed treatment was successful in preliminary trials then the treatment

would be applied to kernels in specific application rates and planted in an imitation environment.

The null hypothesis was that the seeds coated with the novel treat, both the 2.5% and 5.0%

application rates will have no statistical difference in mass when compared to the control wheat

samples. The hypothesis was that the seeds coated with the novel treat, both the 2.5% and 5.0%

application rates will have a statistical difference in mass when compared to the control wheat

samples because the treat is working to the same extent as the soil additive.

II. MATERIALS AND METHODS

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As of right now, seed treatments are applied in either a continuous or batch system. The

treatment prepared needed to be compatible with one of the two systems. A batch treatment was

the easier of the two to replicate. Batch treatment works by treating a specific amount of seed

with the required product for that amount. It can be used for low and high volumes, the batch

system line of machines produced by Bayer CropScience ranges from 25 kg to 100 kg capacity

with the same end result. Due to this fact, the results gained from small volume batches (0.25-1.0

kg) produced during the experiment were accurate representations of the potential of the

chemicals and processes implemented.

To begin with, an adhesive had to be developed to attach the sodium polyacrylate to the wheat

kernel prior to planting. The experimental adhesive comprised of 53.1% water, 8.4% pectin,

21.3% glycerin (C3H8O3) and 17.3% 1 M acetic acid (CH3CO2H). Pectin is a polymer of D-

galacturonic acid that is naturally found in the middle lamella between plant cells where it helps

bind cells together, a natural adhesive (FIG 2). It is also an important cell wall polysaccharide

allowing primary cell wall extension and plant growth. Glycol, or glycerin as it is more

commonly known, was selected for several reasons; first being that it is naturally adhesive and is

used commercially as a preservative. This quality is especially useful when considering the long

term condition of the adhesive. The acetic acid acted as a liquescent and was necessary to keep

the adhesive at the desired viscosity. To prepare the adhesive, the water was brought to a boil on

FIG 2. Presence of pectin in the middle lamella

between two xylem fibers in alfalfa (Wi, 2005).

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a hot plate and then the pectin was added. The pectin solution was simmered for two minutes

when the glycol and acetic acid was then added. The mixture was immediately removed from the

heat after the final additions. Five samples of adhesive were made.

In the prior experimentation with sodium polyacrylate, a 1:40 (2.5%) and a 1:20 (5.0%)

chemical to seed ratio were found to be ideal for increased crop growth (Powell, 2011). In order

to determine the amount of adhesive required to achieve these ratios, the binding agent was

applied to wheat kernels individually followed by sodium polyacrylate. Kernels were weighed

and placed in plastic trays where the glue was administered through a pipette. The seed was

agitated until thoroughly coated. All glue not attached to the seed was deemed excess and

removed. The kernel was weighed again; the increase in mass was assumed to be adhesive.

Sodium polyacrylate, 0.200 g, was then applied onto the coated seed and the seed was massed

once more after the excess chemical was removed via canned air (FIG 3). The mass of the glue

in respect to the mass of the chemical gave an estimate of the amount of glue required to adhere

the set ratios of sodium polyacrylate to wheat. In addition the data collected was compared to the

rates mentioned previously to assess the effectiveness of the adhesive. The kernels used were

soft white spring wheat (Triticum aestivum) of the Louise variety.

The individual kernels were then applied with distilled water to determine the amount of

water the sodium polyacrylate could hold. In increments of 100 μL, water was applied using a

FIG 3. An individual kernel after treatment, note

the uniform coating (Powell, 2012).

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micropipette to 27 of the individual kernel samples (FIG 4). After each round of application the

kernels were inspected to determine the saturation level of the sodium polyacrylate. As the

rounds of application proceeded, when a sample appeared to be fully saturated it was removed

and the amount of water it had received was recorded. Fully saturated was deemed in this

instance to be when the sodium polyacrylate had settled to the level of the kernel while still

remaining one collective body that slid easily on the plastic tray. The water retention of the

kernels was averaged and compared to the calculated theoretical values for the desired full scale

ratio water retention.

