The Free Science Fair Projects Network

Science Fair Project

Title:	How Do Different Cations and pH Affect Bean Growth
Category:	Botany
Student Researchers:	A. & M. Clos
School:
Grade:	6
Teacher:
Awards:

Background Information

Beans originated in Mexico, Costa Rica, Guatemala and Honduras. But now beans can be found all over the world, even in places that you would never think to find them. And there are about 30 different kinds that are used as vegetables. In the United States some of the most commonly grown kinds are garden peas, cowpea, lima beans, snap beans, soybeans, lentils, kidney beans, pinto beans, chick-peas, and fava beans. Beans extract some of the nitrogen in the atmosphere and are a good source of protein when eaten. Many kinds of beans can be found in developed and undeveloped countries. Beans contain proteins, carbohydrates and some essential vitamins and minerals.

The ancestors of snap beans originated between 6,000 and 8,000 years before today. And some beans that are as old as 2,500 years old have been found preserved in the Andes. As well as all the special kinds of beans grown today there are common beans that didn’t have scientific names. Beans are either pole beans (which means they are long and stringy and grow on a pole like a vine), and there are bush beans (they grow short and thick like bushes). The leaves of pole beans tend to be smaller than those of bush beans which tend to be larger. Some beans have multiple leaves in a clump kind of like a clover and others have only one or two leaves in a clump. The rate at which beans produce seeds depends on cultivar type and the size of their leaves, which means that some beans will produce seeds in larger quantities and faster than other kinds of beans.

pH is defined as “the negative logarithm of the effective hydrogen ion concentration or hydrogen ion activity in gram equivalents per liter, used in expressing both acidity and alkalinity on a scale whose numbers less than 7 indicate increasing acidity, and numbers greater than 7 increasing alkalinity.” What this means is that pH 7 is neutral, solutions with pH numbers above that are basic (or alkaline), and solutions with pH numbers below that are acidic. Numbers on the pH scale differ from each other by a factor of 10 in how acid or basic they are (in other words, how many H+ or OH- ions they have). This means that a solution with a pH of 5 has 10 times as many hydrogen ions as one with a pH of 6, and a solution with a pH of 9 has 10 times as many hydroxyl ions as one with a pH of 8.

However, when a chemical is added to water to change the pH of the solution, it is not possible to add pure hydrogen ions or pure hydroxyl ions. The hydroxyl (OH-) ions are bound to a cation to make a stable chemical. Perhaps the chemical used to change the pH affects the bean growth as well as the pH. If so, the response of beans to growing in different pHs would vary depending on what cation was used.

Different plants grow best in different pHs, but in general, most garden vegetables prefer a slightly acidic soil, around pH 6.5. A pH below 6 or above 7 is usually not as good for vegetable growth.

Pinto beans grow best in pH 6, and the higher pH the worse the pinto beans grow. An experiment on the Internet tested how pinto beans grow in different pHs. The person who did that project found that the pH does affect the growth of plants (in this case beans) which was the opposite of his hypothesis. Another person did an experiment on how mung beans grow in different pHs. They found that they grew best in pH 6 and anything below or above that stunted the beans’ growth, causing them to grow shorter.

Purpose

The purpose of this experiment was to test how beans grow in different pHs, and see if the chemical used to change the pH affected the beans’ response to the different pHs.

Hypothesis

The hypothesis used in this experiment was that the higher the pH, the poorer the beans would grow, and that the beans would grow worst in the sodium (NaOH) solution, best in the calcium (Ca(OH)2) solution, and that potassium (KOH) would be in between.

