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SCIENCE EXPERIMENTS ON FILE™ Revised Edition

The Effect of Soil pH on Plant Growth
Louis A. Ventura
Topic Acid rain Time 2 to 4 weeks

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Safety Adult supervision is required. Please click on the safety icon to view the safety precautions. The pH levels of 3 and 11 do not pose a threat of severe burns, but care should be taken not to spill these solutions or get them into youreyes. The concentrated acids and bases used to make the solution should be handled only by the teacher.

Materials 1 package each: pole bean and radish seeds pH testing paper capable of measuring each pH level from 3 to 11 20 lb potting soil plant food (hydrion paper) or pH meter distilled water 100-mL graduated cylinder graph paper automatic timer to shut off lights at night (optional)meterstick shelf with fluorescent lamps attached 3 ft above (windowsill or greenhouse is fine) Procedure
PART A: TEACHER PREPARATION

five trays capable of holding six pots each thirty 3-in.-diameter plastic plant pots Celsius thermometer (Celsius: range 15° to 40°) 1-gal (4-L) solutions of each of the following prepared by teacher: nitric acid at pH 3 nitric acid at pH 5 distilled water (pH 7)potassium hydroxide at pH 9 potassium hydroxide at pH 11

Dilute stock solutions of nitric acid and potassium hydroxide, testing continuously with pH meter or pH testing paper to produce about 1 gal each of solutions at pH 3, 5, 9, and 11.
PART B: STUDENT EXPERIMENT 1. Clean pots and fill to 1⁄ 2 in. from the top with potting soil.

2. Plant three radish seeds in each of 15 pots. Plant the seedsabout 1⁄ 2 in. below the soil surface.

SCIENCE EXPERIMENTS ON FILE™ Revised Edition

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3. 4. 5.

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Label the pots as follows: R1—pH 3 R2—pH 9 R1—pH 5 R2—pH 11 R1—pH 7 R3—pH 3 R1—pH 9 R3—pH 5 R1—pH 11 R3—pH 7 R2—pH 3 R3—pH 9 R2—pH 5 R3—pH 11 R2—pH 7 Plant one bean seed in each of the remaining 15 pots, labeling them B1—pH 3 to B3—pH 11, asabove. Fertilize each pot. Follow instructions on the plant food container, adding exactly the same amount to each pot. Each day until the seeds germinate, water the soil of each pot well with distilled water. (Take care to give each pot the same amount of water.) This should take about 4 days to 1 week. If you are using artificial light, turn off lights at night throughout the experiment. When theradish seeds germinate, remove all but one seedling from each pot. Once the plants have grown to over 1 cm in height, carefully measure and record the height of each seedling. Measure from the soil to the top of the stem, not to the tip of the top leaves. Record your results on the data tables on the line representing day 1. Water each pot daily for 2 weeks with 50 mL of liquid at the pH levelindicated on the pot. Each day, measure the height of each plant carefully, and record results on the data tables 1 and 2. After 14 days, calculate the growth of each plant by subtracting the measurement at day 1 from the measurement at day 14. For the radish plants, find the average amount of growth at each pH level (e.g., add the heights of R1—pH 3, R2—pH 3, and R3—pH 3 and then divide by 3). Recordyour results on a table labeled “Mean Growth pH Levels.” Do the same for the bean plants. For the radish plants, make a line graph showing the relationship between pH and growth. Put pH levels on the horizontal axis and growth in centimeters (cm) on the vertical axis. Make another graph for the bean plants. Summarize your results for each type of plant. In what pH range did the plants grow best? Atwhat pH levels was there the least growth? Explain what your results might indicate about the possible dangers of acid rain.

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SCIENCE EXPERIMENTS ON FILE™ Revised Edition

D ATA T A B L E 1
Radish plants: height of stem in cm

Day

R1

R2 R3 pH 3

R1 R2 R3 pH 5

R1

R2 R3 pH 7

R1

R2 R3 pH 9

R1

R2 R3 pH 11

1 2 3 4 5 6 7 8 9 10 11 12 13 14

D ATA T A B...
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