Inquiry Project:  Effect of pH on Plant Biomass

(Kathleen Bradie (FRC): Radishes Vs Acidic and Alkaline Solutions)

Grade/Course Suitability: Sci20S (Ecology)

Objective: The purpose of this experiment is to determine the effect of soil pH on the growth and biomass of different plant species.

Materials:

Conviron plant chamber

Potting soil

Plastic planting tray(s) (with or without separate compartments)

3 – 20 mL syringes

Electric balance (readability 0.001)

Solutions at pH = 4.0, 7.0, and 10.0

Graduated cylinder

Plant seeds (radishes were used due to their fast growth).

Tap water

Popsicle sticks for labeling

Sulfuric acid or nitric acid

Calcium hydroxide

pH meter

Stir rod

Small paint brush

250 mL & 500 beakers

Tablespoon/scoopula

sharpies

Plastic trays/paper plates (1 for each plant)

Suggested Procedure:

  1. Prepare the different pH solutions that you will be using to water your plants for your experiment.    The volume that you should prepare will depend on how many trials at each pH you have.  pH of 7 will be the control for this experiment.
  2. Next, prepare your planting tray.  Fill all pockets of planting tray(s) with an equal mass of potting soil.  The number of trays that you will need depends on how many plants at each different pH you would like to test. 
  3. Label each pod with a popsicle stick, noting the pH and sample number.
  4. Make a depression in the center of each pod with your finger and plant 2 – 3 radish seeds (or seeds of your choice) in each.  Cover with a small amount of soil, and then water each with an equal volume of the appropriate pH solution, ensuring that the soil is damp.  Syringes could be used for watering.
  5. Place the planting tray(s) in a Conviron chamber with settings appropriate to your plant’s germination and growth.   
  6. Check your plants daily for germination. Once seedlings germinate, thin to leave only the healthiest plant in each pocket.  Continue to water as required, watering all pockets with the same volume on the same day. 
  7. Continue to monitor your plants until they are ready to harvest.  Note any significant changes.
  8. When your plants are ready to harvest, carefully remove them from the soil, one at a time.  Brush off any excess soil and place on a labeled tray.  Repeat for all plants. 
  9. In order to measure dry biomass, you will need to dry the plants.  This can be done by either placing them in a drying oven or leaving them out for a few days.  Final masses for each should be determined over a small period of time, as weight can change significantly over time. 

Recommended Result Observation

Students could measure plant height, and qualitatively or quantitatively record plant health, looking at properties such as seed germination, stem and leaf colour, and number of leaves.

For best determination of plant growth, dry biomass of each radish should be determined after radishes have been harvested and dried.

Analysis:  Analysis would include a comparison of average plant biomass to the pH of the solution. 

Further Exploration/Project Extensions:

This project lends itself to many extensions, as few are listed below.

  • Radishes were chosen due to the short length of time to go from planting to harvesting.  However, many other plants could be investigated.
  • A comparison between root vegetables versus above -ground vegetables.