To determine the effects of the adhesive, if there was any, wheat was planted in the high

school laboratory using the adhesive to coat the wheat kernels with sodium polyacrylate at a

2.5% and 5.0% application rate (percentages are based of the mass of the wheat). To ensure the

sodium polyacrylate percentages were accurate, the wheat kernels were prepared individually

using a Denver Instruments APX 100 scale at a facility located on the Washington State

University Spokane Campus. For the 2.5% sodium polyacrylate application, 0.7 mg of chemical

was applied with 20 µL adhesive. For the 5.0% sodium polyacrylate application 1.5 mg of

chemical was applied with 40 µL adhesive. The coated kernels were then planted in 4 x 4 cm

individual potting containers at a depth of 3 cm. Soil taken from an agricultural area was used in

the pots. 40 control seeds, 40-2.5% application and 40-5.0% application seeds were planted.

FIG 4. Water being applied via micro

pipette (Powell, 2012).

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There were three grow lights available for use and the plants were placed under these, randomly.

The plants were continually rotated under the lights to compensate for any differences in the

light bulb intensity. At the same time the lux for each of the lights was recorded. The plants were

given 1 ml of water every other day and on the days in between, soil moisture percentage was

recorded. Plant height data was collected on a daily basis. On day 27 the plants were transplanted

to larger trays due the increased space requirement. The trays were filled with soil taken from the

agricultural site and measured 35 cm across and 12 cm deep. The plants were arranged in rows

according to their experimental group and each tray contained two rows of each experimental

group. The watering and soil moisture percentage schedules proceeded as planned.

After 3 months, the plants were carefully removed from the soil and massed individually.

They were then dried out for 1 week in the greenhouse. Shoot to root ratio, water loss, and root

mass were all collected. At the same time the roots were photographed and the reach and area

was recorded (FIG 5). Soil samples taken from the test environments were sent to be

professionally analyzed.

The very last step on this project was to apply the seed treatment as it would be commercially,

on a larger scale. 3.78 kilograms of wheat were treated. Due to the size requirements, the

commercial method was replicated exactly in the high school laboratory. Seed treatment

FIG 5. A sample root photograph (Powell,

2012).

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technicians were consulted during the construction to ensure accuracy of method. The wheat was

placed on a conveyor system that passed the wheat underneath a pressurized spray system of

glue and then under a shake system that distributed the sodium polyacrylate onto the seed. The

wheat was then deposited into an auger that churned the seeds until they fell out the other end.

Average seed mass was taken to determine if the seed treatment was effective on a larger scale as

well (FIG 6).

The individual kernel sodium polyacrylate and adhesive experimental rates, as well as the

average water retention for individual kernels, plant height data, root to shoot ratios, average

plant area, average kernel mass prior to and after full-scale application and water loss were

analyzed using two-tailed t-tests to determine the overall effectiveness of the pectin-glycerin-

acetic acid adhesive. In addition the approximate cost of the adhesive was calculated.

III. RESULTS

The small scale tests on the individual kernels were conducted to determine the amount of

sodium polyacrylate the glue could adhere to while coating the seed. The adhesive to sodium

polyacrylate ratio was found over the course of 75 trials; the average amount of sodium

polyacrylate adhered to an individual kernel was 0.006 g (±0.003 g), with a high of 0.013 g and a

low of 0.002 g. The average amount of glue coating each seed was 0.011 g (±0.004 g), with a

high of 0.020 g and a low of 0.001 g. The average kernel mass was 0.038 g (±0.007 g), with a

high of 0.055 g and a low of 0.023 g (Table 1).

The average water retention for the individual kernels applied with the sodium polyacrylate

was 2.4 g (±0.598 g), with a high of 4.2 g and a low of 1.5 g (Table 1).