Materials

The materials used in this project were:

One bag of mixed pinto and great northern beans from the grocery store
26 4-quart plastic tubs
78 ft. of 3/4” PVC pipe
13 9” x 12” pieces of plastic needlepoint cloth
14 one gallon jugs of distilled water
One plastic sprayer
One roll of paper towels
500 gram jar of sodium hydroxide (NaOH) flakes
500 gram jar of potassium hydroxide (KOH) flakes
250 gram jar of calcium hydroxide (Ca(OH)2) powder
One roll of pH paper for pHs 5.5 - 8
One roll of pH paper for pHs 3 - 9
Disposable plastic gloves
One package of 3 oz. plastic cups
Hot glue gun
10 sticks of hot glue
One 25 lb. bag of epoxy-coated aquarium gravel
Black marker
White labels
Ruler graduated in millimeters
Meter stick
Triple-beam balance scale
Scissors
Drill press with 1/2” bit

The Procedure

Cut PVC pipe into 3” sections.
Cut needlepoint cloth pieces in half the short way:
Trim one piece of the needlepoint cloth so that it fits in the bottom of the vat. Do this for each of 13 vats.
Mark the large (untrimmed) halves of the needlepoint cloth with 18 holes in a 6 x 3 grid about 2” apart.
Stack up the large (untrimmed) halves of the needlepoint cloth and drill 1/2” holes in all the marked places with a drill press.
Glue 3” PVC tubes over the holes drilled in the needlepoint cloth.
Make 12 solutions, one gallon each: pH 7.5, pH 8, pH 8.5, and pH 9, for each of the three chemicals (sodium hydroxide, calcium hydroxide, and potassium hydroxide). The 13th solution (control) is plain distilled water. This is done in the garage so if the chemicals spill, they don’t ruin the floor. This is done by adding small amounts of the chemical powder/flakes to a gallon jug of distilled water, and repeatedly testing the pH, until the proper pH is obtained. Remember to wear plastic gloves when handling chemicals.
Label each vat with the chemical and pH, or water for the control.
Put the small pieces of needlepoint cloth into the bottoms of the vats (this keeps the tubes from sealing to the bottoms of the vats, so the solutions can get in).
Fill the vat not quite full with the proper solution.
Place all of the pieces of needlepoint cloth with the tubes glued onto them into the solutions with the tubes down in the solutions.
Soak about 200 beans of each type in plain water overnight.
Feed the epoxy-coated gravel down all of the holes until the tubes are full. (This is so that the beans have something to grow into, and the epoxy coat on the gravel keeps the gravel from reacting with the solution.) The tubes contain each bean’s roots so the roots don’t get tangled, and the bean can be weighed at the end of the experiment.
Fill the sprayer with distilled water.
Place the soaked beans on a wet paper towel, and spray them twice a day. When some of them start to sprout, carefully place them over the gravel-filled tubes and place tops over them (use the other 13 tubs for covers). Use 9 pintos and 9 great northerns per vat.
Make a data sheet for each bean and assign it a bean number, for example, Ca-7.5-P-1 means calcium pH 7.5 pinto bean #1.
Begin taking data on each bean when it is placed over a tube (height measurements after they begin to grow).*
When the beans get too tall, remove the covers and keep spraying them until their roots reach the solution. Any short beans are covered with the plastic cups (personal greenhouses) at this point.
Take height measurements on the beans every day for 40 days.
Rotate the vats once each day in a caterpillar fashion. This is so that none of the vats are closer to the window any more of the time than any of the others, so that differences in light do not affect the results. Bean rotation is done in the following manner:

Vat 13 is moved out of the way.
Vat 12 is moved into the 13 position.
Vat 11 is moved into the 12 position, etc. until position 1 is vacant.
Vat 13 is moved into position 1.

After 40 days, pull out the beans and weigh them on the triple beam balance.

* All the beans were starting to sprout when they were placed over the holes. If a bean died before it put down roots, it was listed in the Appendix as never sprouted and not used in the analysis. window

Research

The data presented here are the averages for all beans in a vat. Click on the images to view a larger picture.

Calcium Charts and Graphs

Potassium Charts and Graphs

Sodium Charts and Graphs

Analysis

In calcium the great northerns grew a little bit better than the pintos. But in potassium and sodium the pintos grew a little bit better than the great northerns. These graphs are shown in the Appendix along with the raw data. But for the most part the growth curves were pretty much the same shapes for both kinds of beans in a vat. Because of this, the average of all of the beans in a vat was used for the final graphs.