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FIG 6. A diagram of the constructed seed treatment machinery including (A) the seed conveyor system,

(B) the spray apparatus, (C) chemical application station and (D) auger (Powell, 2012).

A

B

C

D

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Table 1. Adhesive, Sodium Polyacrylate and Water Average Mass.

The average plant heights as of March 29 were the Control at 24.0 cm (±4.8 cm), the 2.5% (1:40)

application at 24.4 cm (±2.8 cm), and the 5.0% application at 24.3 cm (±3.1 cm). There was no

statistical difference between any of the experimental groups.

Root to shoot ratios also use roots to indicate the effects of drought on plants. Plants deprived

of water will have a low root to shoot ratio. To calculate, the root mass was divided by the shoot

mass. The 2.5% application had the highest root to shoot percentage at 74.2% followed by the

5.0% application at 48.4% and finally the Control 43.7%. The Control and 2.5% were found to

be statistically different at the 99% confidence level (Table 2).

The water loss from the roots was found by subtracting the dry mass from the wet mass of the

plant. The 2.5% application had the highest amount of water loss, followed by the control and

then the 5.0% (Table 3).

Because of the trends seen in the other data collections, that being the 1:40 was preforming

the best, the full scale application was run at that percentage. There was a difference of .005 g

per individual kernel mass which was significantly different at the 99.9% confidence level (Table

4).

Plant Height was recorded as a way to touch base with the previous year’s research, but was

not a primary focus of the study. The control had an average of 15.71 cm, the 2.5% at 16.01 cm

and the 5.0% at 14.94 cm at the last sampling before the plants were terminated (Table 5).

Substance N Average Mass (g) SD (g) Variance (g)

Adhesive 75 0.011 0.004 1.600E-6

Sodium Polyacrylate 75 0.006 0.003 9.000E-6

Water 27 2.800 0.598 3.576E-1

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Table 2. Average Root Area

Table 3. Root to Shoot Ratios

Table 4. The Average Individual Kernel Mass Before and After Treatment

Table 5. The Average Plant Height

Application Rate N Root to Shoot (%) SD (%)

Control 35 43.7 ±26.1

2.5% (1:40) 32 74.2 ±54.4

5.0% (1:20) 34 48.4 ±18.8

Application Rate N Area (mm2) SD (mm

2)

Control 35 1438.8 ±354.8

2.5% (1:40) 32 1689.6 ±398.7

5.0% (1:20) 34 1344.9 ±412.7

Application Rate N Mass (g) SD (%)

Non-Treated 200 0.034 ±0.003

Treated 2.5% (1:40) 200 0.039 ±0.004

Application Rate N Average Height (cm) SD (cm)

Control 38 15.71 ±3.26

2.5% (1:40) 36 16.01 ±2.97

5.0% (1:20) 36 14.94 ±2.26

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IV. DISCUSSION AND CONCLUSIONS

Overall the engineering goal of creating a seed treatment using sodium polyacrylate was

successful. The adhesive, made of 4 ingredients, adhered an average 0.006 g of sodium

polyacrylate the wheat kernels using on average 0.011 g of adhesive. When that is compared to

the average kernel mass, 0.038 g, the chemical adhered is 17.0% of the kernel mass (FIG 7) and

the adhesive is 29.8% of the kernel mass (FIG 8). As seen by the R2

neither the mass of sodium

polyacrylate (R2=0.0565) nor the mass of the adhesive (R

2=0.1787) was correlated to the seed

mass. As stated previously the 2.5% application rates and 5.0% application rates broke down to

0.7480 mg of sodium polyacrylate per wheat kernel and 1.496 mg of sodium polyacrylate per

wheat kernel respectively thus the average experimental rate of 0.006 g sodium polyacrylate per

kernel exceeded the initial the engineering goal (FIG 9). This phenomenon was expected due to

FIG 7. The Correlation Between Sodium Polyacrylate Mass and Kernel Mass.