For calcium pH 8 was the pH that the beans grew best in and they grew worst in pH 9, for both height and weight. They grew better in pH 7.5 than they did in plain distilled water, better in pH 8 than in pH 7.5, but then worse at pH 8.5 and worst at pH 9. From this it is concluded that the best pH for the beans for calcium was 8.

In potassium the beans grew best in pH 8.5 for both height and weight. For height they did better in pH 7.5 than in water, better in pH 8 than pH 7.5, and better yet in pH 8.5 than in pH 8, and worse in pH 9. For weight they followed the same trend except that the pH 8 weights were strangely low. This was probably just a fluke, because the beans varied a lot in how robust or skinny they were, and there seemed to just have been a lot of tall, skinny beans in that vat by chance. The conclusion here is that pH 8.5 is best for beans growing in a potassium solution.

In sodium the beans grew best in 7.5 and worst in 9 for the height, and for the weight. After pH 7.5 they did worse on both height and weight the higher the pH went. In fact it is worse than it looks on the graphs because by day 24 all the beans in sodium 9 died. They had seemed to be growing fine, but then within about 3 days they all bent over and went limp. The beans appeared to have been poisoned by the sodium, although it took a while, as if they could handle just so much sodium, and then they couldn’t take it any more. This could account for why the beans did worse in the more concentrated solutions, because there was more sodium in them as well as a higher pH. Except for an occasional bean here and there, the sodium 9 vat was the only one where the beans all died. All the other vats of beans made it the 40 days and still looked good.

The heaviest and tallest beans on average were in the potassium solutions. Potassium is an ingredient in Miracle-Gro plant fertilizer, presumably because it is good for plants. Calcium and sodium are not ingredients in Miracle-Gro, so they must either be neutral for plants or bad for them. In fact this experiment found that sodium seems to poison beans. Since potassium is a plant nutrient, this is probably why the tallest and heaviest beans were in potassium. In fact the potassium 8.5 vat had an average bean weight of 2.23 g which was the only one that was over 2 grams.

The experimenter learned that the chemical used to change the pH of a solution does have an effect on the growth of the beans, as well as the pH that is in the water.

The hypothesis was partially correct. The sodium solutions did turn out to be the worst for the beans. But the calcium solution did not turn out to be the best. The best one was the potassium. And there was a difference in how the beans responded to different pHs depending on what chemical was used.

The Conclusion

This experiment tried to find out how the beans responded to the different pHs and whether there was a difference between how they responded depending on which chemical was used to change the pH. In calcium and potassium, the beans grew best in the middle range pHs (8 to 8.5) and worst in the high pH of 9. For sodium, they grew best in the lowest pH, 7.5, and steadily worse as the pH got higher. In pH 9 the beans grew so poorly that within a few days during the third week they all died and did not even make it to the end of the experiment.

Therefore, the conclusion is that it does matter what chemical is used to change the pH of the water, because it will affect the results obtained when growing beans.

Bibliography

Cheng, G., Cheung, W., Wong, L., and Yen, C., date unknown. The Effects of pH on Mung Beans. http://members.aol.com/ScienzFair/phmung.htm
Conway, K., Lucarelli, A., O’Connor, J., and Rodgers, J., 1998. The Effect of Different Types of Water on the Growth of Bean Plants. http://jrscience.wcp.muohio.edu/nsfall98/FinalArticles/Final.TheEffectofDifferen.html
Fageria, N. and Biligar, V., 1998. Growth and Nutrient Uptake by Common Bean, Lowland Rice, Corn, Soybean, and Wheat at Different Soil pH and Base Saturation on an Inceptisol. http://www.nal.usda.gov/ttic/tektran/data/000007/27/0000072730.html
Mississippi State University, 2002. Vegetables: the Ideal Soil pH. http://muscares.com/lawn/garden/vegetables/soil/ph.html
Nguyen, M., 2002. Sinking pH. http://www.usc.edu/CSSF/Current/Projects/J1622.pdf

From the Webmaster