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the experimental method and yet remains pertinent because it indicates the adhesive was

effective in attaching the chemical to the seed. The large error bar on the experimental column

was in this case promising, because it indicates that there were seeds that were close to the

desired rates, if not slightly above.

On average the sodium polyacrylate was 36.5% of the treat (adhesive + chemical). This ratio

of adhesive to sodium polyacrylate is acceptable because it provides that there was plenty of

adhesive for the chemical to attach to. It is better to have a slight excess in adhesive then risk not

having all the sodium polyacrylate coat the seed, the sodium polyacrylate being more expensive

than the adhesive.

FIG 8. The Correlation between Kernel Mass and Kernel Mass.

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The average water retention for the individual seeds, 2.400 g, fell within the chemicals

absorbency potential 300-500 times the chemicals mass in water. Since the average mass of the

sodium polyacrylate adhered to a seed was 0.006 g the amount of water it should absorb should

be between 1.800 g (300 times mass) and 3.000 g (500 times mass) of water, which it was. In

fact 2.400 g is approximately 400 times the average mass of the sodium polyacrylate. This data

showed the chemical was absorbing the amount of water expected and the adhesive was not

interfering in the process. Ultimately, this data indicates the overall success of the seed treatment

because it fulfilled the goal to develop a seed treatment using sodium polyacrylate. Granted there

is future experimentation to be done to lower the sodium polyacrylate application rate to the

desired levels but the adhesive successfully adhered sodium polyacrylate to the seed.

The statistically higher root to shoot ratio supported the theory that the 1:40 application was

helping the plants sustain during a drought environment. The plants had the ability to produce

more growth (FIG 10).

FIG 9. The Theoretical and Experimental Mass of Sodium Polyacrylate Adhered

per Individual Kernel.

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FIG 10. The Root to Shoot Ratios for the Control, 2.5% Application and 5.0%

Application.

FIG 11. A Comparison of Average Kernel Mass Before and After Full-Scale Application.

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The cost of the seed treatment including the sodium polyacrylate would be approximately $1.59

for the 1:40 ratio ($0.86 pectin + $0.64 glycerin + $0.09 acetic acid) and $3.18 for the 1:20 ratio

($1.72 pectin + $1.28 glycerin + $0.18 acetic acid). If you factor that cost into a full scale cost

analysis with the previously recorded yield increases from the sodium polyacrylate

(Powell,2011) a 640acre field without sodium polyacrylate would harvest approximately 52

bushel/acre (the state average for spring wheat in 2010) resulting in a total of 33,280bushels

(Knopf, 2010). If this was multiplied by the price of one bushel, there would be a gross of

$246,605. If the same field was treated with a 0.68kg (1.5lbs) per acre application rate of sodium

polyacrylate, there should be an expected then a 22% increase in bushels/acre. This would

increase harvest to a rate of 63 bushels/acre, which translates into 40,320 total bushels or

$298,771. That is an increase of $52,166 in revenue. If you take out the cost of the sodium

polyacrylate to seed that same area ($531) and the cost of the seed treatment ($1018) then the

revenue increase would be $50,617 and the gross total would be $297,222. The use of the 1.36kg

(3.0lbs) application rate was also cost effective. It resulted in 66 bushel/acre harvest (27 %

increase), 42,240 total bushels, $310,963 gross, and a $63,302 revenue increase (cost of sodium

polyacrylate,$1056, seed treatment, $2035) (Powell, 2011) (FIG 12).

This research has much potential and future experiments are in the primary stages. A full scale

10 acre application to winter wheat is planned for the fall of 2012 facilitated by the Odessa

Grange. I have already formulated hypothesizes for this experiment which can be seen here. In

additional investigation into possible additions and improvements to the adhesive as well as the

environmental effects will continue to be investigated.

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FIG 12. Comparison of Application Rate, Total Bushels and Revenue Including Cost of Adhesive

and Chemical.

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